Faulty EGR?
Thread Starter
Instructor
Joined: Jan 2007
Posts: 233
Likes: 41
From: Simpsonville SC
Faulty EGR?
I’m going through my emission system on a 78 replacing collapsed and rotted vacuum lines. I’m also checking various components with my mityvac as I go along. I need a sanity check here, shouldn’t I be able to apply vacuum and hold it on the EGR and air pump diverter valves? Neither will hold a vacuum.
Burning Brakes
Joined: Nov 2005
Posts: 1,143
Likes: 0
From: Leander Texas
Positive back pressure EGR valves will not hold vacume. Negative Back pressure, and Ported EGR valves will hold vacume.
They can be identified by the stamp on the top side of the valve below the build date
P: stamp= positve back pressure
N: stamp= negative back pressure
I sourced this out of the Chilton manual. There is a good explanation of how the different EGR valves function.
They can be identified by the stamp on the top side of the valve below the build date
P: stamp= positve back pressure
N: stamp= negative back pressure
I sourced this out of the Chilton manual. There is a good explanation of how the different EGR valves function.
Last edited by DR.Jay; Feb 2, 2007 at 08:26 AM.
Melting Slicks
Joined: Jul 2005
Posts: 2,740
Likes: 3
From: Aurora Ontario
I’m going through my emission system on a 78 replacing collapsed and rotted vacuum lines. I’m also checking various components with my mityvac as I go along. I need a sanity check here, shouldn’t I be able to apply vacuum and hold it on the EGR and air pump diverter valves? Neither will hold a vacuum.
Jim
Race Director
Joined: Sep 2002
Posts: 10,362
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From: San Diego - Deep Within The State of CONFUSION!
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
Opening the EGR valve at idle will cause it to stall or run rough, it creates a big vacuum leak. EGR valves are closed at both idle and full throttle. If it doesn't change the idle when opened, the port may indeed be clogged.
Racer
Joined: Jul 2004
Posts: 400
Likes: 1
From: California
My crossover on my manifold was so clogged when i went to clean the manifold, i almost overlooked the port because it was TOTALLY covered in carbon buildup. i used Seafoam Brand engine stuff and it melted the carbon like it was nothing. i tried chiseling it out and nothing worked except that Seafoam. Im assuming witht he port unclogged the engine might run better?
Thread Starter
Instructor
Joined: Jan 2007
Posts: 233
Likes: 41
From: Simpsonville SC
Positive back pressure EGR it is.. Blow a light stream of air into the exhaust in port while applying vacuum and it will open. That's $50 I don't need to spend. The A.I.R diverter valve is a different story.
