Supercharged C5 Running very rich please help

[4horseman]

I have a 1998 c5 that is 2 bar Speed Density.Started running rich a few days ago and is worse. I have changed the O2 sensors and no change. Reset PCM and re-flashed multiple known good tunes. Checked fuel pressure. (55 Lb idle and 58 rev) When car is in open loop it runs fine but as soon as it goes closed its a real loss of power. -19 STFT!!! or worse. Map sensor voltage (2 bar) is .77 idle and 2.57 WOT and ECT seems to be working fine, no fluctuations. I do not run a maf or IAT sensor.

Here are some logs I have . I am stumped and need advice from more advanced tuner. The" new O2 log" did not have the lc1 wide band connected, I was just checking if I had a different STFT and I did not.

[4horseman]

Anyone have any ideas? I am going to check injectors on a tech 2 tomorrow but was wondering if anyone has any experience with this. My brothers coming back in a couple of weeks and I really need to get this fixed. Thanks everyone!

[GHuggins]

What kind of force induction are you running? Just wondering if your running turbos and possibly it or one of "they" aren't freespinning providing the airflow at idle or the rest of the time. I'm not sure on the map voltage, but isn't this kinda low at wot? OR has it always been around this? Has the car been tuned on any recently? I don't have my laptop to look at your datalogs at the moment? Build info?

[GHuggins]

Just did a quick check. Basic GM 2 bar map is 2.45v at 0psi, so if your close to this with your 2 bar map, I would start checking to see if your power adder is actually working - turbo spinning without play, BOV not stuck open, something to this nature.

[4horseman]

Hi, Its a supercharger p1sc1. The GM 2 bar output is .77Volt at 20 inHG/38Kpa which is idle and when going into boost levels ,100+ KPa, it should read 2.45 volts ( 50% load) so my MAP voltage is right on according to my scan. My brother had it tuned by a forum member but Im not sure who.Sure it was a good tuner. Car was dynoed at over 500RWHP with no KR whatsoever from reading past log files. The tune has not been changed. The car's STFT have been degrading towards rich for a couple of days. They are now as low as -32. Four days ago they were maintaining a stable -2 to -4. My first impressions were it is electrical like a sensor so I started with the obvious by changing the O2 sensors, checking ECT, and MAP signal voltage.But that did not pan out so Im now thinking it could be mechanical. Im not sure if the methanol is hurting the injectors or cats but I do not believe the cats would do this. Maybe a massive injector leak could. Not sure. Was hoping someone has seen this before.

[4horseman]

The blow off valve allows air to blow out the outlet filter at idle. It closes when I hit the throttle allowing for build up to boost pressure so that looks ok.Opens and closes nicely.Besides wouldn't a vacuum leak cause positive fuel trims because of the introduction of unmetered air into the system? I could be wrong though just deducing at this point.

[GHuggins]

I really thought from the problem you were talking about that you were turbocharged - (what I get for making assumptions), thus the BOV's stuck open and so on, but even that wouldn't have effected it at idle. Restricted cats can cause one to do this and you did say it's low on power. If it's too rich during WOT it can kill cats in a hurry. Obviously this has taken quite some time, but still something that needs to be checked. Does it spit and sputter durring WOT? If it does any then definately check the cats. When you changed the O2's, were they really, really black with possibly some white specs?

[PST]

Clogged cats will cause positive fuel trims, not negative.

Look to the basics.. exhaust leaks/cracks/pinholes, faulty injectors, compression, etc.

[4horseman]

Thanks for the replys! Ran an injector balance test with tech two and two injectors were bad. One was completely stuck open.! Replaced and all is well.

great forum BTW reason I bought HPTuners instead of EFI Live.

[GHuggins]

Clogged cats will cause positive fuel trims, not negative.

Look to the basics.. exhaust leaks/cracks/pinholes, faulty injectors, compression, etc.

Yes I know, but with AM exhaust involved, I have seen this go either way due to air leaks corresponding with the restricted cats giving the building up exhaust somewhere to go. Again making assumptions. Dang... AND typically I'm the one preaching to Keep it Simple on top of everything. Good call on the injectors.