EGR Troubleshooting
Thread Starter
Le Mans Master
Joined: Sep 2002
Posts: 5,235
Likes: 898
From: Myrtle Beach SC
EGR Troubleshooting
I did a search of the forum but unsuccessful. I'm troubleshooting a bad running 78 L82 and at a point that I need to test the EGR valve. As background, I've have gone through fuel system, ignition system and now EGR. Stumbles and runs erratically at idle...still after fuel pump replacement and carb rebuild. Just checked plug wires and resistance is consistent among all wires. Have also inspected hoses and no obvious leaks...headlamps pop-up smartly!
So the EGR valve. I've removed and inspected valve opening...not carbon bound. Diaphragm moves freely and plugged it into another 78 at both a port and TVS switch hose...but diaphragm does not move. Now, I did not increase rpms past idle.
Suggestions?
So the EGR valve. I've removed and inspected valve opening...not carbon bound. Diaphragm moves freely and plugged it into another 78 at both a port and TVS switch hose...but diaphragm does not move. Now, I did not increase rpms past idle.
Suggestions?
Melting Slicks
Joined: Mar 2008
Posts: 2,989
Likes: 198
From: Meriden CT
As a quick check I push on the diaphragm while the engine is running. If it stumbles and RPM drops you know that the EGR is closed at idle. This doesn't mean that it's working as you drive, but you can find out if it's effecting the idle.
Drifting
Joined: Apr 2008
Posts: 1,305
Likes: 2
From: Lewisburg WV
thegazman
I have a 79 L82 that had a similar problem. My plugs were fouling from carbon deposits. If your problem is at idle only it could well be your EGR. A faulty EGR is usually a problem only at idle as it normally opens at higher speeds. Maybe you're getting vacuum to your EGR at idle through a defective vacuum switch. Pull the vacuum line off of your EGR and plug it for testing.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
I have a 79 L82 that had a similar problem. My plugs were fouling from carbon deposits. If your problem is at idle only it could well be your EGR. A faulty EGR is usually a problem only at idle as it normally opens at higher speeds. Maybe you're getting vacuum to your EGR at idle through a defective vacuum switch. Pull the vacuum line off of your EGR and plug it for testing.
Good advice! ( Pull the vacuum line off of your EGR and plug it for testing.[/QUOTE] ) As recommended above, if you can lift the diaphram at idle and it causes the engine to stumble, it not leaking at idle.BC
Thread Starter
Le Mans Master
Joined: Sep 2002
Posts: 5,235
Likes: 898
From: Myrtle Beach SC
Thread Starter
Le Mans Master
Joined: Sep 2002
Posts: 5,235
Likes: 898
From: Myrtle Beach SC
Conducted that test and it performed normally...engine stumbled.
Thread Starter
Le Mans Master
Joined: Sep 2002
Posts: 5,235
Likes: 898
From: Myrtle Beach SC
I have a 79 L82 that had a similar problem. My plugs were fouling from carbon deposits. If your problem is at idle only it could well be your EGR. A faulty EGR is usually a problem only at idle as it normally opens at higher speeds. Maybe you're getting vacuum to your EGR at idle through a defective vacuum switch. Pull the vacuum line off of your EGR and plug it for testing.
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Tech Contributor
Joined: Dec 1999
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Is that the sensor that you were refering to?
Bill C
Drifting
Joined: Feb 2005
Posts: 1,738
Likes: 2
From: San diego ca
Theres a single wire sensor on the EGR Valve base.. That sensor "detects" heat from the exhaust flow when the valve is open and flowing exhaust gas. That switch closes when the EGR is flowing hot exhaust gasses into the manifold and tells the ECM that the EGR valve is open. The PCM comfirms that the EGR is suppose to be open (flowing exhaust Gas into the manifold. If it is NOT suppoes to be flowing gasses it sets a check engine light.
Is that the sensor that you were refering to?
Bill C
Is that the sensor that you were refering to?
Bill C
Thread Starter
Le Mans Master
Joined: Sep 2002
Posts: 5,235
Likes: 898
From: Myrtle Beach SC
That switch closes when the EGR is flowing hot exhaust gasses into the manifold and tells the ECM that the EGR valve is open. The PCM comfirms that the EGR is suppose to be open (flowing exhaust Gas into the manifold. If it is NOT suppoes to be flowing gasses it sets a check engine light.
Is that the sensor that you were refering to?
Is that the sensor that you were refering to?
Advanced
Joined: Sep 2006
Posts: 55
Likes: 0
Better late than never to post a reply I guess. I have a 78 as well. L-82. All stock. Mine idles like crap especially when the AC is on. But I happen to know that my intake valves are carboned up pretty bad. I took the intake off to replace the gasket a while back and I observed this by looking down the intake ports. My assumption is that the carbon is causing the bad idle. Last I checked my EGR was fine.
Instructor
Joined: Sep 2013
Posts: 175
Likes: 3
From: Palmyra NY
When I drove my 1980 on it's very first run after my purchase last August the engine stumbled and the power was terrible. I drove it right home and was very disappointed with it's performance. All filters, plugs, etc. was changed. For the heck of it I plugged the EGR hose and took it for another ride. Problem GONE! The car runs and drives excellent ( knock on wood!). I left the original EGR valve on the car for the original look and it's still plugged to this day. I'm not sure what it's problem is but I'll deal with it some other day.
Advanced
Joined: Sep 2006
Posts: 55
Likes: 0
When I drove my 1980 on it's very first run after my purchase last August the engine stumbled and the power was terrible. I drove it right home and was very disappointed with it's performance. All filters, plugs, etc. was changed. For the heck of it I plugged the EGR hose and took it for another ride. Problem GONE! The car runs and drives excellent ( knock on wood!). I left the original EGR valve on the car for the original look and it's still plugged to this day. I'm not sure what it's problem is but I'll deal with it some other day.
Advanced
Joined: Sep 2006
Posts: 55
Likes: 0
Oh and by the way, the EGR on the 78 is the kind that requires exhaust back pressure to work. If the car is off and you connect a vac pump to the valve it will NOT hold a vacuum. That's normal operation. The car must be running to properly test the EGR system.
Instructor
Joined: Nov 2013
Posts: 166
Likes: 8
From: Acworth GA
I have a 78 also. My had a leaking EGR diaphragm so I changed it. My research indicated that it was not the type that required exhaust pressure to seal the diaphragm so the vacuum will operate it. Can you point me to your information source. If mine is wrong I would like to know it. Mine now runs rough at 2500 rpm.
Burning Brakes
Joined: Mar 2014
Posts: 904
Likes: 46
From: Crestline CA
As stated before, the best way to eliminate the EGR as a possible culprit to rough running is to disconnect the vacuum source to it and see if the problem goes away. Its very common for back pressure type EGRs(not sure if 78s used this type) to go bad and open too much/too early and cause driveabilty problems. Also, when replacing these types of valve you often need to stake a restrictor in the valve orifice and often a tech will install the incorrect restrictor or neglect to install it at all.