Hey guys... my first post. Went to get the 95 Z28, smogged in California and just before I went I got a code 29 and 32. Air pump and EGR. I replaced the fuse for the pump, passed smog. I had a real high NO reading and discovered that I have an Air pump going bad, (blown fuse) IE not pumping the inert gasses thru to lower Combustion Temps and therefore raising the levels of NO. Bought a pump on EBAY, went to install and found that the existing pump has two wires, orng and blk. The new pump has 3, orng,red and blk. My car had the recall done so I am hoping that I dont need a special pump. My question would be, can I use the new pump by capping off the red wire? I will go on to say that my car is mildly built, rebuilt heads Crower cam 254/485 intake 262/504 exhaust,1.5 rockers, Edelbrock shortys, Lingenfelter CAI, Hypertech tuned. The trans was rebuilt with upgraded clutch pack, sonnax boost valve and sleeve upgrade, sonnax superhold servo piston and 3-4 clutch upgrade kit. Also a shift kit and heavy duty reaction shell. TRUST me if I didnt live in California I would have long tubes, no Cats and God knows what else. But since I am here, and the smog laws suck, my car just is what it is. Hey it still hauls ***. I have seen Shoeboxs' tech aids and they have been a big help allready, just had this question and decided it was time to join instead of being a shadow visitor. Thanks in advance, looking forward to being a member

 

You have AIR and EGR totally confused.

The AIR pump only pumps "air" into the exhaust manifolds for the first three minutes or so after startup, to help the cats heat of faster. AIR has NOTHING to do with EGR (except in the 93 LT1 where they share a common pipe). After the first few minutes, it doesn't run again until you restart the engine.

EGR operates at part throttle, primarily when lugging the engine at low RPM, causing high combustion chamber temperatures. The flow is controlled by pulse width modulating the vacuum solenoid that activates the EGR valve. The flow is caused by the fact that there is a backpressure in the exhaust system, and a vacuum in the intake manifold. There is no pump involved.

Changing the AIR pump will not correct the EGR fault, or reduce NOx. DTC 32 indicate inadequate flow through the EGR valve, as determined by the PCM cycling the EGR valve and looking for the expected changed in manifold absolute pressure. Valve could be bad, vacuum system could have leaks, vacuum solenoid could have mechanically failed, the pintle on the EGR valve is carboned up, or the passage in the manifold is carboned up.

Or, your exhaust system has so little backpressure that there is inadequate flow.

 

Thanks Injuneer for your response. Thank you also for clearing up my misunderstanding of the AIR pump function. I will reinstall the old pump, I havent had a code 29 since the smog but have had a 32. I understand that the hypertech stuff could cause the high NO as well. Another symptom I have is a muffled popping upon acceleration.. sometimes. I assume this is an intake backfire due to a lean condition caused by O2 sensors not working properly... bad EGR system?? ( AIR pump working improperly,? which you cleared up!) I will look at the EGR and Solenoid. The problems have been recent in light of you mentioning the backpressure. I forgot to mention that I have a flowmaster Exhaust as well. I often wondered about my backpressure with my mods. New stuff installed recently have been IAT,MAP,TPS, ECM Temp Sensor, Coil, ICM and O2 sensors other wise no changes since the Cam etc., 3 years ago. So my symptoms are the DTC 32 and popping. What do you think? Your thoughts on this are much appreciated, thanks.

 

The Hypertech doesn't alter the closed loop, part throttle tune. It actually doesn't do much of anything, and has been shown to lose HP. But that's not causing high NOx. I;m surprised you'd rely on the Hypertech for a tune with a cam.

High NOx can be caused by a lean condition, or high coolant temp. Not sure what you mean by "popping" in the exhaust under acceleration. Are you sure it isn't a misfire? If you think it's running lean, have you checked the fuel pressure. Popping in the exhaust would only happen if you had excess fuel in the exhaust.

Generally, you will have a problem with low backpressure when you delete the cats (I assume your 95 A4 is CA emissions and hence has the dual cats), and I know you can't have deleted them.

 

I am considering sending my cam specs etc. to PCMs for less and get rid of the hyper tech. Just waiting to allocate the funds. I like that my fans come on sooner with it and I do feel a improvement. I also think it advances my timing a bit, could be wrong though, have been in the recent past ;-) As for the popping it is upon hard acceleration and has happened just going around a corner, at a light. It sounds like it comes from under the hood more than the back. High coolant temp I do not think is the issue, gauge is always "in the green" per se. Never gets too hot, thats why I like the fans on early. I blew a head gasket which prompted the cam and head work so high temp frightens me. I was doing a very high rate of speed and came off the freeway with my temp pegged and a blown gasket. Without the fans coming on at 160 it seems the gauge is showing way to high of a reading, just makes me uncomfortable. As for the lean condition, I have read that it is possible because the O2s get a false reading, and lean out the fuel, because the EGR isnt working right. I try to keep the car emission compliant so yes both cats are present. The engine generally runs well, and recently has had these issues. Just gotta get it running right, otherwise it bugs the hell out of me. With this said I think my fuel pressure is ok. That is just by the seat if my pants though, I will need to purchase a fuel pressure gauge, is it possible that it is an intermittent pressure issue? I definatly have the high NO it was just 20 points below passing at 463ppm 483 max and 256 average. CO2 was 14.6, O2 was 0, HC was 20, CO was.03 all at 15 mph. At 25mph the CO2 and O2 stayed the same HC dropped to 11, CO went up to.06, NO dropped to 369. I thought these numbers might help in seeing what is going on.

John