Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

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Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

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Well, thank you, but they're already on my list cause I went through the whole thread https://www.cadillacforums.com/foru...e-cadillac-eldorado-forum/894370-extensive-list-websites-vintage-parts-etc.html

And as I stated above, I'm looking for a way to FIX it instead of contacting shops and junkyards if there is a way.
And maybe someone can verify the cause of the problem before.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

Drill out the hole clean. Tap it. Take a piece of hard line that fits in the hole (slightly over), tap that to screw in the hole.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

Drill out the hole clean. Tap it. Take a piece of hard line that fits in the hole (slightly over), tap that to screw in the hole.

Well, that sounds like a good idea and way better than to weld it. Will try it and see if I can do it on my own.
Thank you! I will let you know if it worked.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

I'll bet that primitive ECM wouldn't even notice if the EGR was disconnected.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

I'll bet that primitive ECM wouldn't even notice if the EGR was disconnected.

Yeah, but if the engine itself gets a reduced oxygen mixture due to the leaking exhaust gas, the effect would still occur, don't you think? No matter what the ECM tells.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

Just to make things a little clearer – this is how it works:

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

I doubt very highly that that tiny hose even carries exhaust, much less would be able to dispense enough to stall an engine if it did. Methinks without input the transducer is allowing vacuum to pass and the EGR valve is opening at idle or very low engine speeds as you describe. If you are unable to satisfactorily repair it the high octane gas in your part of the world will allow you to run the car without the EGR system without any adverse effects.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

I doubt very highly that that tiny hose even carries exhaust, much less would be able to dispense enough to stall an engine if it did.

Well, here is a picture of the bottom side of the back pressure transducer with that tiny hole where the line was meant to lead. Looks like one half is totally blackened by exhaust gas over time:

Methinks without input the transducer is allowing vacuum to pass and the EGR valve is opening at idle or very low engine speeds as you describe.

Sounds logical. But I wonder, shouldn't the problem then occur immediately and not just after some time of driving?

Anyway ... I'm trying to repair it as jayoldschool recommended and see if it works. This should fix it no matter if it's leaking exhaust gas or an improper vacuum which causes the problem. I will keep you up to date.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

I would imagine that it only happens after some driving because when the engine is cold the idle is much higher, maybe high enough where it's not affected as much.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

I would imagine that it only happens after some driving because when the engine is cold the idle is much higher, maybe high enough where it's not affected as much.

Sounds logic.
But what exactly would cause the engine to stall then?

I fixed the tube and it shouldn't let exhaust gas through the transducer. But the problem still persists.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

I'm currently facing a problem with higher priority, so if you'd like to check this out:
78 Seville – No 2-3 Upshift

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

Hug, if I were you I would fill the tank with 93 octane fuel, purchase a block off plate for the entire EGR assembly or fabricate a piece of metal to seal the EGR opening, plug all vacuum hoses impacted by this change, and drive the car. My bet is that the problem will be gone.

I believe the EGR valve is opening when the engine is warm (as is normal) and for whatever reason not closing at idle-either due to a vacuum source not being closed off before the engine reaches idle, or by a binding valve that doesn't fully close when hot. IMO the vacuum source scenario is far more likely, but let's see when we get there. Take the car for a test drive with the changes stated above.

Is this "hose" a rubber hose or a metal tube?

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

Thank you smokus

And I know testing it step-by-step, but I'd like to test as much as possible the next time, so some more questions ...

Is this "hose" a rubber hose or a metal tube?

It's a metal tube.

Hug, if I were you I would fill the tank with 93 octane fuel, purchase a block off plate for the entire EGR assembly or fabricate a piece of metal to seal the EGR opening, plug all vacuum hoses impacted by this change, and drive the car. My bet is that the problem will be gone.

Can't I just plug the vacuum hose instead (w/o blocking the exhaust passages)?
But I will try driving without EGR system definitely.

I believe the EGR valve is opening when the engine is warm (as is normal) and for whatever reason not closing at idle-either due to a vacuum source not being closed off before the engine reaches idle, or by a binding valve that doesn't fully close when hot. IMO the vacuum source scenario is far more likely, but let's see when we get there. Take the car for a test drive with the changes stated above.

I can't imagine that the valve would be stuck only at higher temperatures, and don't know how to check this. For me, the valve looked all fine and pushing it up let it go back smoothly.
Neither would I know how to check if there is a vacuum source not being closed off ...

I did some more research again and there are now more things on my checklist like
- MAP Hose
- EGR Signal Port
- Throttle Body Gasket
- Injectors
- ...

But as I read the following, I thought about the open air bleed at the pressure transducer that will – as far as I understood how it's working – let air be pulled in when the transducer is not closed through exhaust gas pressure. So what if the engine is getting too much air at idle causing the engine to sag BECAUSE of the open air bleed of the transducer?
(And as hot air is less rich of oxygen, the problem occurs when sucking in hot air of the engine after some driving or almost immediately at hot summer days.)

"What is happening is that the fuel/air mixture is off. At idle or lower speed there is more air than fuel being mixed because of the vacuum leak causing the engine to stall out. That is why it runs fine as it warms up because the fuel mixture is richer, as the car warms up the fuel mixture decreases. As you drive the car at normal speeds such as on the freeway, the fuel mixture increases bringing balance to the fuel/air mixture. The vacuum leak in the hose is causing too much air to be added into the fuel/air mixture causing your engine to run lean while at an idle. "

So maybe bypassing the transducer and plugging or just using the system without the transducer would also be worth testing, right?



As reference: http://www.cadillacseville.org/technical.html#18


BTW: Does that look like there hasn't been any exhaust gas let through the EGR valve lately (because of it's very white there and not dark)?

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

Plugging the vacuum hoses is another option, I would choose to totally isolate the system though.

I didn't realize that other parts of the fuel injection system are questionable. The "air bleed" function of the transducer is to relieve vacuum to the valve and get it closed quickly. While possible that it could pull air into the engine if totally defective (highly unlikely to fail like that), I don't see it being enough to stall the car-again, this assumes that the rest of the system is working properly.

My course of action would still be largely the same-isolate the EGR system, and see how conditions change. If the issue goes away, we know where work has to be done. If it doesn't correct it, I would still leave it off the car, and proceed down your checklist, one item at a time. Fuel pressure, MAP sensor and connections, TB gasket, injectors (also check injector seals for external leaks as they can start a fire), temp sensors, etc. That seems like a great site for information, I assume you also have the factory manual for this year car too?

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

Plugging the vacuum hoses is another option, I would choose to totally isolate the system though.

I will try to get a plate to do so.
I was just wondering, if this could do any harm to the engine?

I didn't realize that other parts of the fuel injection system are questionable.

Well, initially not, cause it seemd obvious that the broken metal tube at the EGR transducer caused the symptoms.
But as I fixed this, changed the gaskets, the small air filter at the transducer and test drove without any improvements, I tought I need to step back again and start from the beginning.
Just wanna mention that I renewed almost all vacuum hoses as well. Just need to check the MAP hose again, cause I didn't changed that.

The "air bleed" function of the transducer is to relieve vacuum to the valve and get it closed quickly. While possible that it could pull air into the engine if totally defective (highly unlikely to fail like that), I don't see it being enough to stall the car-again, this assumes that the rest of the system is working properly.

Thanks for clearification, that it relieves vacuum (to fully close the valve at idle).

My course of action would still be largely the same-isolate the EGR system, and see how conditions change. If the issue goes away, we know where work has to be done. If it doesn't correct it, I would still leave it off the car, and proceed down your checklist, one item at a time. Fuel pressure, MAP sensor and connections, TB gasket, injectors (also check injector seals for external leaks as they can start a fire), temp sensors, etc. That seems like a great site for information, I assume you also have the factory manual for this year car too?

Yes, agree.
I will do this and proceed as you suggested.

And yes, it's a great source and perfect addition to 1977 service manual, 1978 service manual (supplement) and 1978 body manual.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

You will be more than fine running without the EGR with hi-test in the tank. Test it out and report back :thumbsup:

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

Just one question until I get to work and report back soon:
In Germany we have 95 and 98 octane gasoline. I used 95 all the time. Would you go for the 98 next time?

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

Not sure if it's throughout Europe, but I know in certain countries the octane rating listed is numerically higher than the equivalent in the US. I would go for the highest available (even though it likely won't ping anyway-just being on the safe side)

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

I unplug the EGR on every old cast iron engine that I own and they run fine on 87 octane. High octane just carbons up low compression engines. I wouldn't think twice about disconnecting it and plugging the vacuum source.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

Guys, I got a plate fabricated to block off the EGR openings, plugged the vacuum hoses and did a 20-30 min test drive yesterday evening.
And guess what? As you hinted: The problem seems to be gone! I had no problems at any time. No more sag.

I will re-test it some very hot day soon, just to add 1% to the 99% of that I'm sure it's fine now.

@smokuspollutus: What would you recommend how to proceed? I mean it's fine for me to drive without the EGR (and focus on my 2-3 shift problem), but if I can repair the broken part and get it back working, I would do so.

For me it seems like the transducer causes the problem, but I can't really look inside or would know how to test ...

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

After some more driving, I had to realize that the problem still exists.
Last time the engine stalled 2 times and driving in traffic was really hard. Shifting directly to PARK as car came to a stop helps to keep the engine running, plus immedate accelaration when shifting in DRIVE.

So ... as I see, the problem may not be caused by the EGR, even if it seemed to work the other day.

Really, I don't know how to continue ... do you have any ideas?

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

Check the vacuum. It could be a simple vacuum leak.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

Check the vacuum. It could be a simple vacuum leak.

It's the vers first thing I did a year ago. As you can see on the image below I exchanged almost every vacuum hose with new ones, just to makes sure, there is no leak.
I did not exchange the vacuum hose that leads to the ECU, but I tested it and it holds vacuum all the time. So no leak there.

Can you tell where to check for a vacuum leak despite of the hoses mentioned above?

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

If it has 18" of vacuum then it is fine, if it has less then it must be leaking. I used some cheap ass colored vacuum lines once and the stuff would collapse under vacuum. I had to remove it all and replace it with real rubber stuff.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

You mean when it holds 18" of vacuum? (Or a constant 18" somewhere?)

The new (red) ones are silicone and good quality - no problems with them. The old rubber hoses had some cracks and got hard, so I wanted to exchange them with some more durable and easier to work with (red color) ones.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

It doesn't have to hold vacuum but it should pull between 15-18 while running. I used the blue silicon vacuum hose but it must have been cheap because it collapsed. The best place to check the vacuum is at the ECM. The ECM needs the vacuum signal the most. The engine could pull good vacuum but the ECM may not be getting it.

 

Re: '78 Seville Broken Exhaust Exhaust Pressure Transducer at EGR Valve

Okay, just to clearify the testing procedure for the ECU/ECM hose:
Can I just run the engine, unplug the hose at the ECU/ECM, and attach a gauge to read the vacuum?
Not sure, if the engine will fail after unplugging the hose ... and don't know if a T-split to attach a gauge will alter the vacuum reading... ?!

Or how would be the best way to test?


Thanks in advance!

 

Good point. I don't know how the engine will run if the vacuum hose is disconnected from the ECM. You might have to T into it. I always check vacuum first any time I have a running issue. You stalling condition sounds similar to a bad MAP sensor which is why I am curious about vacuum. I don't know how your timing is set or if you have checked fuel pressure but those could also be a factor.

 

Alright, will test it by bypassing the whole line/hoses to the MAP sensor / ECU first. Then perhaps do the T split check.

Appreciate your input!

 

So, I did a quick vacuum check test run.
Vacuum says around 18 in idle.
During drive it depends on the condition. Without gas it is around 20 and with increasing gas it drops and has 0 vaccum on full throttle / kickdown.

Does that seem alright so far? Don't know the vacuum specs at the specific conditions ...
And I will do a longer test run and wait for the problem to appear and check the vacuum then again. Didn't had the time yesterday.

 

That's good vacuum. Is it still running rough at idle? If the ECM and trans are seeing 18 in of vacuum then they should be working fine.

 

Well ... I referred idle to be in park position, but is it in drive and during a stop also called "idle" for automatic trans cars?

The reason why I'm asking is: In contrast to the vacuum at parking position, the vacuum at a stop while in drive was a little lower - guess around 15".
Then I did some research about the different readings here: https://www.classiccarrestorationclub.com/article/engine-vacuum-troubleshooting/
And there it says, that if that's the case it would be Poor Rings (Piston?) or Oil (what exactly?). In addition to that it says, that if the vacuum drops to 0" during acceleration: "If the needle drops steady during acceleration there’s a restriction in the exhaust or intake. This is typically due to a clogged muffler or exhaust system."

So, I'm curious if that troubleshooting appleis to my car/condition as well?


But if we assume that the vacuum is all fine – I will do a longer test drive on Friday to see if the problem still occurs – what are the next things to check?
There are some things on my list like TPS, Throttle Body Base Gasket, Intake Manifold Gasket, MAP Sensor, Injectors, Fuel Pressure, ... but I'm not sure what's more possible to cause the problem.

One more thing to mention is that I think that the shifting problem, which also occurs sporadically but most of the time, seems to be connected to THIS problem. Not quiet sure but I think I can fix both at the same time, because last time the car drove all fine and where I thought the problems are gone, BOTH problems were gone.

Do you have any ideas what things acould cause BOTH problems (other than vacuum)?