Cheerio,

I finally found some time to go and work on my car, so I chose to cleanup the gremlins first..

I get the EGR code from time to time, during that proverbial time when being in ~2000RPM in OD.

So this time I have a vacuum gauge (boy, I felt so advanced ), and I read 22 inHg at idle (750 RPM).... Holy moly! 22 inches of mercury on my hissy-sounds-like-humungous-vacuum-leak junker. I felt warmth and pride.

Those 22"Hg come from the nipple on the throttle body inteded for the long gone THERMAC.

Then I checked out the hose leading to the EGR solenoid. Yep, 22"Hg.

Then I checked out the hose going from the EGR solenoid to the EGR valve: 0"Hg at idle. When I applied some throttle, boing, back to around 20"Hg (depended on how wide I would open the throttle).

I pushed on the EGR diaphragm and sure, the engine did bog in idle, until I released it so it would close.

=========

What gives?

The spring in EGR got rusty and too tough for vacuum to move?
Did I check everything I needed to check as far as the solenoid goes?

 

I just changed the vacuum tube from TB to the EGR solenoid. I don't think the old one was damaged, but just in case, maybe this helps.

 

Marin,

Is this on your '92 RS? I'm thinking that the EGR solenoid should be modulating the vacuum a little lower than that at just above idle. You likely also have a positive backpressure EGR valve, which will prevent the EGR valve from operating until the exhaust pressure is adequate. It is not a direct acting EGR like on the late '70s and early '80s cars.

 

MIne showed and tested as working find, what I happened to find out tho was the EGR was slow, it wouldnt return instantly, gave me a bad idle, bog on decleration/idle.. popped a code only once in a while in od for more than 5 minutes replaced the EGR valve.. no codes in a week, and much smoother running..


let us kow how it turned out eh?

 

Sure, thanks for additional info to you and Vader. I changed the vacuum tube and it still drops a code. I didn't notice any bogging or in fact any wierd behavior and when i try to open it with my finger it gives, I hear the engine bog and when I release, it closes and everything's back to normal. Maybe it's too hard to open, I dunno. PepBoys doesn't have it, I'll try Kragen. I'll try to have them open the box for me and then I'll try and press the diaphragm. If it resists less than mine, then my spring might be rusty...

Vader, from what I see on the diagram you posted, the vacuum assists in lifting the diaphragm: the exhaust pushes on it and when the pressure above the diaphragm gets reduced enough, the diaphragm lifts and allows the exhaust to enter the intake hole. Now if the exhaust or intake holes are clogged, I'll get a code. Or if the spring is to stiff. If the spring is not too stiff then when the vacuum and backpressure are right, EGR will lift and let the air through.

Could it be that my 3" exhaust (even with the new 3" cat that I just installed) drops the backpressure enough to leave EGR closed all the time? If so, what aftermarket part do you recommend?

Thanks guys!

 

Marin,

There is a pilot valve under the diaphragm in the valve. Exhaust pressure holds the pilot valve closed so that the vacuum can lift the pintle from the valve seat. When the pilot valve is opened, vacuum will leak through to atmosphere, and the main spring will close the valve pintle.

 

Vader,

you seem to be the guy to ask about EGR valves...I have a 91 L98 Z that Im having idle problems with. It "seems" to idle ok when cold but after it goes into closed loop, it starts running really rough. Here's a list of everything Ive changed

New header pipes with two catco converters
spark plugs
O2 sensor
vacuum lines

I checked the wires, cap, rotor...all ok(only about a yr old). I dont have the catback on yet.....could that cause my EGR to act up?? It didnt do this before I switched exhaust. I have checked about everything I can think of. I have ruled out fuel and timing because Im thinking it would be constant, correct?? I have also adjusted the tps and cleaned the IAC valve and adjusted min air. Am I right in saying its probably the EGR valve??? Its running way rich too. I even double checked the O2 sensor today to make sure nothing was melted...no luck there. I even put the old sensor back in, and no change again. I even unplugged the sensor....still idled the same. I also checked the purge and control valve on the charcoal canister, as well as the PCV system and valve....please help. I dont want to have to drive my car off a cliff....

SOrry this is so long.......just need a second opinion....thanks

 

Speaking of driving off a cliff, my transmission blew up on me a week ago. After 160Kmiles. I guess it lasted pretty long already.

 

So if my car idles rough after it warms up, like at 650-700 rpm bouncing back and forth, replace my EGR?