I am wondering what the exhaust backpressure should be on a 98 PA ultra, Mine reads a vacuum at the O2 sensor! I am having NOX issues and wonder if thats the problem? Welcome to Calif!

hmm..im not certain..do you have a repair manual? and i assume that it is throwing a code?

I have the service manualsss (3) and there is no reference to specific backpressure,only excessive. the eng has been transplanted to a 88 fiero, the only code is "lean condition" and it thows the NOX off, not always just sometimes. I have headers on the engine and hand made exhaust with a new GPX cat, O2 sensors,EGR valve,yada-yada. But with a vacuum in the exhaust(just got a backpressure gauge,woo-hoo) I fiqure its robbing the EGR valve and thereby creating a lean condition. I read that headers reek havoc with NOX because of EGR starvation. My neighbors got a 2000 regal with the same motor(Karma) I will check it today. larry

Shouldn't go above 1.5 psi

The neighbors 2000 Regal reads "0" mine goes slightly negative???

That is wierd. I've never seen that before but I've never seen a fiero with a 3.8 either.I bet that thing is fast. Is there any posibility the camshaft isn't times right? could the exhaust valves be staing open too long and sucking exhaust back into cyl. I doubt it but just something to check or think about if the engines been apart. I would think there would be other drivabilaty problems if the cam wasn't timed right too.


Is the only problem spark knock from egr not working or are you tring to pass an emissions test? I think that you need to run premium gas in the supercharged engines. Higher octane.

The car passes perfectly........90 % of the time! I can't figure out (nor can anyone else so far! Lots of shrugs!) It will all the sudden jump up the nox. The reason its a problem is that the car must pass 'Federal Certification" on the headers. The design is fiero but larger pipe to handle the supercharged eng. No code other than lean condition come up, the car runs perfectly (and yes its way fast!)and the motor looks factory. I went through this test once and it did everything fine(they keep the car 4 days, run a 50mile test and suck ALL the exhaust in a sealed room and run it through a computer to see if it adds smog!) I dropped $1500. and I don't want to fail again!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I don't really know what your problem is I only work on stock buicks.Usally when I get a lean code P0171 I find vacuum leaks. Could be low fuel pressure and I can't remember if a dirty MAF sensor would cause a lean or rich exhaust but you might want to check that too.


One of my co workers has an old fiero that has a 4 cylinder in it that died.He was talking about puting some other engine it it at one time but he hasn't talked about it for a while. I'll have to tell him that he should put a supercharged 3.8 in it. How hard was it to do? What trans did you use? Did you use the Park Avenue transmission? What about the radiator? Does it stay cool.

I will check for vacuum leaks but it idles smooooooooth..I have a 3 core radiator(copper /brass) made to fit the stock location, I run the stock trans the unit went in as a package, you must put in a corvette fuel pump for proper fuel pressue it has a new cat (pontiac GXP) and in CA you must use the evap from the donor car,you need to do some half shaft work and of course exhaust( for size). I put a thrasher shift kit in, and have a smaller blower pulley (25-40hp gain)to install after it passes certification.Cruise and A/C work from stock and a smaller serpetine belt (no p/s) , You can check www.westco.com for complete info. Chris West is the man on Fieros,


My Buick is as stock as a Stove so it otta pass!!!

Hoo-raw! Problem solved!!! I had made a "cold air" intake which went into the wheel well, it appears that the air temp around the K&N type filter in the engine bay was to hot ,and as it heated it changed air flow volume to the engine and kept the computer changing the mixture. As the air heated intake air volume decreases and so the eng ran rich, the computer then went to lean, this went on and on till we had a lean condition!!! I just had it tested at the state referee and it flew through! So heed this if your changing engines , computers are really sensitive to changes. All new car intakes are cold air for that reason. I grew up in the 60's and hung around cars before that (see flatheads) so I didn't put 2 and 2 together right away. DUH!