: Troubles with the 77 CDV



77CDV
08-07-13, 08:04 AM
If you've been following my travel thread in the lounge, you know that my road trip got cut short by car trouble. I'm wanted to post in here to see if anyone has some ideas, because I'm stumped right now.

The car ran great from LA to Boston. Interstate highway travel, sustained speeds of 65-70, elevation changes from sea level to 8000 feet and back down. All normal stuff and no issues. However, after leaving Boston and running for about two hours at interstate speed, the car started bucking like it was starving for fuel. I stopped, let it cool down, checked what I could, and couldn't find any issues. The carb is getting fuel (low pressure aux electric fuel pump installed last year to combat vapor lock) and there is spark to all cylinders. I tried going on, but the condition recurred.

The car runs well at lower speeds, idles smoothly, and though it will die with this condition if pressed, it will start right back up with no delay.

Thoughts?

1980coupe
08-07-13, 10:23 AM
Clogged fuel filter...???

amunderdog
08-07-13, 10:30 AM
catalytic converter?
They claim you can use one of those fancy thermometers that you point and shoot.
Check the inlet temp versus outlet temp.
There are a few other ways to test one.

cadillac_al
08-07-13, 10:38 AM
I'm stumped. The car is undriveable due to bucking. Is this a CA emission vehicle? On newer fuel injected cars (Buick 3.8) a malfunctioning EGR will make it buck. I can't recall having a bucking condition with any of my old cars in the past. It doesn't sound like ignition cutting out or it would backfire. Will it rev up in neutral? Can you watch the secondaries kick open with the air cleaner removed? It must be starving for fuel for some reason. Is there any way to disconnect a line to see how strong the fuel flow is? I hope the filter sock in the tank isn't clogging up. Just for kicks I would try unplugging the EGR and see what happens. There is a good chance this could all be emission related. I think if fuel flow is low, it may buck but I don't think it would necessarily stall. I would think the engine would catch itself once the rpms dropped and continue to idle. I hope unplugging the EGR will do something for it. Good luck.

77CDV
08-07-13, 11:24 AM
It is a CA car. I'm leaning toward something emissions-equipment related. Fuel flow is good, secondaries open normally, revs fine in neutral, no evidence of backfiring. It does seem to be running a little rich, but nothing extreme. The only time I've seen a car act this way is due to exhaust backpressure choking the engine, but why would the car only have a problem after extended cruising?

I'm having the car shipped back to CA, because I just don't have the resources to deal with it properly 3000 miles from home. I'm just trying to get a few more people thinking about the problem to see if I'm completely off base in my thinking.

jayoldschool
08-07-13, 12:08 PM
Over rich could have killed the cat. If it were me, I'd cut it out, put in a straight pipe, and get home. At least it won't cost much to find out (even if you have to buy a sawzall). I know you have to deal with CA emissions, so get a new cat when you get there.

Bro-Ham
08-07-13, 12:33 PM
Craig, sorry to hear about this. It is all part of the fun and adventure of driving an old car cross country isn't it! I hope you get things squared away in a hurry!

outsider
08-07-13, 12:45 PM
I agree with Jay, cut out the cat and see if you can make it back like that. The cost will be way cheaper than having the car shipped.

I don't think it's the EGR because any time I've had EGR trouble it would happen no matter what the driving condition, and more so at low speeds and idle was very rough.

It is odd that it runs fine at lower speeds but only bucks and dies when at highway speeds though...very confusing situation.

lacville78
08-07-13, 06:32 PM
This is strange, how would a plugged cat affect the engine operations at speed? It seems like if it is clogged, it is clogged regardless of how fast the car is going. I could see it affecting performance at certain engine r.p.m.'s but that would happen going through all of the gears.

The Ape Man
08-07-13, 06:41 PM
A clogged cat can sometimes act worse when hot. A manifold vacuum gauge will prove an exhaust restriction. If vacuum drops with steady 1800-3000 RPM engine fully warmed up there's a restriction. More revs lower vacuum.

My guess is if the booster pump is just inline with the factory pump it's the factory pump's pressure relief valve. Diagnosis is to pinch off the smaller return hose and take it for a blast.

The other one that could fit would be the HEI pickup connection to the module is just about broken in half. You did not mention backfiring though.

Good luck.

lacville78
08-07-13, 07:07 PM
Ok so when it is warmed up why wouldn't the car act bad in first or second gear, wouldnt the rpms be the same as third?

The Ape Man
08-07-13, 08:06 PM
Ok so when it is warmed up why wouldn't the car act bad in first or second gear, wouldnt the rpms be the same as third?

Plugged cats can be elusive. They are not usually completely plugged. Temperature makes a lot of difference. Exhaust restrictions pretty much destroy the vacuum signal to the carbonator's metering rods.

All kinds of unexpected things can happen with a bad cat.

I'm still not sold that this is his problem though.

lacville78
08-07-13, 09:27 PM
I'm not the most knowledgeable but im wondering if maybe when the car reaches speed on the highway if the emissions system is trying to suck through the charcoal canister and it is plugged causing trouble at highway speeds.

Benzilla
08-07-13, 09:32 PM
Lol! Great minds think alike. Just now found this thread, But I was talking to Craig after it happened on the phone & we came up with about all the same ideas posted here. Initially thought carb flooding or restricting, I thought it was strange how it only happened at a certain speed, and not with the rpm through shift changes, suggested bad cat converter & discussed rich running & back pressure.

The mechanic he found said it was the egr valve, tried to order a new one (cleaning not attempted), ended up receiving just a gasket (these cars don't even have an egr gasket, unless fuel injected). Mechanic said he bypassed it sent Craig on his way. Problem arose again after roughly 3 hours of driving, on the bridge connecting New York to Jersey of all places. No mention I could find in the service manual diagnostics about an egr valve causing this kind of problem.

Stumped. Still thinking cat or carb, but very curious what the 11 toed mechanic did to the egr valve...

77CDV
08-08-13, 07:16 AM
Looks you all are thinking along the same lines I am. I'll be interested to see what I can find once the car gets home.

deVille33
08-08-13, 11:11 AM
Too bad I didn't see this earlier, You weren't too far from myself and drmenard when this started. :o

cadillac_al
08-08-13, 03:05 PM
Too bad I didn't see this earlier, You weren't too far from myself and drmenard when this started. :o

I was hoping you would swoop in and save the day Mr. 1977. I know we all have lives and can't check in here every day. I am hoping to have my 77 Fleetwood on the road next week like you guys. Cheers.

Bro-Ham
08-08-13, 07:27 PM
I was hoping you would swoop in and save the day Mr. 1977. I know we all have lives and can't check in here every day. I am hoping to have my 77 Fleetwood on the road next week like you guys. Cheers.

Craig seems to have a good attitude about this problem as being all part of the fun and adventure, if you wanted an uneventful drive cross country you could always drive some boring appliance like a Toyota that will always start and stop and never break down and then what fun would life be?!

And to Cadillac Al - - since when do you have a 77 Fleetwood?? Have we seen pictures of this car, well, let me say I haven't seen any, one of my all time favorite cars, please direct me to any threads that tell the story of your car! :)

talismandave
08-08-13, 11:25 PM
Craig seems to have a good attitude toward life in general, and specifically to Cadillac road trips!

CadillacLuke24
08-09-13, 01:53 AM
Craig seems to have a good attitude toward life in general, and specifically to Cadillac road trips!

Craig seems to be fantastic in general. The attitude will naturally follow :D

cadillac_al
08-09-13, 09:18 AM
Craig seems to have a good attitude about this problem as being all part of the fun and adventure, if you wanted an uneventful drive cross country you could always drive some boring appliance like a Toyota that will always start and stop and never break down and then what fun would life be?!

And to Cadillac Al - - since when do you have a 77 Fleetwood?? Have we seen pictures of this car, well, let me say I haven't seen any, one of my all time favorite cars, please direct me to any threads that tell the
story of your car! :)

Yeah, I haven't updated my sig in years. I'll post up some pics when I get her cleaned up.

outsider
08-09-13, 09:29 AM
Where in maine are you? I'm down in Buxton.

Garys
08-09-13, 11:45 PM
Wow, I have been thinking about this a lot. I am leaning towards a bad coil or pickup, but it could be exhaust related too. My nephew Mike, sure thinks it's an exhaust blockage. Too bad it is so hard to find competent mechanics. This issue, once properly diagnosed, will probably be an easy fix! Yes, Craig is a great guy, and an awesome Cadillac enthusiast.

Bro-Ham
08-11-13, 09:06 PM
Half the fun of a breakdown is getting to ride with the chain smoking flatbed tow truck operators and having the car fixed by the local "expert" and then getting back on the road. You may pick up a tobacco addiction along the way... all part of the fun! :)

77CDV
08-12-13, 03:38 AM
Craig seems to have a good attitude about this problem as being all part of the fun and adventure, if you wanted an uneventful drive cross country you could always drive some boring appliance like a Toyota that will always start and stop and never break down and then what fun would life be?!




Craig seems to have a good attitude toward life in general, and specifically to Cadillac road trips!


Craig seems to be fantastic in general. The attitude will naturally follow :D


Yes, Craig is a great guy, and an awesome Cadillac enthusiast.

Golly, guys! I'm blushing already! I'll be sure to post up the final conclusion once the car gets back to CA.

talismandave
08-12-13, 05:53 PM
Hard life being the forum's rock star!

mshamba
08-14-13, 09:19 AM
I had a similar issue with a 76 Catalina. The problem was carbon from long use in the city breaking down due to 13 hrs on the interstate (SC to MO). A local mechanic ran some cleaner through it and it drove back to SC without a hitch. Cost me $20.

CADforce69
08-15-13, 09:00 AM
It´s more than a month since I last entered the forum and now I´m reading this thread. Sorry to know about your problem with your '77, Craig but -as other members said- that´s part of the fun. At least you did more than 3.000 miles in a row without any problem; that´s considerably more than I would dare to do with any of my classic cars. Many years ago, I suffered something similar with a totally different car, an Audi A3; it was due to a fail in the Lambda probe so I would vote for trying to override catalytic converter.

Good luck and I hope it is an easy repair. The car and the driver well deserve it.

77CDV
08-17-13, 11:47 PM
Bypassing/removing/permenantly altering emissions equiptment is not an option, since the car still has to pass CA's biennial smog inspection. :(

Bro-Ham
08-18-13, 12:56 AM
Bypassing/removing/permenantly altering emissions equiptment is not an option, since the car still has to pass CA's biennial smog inspection. :(

You love that government intervention stuff, make it happen! You could always trade it for a Preus! :)

CADforce69
08-18-13, 08:33 AM
Bypassing/removing/permenantly altering emissions equiptment is not an option, since the car still has to pass CA's biennial smog inspection. :(

You could bypass it just to be sure the problem comes from there. If so, it will be easier to find and replace the bad part.

77CDV
08-30-13, 11:31 PM
OK, so the car is back from the mechanic, and here's the deal. The throttle wasn't getting voltage from the oil pressure switch, and there was no vacuum to the distributor advance and the diverter valve was faulty. I'll be giving her a thorough test drive this weekend to make sure the issue is resolved.

Cadillac_Fan
08-31-13, 12:20 AM
OK, so the car is back from the mechanic, and here's the deal. The throttle wasn't getting voltage from the oil pressure switch, and there was no vacuum to the distributor advance and the diverter valve was faulty. I'll be giving her a thorough test drive this weekend to make sure the issue is resolved. Wow. That does not sound like an average run-of-the-mill diagnostic routine or battery of tests. How did the car do otherwise on the cross-country trip? (I had my fingers crossed that it would make it home to you without any blemishes or mishaps on a car carrier.)

77CDV
08-31-13, 01:01 AM
Wow. That does not sound like an average run-of-the-mill diagnostic routine or battery of tests. How did the car do otherwise on the cross-country trip? (I had my fingers crossed that it would make it home to you without any blemishes or mishaps on a car carrier.)

You mean, other than that, how was the play, Mrs. Lincoln? :lol: Aside from her crippling malfunction, Rebecca performed beautifully. AC blew cold, XM (via 8-track adapter) kept me entertained, rode like a dream, and generally crossed the country in a manner befitting a proper Cadillac. But, for all that she looks stunning, she's still 36 years old, and there will be times when her age catches up with her. Still wouldn't trade her for the world, and wouldn't hesitate to take her out on the road again. :)

Cadillac_Fan
08-31-13, 01:10 AM
That is outstanding. Your '77 Cadillac is one of my all-time favorites on this forum. I was a little nervous when I read you were going to have to load her up on a car transport for the trip home. So glad she's back and getting the first-class treatment for some more world-class motoring!

lacville78
08-31-13, 09:13 AM
I am really glad you got her all sorted out! Nothing like these cars. :duck:

CADforce69
08-31-13, 10:09 AM
You mean, other than that, how was the play, Mrs. Lincoln? :lol: Aside from her crippling malfunction, Rebecca performed beautifully. AC blew cold, XM (via 8-track adapter) kept me entertained, rode like a dream, and generally crossed the country in a manner befitting a proper Cadillac. But, for all that she looks stunning, she's still 36 years old, and there will be times when her age catches up with her. Still wouldn't trade her for the world, and wouldn't hesitate to take her out on the road again. :)

I´m glad the breakdown was located. Hope everything goes quiet and comfortable like it was until the problem happened. Cross my fingers too. We have to be understanding with these cars as although they are well maintained and even pampered, they still are near 40 year old vehicles (And in many cases they have a lot of miles on their backs) and some parts may fail at some point (most electronic failures are unpredictable). After all, I´m sure they were not designed to last for so long. Your loyalty to Rebecca is laudable and your long trip with her is an example of courage and trust in your car.

BTW, did you consider the option of following the trip home at a speed this malfunction didn´t happen?

The Ape Man
08-31-13, 02:58 PM
If the carbonator was not getting a good power source from the oil pressure switch the car would have hung up on high idle and the gas mileage would have been very poor.

The diverter valve being bad would cause exhaust pops under high vacuum deceleration.

Vac advance not working would make the car idle smoother and really lousy fuel economy.

None of these things would cause the car to do what you described.

I'd be real careful before doing any long trips.

Just put 500 miles on my own car with a 1975 drivetrain last week. I'm a fellow who likes to weigh risk too : )

talismandave
08-31-13, 08:45 PM
If the carbonator was not getting a good power source from the oil pressure switch the car would have hung up on high idle and the gas mileage would have been very poor.

Vac advance not working would make the car idle smoother and really lousy fuel economy.


10% to 20% worse would be hard to tell, 1 or 2 MPG?:lol:

The Ape Man
08-31-13, 09:54 PM
10% to 20% worse would be hard to tell, 1 or 2 MPG?:lol:

A good working 77 Deville can get 18MPG on the highway at under 65MPH. Less at 70, probably 14.

Without the vacuum advance I'd expect maybe 11 or 12 MPG at either speed. There's a giant difference in economy with the later manifold vacuum sourced vacuum advances.

77CDV
09-01-13, 12:12 AM
Rebecca, like all my 77s, is a CA spec car, so her mileage is a bit lower than you might expect from a federal spec car. Most I've ever gotten out of her is 16mpg at a steady 55 over flat terrain. Anyhow, we'll see what happens when I give her a good road test, probably tomorrow.

Bro-Ham
09-01-13, 11:39 AM
Crossing my fingers your car is fixed!

I always chuckle when I read that a 425 Cadillac is capable of 18 MPG. I drive my 79 Cadillac with 425 daily - have put on 65,000 miles on it in 8 years. I also use the car as my magic carpet for trips from Florida to Wisconsin at least twice per year and wherever else I may go, near or far. It is a 14 MPG car regardless of if highway or local driving. My highest was 15 once on a trip. I have never driven a sustained 55 MPH on a trip, which is the world these cars were designed for (see, there's hope!), it would probably help fuel economy but 18 MPG out of a 425 just seems like dreaming the impossible dream to me. :)

Garys
09-01-13, 12:34 PM
Crossing my fingers your car is fixed!

I always chuckle when I read that a 425 Cadillac is capable of 18 MPG. I drive my 79 Cadillac with 425 daily - have put on 65,000 miles on it in 8 years. I also use the car as my magic carpet for trips from Florida to Wisconsin at least twice per year and wherever else I may go, near or far. It is a 14 MPG car regardless of if highway or local driving. My highest was 15 once on a trip. I have never driven a sustained 55 MPH on a trip, which is the world these cars were designed for (see, there's hope!), it would probably help fuel economy but 18 MPG out of a 425 just seems like dreaming the impossible dream to me. :)

Yeah, the best mileage I have ever got with my '79 FWB is 15 mpg (Federal car)also. I am hoping that the mechanic has in fact found the problem with Craig's car. Not getting power to the carb from the oil pressure switch seems odd to me. I don't recall the carburetor on a '77 having a power lead, except maybe the choke.
140698

The Ape Man
09-01-13, 03:56 PM
Guess some of you guys would have a stroke if you saw the mileage I got from my 1980 Fleetwood when it was all factory eqipped. Not to worry. I've dropped in a 500 now and am way down to 15 MPG mostly highway, 70 MPH.

Bro-Ham
09-01-13, 04:01 PM
Yeah, the best mileage I have ever got with my '79 FWB is 15 mpg (Federal car)also. I am hoping that the mechanic has in fact found the problem with Craig's car. Not getting power to the carb from the oil pressure switch seems odd to me. I don't recall the carburetor on a '77 having a power lead, except maybe the choke.
<img src="http://www.cadillacforums.com/forums/attachment.php?attachmentid=140698"/>

Nice looking 79 Fleetwood! :)

----------


Guess some of you guys would have a stroke if you saw the mileage I got from my 1980 Fleetwood when it was all factory eqipped. Not to worry. I've dropped in a 500 now and am way down to 15 MPG mostly highway, 70 MPH.

So what is the secret? :)

jeff_herry
09-01-13, 05:04 PM
Hello 77CDV,
sorry to see that you got in trouble with your cad. I hade the same issue than you with my 77 fleetwood 4 years ago, and more recently with my 78 fleetwood fuel injection. Exactlty the same things: good idling, and bucking at high speed. With my 77 carb, there were no evidence of backfiring. just a gazoline smell int he exhaust system, just like the engine was running a little bit too rich. With my fuel injected 78, I had lots of bacfiring. I solve the problem when I replaced the vacuum timing advance on the distributor, and the pickup coil. Have you check these part? of course you need to open the distributor, and remove quite everything inside to get the pickup coil and the timing advance system. I have the shop manual, so if you need any other info, just let me know !
Good luck. Jeff.

Garys
09-01-13, 05:31 PM
Guess some of you guys would have a stroke if you saw the mileage I got from my 1980 Fleetwood when it was all factory eqipped. Not to worry. I've dropped in a 500 now and am way down to 15 MPG mostly highway, 70 MPH.

Maybe not a stroke, but I would go ape man! :duck:

The Ape Man
09-01-13, 08:53 PM
Maybe not a stroke, but I would go ape man! :duck:
The FCC made me the Ape Man.

Bro-Ham
09-01-13, 11:12 PM
The FCC made me the Ape Man.

If they made you that way in the 70's I bet it is a CB handle!

talismandave
09-01-13, 11:45 PM
If they made you that way in the 70's I bet it is a CB handle!KXW 3878 mobile here, "The Shenandoah", ya got your ears on!

Bro-Ham
09-02-13, 10:43 AM
KXW 3878 mobile here, "The Shenandoah", ya got your ears on!

21-50, by

talismandave
09-02-13, 10:53 AM
I can't remember what I walked into the bedroom for, but my FCC number I haven't used in 40 years, that I remember!:duh:

The Ape Man
09-02-13, 01:03 PM
Nah it was a ham callsign. Sri fer hijack.

77CDV
09-02-13, 03:31 PM
Sadly, your prediction is correct. Test drove the car last night. Got about 15 miles on the freeway when the symptoms reappeared. Got off ASAP and headed home on surface roads. The car could barely maintain 30 and stalled out completely a dozen times. I barely managed to limp her home and at this point, she's basically undriveable. I'll have to have her towed in Wednesday. The saga continues.


If the carbonator was not getting a good power source from the oil pressure switch the car would have hung up on high idle and the gas mileage would have been very poor.

The diverter valve being bad would cause exhaust pops under high vacuum deceleration.

Vac advance not working would make the car idle smoother and really lousy fuel economy.

None of these things would cause the car to do what you described.

I'd be real careful before doing any long trips.

Just put 500 miles on my own car with a 1975 drivetrain last week. I'm a fellow who likes to weigh risk too : )

Bro-Ham
09-02-13, 04:42 PM
This seems so uncharacteristic of a 425 Cadillac, I hope it turns out to be something severely simple! My thoughts and prayers are with you for quick resolution of this madness! :)

The Ape Man
09-02-13, 05:12 PM
Sorry it isn't fixed but at least you didn't get stuck in da 'hood.

I remember you said there's a booster fuel pump somewhere. If the car is still also using the factory mechanical pump take a look at the 2nd line in post #10.

The pump has a pressure release valve that's suppose to circulate fuel back to the tank. Keeping the fuel circulated helps with vapor lock.

Sometimes these valves get gunked up or just plain don't hold pressure. When that happens the carbonator only gets enough fuel to keep the car moving at slow speeds. Usually a cold restart allows almost normal pressure.

Easily the worst pre-computer Cadillac problem to diagnose I've run into in 34 years. My car had an almost new fuel pump when this happened to me.

Pinching off the smaller return line with needle nose vice grips with a couple of fuel lines slid on their teeth is a quick way to check. Watch out for steering linkage clearance if you try this.

If this IS your problem I'm really sorry I didn't take the time to describe it in detail earlier.

Been there in 1983 or so.

Bro-Ham
09-02-13, 10:14 PM
Ape is the greatest! Craig, I hope this helps you get your car fixed! Now, Ape, when are you going to reveal all the secrets to having a trouble free 81 Cad with V8-6-4? :)

The Ape Man
09-03-13, 06:28 PM
There's nothing in an 8/6/4 that wasn't in later DEFI cars which were regarded well except the modulated displacement itself which was extremely reliable.

Cut the 3rd gear pressure switch wire and poof, no more modulated displacement. It didn't save much gas anyway.

The V6 mode vibrated and made these cars feel like something one would want to trade in. Another annoyance was the idle speed motor could make drivers feel like the car was controlling them. Imagine waiting to pull out into traffic with just enough brake pedal pressure to hold the car. The AC compressor kicks in, the idle motor tries to compensate for the load and the idle increases 125 RPM. Now the car seems to lurch forward....................

Probably best for a seperate thread.

CADforce69
09-03-13, 07:45 PM
Sorry to know the problem is not solved yet but I hope you get it solved soon with this good info, Craig.

77CDV
09-05-13, 03:32 AM
Back in the shop today. We'll see what happens. Fingers crossed here.

Bro-Ham
09-05-13, 03:47 AM
My fingers AND toes and arms and legs are all crossed for you Craig! :)

77CDV
09-05-13, 05:24 PM
My fingers AND toes and arms and legs are all crossed for you Craig! :)

Sounds like you won't be going anywhere fast with all that! :lol:


Thanks, Dave. :)

The Ape Man
09-06-13, 10:55 AM
The problem with having a shop diagnose this is they need to make a profit for their time. Your problem is not constant and requires a warm-up and test drive.

I hope they finally get it.

Best of luck.

CadillacLuke24
09-07-13, 08:16 PM
Good luck!

Koooop
09-14-13, 02:40 AM
Baffling issue. I have one of those in my old vette, I'm down to it being a fuel system issue. At least I hope it's a fuel feed issue .

I've driven 425's Hundreds of thousands of miles, never experienced this.

On another note, I never saw 18. MPG either not even downhill with a tailwind. 18? Someone is feeding exhaust into the interior.

The Ape Man
09-14-13, 10:12 AM
First mistake is disconnecting the EGR valve. It needs to work for max fuel economy. Sorry so many of you guys belong to the friends of OPEC club.

csbuckn
09-14-13, 11:51 AM
My money is on the egr or cat also. Maybe get it to repeat the problem and take the temp before and after the cat. I'd also do the vacuum test to test the egr valve also. The egr feeds right off the cat converter, right? Does it hesitate a little off the line?

Koooop
09-14-13, 05:49 PM
Come to think of it, I did have somebody put a plug in place of the EGR in an LT1. That caused a similar issue. That's easy to test, Just pull the EGR off the valve cover and take it for a ride. Cover it or you will have a big Oily mess on your hands.

Once I drove the LT1 with that issue for a while, the vacuum pressure buildup inside the motor made it buck, cough and stall but it took 20 minutes or so. It was over pressurizing the crankcase.

I do recall having some bizarre EGR problems with some of my 1977 sedan Deville's. the giant poof of blue smoke going up a steep hill every now and again was a real stumper to figure out.

The Ape Man
09-14-13, 06:23 PM
It isn't the EGR in this case. He already went down that road. I mentioned that only for the fuel economy scoffers.

Hey did you guys see my fly by while you were stopped at the gas station?

akimball442
09-14-13, 08:38 PM
First mistake is disconnecting the EGR valve. It needs to work for max fuel economy. Sorry so many of you guys belong to the friends of OPEC club.

... no..... EGR actually measurably reduces fuel economy, on all older engines. It's particularly obnoxious in diesel engines, but certainly doesn't do anything for performance or fuel economy in a gasoline engine.

EGR is particularly evil on older high mileage engines because of the amount of carbon deposits it forms, eventually negating its own purpose because carbon deposits in the combustion chamber cause the pre-ignition condition (say that 3 times fast) that results in excessive NOx emissions to begin with.

Now if everything on the engine was new- that would be a different story. It still would likely not cause a major increase in mileage, but it would definitely not cause as big of a decrease as a malfunctioning system. PS. most EGR systems are not operating optimally on 30+ year old engines. There are exceptions, of course. But I just replaced an EGR valve on a 22K mile 368 that was leaking.

The systems used today are significantly better with electronic controls, but the standard vacuum operated EGR valve on pre-computer cars ONLY helps reduce NOx emissions (which is a good thing, don't get me wrong), and does so at the expense of performance and fuel consumption.

csbuckn
09-15-13, 01:16 AM
So was the egr valve replaced or tested with a vacuum guage? Can you get a temp gauge on the exhaust? Any original rubber gas lines in the system that may be collapsing when it warms up? Just thinking out loud.

Bro-Ham
09-15-13, 04:36 AM
I grew up with 77 and 78 deVilles from new, they were 15 MPG max cars even then, I chuckle when I remember my Dad always madly calculating mileage during the gas crisis in 79 so we could make it between rationed fuel ups. :)

The Ape Man
09-15-13, 11:59 AM
... no..... EGR actually measurably reduces fuel economy, on all older engines. It's particularly obnoxious in diesel engines, but certainly doesn't do anything for performance or fuel economy in a gasoline engine.

EGR is part of the fuel system and spark timing calibration. If it is removed the calibration must be maximized. Your theory may be correct but practice requires more than plugging a vacuum line.

I speak in terms on old Cadillac manufacture engines. Old Cadillac engines do not have issues with carbon deposits in the combustion chambers. The entire innards of most of these engines are usually remarkably clean except intake valve stems which need periodic decarbonization. This holds true for old high mileage engines also. The usual death of a factory 368/425/472/500 is from main bearing slop resulting in low oil pressure to rod bearings.

deVille33
09-15-13, 12:36 PM
I grew up with 77 and 78 deVilles from new, they were 15 MPG max cars even then, I chuckle when I remember my Dad always madly mileage during the gas crisis in 79 so we could make it between rationed fuel ups. :) I don't want to burst your bubble of observation here, BUT, one of my '77 CDV's got 16.5 mpg on the average and our venerable Bruce Roe has tweaked his efi '79 close to 20. 15 may be common, but it is possible to tweak more out of the beasts. :lildevil:

Koooop
09-15-13, 02:55 PM
It seems silly to try to get good MPG out of a big block.

Bro-Ham
09-15-13, 04:35 PM
It is splitting hairs, 14, 15, 16.5, 18 - - and even though some may have been lucky to break 15, I have not that I recall. So put that in your pipe and smoke. I will cocktail! :)

The Ape Man
09-15-13, 07:27 PM
When you drive Cadillacs for many years the savings adds up. I've been driving them 80 percent on / 20% off for 34 years.

No matter what size the engine is, cost is a factor. The large Cadillac engines were designed to behave like smaller earlier engines with less stringent emissions requirements. Economy was part of the design hence the rear axle ratios.

I see a pattern of comparison to other auto manufacturers. Later Cadillacs were more generic. These older engines were much better quality than lower level GM makes. They were built to last longer and deliver decent fuel economy.

Modifications and tuning can ruin economy. Cheaper makes are sometimes way easier to properly maintain.

As said here before, it's a shame a real Cadillac engine never received a smart sequential fuel injection / advanced ignition timing overdrive transmission treatment. It would have stacked up very well compared to the ancient Small Block Chevy which was pressed into RWD Cadillac service.

See you at the gas station.

deVille33
09-16-13, 11:42 AM
It is splitting hairs, 14, 15, 16.5, 18 - - and even though some may have been lucky to break 15, I have not that I recall. So put that in your pipe and smoke. I will cocktail! :) LOL, A lot of this is related to how you drive, how heavy your right foot is, and the conditions relative to the routes and speeds you travel. I had a Pontiac Grand Am, that could get close to 18 if I could keep my foot off the floor. How I loved to hear that quad at WOT and feel my back side pushed into the seat, plus the rush of a buck twenty down the Interstate. :shhh: I drive more conservatively now. Let those go around me, I catch up to them at the next stop light. :yawn:

Koooop
09-17-13, 10:45 AM
Come to think of it, I did have somebody put a plug in place of the PCV in an LT1. That caused a similar issue. That's easy to test, Just pull the PCV off the valve cover and take it for a ride. Cover it or you will have a big Oily mess on your hands.

Once I drove the LT1 with that issue for a while, the vacuum pressure buildup inside the motor made it buck, cough and stall but it took 20 minutes or so. It was over pressurizing the crankcase.

I do recall having some bizarre PCV problems with some of my 1977 sedan Deville's. the giant poof of blue smoke going up a steep hill every now and again was a real stumper to figure out.

I need to correct this.

It's been a long time, when I had this issue it was PCV related, not EGR.

Maybe that'll make sense now.

I'm losing it...

Bro-Ham
09-22-13, 01:19 AM
Craig, is there resolution? We need to keep these yellow Cadillacs rolling! :) Dave

77CDV
09-24-13, 05:28 PM
Finally got her back yesterday. The final culprit turned out to be the mechanical fuel pump. Seems the diaphragm had disintegrated, and the aux electric pump doesn't develop enough pressure to keep the car running beyond idle. I would never have suspected it, since the pump was replaced 5 years ago. Guess that ethanol is just doing wonders for our cars! :bigroll:

Anyway, she's back home now and runs like a dream again. :cloud9: Thanks for all the help, guys! :)

CADforce69
09-24-13, 05:44 PM
I´m glad to know finally Rebecca is fixed and above all, the solution was so simple. :highfive: Anyway, I think today´s parts for yesterday´s cars have not the same quality than those made when these cars were new... I could tell you a few examples with my dodge (which has made 24K miles with me).

Bro-Ham
09-25-13, 08:56 AM
Glad to hear it is on the road again! I always try to fill with ethanol free fuel, I could have sworn there were folks on this forum who said it made no difference. :)

jayoldschool
09-25-13, 02:30 PM
I use ethanol-free in all my classics, my John Deere, and my snow blower. Only the 90s and later cars get the E10. Although, I do recall reading in mom's 1984 FWB owner's manual that the car is "gasahol" safe...

jamespowers
09-25-13, 10:05 PM
I use ethanol-free in all my classics, my John Deere, and my snow blower. Only the 90s and later cars get the E10. Although, I do recall reading in mom's 1984 FWB owner's manual that the car is "gasahol" safe...

Riiiiggghhhtttt.....Gasahol safe. Riiiiggghhhttt. lol lol lol As the ethanol rots the gas lines and ruins the engine. :p

talismandave
09-25-13, 10:07 PM
Hey! They only warrantied them for twelve months back then, they were safe making that statement!:lol:

jamespowers
09-26-13, 01:13 AM
Hey! They only warrantied them for twelve months back then, they were safe making that statement!:lol:

Yeah and twelve months and one day later they blew like Mt. Vesuvius. :p

The Ape Man
09-29-13, 11:16 AM
Finally got her back yesterday. The final culprit turned out to be the mechanical fuel pump. Seems the diaphragm had disintegrated, and the aux electric pump doesn't develop enough pressure to keep the car running beyond idle. I would never have suspected it, since the pump was replaced 5 years ago. Guess that ethanol is just doing wonders for our cars! :bigroll:

Anyway, she's back home now and runs like a dream again. :cloud9: Thanks for all the help, guys! :)

Glad the problem is corrected but the explanation needs work. If the diaphragm were at fault the pump would either not work at all or it would dump raw fuel into the engine oil. Not a normal failure for Cadillac engines of this vintage. Additionally the problem you had was intermittent.

What was really happening was the pump's internal bypass valve was hanging open. This reduces fuel pressure to a very tiny amount.

Anyone driving these cars anywhere distant should bring along needle nose vice grips with a pair of fuel lines slipped on the teeth. This can be used to pinch off the fuel pump to tank return line as described in my previous posts in this thread. That will get you home.

Garys
09-29-13, 12:04 PM
Glad the problem is corrected but the explanation needs work. If the diaphragm were at fault the pump would either not work at all or it would dump raw fuel into the engine oil. Not a normal failure for Cadillac engines of this vintage. Additionally the problem you had was intermittent.

What was really happening was the pump's internal bypass valve was hanging open. This reduces fuel pressure to a very tiny amount.

Anyone driving these cars anywhere distant should bring along needle nose vice grips with a pair of fuel lines slipped on the teeth. This can be used to pinch off the fuel pump to tank return line as described in my previous posts in this thread. That will get you home.

Just added to my '79 Fleetwood's tool box!

CadillacLuke24
11-01-13, 09:36 AM
Finally got her back yesterday. The final culprit turned out to be the mechanical fuel pump. Seems the diaphragm had disintegrated, and the aux electric pump doesn't develop enough pressure to keep the car running beyond idle. I would never have suspected it, since the pump was replaced 5 years ago. Guess that ethanol is just doing wonders for our cars! :bigroll:

Anyway, she's back home now and runs like a dream again. :cloud9: Thanks for all the help, guys! :)

FWIW there's a site where you can check for local stations that offer ethanol free brews.

cadillac kevin
11-01-13, 01:02 PM
FWIW there's a site where you can check for local stations that offer ethanol free brews.

In alot of areas, you can't get ethanol free gas. In MO, you can only get it in the more rural areas.

77CDV
11-02-13, 01:57 AM
I live in CA: You VILL comply und you vill LIKE IT!!!!!!!!!!!!!! :lol:

Bro-Ham
11-02-13, 11:32 AM
I live in CA: You VILL comply und you vill LIKE IT!!!!!!!!!!!!!! :lol:

You seem to be a willing follower of that sort of mantra. :)

Did you ever get this car running right?

77CDV
11-02-13, 10:45 PM
Yep! She runs perfectly again. :)

jamespowers
11-03-13, 02:12 PM
I live in CA: You VILL comply und you vill LIKE IT!!!!!!!!!!!!!! :lol:

I will not AND I won't like it! I do as little as I can. Spare the air day? Drive three cars and use the fireplace. Ethanol? I take all my cars to the place that has barely 10% of it in the gas. The pollcats here get a swift kick in the ass if they come around. :p

cadillacmike68
01-27-14, 05:22 PM
Craig, I'm glad you got it running again. I'm getting a 2nd spare fuel pump for my car. It's a one off year part, like so many 1968 items.

As for the following:


... no..... EGR actually measurably reduces fuel economy, on all older engines. It's particularly obnoxious in diesel engines, but certainly doesn't do anything for performance or fuel economy in a gasoline engine.

EGR is particularly evil on older high mileage engines because of the amount of carbon deposits it forms, eventually negating its own purpose because carbon deposits in the combustion chamber cause the pre-ignition condition (say that 3 times fast) that results in excessive NOx emissions to begin with.

Now if everything on the engine was new- that would be a different story. It still would likely not cause a major increase in mileage, but it would definitely not cause as big of a decrease as a malfunctioning system. PS. most EGR systems are not operating optimally on 30+ year old engines. There are exceptions, of course. But I just replaced an EGR valve on a 22K mile 368 that was leaking.

The systems used today are significantly better with electronic controls, but the standard vacuum operated EGR valve on pre-computer cars ONLY helps reduce NOx emissions (which is a good thing, don't get me wrong), and does so at the expense of performance and fuel consumption.

THIS is why I stay way far away from 1973 thru 1991 cars.

I have enough trouble keeping this 45 yr old Climate Control system working to go down that road as well.

The Ape Man
01-27-14, 08:18 PM
Glad that guy had the time to check each and every EGR system on every older engine. He must have been very busy.