Screaming EGR

Guest · Post by **Guest** » Mon Apr 03, 2006 10:57 am

'90 GT 3.1L suddenly loses power after a short ride. It limps home under limited power. A day later, same problem after only two miles traveled and much less power.

Condition deteriorates until it can only be started at wide open throttle. Sometimes, it will relax into an idle (850-1200 RPM) but usually stalls.

EGR (the three solenoid type, not the digital one) was broken at the base, I replace the unit with another in good condition. When it will run the EGR screams with a kind of rapid open/close sound. Code 33 persisted (indicating MAP sensor). MAP sensor checks out, vacuum lines replaced. Good pressure at tail pipe. No Change.

Compression test reveals an even 170 in all cylinders. Plugs and wires replaced, no change. Code 33 dissapears at some point during the day (before swapping MAP sensor). I change the crankshaft position sensor and the engine started and ran much better. Still runs unevenly, stuttering scream of EGR reduced to a howling, inward whistle. Starts easier, but still very wrong on acceleration, hesitating momentarily or stalling outright.

I had the front valve cover off and the valves seem to be functioning well.

Duty cycle test of plug wires reveals a reading of 0 on plugs 2 and 4. Plug 1 fluctuates between 0 and 99. All other plugs reading 99. I pulled all of the coils (could they be stuffed in a more annoying place?) and replaced them.

Changed the oil at the same time.

New coils made it run still better, but not right. EGR still acts strangely, whining sound is not as bad but still present. Still hesitates on acceleration, but will run through full RPM range without stalling.

Tested wires on duty cycle again- same results. Packed it up and walked away after a long and frustrating day.

I tested the system throughout the day using a Snap-On diagnostic tool, everything appeared to be normal (when I could get it to run long enough for a reading) except that it was reporting a lean exhaust later in the day, as opposed to a rich exhaust when I first tried it in the morning. The system is OBDI and, I confess, I was a bit dissapointed by the amount of info the tool could give me without a computer hooked into it.

Now I know that a bad O2 sensor could cause some inefficient operation, but this is a serious driveability issue. The car isn't usually driven often, but at the time that it began to fail it was in use regularly.

As I replace components, the symptoms improve. What could be the root of these problems? I really don't want to start the expensive trial and error process, but I'm really at a loss here. I've been reading this forum for some time, and found it very helpful and instructive.

This is my first big stumper, little help?

rweatherford · Post by **rweatherford** » Mon Apr 03, 2006 9:32 pm

Are you sure that the "newer" EGR you put on is exactly like the old one and is actually working correctly?

Does the exhaust still have a converter on it and have you checked the exhaust backpressure at the oxygen sensor?

Mr Goodwrench · Post by **Mr Goodwrench** » Mon Apr 03, 2006 9:56 pm

You Probly have the wrong EGR valve.. check the tube for brakes an leaks. Get the corect valve for the car..
inside the egr valve are 3 inlets 1 for each solenoid..
inside the inlets are the orfice tube. each car brand will have a little different size of inlet.

Mr Goodwrench

Guest · Post by **Guest** » Tue Apr 04, 2006 9:33 am

I took an EGR off of a junk yard 'retta. When I still had problems I swapped with my father's Lumina Z, as they looked identical. It didn't help me, and din't hurt him. There was no change in his vehicle and my problems continued.

It still has a cat converter. What kind of pressure am I looking for? Pressure built quickly at the tailpipe when I checked it out. I will pull the O2 sensor (any tips on coaxing that sucker out?) and test for pressure. A new O2 sensor is pretty cheap, and there's no harm in replacing it.

Could a PCV valve be at fault? It seems strange that so many parts could go so wrong at once...

And what would yield a 0 on those two plug wires?

Guest · Post by **Guest** » Tue Apr 04, 2006 6:39 pm

Thanks Rex! You get the prize!

"Does the exhaust still have a converter on it and have you checked the exhaust backpressure at the oxygen sensor?"

Disconnected the pipe, and she roared to life. Sure, all of my work to this point amounts to a very thorough and expensive tune-up; but I've neglected my baby for too long.

Now... Can anyone recommend a performance exhaust?

Thanks again!

berettajunkie1991 · Post by **berettajunkie1991** » Sun Apr 09, 2006 1:05 am

on the 3.1 it never end i have just replaced my 3.1 with a new bored over 3.1 and im still getting all the glitches out of the car and i have had it for a year already

Capt Crazy · Post by **Capt Crazy** » Tue Dec 19, 2006 2:21 pm

I believe that there are two maf sensors - one on the firewall and one in the air filter channel pipe - for the maf sensor code problem...

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