Help!! Car won't pass smog
 

Hey everyone. Me and my sister are having trouble getting her car to pass smog. It is a 94 Z28 and has pacesetter mids, cai, magnaflow muffler and a cutout in the i pipe. All of the smog equipment is still hooked up and functioning. It has a new cat and egr valve. It was in the shop for a week and they couldn't figure out why it wouldn't pass. It fails on the NO(PPM), the readings are.
MAX AVE MEAS
689 150 804
706 136 757

The first readings are the 15mph measurements and the 25mph is the second one. Any help would be great. Thanks in advance.
NoMoneyZ

Is it getting warm enough before the test?

Find a way to cork your exhaust more.Your egr will not work properly with an good freeflowing exhaust system.
That will bring the nox down.
Also some headers such as mac's have poor placement of the egr tube and do not get good flow to the egr.

Good Luck let us know what happens.

Yeh it's true a good flowing exhaust won't allow the EGR to work well.
If I were you, I would uncap the cut out half way. However much you can without the mechanic realizing. That way most of the fumes exit there. :D

I'll see if that works. Thanks guys

yea make sure its warm.

haha yea try the cut out half way

What are your hydrocarbon readings? I had a problem similar to yours, I replaced the egr valve and put a new cat on but still ended up with the same readings. Have you checked your fuel pressure? If it is low it could could cause you to run lean which will lead to a high NOX reading.

I didn't think of that I'll see if the shop could check that I dont have a fuel pressure gauge.

The shops probably gonna charge you a minimum of an hour labor, I picked up my fuel pressure gauge for like 38 bucks, and its easy to check.

OK I'll see where I can get one.

I know you mentioned mid lengths and an exhaust, but does you're car still have the A.I.R pump? the air pump only injects fresh air into the exhaust stream but it's enough to change the reading. The reading that the H2O sensors read from that will either inject more fuel or less even if the engine doesn't need it. I have personally seen lt1's do weird things when the air pump quites working. It won't set a code for the PCM. It would only set a code if the fuse was blown. I could tell you an easy way to check it, but you probably don't have a tech 2. Sorry. That's all I could think of. I am a professional technican and I specalize in lt1's.

Yah all the smog stuff is still there. AIR, EGR and all that good stuff. Still has the cat and it only has a magnaflow muffler not a cat back. The only thing I have to scan is an ALDL cable and tunercats. Thanks for the help I'll have to find some way to check the air pump also.

Tunercats is not a scan tool. However since you have a cable you can download datamaster or freescan and that will tell you whatever you need to know as far as codes and things.

The air pump only works when the car is cold or for a few seconds upon start up.

Actually the air pump will operate anytime the car is at idle and at warm temprature. It will usually only run for about 10-15 seconds, and then shut off. It operates when the egr valve doesn't. At idle you're egr valve is closed, and also at wide open throttle. All F body's have a performance switch that is factory programmed into the computer that shut's it off at wot. the air pump works randomly even driving down the freeway. The only time it doesn't work is at wot, but like I said it will only run for a couple seconds then shut off and it doesn't run all the time only when the pcm detects a change in h20 readings. I have a tech 2 scan tool at work that I can change any paramiter of the vehicle with my lap top, but I really can't help much without having the car in front of me to look at. If you have a cat on the car, and no exhaust leak. I would just make sure every thing on the emissions side is actually working.