EGR Problems and failed Emissions test

Well my trusty '93 RMW has failed it's e-test. Passed on everything at idle but failed on HC and CO at cruise. It started surging at cruise about a week or so before I went to get it tested. I went thru everything in the Factory Service Manual and swapped out most of the sensors with other spare ones that I had. Using my friends scan tool I did some data streaming and I can see that the Integrator value is about 120 and the Block Learn value is about 108 when driving down the road. This suggests the car is running rich and that the computer is compensating for that.

To make a long story short. I've narrowed it down to the EGR circuit. With the EGR connected it surges, sometimes rather badly at cruise. It feels similar to towing a trailer. It runs smoothly at idle, closed throttle deceleration and full throttle acceleration.

When I disconnect the EGR the car runs smoothly under all conditions except for some very heavy pinging. This is what I would expect because the computer is advancing the timing to compensate for the Exhaust gases entering the combustion chamber.

So I have done all the tests in the FSM on the EGR valve and solenoid and everything checks out normal. I can't understand why the EGR system is adding too much exhaust gas. My car has a negative pressure EGR valve which uses exhaust backpressure to control it. I did swap out the stock exhaust for a complete 3" single system about a year ago, but the car has been running great up until about a month ago.

Any ideas guys? My '91 Caprice sedan had similar symptoms before I scraped it, and I never did figure it out.

change the cat,. it'll pass,. even a cheapie $90.00 3",.rich is actually good, makes the cat work properly,.i,d just add the cheapie cat behind the oroginal,. take it out after you,ve passed,..use it again in two years,.

Nick

Hey Nick, I know you had a huge headache with your Black wagon and E testing. My car actually has a 3" Magnaflow cat on it that is about a year old. I know the aftermarket cats don't last too long, that's why I kept the original cat. The thing is I don't wanna hack up a really nice 3" exhaust to fit the stock cat back in just yet.

I really need to figure out the surging problem caused by the EGR first. The car is a real pain to drive right now. Once I fix that if it still fails I think I will try patching in the old cat. Or burn the F@#*ing car to the ground and buy a Hybrid. No Etesting for them at least.