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Discussion Starter · #1 ·
I checked the pressure if its around the right pressure but the guage moves around when it should be still. My fuel pump doesnt make any noise and runs great, but on WOT it is getting lean. Anyone know? Im getting my truck tuned by Justin and this is how we figured out it was lean. Heres what he said:

"He has one of my scan cables, working on his tune. Extremely lean at heavy throttle (in PE mode). After one look at the log, he's not allowed to go above 2/3 throttle til this gets figured out. No apparent intake leaks, although that is still the likely culprit (in speed density, it's nice and rich in PE mode). Had him check fuel pressure and it is erratic. 56-59psi with vac line to the FPR disconnected, should be a rock solid 58.

He's replaced the MAF, that fixed part of the problem (fuel trims diving to -15 at closed throttle), but it's still lean with any amount of throttle.

Does anybody know of the 8.1Ls are known for intake gasket leaks like the earlier small block gen-IIIs?

Justin"
 

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Leaking intake manifold is not going to make it run lean-- At WOT there is lots of volume, but very little vacuum in the manifold. :)
 

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Discussion Starter · #3 ·
Also, the truck runs alot better with the MAF disconnected.
 

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Discussion Starter · #5 ·
I just replaced the fuel filter.
 

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fuel pump, fuel pressure regulator, maybe the stock pump can not supply enough fuel?
 

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Are you a guy named Justin getting your truck tuned by another guy named Justin or who?

When you say lean and fuel trims at (-15) you are contradicting yourself. -15 means the computer has shortened the injector pulses 15% due to excessive fuel, or a rich mixture. Can you clear this up? Is it pig rich at idle then lean at WOT or is it +15 fuel trim. What are the fuel trims at WOT?

For what it's worth I've never been able to maintain a rich mixture at WOT with mine, tried everything. I've decided it will have to be reprogrammed to change it. At WOT mine stays relatively rich once the PCM has learned the fuel trim. It doesn't matter what set-up I've had in it, once it knows how much fuel is needed it walks the fence. It took running E85 to cut out the obligatory knock retard that came with it on gasoline. The O2 voltages at WOT will dip into the 200-300 mv. range the whole time while averaging above 750 mv.

If you replaced the fuel filter and MAF and it's still doing it I would check the ducting between the MAF and the trottle very carefully for holes, cracks, or a loose seal. A vacuum leak on the intake manifold will be lean all the time. But when it's on the intake ducting it may only be slightly lean or fine at idle but when you open up the throttle the pressure inside it drops big time and the leak becomes huge. The MAF only sees what goes through it and not what gets in behind it.

Vernon
 

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Discussion Starter · #9 ·
Well, I dont to much. My tuner is Justin but my name is justin also. The -15 was BEFORE the new MAF, now that is fixed. Now is just lean on WOT i guess. I have checked the K&N fittings atleast 3 times to make sure there tight. So he is thinking that the fact that it runs better with the MAF disconneted means its not a fuel problem, but instead a vacuum leak somwhere.
 

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Discussion Starter · #10 ·


 

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I'm the Justin tuning it.

The lean condition is apparent now with PE mode being legitimately enabled (60 second delay removed).

With stock MAF, fuel trims dove to -15 at low throttle, +20 at heavy throttle. With new MAF, fuel trims don't drop below 0, would still attempt to jump up to +20 if trimming occurred at WOT. Instead, O2 sensors show a significantly lean condition.

MAF disconnected, trims are MUCH more reasonable and PE mode shows NBO2 voltages that are to be expected.

Problem isn't the tune, his issues existed on the stock tune.
 

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Discussion Starter · #13 ·
Anyone else?
 

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Turbulence going into the MAF at WOT? Does it still have the screen? What kind of filter?

I find bad grounds that cause wierd stuff all the time. Might try cleaning and tightening the grounds.

Vernon
 

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Discussion Starter · #15 ·
Im running a new MAF with screen and a K&N intake system that I have checked at least 3 times to make sure there are no leaks. It looks like though since I cant fix this problem were gonna change over to a "Speed Density tune" with out the MAF till i can figure out this problem.
 

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Somewhere in this I'm seeing an over oiled K&N that's leaving an oil film on the MAF wires, causing a lean condition(???) and some GM systems can go to +/- 28 on the fuel trims.

Are the trim readings LT trim or ST trim? B1 LT, B1 ST B2 LT,B2 ST

If what you're reading is the short term trim values I wouldn't worry, if both ST and LT are pegged then I'd look into it

There's a way to crank the stock pressure regulator a bit, try raising the PSI by 5 and let it rip.
 
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