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Where do I go from here?


Devin O'Conor

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My 1991 DeVille just won't run right. It feels like it is running on 6 or 7 cylinders and is very anemic where power is concerned.

I have replaced the plugs, wires, cap, rotor, coil, ISC motor, and no change to speak of.

At first it would clear up and run better after the engine was at full operating temp but now it runs that way all the time. Since the beginning, I had one code....E71 which is an Intemittent MAP signal. After replacing the plugs, the car would stall often. Upon further investigation, the wiring connector going to the MAP sensor was bad. If the car was running and I would wiggle the wires, it would stall. I replaced the connector today and it cured the stalling but not the rough running.

I have checked the EGR valve by pressing up on the plunger with the engine running which causes the engine to run very rough. I read that this meant the EGR valve was fine. The fuel pressure regulator seems to be fine. No leakage from it in the vacuum lines.

After replacing the MAP sensor connector today, I cleard the codes. After driving about 25 miles with the engine running rough the whole time, no codes have returned.

I thought I might have a bad or leaky fuel injector but when I had the spark plugs out, none showed signs of a lean or rich condition.

Perhaps my catalytic converter is getting clogged?

I just don't know what to check next. I am getting very frusterated. Can anyone offer any more ideas? It would be greatly appreciated.

Thanks.

K.O.T.

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Devin,

You never mentioned throttle body, did you clean it up really good? Perhaps it was the easiest thing among all the stuff you have done but it REALLY could make the difference.

The saddest thing in life is wasted talent

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Yes, I read that. I pushed the EGR diaphram up and it did start ideling rougher like that post said it would if it was flowing fine. Is it possible that the EGR is stuck open and flowing exhaust gasses at all times? If that's the case, it would be easier to just block it off.

K.O.T.

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I know if the EGR valve was stuck open it would cause it to run rough but it wouldn't if it was blocked would it? Anyone else have any ideas?

If the EGR was the problem, it would go away if you blocked the EGR, yes. But I don't think that's your problem. When you say it runs "rough", can you explain that further? Does the engine vibrate at idle and when it's running, like cylinders are misfiring? Or does the power kind of come and go, like maybe it's an airflow problem. If all the above is combined with it being very sluggish, as you say it is, I would be led to suspect the catalytic converter, or some other part of the exhaust that is plugged. Unfortunately, it's hard to actually check that without taking it off. And typically, once you remove a converter, it's technically illegal to reinstall it...so I don't know how a shop would treat that situation. It'd be easy for them to cut it out, but as far as reinstalling it if it's good...I don't know.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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Well, it wasn't the EGR valve. I removed it and as it turns out, it has a leaky rubber vacuum upper part (not sure what it's called). Because of this, it was not opening anyway. I blocked it off none the less. As for how it seems to be missing.....

It idle's kind of rough. Usually the problems get worse as the engine warms up. I have found that it runs roughest at lower rpm's. If I am driving down the street at 35-40 mph, giving it only enough fuel to maintain speed, it seems like the engine is missing and sometimes sounds like a bad main bearing thump and the engine seems to shake(this engine has little if any main bearing thump...the noise when it is running rough isn't as bad as a knock though) It is the same when accelerating from low rpm's. It seems to smooth out as the rpm's go up. I have found that if when I am driving at 35-40, if I put the transmission in 2nd gear, the roughness seems to smooth out.

Perhaps this will help someone who has experienced this identify the prblem.

What is the best way to test the injectors so I can rule that out?

Thanks.

K.O.T.

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Dah...91 deville. I must have had a blonde moment. You are very right...no coil packs. And I would have known that if I would have noticed the year.

Caddy_Grill.jpg2008 DTS
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I cannot help you with your problem, but if it's cat related, I can help explain the leagle issues with cat repairs. When the cat has been replaced, the shop will give you a written document, explaing why the cat was removed and replaced. That written document must remain in the car for the rest of its life.

I don't know the fine details as to why a cat would be removed, but the documents I have seen state "cat failure, cat plugged, whatever. Replace cat." I don't know about testing cats, it seems logical that if a shop removes a cat, they install a new one. That way, it makes it easy with the documentation and keeps the feds off their butts. After all, with all the b/s involved with federal regulations, and the $25,000 fine issued for altering emission equipment, if removing the cat as suspected cause of running problems, it's probally in everybody's best interst to install a new cat and issue a document that says "cat plugged, install new cat."

If you do resort to the cat as a suspeced problem, make sure you go to a well known professional exaust shop so that the repair complies with laws.

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When it is running at full operating temperature, instead of the normal exhaust sound, it sounds strange like pfft pfft pfft pfft pfft. It sounds like an old model T or something.

Despite I cannot recall the sounds an old T-model made, the newer car (1991 Seville) makes the sound you described only then it is 180 and up. The source is still under investigation. :D

The saddest thing in life is wasted talent

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Check that CAT!!! See my OT post on my Monte Carlo, the 91 (which I had) will destroy the CAT and its possible that your CAT is destroyed inside and is blocking the exhaust, Mike

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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