: Rough Running 4.9 - Please Help !

08-04-11, 04:06 PM
Hello All,

I've been reading posts here for a good while and recently decided to join because I finally need to ask for some help. Please, please help !

I'm a competent DIY mechanic, and I'm not afraid to take things apart. But I don't understand everything and I don't have any specs or manuals.

My Mom's car is a 1995 DeVille with the 4.9. A few months ago it started running rough. It seemed like it was missing. The severity of the roughness would occasionally diminish when the car was warm. Occasionally but not always. My Dad said that once he noticed that at a traffic light it got almost all better within the 1 minute they were at the light, and it ran much better than before the traffic light. They drove it home and parked it and the next time it was started it was back to running poorly. I didn't experience this, and I don't always trust that my Dad's senses are as mechanically attuned as mine. Since the car basically has only had oil filter and synthetic oil changes every 3,500 miles (and basically nothing else) since 1995 I figured it was time to give it a thorough "tune-up" and I didn't mind spending money on it. It now has 80,000 miles on it. So,

I replaced the car, rotor, plugs, wires, and PCV. I went for the copper terminal distributor cap (much more expensive). All aftermarket parts. That didn't fix it. All the spark plugs that came out of the car looked used but fine. Same with the wires. Same with the cap. The car continued to run poorly.

Then I read a ton MORE on this forum and started learning how to use the Climate Control Center to go through the computer and get the codes. No codes. Repeat- NO CODES. None stored and none current. I went through all the values of the engine monitoring systems one by one, and although I did it quickly everything seemed reasonable (but I didn't spend a ton of time). So based on what I read in the forum I decided that the two parts in the distributor (the Hall-effect pick-up and the Ignition Control Module) could likely be giving me a hard time, so I replaced the entire distibutor (a $100 Cardone-esque unit from Advance Auto), as the cost was only about $10 more than the Hall effect pick-up and the Ignition Control Module put together, and I could get it quickly. I put it all back together just right, but that didn't fix it. The timing is close enough. I moved the dizzy around by hand, as I've been doing for 30 years, and nowhere does the car run without the roughness. I did not replace the coil on top of the distributor.

So I read even more on this forum (now I do nothing but read on this forum in hopes of fixing my Mom's car) and decided that the next thing would be to replace the fuel injectors. I knew that it would be a bigger job but she loves this car. I went through and shut down the individual fuel injectors one by one via the Climate Control Center. I did it three times over the course of 2 days and it seemed that the car would run the same when the number 4 and sometimes number 3 injectors were turned off. I figured that was enough of a reason to get new fuel injectors. So I researched fuel injectors until I was having nightmares about them (fuel rates, fuel flows for different pressures, brands, different models, design I vs. II vs III, pintle designs, etc.). I wound up buying a set of 8 brand new Bosch Type III for $280 delivered. The day the fuel injectors arrived I used the CCC to shut off the individual fuel injectors and number 3 and 4 didn't seem to react as they did before. I started getting nervous. I also bought a GM throttle body gasket and the EGR valve gasket. I removed everything and cleaned everything. The vacuum hose coming off the fuel pressure regulator was dry. I cleaned out the EGR tubes under the throttle body (and they were not totally obstructed, maybe only about 25% for the rear one and 50% for the front one. Now they are near perfect). I thoroughly cleaned the throttle body. It looks shiny new now, top and bottom, and all vacuum passages are clear. I bought new vacuum lines and connectors where needed, and checked all those.

I reassembled everything this morning, making sure there were no places that didn't either have a new piece of vacuum tubing or where I felt confident that the old ones were OK: I replaced about 50% of the vacuum connectors and tubing. Then I started the car. It is STILL missing. And it even more noticeable than before!!! HELP !!!!!!

With the new fuel injectors and vacuum lines i sense that the engine is more powerful, but the miss/missing/rough running is now more violent. I rotated the distributor back and forth and the same thing. I can tell where it "should" be but the roughness is bad everywhere.

Now I feel badly for having spent so much money on the car and have not yet fixed the core problem!!!! I feel badly.

After I started the car I listened closely to the motor. The only thing I could hear that sounded strange to me was that I could hear arcing in the distributor. Now I know that the distributor is supposed to arc between the rotor and the cap, but I've never heard it that loudly before in my life. I've never worked on Cadillacs, V8s, or this car before (with the exception of replacing the tensioner pulley from that poorly designed plastic one to a new GM metal one). And the other thing is that I found a line that looks like an unplugged vacuum line running parallel between the engine and the firewall. I traced it and it comes from under the car on the left side (driver's side in the USA) along with what I think are the fuel lines. It has a 2.5 inch piece of rubber tubing on the end that looks like it should be connected to something. I've temporarily plugged it up, hopefully it might cure an open vacuum leak, but it doesn't seem to make a difference. But maybe whatever it GOES TO is sucking and an open vacuum still exists, and is causing the roughness problem. I need to figure out where that line goes.

I'm feeling embarrassed at this point. The three things that people have most frequently mentioned (that I haven't yet done) are the PCM ($100 Cardone), the coil ($30), and the EGR valve/solenoid ($86/$40).

First, I want to check the coil on the top of the distributor. How do I do that with a multimeter? What are the specs? Can I measure the resistance of the coil? and also the resistance to "ground"?

Next, can someone give me specific instruction on how to precisely check the EGR valve and solenoid.

And lastly, and maybe most importantly, can someone tell me where the heck that vacuum line behind the engine goes?? I've looked and I don't see anything. Not that I can see anything behind the engine. So a little help would be greatly appreciated.

Thank you kindly,

08-04-11, 04:44 PM
Sounds like vacuum to me. A vacuum gauge from Autozone costs about $15 and is worth having. Put a tee-fitting somewhere and use the gauge to monitor the pressure, should be 15-20 hg inches.

Could also be the fuel pump dying out. You need a fuel pressure gauge that goes up to 50 PSI to check that and they aren't as cheap.

A picture of the line you found would be helpful.

08-04-11, 07:36 PM
Here is a picture of the line behind the engine (the one I don't know where it goes to).

Who can tell me what this line is, and where it is supposed to go. Is it a vacuum line?

08-04-11, 10:07 PM
Dude you are one helluva writer! Now go to ebay and get your FSM. It's pennies compared to what you have spent on parts. All of your questions are answered there. You are probably a hair from finding the real problem

08-04-11, 11:06 PM
You have my sympathy, I have the same problem with a 90 Deville 4.5. Lots of money and time invested, all new parts and still misses. The only thing I could add to help would be for you to get a mechanics stethoscope to check that the injectors are clicking while the eng is running. If they are you can probably rule out the ECM and not waste more money on that. The other issue discussed in another post here is defective NEW parts right out of the box. No longer can you assume that because the part is new or rebuilt it can be ruled out as the problem. The more you are able to test, measure or put a gauge on the less money wasted. Good luck

08-04-11, 11:21 PM
I didn't see anything about the O2 sensor, may have missed it but those can cause havoc also. As mentioned I installed a new Bosh O2 sensor as preventative maint along with other repairs. It was bad right out of the box but becuase I had done a lot of other work I really went round a round with much expense before I figured out what was going on. A new AC Delco O2 sensor helped a lot but there are those who have had problems with AC Delco as well.

08-04-11, 11:54 PM
A little more info: the engine doesn't surge. The idle stays rock steady, even though it's running rough/missing. It is approximately at the correct rpm range too at idle. The vacuum hose off the fuel pressure regulator was dry.

Getting a Factory Service Manual for the car is a good idea. I've started looking into it, but I don't see any on eBay (1995 Cadillac Sedan DeVille 4.9).

I'm not bothered by having spent money on the new spark plugs, wires, cap, rotor, PCV, vacuum hoses, gaskets, and even the fuel injectors. Mom would be happy to use this car for another 15 years (if she's able to drive that long). In hindsight the distributor wasn't needed but I'm not about to start crying over spilled distributors.

I know that I now need to do tests and use more brainpower.

I want to check the grounds on the PCM. Who can tell me where the PCM is located on this car?

Does anyone know if AutoZone (or anyone else) has a loaner fuel pressure gauge?

More thanks.

08-05-11, 09:28 AM
Getting a Factory Service Manual for the car is a good idea. I've started looking into it, but I don't see any on eBay (1995 Cadillac Sedan DeVille 4.9)

This pair looks kinda raunchy, well used but both volumns are there.


Tons of information in these manuals from front bumper to rear.

I want to check the grounds on the PCM. Who can tell me where the PCM is located on this car?

Not sure, but I do know you have a lot of components on the backside of the rear seat accessed from the trunk. You might want to take your power connections and grounds off and clean them just to be sure if you haven't already.

Does anyone know if AutoZone (or anyone else) has a loaner fuel pressure gauge?

Yes, most of them do. When you check the pressure, you turn the key on for a few seconds, turn it off and your pressure should hold. You should have between 40 to 50 lbs. You can also check it running, don't remember what it should be specifically, I think a bit less which will tell you if your pressure regulator is ok. Also take the vacuum hose off the pressure regulator, it should be dry and if it is wet inside the hose you have a leaker and will need changed. You can usually tell this if the mileage drops.

the recluse
08-05-11, 07:10 PM
Fuel pressure sensor would be my guess as a place to start. It's not monitored by the computer and can cause a rough run and yet, not a rough idle. When fuel demand needs to be increased, a failing pressure regulator can't keep up. Costs about $30 on Rockauto. Can be checked with a fuel pressure gauge.

08-06-11, 09:20 PM
http://www.asashop.org/autoinc/sept99/techtotech.htm I found a computer at a junkyard for $10 and just plugged it in. No more searching, no more miss. Also give your wires a check and make sure they are all where there supposed to be 1-8-4-3-6-5-7-2 is your firing order, your distributor turn's counterclockwise.

08-07-11, 10:17 AM
[QUOTE=Moms95DeVille4.9;2673065]Hello All,

And the other thing is that I found a line that looks like an unplugged vacuum line running parallel between the engine and the firewall. I traced it and it comes from under the car on the left side (driver's side in the USA) along with what I think are the fuel lines. It has a 2.5 inch piece of rubber tubing on the end that looks like it should be connected to something. I've temporarily plugged it up, hopefully it might cure an open vacuum leak, but it doesn't seem to make a difference. But maybe whatever it GOES TO is sucking and an open vacuum still exists, and is causing the roughness problem. I need to figure out where that line goes.

I'm not familiar with your car, but if I had to render a guess I would say that it's a vapor pipe that goes to or maybe from your charcoal canister. I believe the pipe is made of nylon and is assembled together with your fuel lines.

08-07-11, 01:46 PM
You might want to see if you can match lines from this diagram, it could be a fuel line vent or otherwise.


08-07-11, 02:45 PM
Hereís a vacuum diagram that may or may not prove to be useful. Itís not for a 95 Deville but it probably reflects the vacuum layout for a 4.9 of that era.

08-07-11, 03:28 PM
I reassembled the fuel injectors and rail, the thoroughly cleaned throttle body, almost all new vacuum lines and connectors to the throttle body, the old EGR valve with a new gasket (the old gasket was fine), and the distributor cap/coil/wires. I installed an auxiliary ground (from regular 14 gauge wire) running from the chassis just in front of the battery (where the negative battery cable attaches to the chassis) to under one of the bolts of the cross member on the same side, just to hopefully improve the chassis ground.

I turned the key and it pretty much started right up. I don't think it is running as perfectly smooth as it used to run before it started running badly a few months ago, but it isn't missing badly now. So that is a huge improvement. I did hear a slight knock but then I have only timed it by ear so far.

With the car running I then removed the fuse for the fuel pump and the car died within one second. So I followed the procedure for checking the fuel pressure with a gauge borrowed from AutoZone. Connect gauge, then re-install the fuse. Turn the key on (and cycle it several times, since the fuel pump only runs for 2 seconds until the engine starts) and take the first reading:
42psi - with the ignition turned on and the engine not running. I maintained that pressure for a few minutes.
Then start the car and take the second reading:
37psi - with the engine running. Another steady reading.
Then I decided to remove the vacuum line from the fuel pressure regulator to the throttle body:
45psi - with the engine running and the vacuum line to the fuel pressure regulator removed. Also steady.

I think those are good readings, right? I thought 43.5psi was standard, is that right? And with these new Bosch Type III injectors a 42psi reading should be fine, right?

I still can't figure out where that open-ended vacuum-looking line goes, or what it is. I traced it back along with the fuel lines to above the gas tank. I capped it off for a few days and then opened it up today and heard a slow hiss and it smelled strongly of gasoline. Could it be a crazy gas tank vent tube? And if so, why just leave it hanging between the firewall and the engine and not vent it somewhere else? I did NOT find it in any of the diagrams from compnine.com The charcoal canister is on the left (driver's side) and I didn't take a close enough look at it, but I thought I saw that all isn't ports and lines were accounted for.

Thanks cctgene for the vacuum diagram. It is exactly like my car, but I don't see my mystery open line on the diagram. I have all other vacuum lines accounted for.

If I can find a inexpensive Engine Control Module (ECM/PCM) then I'm going to buy it just to compare it with the one I have. Or if anyone is in Delaware and has the same car, I'd be interested in swapping for a few minutes just to do the test. The car was silky smooth until a few months ago. It is much, much better now after all I have replaced.

Let me know if anyone has an idea about that mystery open line behind the engine, or if anyone has an ECM that they can lend or sell me.

08-07-11, 04:39 PM
Sounds like junkyard time to me. You might be able to kill 2 birds with one stone, an expensive PCM (doubt you need it as it appears you had a poor ground) and do a comparison on that line. It's possible that line got moved from it's original location? It has to go somewhere. You don't want gas fumes or anything like that above the exhaust. Where does the other end of that tube go?

08-09-11, 05:52 PM
OK, so I think I found out where that open line went to. Thank you dennis93coupe and cctgene for the diagrams. It seems that it went to the Evaporative Emissions Canister. At first I didn't think so because it was so far away from there (behind the engine), but in the end I found one open port on the canister and the open line smelled of gas after I uncapped it. And the line does travel up along with the fuel lines, as the diagram indicates from cctgene. Rerouting my line (hopefully) "back" to the canister wasn't difficult but neither was it necessarily easy. Someone must have re-routed the line behind the engine intentionally at one point because it didn't get there by itself. And I can't understand why anyone would do that!!! And it must have been that way for many years (my parents haven't had the car in a shop for many years. The only thing my Dad does is change the oil filter and oil with synthetic every 3500 miles). Interestingly, the line wasn't long enough to reach the canister; it was like 2 inches short. I figured that I might not have used the same routing as the factory. I used a new, longer piece of vacuum/fuel hose for the connection and now it is on. I haven't driven the car around yet but I started it up and nothing blew up or set codes. Does that all sound reasonable?

And while car is not missing badly like before I did all the work, it still doesn't idle as silky smooth as before. It feels quite "lumpy", if that makes sense. And it ran silky smooth from the time it was born in 1995 until about 3 to 5 months ago. I'd like to get that "silkiness" back, so I'm going to buy the Factory Shop Manual and I'm also looking into buying a used Engine Control Module (Powertrain Control Module). I'm also going to test the MAP sensor, the Throttle Position Sensor, the EGR solenoid and the EGR valve, if I can. From what I've read, those seem to be likely culprits.

I just wanted to let everybody know what is going on and, as always, I welcome any comments or recommendations.

08-10-11, 09:48 AM
The vent line was 2 inches short because it connects to the tank pressure control valve rather than the charcoal canister itself. There should be another short hose that connects the two together. At least that's the way my 92 4.9 is set up.

08-15-11, 03:23 PM
After replacing the fuel injectors and driving the car a few times I determined that the new fuel injectors that I installed 1.5 weeks ago did seem to solve the strange miss. But the car was still idling poorly, and running roughly at lower rpms.

Everyone told me to get the Factory Service Manual in order to start diagnosing everything, so I found one at a great price. While looking around online I found a used computer for $40 delivery included and decided to splurge.

Well, they both came today. I unplugged the old computer and plugged in the "new used" one I bought. I started the car up and it was immediately obvious that the car ran smoothly again, like the day it rolled out of the factory. YEAH!!!

So I think the original poor running condition was a combination of both a few fuel injectors and the PCM (ECM). So the only work that I feel was completely unnecessary was the installation of a new distributor I got from Autozone for $100; that was when I thought it was either the Hall Effect switch or the ignition control module.

The only thing that remains is to time the distributor correctly and maybe re-learn the ISC (though the idle seems at a reasonable level).

I finally went through Dad's receipts for work done to the car (he saves all that type of stuff) and the car had a new GM ISC installed at 54,000mi by a dealer for a total of $310.

Mom has to start driving Dad to his chemotherapy tomorrow, so just in time.

Thank you again everyone for all your help. Not only were you all great, but it meant a lot to me to not feel alone in dealing with it.


08-16-11, 09:33 AM
One more thing of interest: after removing the old and ORIGINAL PCM "computer" that was in the car, there was a sticker on it that read "Remanufactured by General Motors". My Dad doesn't ever remember a Cadillac dealer doing anything with the computer, he doesn't remember any recalls being performed, and he has no receipts for a replaced computer or anything having to do with the computer at all.

So we are thinking that the car might have rolled off the production line with a remanufactured PCM. It isn't a big deal but I'm curious: could the car have been sold new with a remanufactured PCM or is it more likely that the dealer did a recall (or something) without telling us?

08-16-11, 09:39 AM
Maybe a PROM upgrade and the dealership just swapped the box instead of trying to replace the chip

08-16-11, 01:35 PM
Hard to say how it got there in place of the factory installed unit, might have been a campaign they never said anything and just changed it out. I know from looking in my C body parts book, (predeccessor to your Mom's 95) and only a reman PCM and BCM were listed in the catalog. There was no part number for a new unit and they were only listed without the PROM chip.

08-23-11, 03:17 PM
Well, it has been a week and it continues to run perfectly smooth. So I feel confident that it was both the PCM computer and the fuel injectors. Boy, does that engine pick up and go nicely when it is running correctly. I love the torque and the smoothness. Mom and Dad are happy again. I'll try to remember to give an update after a few months.

08-23-11, 03:36 PM
Thanks for the follow-up

The Gold
09-11-11, 11:18 PM
Nice write up.
How's the car running??

BTW where did you get the computer?

09-12-11, 02:37 PM
The car continues to run perfectly.

I don't know if it is related, but the check engine light came on 3 days ago and I haven't had time to take a look at it yet. After I did all that work I never set the timing correctly (jumping the connector under the dash, etc), so I hope it is something simple like that.

I found the computer on eBay for $40 delivered (and with guarantee).

The Gold
09-13-11, 01:47 PM
Thanks for the update. Your DTC dash codes ought to reveal why you get the CE-Light.

Keep us up to date. This was a very informative thread !!

The Gold
09-17-11, 09:14 PM
HeyMoms95Deville, I was so inspired by your thread that I deiced to finally go to a local Pick n' Pull and get an
engine computer.

The 92 Eldo was stripped of it as was a 92 Seville so I found two 92 DeVilles.
One Deville had a bit of oxidation on the 'puter retaining bolt and the engine parts had been ignored.
The other had no oxidation on the computer retaining bolts and it had a recent DMV temp operating permit on the window. Plus the 4.9 L engine had been hit up and the injectors pulled, so I figured this car had had some updates.
Lo and behold, I pull the computer and its a new replacement. Not the original factory but the same part no. 16132240 as my '92 Eldo.
So I feel fortunate. ($50 plus tax etc).
Now it will take me couple of weeks to swap and see if that smooths my idle.
I have an idle/missing problem. very slight and have done all the due diligence.
Normally I don't like to throw parts at a problem but your story was so close to mine (idle part) that I decided to move on what had been on the back burner.

I'll post an outcome when time permits the swap.

BTW besides disconnecting the battery, was there any other thing you did before/after swapping 'puters?
Did you have to do the idle learn after?

EDIT: after referring to my FSManual I do have to do the idle relearn as well as clear codes. The PROM (MemCal) in my Deville unit is for a Deville only so I have to swap my Eldo MemCal prom into the new computer also. I cross refernced rockauto ac/delco prom part numbers and they were different.

10-02-11, 10:08 PM
I did NOT do a "re-learn" of the Idle Position Sensor (IPS). I simply unplugged the old computer and plugged in the new one. Night . . . to . . . day. With the new computer plugged in it ran perfectly smoothly and idled where it was supposed to.

I finally got the code from it though ------> P048 and P052.

So it seems that the EGR system is not not quite right. (?) It makes me wonder if it has to do with me plugging that "mystery" line back into the Evaporative Emissions Canister. Maybe someone unplugged it for that reason? Or does it have to do with the EGR valve? Does anybody know? Or could the fuel injectors be causing it? My parents say they don't care, since it runs perfectly, has lots of power and the fuel consumption seems correct. I'd like to leave it perfect.

Let me know what you think! And thanks again.


The Gold
10-03-11, 01:38 PM
Hey, I figure that if one does not disconnect the battery before swapping computers, there is a better chance that the idle will still be ok.
The manual requires the idle learn after replacing the computer and or eprom (memcal).
Anyway, the procedure is easy and it is meant to assure that you don't get idle surges while slowing down etc... possible danger.

The PO52 (same as EO52) simply states that the PCM memory was reset. After a couple of ignition cycles it ought to become PO52 history.

The P048 (same as E048) tells ya that "EGR system fault"

among other things, you can manually lift the EGR valve diaphragm after engine reaches greater than 80 deg centigrade coolant temp.
with air filter asembly off, and engine idling, reach both hands under the EGR valve in order to lift the underside diaphram. This out to cause the engine to stall. That simply tells ya the diaphragm seems OK and/or there are not excess carbon deposits.

the next tets are vacuum tests and testing the EGR solenoid vacuum.

An easy vac pre-test is to examine all the vac lines for the valve and solenoid and also look at harness connection for solenoid.
You may have a small hairline crack somewhere...

the solenoid has a funky filter on the end of it. Foam like packing foam. Yours may already be cooked off. Try removing the solenoid and looking at the bottom nipple where the filter attaches to make sure it is not clogged.

What kind of gas mileage you all getting CITY, Hiway, City-Hiway combined?

I did replace my computer with the junk yard one. The only difference was the ED36 and ED37 data readings seemd to change from slightly rich for both injector banks to slightly lean for both injector banks.

The sublime missing/idle discrepancy remained the same.

(I need to check my MAP next before suspecting injectors, since I have done all other points.)
My gas mileage varies, it can be 13-14 pure city driving, to 16- 18 mixed city/hiway and a bit better pure hiway driving. Otherwise the engine operates fine and starts up right quick.