Interesting 3400 tuning issue...

[atc3434]

I posted this on GrandamGT.com, but figured you folks might have some good input as well. This is on a 99 Grand Am SE with the 3400. 95k miles, most real easy. Tog headers, SLP exhaust w/ cutout, and cold air intake. Discuss:

Ok, went to New England Dragway for some Friday night street drags. Started at 6pm, pretty cool out, track sucked traction wise. My first run of the day was my best, 15.541 @ 88.37 and a 60' of 2.312. It got worse as it cooled off. My 60's got worse, my MPH went worse, down to 86mph. The car was running pig rich, o2s were over 1000mvs at points, I saw pulse widths of 20-21ms. 0KR all night, good 93 octane from Hess and keeping cool in the lanes took care of that. Its got the stock computer, tog headers, slp w/ cutout, and a DR. Speed CAI. O2 sensor is about 95k old, the maf is new. What the hell is a header equiped 3400 doing trapping at the same speed it did before headers and exhaust? Any idea why this car is so darn rich? I'm sure thats whats killing my top end.

[Doubt_Incarnate]

what is a DR? your not running leaded gas are you, that messes up the o2 sensor. check the line to the fpr to see its getting vacuum. if that even matters at wot. if it was cold out that could account for the rich condition, if the ecm sees the colder denser air it will, or should, add fuel to compensate, combined with the CAI it might have been a little too cool. but then if the o2 sensor detects rich its supposed to lean out. whether or not it actually burns is an ignition thing, maybe a hottr ignition might be whats needed to cap of the setup. be interesting to see what it runs in july in the current state. i know there are other factors, but still, cars suck a ton of gas in the winter when its really cold out, need a hot spark to burn it all.

[bszopi]

Its a "Dr. Speed" CAI

[geoffinbc]

O2 sensor dont mean shit at WOT. The ECM will revert to closed loop at WOT. Fuel pressure and pulse width adjustments are you only adjustment.

Are you running stock fuel pressure?

[atc3434]

O2 sensor dont mean shit at WOT. The ECM will revert to closed loop at WOT. Fuel pressure and pulse width adjustments are you only adjustment.

Are you running stock fuel pressure?

O2s are still good for a ballpark, at any rate. 1000mvs is pretty darn rich. In Power Enrichment mode the PCM is not in closed loop. Closed loop uses o2 reading to adjust short term and long term fuel trim. When you're at 70% throttle or more, o2 readings arn't used, and you pull fuel based on MAF readings. Fuel pressure is stock, btw.

The cold air using more fuel makes sense, but you shouldn't go rich, the amount of fuel added should even up to the extra air you're pulling. More power, yes, but the mixture should be the same.

[Doubt_Incarnate]

yeah i know, the pcm should add just what it needs, but its not a formula one race quality pcm just a plain old gm unit, not exactly performance oriented. bumping up the ingition still seems to be a good place to start.

[spacecadetz26]

did you run back to back or did you let it cool down inbetween runs?

[atc3434]

I had plenty of time to cool between runs. Most runs were made at about 180degrees motor temperature, outside air was in the 50s, and IAT was seeing about 60 degrees for intake air temps. I'm not sure whether the actual issue is that the was running too rich, or the PCM thought the car was running rich (bad o2 sensor maybe) and was actually going lean. I might see what the plugs look like, if the car is really that rich I should think that the plugs would be pretty dark.