decipha

I posted this on hptuners website with no response so figured i would try my luck here

I have a bone stock all original 98 camaro ss 6spd, it is completely unmolested and I mean completely untouched it still has the factory radiator hoses. I did change the original plugs, wireset, and hego's within the past few weeks.

I've been playing with the PCM and since this vehicle is completely bone stock I figured i wouldn't have to do any tuning just adjusting, obviously thats not the case. So I changed the PE table to 1.141 eq_ratio and went for a drive under the false impression that stock is close. This is with the stock MAF ONLY FUELING rpm set at 4000+ rpm, so over 4000 rpm only the MAF is used for fuel calcuations.

at 5500+ the engine leans out to the 15s approx. 1.04 lambda (~15.2), this is with the LTFT adding 10% additional fuel as well

so simple math tells me, 14.1%(eq_ratio) + 10%(LTFT) + 4%(AFR correction) = 28.1 %

From a production stand point I dont see how GM can let a production vehicle leave the factory with the maf curve needing 28% correction, I can see a variance of up to 8% being acceptable but this is just too unreasonable. I have verified that the MAF is original, lid and screen are stock and I have absolutely no vac leaks, I even cleaning the MAF element to no avail.

BTW, at idle (MAF ONLY) my fuel trims are -1% to +2% (which i expected since i have no vac leaks), during cruise and part throttle load my fuel trims are +5% to +8%

Before I go adding 28.1% to the upper flows of the maf curve I'd like to see what others have experienced as well.

Bowtie316

iTrader: (1)

You might be experiencing the systems of a weak fuel system. If fuel pressure is low or fades at high loads, you will be forced to increase the fueling in the tune to compensate. i would check fuel pressure during WOT.

decipha

that was the first thing i checked, I even replaced my fuel filter for good measure, my fuel pressure stayed consistent a **** hair below 60 on a hood mounted gauge

does anyone know what a typical bone stock 98 camaro does AFR wise?

sweet-94z28

iTrader: (30)

My Trans Am was about 12.0-12.3 bone stock at WOT. I would unplug MAF, set MAF Failure to 1 Hz, and move the 4000 RPM to 6500 RPM. This essentially puts you in closed loop speed density. Run it and see what the AFR does then.

LSX Power Tuning

iTrader: (4)

I see 4th gens all the time with bad maf's. 100% of them have ran lean when the MAF was bad. There is a good chance no matter what you try to add to the MAF it won't make any difference at wot. With the newest 4th gen being over 10 years old its not that surprising tod me.

bmax

iTrader: (1)

I would clean the MAF as well.

Just food for thought.

Brad

FEAR LS

iTrader: (8)

Breakfast, Lunch, and Dinner

decipha

Yeah cleaning the maf was my first step, that did nothing

I just went out and stood on it, at 5600+ it looks like I'm around 9200hz on the maf (kinda difficult to watch the tech2 and beat on her at the same time), I don't know what a stock ls1 should be around but it appears to jive with what I would expect the maf to be

sweet-94z28... thanks for that info thats the exact info I'm looking for that AFR I would expect considering the pcm is commanding 11.7 in the PE table stock, obviously something is amiss with my car, ill dig deeper and post back with my findings, thanks all

decipha

finally resolved my issue, by coincidence really. I'm getting voltage drop to the pump

after cleaning the injectors and rails I went out and loaded in the stock MAF curve then went and stood on it, AFR stayed at 12.8 to redline then last night i went beating on her and she went lean again, absolutely nothing changed, so I turned my radio down and my ac off to hear the engine better, just like that my afr dropped

I've been searching and this appears to be a common issue, racetronix has a wiring harness that ties the pump into the alternator, soon as I get a chance ill be doing the same

hope this helps someone

Bowtie316

iTrader: (1)

See post #2 lol.

Ed Wright

iTrader: (1)

I think you have alternator problems, not a wiring-needing-band-aids issue. Your system voltage won't change that much when turning accessories off & on if the rest of the car is right. Not only fuel pump voltage will change (and you said your fuel pressure doesn't drop, which eliminates that anyway) Back when I ran two 12 batteries in my car with an alternator, I flipped the belt off a couple of times. The car slowed both times, and the data logs showed it leaned.
Voltage levels effect injector opening rates, thus air/fuel ratios. I found how much first time I put my race engine on an engine dyno that had 12 batteries to run the engine. I use two 16 volt batteries in the car.
That two volt difference made a huge difference. I now have a 16 volt dyno battery just for that to take with me.
Sounds like what you are seeing.
Hope this helps.