I have an 89' GTA that I just built a new motor. I Have an egr problem. The egr valve holds vacuume with the motor not running, when I start it I can't pump it up. I also tried pumping it up before starting and once it cranked it took the vacuume. I am scratching my head and can't figure this out. I tried another valve that I had laying around and the same thing happens. I have a Big Mouth intake from TPISpecialties and AFR heads. Any help would be greatly appreciated. Thanks

 

That is normal.

When the EGR gets the backpressure from the engine running it releases the vac. at the EGR valve.



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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R

R.I.P. #3
My favorite quote about D.E. "He can see air"

 

John,

Welcome aboard!

EB is correct (as usual). There are at least five types of mechanically actuated EGR valves, and at least two types of digital (electronic stepped) EGR valves.

The old style straight vacuum valve would open any time you applied vacuum to the diaphragm.

Both the positive and negative backpressure valves require either positive of negative exhaust pressure to seal a pilot valve in the diaphragm housing before the valve can actually open.

It sounds like you have a negative backpressure valve if you can open it with external vacuum when the engine is not running. The top of the diaphragm should have the part number, and it should begin with an "N" or have a larger "N" stamped into the top of the housing. A positive backpressure would have a "P" in those places.

The other mechanical types are a dual diaphragm that was used in the late 70s and early 80s before the advent of the backpressure pilot valves, and an air pressure EGR that Ford used for a short time that used pressure from the air injection pump instead of vacuum to operate the valve - another of their "better ideas".

The digital EGR uses a stepper motor similar to the IAC control to position the EGR pintle. An electronic EGR uses a solenoid directly attached to the valve to regulate vacuum to operate the valve.

You have neither of those, so never mind my aimless ramblings.

Your EGR could be just fine, or could be toast. The backpressure pilot vales can be very difficult to diagnose without elaborate fixtures and equipment. Are you getting an EGR error code?

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Later,
Vader
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"I'm'a do Things My Way - It's My way or the Highway."
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Thanks for the help guys. In response to vaders question, I didn't get a code yet. I just assembled the motor and I am trying to tune it. The prom that I recieved from TPIS was programmed wrong whitch led me to check the egr valve for a pinging sound ( alot!)from engine. With the stock chip the car seems to run better but still a little pinging is goin on. The stock chip was for the old motor whick was a 305. Now I have a 355 with aprox. 10.86/1 compression and before I sent the chip back I wanted to make sure everything is working properly. About how long would it take for the code to show up? I drove the car for aprox. 150 miles