MAF off significantly - Stock 98 Camaro SS 6spd Tuning Tips/Advice

[decipha]

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 1.281% 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 +5% (which i expected since i have no vac leaks), during cruise and part throttle load my fuel trims are +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.

[SSUte01]

Have you verified fuel pressure? It's difficult to tell from the above, but I would certainly be verifying a fuel variables first, namely fuel pressure.

[decipha]

yeah fuel pressure stayed right below 60 the whole time using a hood mounted gauge

I think my issues are due to some dirty injectors, ill post back with my findings

[Russ K]

Unplug the Maf, if the fueling is closer, then the Maf is bad. Very common problem.

Russ Kemp

[johnm545]

What are your g/cyl readings at WOT? This will help identify if it's a fuel issue or bad MAF. My fuel trims are spot on and I usually see 0.72 g/cyl at 5000 rpm, dropping to 0.66 at 6000 rpm. That's at 600 meters elevation with a stock 2000 LS1 (with LS1 intake and restrictive holden exhaust). If you're seeing much less than this I'd suspect the MAF.

[decipha]

i have a tech2 i can't log g/cyl or if i can i don't know how

i can reach approx 9200hz on the maf at WOT on the big end 5000+ this seems to jive with what i would expect to see

im anywhere between -6 to -18 feet (below sealevel) here in new orleans

i'll unplug my maf hopefully tonight and do some tinkering

[flame]

i have a tech2

So you don't have HP tuners? Or don't know how to use it?

[decipha]

nope no hptuners

[flame]

So why are you here? Even if we tell you to tune the maf table you can't........

[decipha]

I can tune the maf table, I know the eq_ratio and I can log maf freq and I can look at the wideband for correction, I've tuned hundreds of vehicles, not a noob by a long shot

In any case i 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