What did you do to your NNBS GMT900 Tahoe/Yukon Today?

j91z28d1 said:

I know its different but I think we have the same fuel pump module? mine the fuel pressure spikes like that any time the truck shuts off. I found it odd too, especially since it stops and starts non stop, you'd think 70+ psi would mess with the starting fuel.


if I remember right you have a tech 2? under fuel can you watch the target fuel pressure and actual psi and compare to your gauge?

since these aren't old school vacuum biased regulators, I honestly don't know what it should do when you Rev it quickly. I would think increase as that's what older return systems do, not decrease but since it's a pwm dead head setup. maybe there's a lag in the pwm before it can ramp up speed to match demand from a big pump shot? Hopefully you can see something useful with the requested fuel pressure.

if you can tape that gauge to the windshield and go for a drive a quick wot pull will tell you of the pump can keep up. I've done that a lot

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Doubeleive said:

Been doing some testing replaced the rear 02 sensors and swapped in a known good maf, misfires increased???? Did a crank relearn misfires decreased and now I just get a couple on 5 & 7 which is the noisy side, swapped coil 7&1 no change, checked fuel pressure prestart is normal around 55 running it's around 43 but drops and increases 30-50 if I rev it fast. Seems like it should stay pretty stable but not sure.
And what's strange to me is after I shut if off fuel pressure increases (slowly) up to about 82 and after a few minutes it has dropped about 5 psi so it's sitting on around 77 now is that normal?
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gooffeyguy said:

At 120+ mph does it really matter? Lol

How many miles on that engine?

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Doubeleive said:

I guess I'll presume the rise is due to heat and being a closed system no restart issues at all anytime

I'm think I'm looking at bank 1 lifters at minimum going to call the dealer in the morning and see what they would charge me generally they are pretty fair with me since I have been going there for 30 years the service manager has historically been more than fair with me. But if the cam is fkd I don't know. I think it needs a deeper look I reset the ecm, relearned the crank, maf, 02 sensors, swapped coils. I don't have the time to tear it down and with my luck bolts will break and that's a headache I don't want to deal with.

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j91z28d1 said:

I think that makes sense. Just heat soak.


of you tired to plugs? maybe toss a set of cheap non all these new fancy metals plugs as a test?

I found a spark plug loose once that caused a miss fire on the scanner but felt smooth. also something about these new plugs not needing anti-seize? and it can keep from having good ground contact.

just a thought. I forget, is this a deleted engine?

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Sparksalot said:

I have KO2s on both of mine. Mid life they seem to be a booger to balance. I’m looking at options as well. I may pull them off thethirdtwin way early.

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