Ok, here goes. The motor is a '89 LO3 w/ 67k. I have added true dual exhaust to it a while back and ever since have had a CEL on the highway. The exhaust has duals cats and mufflers. My egr valve is working properly.

The solenoid needs a few things like coolant temp, tps, ecm control etc in order to ground the solenoid and have vacuum enter the egr valve.

I'm assuming the problem is the lack of backpressure to the easier flowing exhaust. So i got to thinking and i installed a '96 LT1 Camaro EGR valve. It worked for one day and then i got the code again. Another valve i could try is the 96 Camaro 5-speed egr valve since it was made for an even lesser restrictive exhaust.

Anybody have anything to add? I'm kinda stuck and I can't really find an actual solution. Thanks,
Adam

 

get a negative backpressure valve from a TBI truck 87-95. My positive backpressure valve was not opening and throwing CODE 32, then i switched to a negative backpressure valve off of a 91 350 TBI truck and it works great. You can tell that the valve is negative backpressure because of the N stamped or printed on the valve.

 

Ok, so how does a negative back pressure one work? I didn't know that there was a negative/positive lol. Also, does it matter what motor the TBI truck has? I never thought of that lol. Also i looked at advance auto parts and they list the same egr valve for the 89 LO3 and 89 C2500 305. There is another egr valve for the c2500 but it doesnt say what kind. Is there a certain model/engine i should look for?

 

the EGR valves will have the same part number but one will have a P for positive backpressure and one will have an N for negative backpressure. Mine had the same part number but one was stamped with an N and the other with a P, you are going to have to check them out when u go to the parts store, also, im pretty sure it doesnt matter what engine they came off of, mine came off of a 350 and i have a 305.

 

Ok ill try that next then. So basically instead of sucking air, it works by pushing air? I'll see if i can finally get rid of this bs lol. Thanks for your help.

 

it still uses vacuum to open...a postive backpressure valve needs a certain amount of backrpessure to build up in the exhaust before it can open this is to make sure that the valve does not open up to early causing the car to stall......the negative backpressure valve doesnt need this build up of backpressure and thats why it works with a free flowing exhaust. Do a search or buy a chiltons manual there are some very detailed explainations in those two sources, i kinda just scratched the surface, i would get more in depth buti have a midterm to study for lol

 

Ok, and one more question lol. This LO3 is in my Caprice rather than a F-body. Do these motors differ with regards to using backpressures or are they both positive backpressure? Thanks, and im also studying for finals :P

 

well, here is my story in full detail........A year after i bought my car i installed my headers, hi flow cat and 3" hooker cat back. A few months later i was getting a CODE 32, so i figured it was because of the reduced backpressure and the positive backpressure EGR valve was not opening. So just in case i was wrong i went and bought another EGR valve (one of the universal kinds) from autozone. I was still getting a CODE 32 on the freeway when i was in OD. The this last year it was time to get my car smogged and we have enhanced testing now, so they test for NOx. The main purpose of the EGR system is to lower combustions temps to help lower NOx numbers. I figured that i better try out a negative backpressure to see if they work and it did. Well, i saved the EGR valve that orginally came on the car, so i desided to check it out and too my surprise it was a negative backpressure valve. So i was confused because if that was the original EGR valve that came on the car, that means that some L03 F-bodies got negative backpressure valves, and the reason it was giving me a code in the first place is because it was just bad. The reason my second valve was getting me a problem is because it was a positive backpressure valve. So i guess some camaros got negative valves and some got positive, so the point of my story is "with GM you never know", you are going to have to take your valve off and see what it is, if it is a N valve then it is probably just bad, if it is a P valve then it is either bad or you are not getting enough backpressure in your exhaust and need an N type valve. hope this helps

 

LOL that explains it. Thanks for you help.