EGR problem
Thread Starter
Melting Slicks
Joined: May 1999
Posts: 2,037
Likes: 0
From: Sarasota FL
EGR problem
I'm not getting any help on thirdgen.org, so I figured I'd cross post here and so if you guys can help.
1991 GTA - has a tip in stumble and chuggle in low-rpm/high-gear, cruise BLMs of 108. I went through all the test on everything to no avail. Even the EGR tested well according to the service manual. On a hunch, I pulled the vacuum to the EGR and plugged the hose so there was no vacuum leak. All my problems were solved.
EGR duty cycle is going to 99% as soon as I touch the throttle. I think that is normal. But, since it's a negative backpressure design, I wonder if the vacuum bleed off isn't working well. The manual says to apply vacuum to the EGR valve and start the engine - the vacuum should drop and the valve should close. Well, it does, but not instantly. So, maybe the backpressure bleed-off diaphram isn't working well?
Or, maybe the exhaust gas is somehow too rich and the slightest EGR bogs the engine?
Any ideas before I pull the plenum and throw on a new EGR? BTW, I took out most of the EGR wall in the plenum and the exhaust is catless with a flowmaster.
1991 GTA - has a tip in stumble and chuggle in low-rpm/high-gear, cruise BLMs of 108. I went through all the test on everything to no avail. Even the EGR tested well according to the service manual. On a hunch, I pulled the vacuum to the EGR and plugged the hose so there was no vacuum leak. All my problems were solved.
EGR duty cycle is going to 99% as soon as I touch the throttle. I think that is normal. But, since it's a negative backpressure design, I wonder if the vacuum bleed off isn't working well. The manual says to apply vacuum to the EGR valve and start the engine - the vacuum should drop and the valve should close. Well, it does, but not instantly. So, maybe the backpressure bleed-off diaphram isn't working well?
Or, maybe the exhaust gas is somehow too rich and the slightest EGR bogs the engine?
Any ideas before I pull the plenum and throw on a new EGR? BTW, I took out most of the EGR wall in the plenum and the exhaust is catless with a flowmaster.
Racer
Joined: Jun 2002
Posts: 428
Likes: 0
From: Dallas Tx
Re: EGR problem (Aaron's 87)
Based on your diagnostics so far, it almost has to be the EGR valve. If the engine runs right without it connected (with no vacuum EGR flow is zero), then you have just about ruled out other causes. The symptoms sound like too much EGR, causing poor combustion. Do you have a diagnostic chart for the EGR valve?
Burning Brakes
Joined: Feb 2000
Posts: 824
Likes: 2
From: Camden SC
Re: EGR problem (65Z01)
OK
Not exactly sure how this particular system works but am wondering if the vacuum should be there at idle. Is the vacuum control solenloid for the EGR system providing the correct vacuum signal to the EGR valve. If your problem went away immediately by removing the vacuum signal, would that suggest the device controlling the vacuum signal needs checking. If that EGR held vacuum and tested correctly according to the manual, I would go upstream and do some more checking. Once again, not exactly sure how this system is set up but you are definitely in the right neighborhood. Let us know.
dlmeyers 90 coupe zf6 3 speed shocks
Not exactly sure how this particular system works but am wondering if the vacuum should be there at idle. Is the vacuum control solenloid for the EGR system providing the correct vacuum signal to the EGR valve. If your problem went away immediately by removing the vacuum signal, would that suggest the device controlling the vacuum signal needs checking. If that EGR held vacuum and tested correctly according to the manual, I would go upstream and do some more checking. Once again, not exactly sure how this system is set up but you are definitely in the right neighborhood. Let us know.
dlmeyers 90 coupe zf6 3 speed shocks
Thread Starter
Melting Slicks
Joined: May 1999
Posts: 2,037
Likes: 0
From: Sarasota FL
Re: EGR problem (Aaron's 87)
Solenoid and vacuum is fine - the only problem is slow vacuum leakdown on the Valve itself when the engine is idling - I believe it should leak quickly being a negative backpressure design. The book only says it should go to zero, not how fast.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: EGR problem (Aaron's 87)
I believe the bleed off is controlled by the EGR solenoid??
Notice that the solenoid has the vacuum and the air bleed tubes, whereas the EGR valve has only the vacuum line.
However, it is possible that the EGR valve is dirty and so not responding quickly to the vacuum/air on/off signal.
You might try monitoring the vacuum to the EGR valve to see if this control signal is responding quickly. If so, the problem would be in the EGR valve itself.
[Modified by 65Z01, 2:58 PM 8/2/2002]
Notice that the solenoid has the vacuum and the air bleed tubes, whereas the EGR valve has only the vacuum line.
However, it is possible that the EGR valve is dirty and so not responding quickly to the vacuum/air on/off signal.
You might try monitoring the vacuum to the EGR valve to see if this control signal is responding quickly. If so, the problem would be in the EGR valve itself.
[Modified by 65Z01, 2:58 PM 8/2/2002]
Thread Starter
Melting Slicks
Joined: May 1999
Posts: 2,037
Likes: 0
From: Sarasota FL
Re: EGR problem (65Z01)
The valve itself has an internal diaphram that works with exhaust backpressure (or lack thereof, I'm not sure) to bleed vacuum from the EGR valve, even though the solenoid may be commanding it. One of the tests is to apply vacuum to the valve itself with the solenoid lines disconnected so only your vacuum pump is keeping the EGR open. You then start the car and the vacuum should drop and the valve should close. Mine does, but it takes a couple seconds. This leads me to believe it's kind of sticky and not closing as well as it should.
But, I have lots of other things to consider that aren't covered in the book. The valve could have a piece of carbon keeping it slightly open. I may have a couple of clogged injectors compounding the problem. Maybe the ported plenum or exhaust is causing something. The motor might not have enough compression left to burn the EGR. I'd just hate to pull it all apart and spend money on the EGR with no results.
But, I have lots of other things to consider that aren't covered in the book. The valve could have a piece of carbon keeping it slightly open. I may have a couple of clogged injectors compounding the problem. Maybe the ported plenum or exhaust is causing something. The motor might not have enough compression left to burn the EGR. I'd just hate to pull it all apart and spend money on the EGR with no results.
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