H-BOMB

Ok, I failed CA Emissions (NOX too high) and I still think its the EGR has something to do with it even though I replaced EGR valve.

When testing the EGR valve you should test it at idle with a vacuum pump and if it works it should start bogging like its about to die when u pump the EGR valve right?

Well, I hooked up the vacuum pump to the EGR valve and it wouldnt hold vacuum and the idle wouldnt change while i was pumping it. Is the EGR valve supposed to hold vacuum? Did I install the wrong EGR Valve? HELP!!!

Raiden

I think it depends upon which egr valve you have. I tried the same test on my Z and had the same results as you. I did apply vacume to the valve while the engin was off and the egr valve held vacume...with the engine off.

Vader

If this is for your '89 L98, and you installed the correct EGR valve, you will probably not be able to operate the valve with a vacuum pump. The EGR on your engine should have a negative backpressure pilot valve on the main valve diaphragm. This type valve requires a pressure differential between the exhaust port and atmoshpere. When exhaust backpressure increases, the pilot valve opens and the main valve diaphragm will no longer hold vacuum, thus closing the EGR.



You can use this flowchart to help diagnose your EGR:



Hopefully, when you removed and replaced the EGR valve, you thoroughly cleaned the mating passages in the intake. Is your exhaust system altered?

H-BOMB

I have stock exhaust manifolds and y pipe, I have Catco Cat and 3 Inch Flowmaster (American Thunder) Cat-back

I now think the problem is with my EGR Solenoid, I should be getting vacuum right? I hooked up a vacuum gauge and there is no vacuum at idle or when I rev it.

Raiden

Is there vacume while the engine is off?

Vader

Vacuum to the EGR solenoid (and EVAP purge) is supplied from a timed vacuum port on the underside of the throttle body on a TPI. There will only be vacuum present at part throttle or higher, if the TB minimum air position has been adjusted correctly, and the TB is clean.

You will only get vacuum on one side ot the EGR solenoid unless the solenoid is opened (operating). The solenoid is sensitive to the location of the vacuum source line, since it is a three-way valve, and vents EGR vacuum to atmosphere when de-energized. Make sure the hoses are connected correctly at the EGR solenoid valve. There should be no vacuum while the engine is not running - unless you have one massive vacuum reservoir in your fender...

H-BOMB

Sounds so complicated..

Ok, so on the EGR solenoid does it matter which vacuum hose goes to EGR Valve and which one goes to underside of throttle body? Maybe I have them mixed up.

Im 3 months overdue for registration all because I failed NOX!!!!