SuperL98

Sorry this is so long….
I’m having an odd problem with the oxygen sensor readings in park at idle. I posted the original details in the tech section (but its such an odd problem I didn’t expect much help) …. Also stumbling a little at low speeds. http://forums.corvetteforum.com/zerothread?id=275056

In a nutshell the oxygen sensor reads lean at idle in park\neutral and operates what looks like normally in drive and out on the road. Tried all the things you would, no vacuum leaks, swapped oxygen sensor, MAF, ECM, etc. no change.

I think I figured out the cause, but need opinions on a solution……
Here is what’s new, I pulled the pipe connecting the supercharger to the MAF (let the supercharger blow into the air) and everything went back to normal the oxygen sensor started to cycle, block learn worked back from 160 to 132 after a few minuets.
History: I upgraded the supercharger early last year from an old Paxton SN93 to a new SN2000 with the high output impeller (6psi to 10psi) and at the time had a ported MAF with no screens, the car started running like %$#%&. Bought a new MAF and left the screens in and all seemed OK. Took the screens out (off the new MAF) over the winter and I’m back in trouble.

With the new supercharger there is a lot of air pumping out, even at idle (I mean a LOT - I can't hold my hand over the outlet), and this takes a 90 degree turn right into the MAF. I think all this turbulent air is effecting the MAF’s ability to read the airflow correctly, after all it works on the passing air cooling the wires.
I guess those screens are in for a reason afterall.

Is anyone else blowing through the MAF on an L98, have you ever looked at your oxygen sensor at idle, and does it do this. I can put the screens back in, maybe lengthen the pipe between the supercharger and the MAF. Maybe even put more straightening baffles in the pipe. Anyone sucking through (rather than blowing into) an MAF with a supercharger, and how does that work?
Maybe a Microtech or Wells foil MAF would work better?

I’m worried, because they emission test my car off the dyno rollers (they are afraid of the posi-traction) with a two speed idle test. Doubt I will pass with the setup as it is.

lead foot 85 vet

I think your right in your thinking I removed the screen from mine and then latter learned part of its purpuse is to strighten the air passing by the sensor, also I don't think that flexable pipe is helping.

8388

I'm speed density now, but back when I was Mass air, I never ran the screens either and never experienced what your describing. Ultra slow, another C/F member still runs Mass air without screens and also like me runs a Paxton SN 2000. Have you checked your tps setting ? Are you still using the single wire 02 sensor ?

LPDesRoche

For what its worth, when I had my mustang with the paxton on it i was sucking through the mass air instead of blowing through it. It worked much better that way. The wires in the ford mass air were very sensitive as to how the air flowed over them. I never had to deal with mass air on a supercharged vette only speed density.

SuperL98

I still have the stock oxygen sensor - single wire.
The tb voltage is about .62.

I've glued my screens back in and will have another go at it this weekend.
Also have an idea to extend (temporary) the u-duct out about 8 inches on each leg and see if that helps.

Thought I might have a bad (new) MAF with a loose sensor wire, borrowed a friends (from a L98 camaro) for a day (also had the screens out) and it acts the same way?

I still think I'm missing something here?????




[Modified by SuperL98, 9:27 PM 4/12/2002]

4cefed

Blow through MAF's = problems. Suck through is a much more stable configuration. Why are you guy's running blow through MAF's? I don't know if can change or not but if you try it you will never go back.