Stumped. Help me out smart guys... Lean

[nyceguy01]

Well... Im stumped.

97 Tahoe, 5.7 auto.

Getting lean codes left and right.
P0151, P0131 and then sometimes also the other 2 lean codes 147 and its matching code for the other bank (cant remember off the top of my head).

Fuel psi is 60 at KO and then drops to 52 ish when running.
Pulling 16" or so vacuum at idle and of course less when you open the throttle.
I think the pump is ok and Im hoping no vacuum leaks at those pressures.

Intake gasket just done. Lower and upper.
Had a couple small vacuum leaks that are now fixed.
Had an exhaust leak but it was well after the cats and that is fixed now as well.

Watching the scanner the LTFT are high. Seen as high as low 20's...
It seems like the bank one sensor drops low a bunch more than the other, I swapped the sensor side for side and the issue stayed on bank one. I think the o2's are good.

Sealed the intake good so no extra air getting in post MAF.

Cleaned the MAF and also swapped for another one I also cleaned from a parts truck with no change and the reading on booth looked OK on the scanner from what I found on google.

I added another heavy ground to the passenger rear of motor with the ground strap and harness ground to be sure there as well.



I have a bunch of parts here and on the way but want to get it to stop throwing codes before I upgrade to headers, no cats, and the Blackbear tuned computer ( deleted the rear o2's and EGR )

Any ideas on why I keep going lean ?

 

[nyceguy01]

Just checked the fuel pressure again and Im still seeing 59-60 with KO but then the pressure bleeds down after the pump shuts off.

Im leaning towards just tossing a new pump in . I have one on the shelf so it prob cant hurt...

 

[PlayingWithTBI]

Not sure but, if it bleeds down then it may be your pressure regulator?

 

[nyceguy01]

So....
I said screw it and threw in a new pump and the readings didnt change much but it didnt bleed down anymore.

Also, I had a new upgraded spider on the shelf so I went ahead and pulled off the top of the intake and installed that as well.

Just got back from a 20 min drive and no codes but watching the scanner bank one is still running lean, apparently not quite enough to throw a code yet though...

Just not sure why one bank is still runnng leaner. There must have been something up with the regulator of spider though as the LTFT looks a bunch better. Sitting at 7-10 instead of low 20's so something changed for the better..

Gonna drive it a bit while I wait for the rest of my parts to show up and Im hoping it doesnt throw codes..

 

[stutaeng]

Lean on both banks IS suspect for fuel delivery...I think LTFT of 10 is okay.

I had a persistent lean code for a while P0174, I think. Also, an intermittent O2 low voltage code (P0151?) I checked everything suspecting vacuum leak, but turned out to be O2 sensors, but you mentioned you swapped them whiteout change...

Also, the vacuum reading seems low, no? I thought it was supposed to be around 20-22 in Hg? That's what mine was when I checked it a few weeks ago. I have this gauge, and 16 puts in the "timing" range off:
https://www.harborfreight.com/Fuel-Pump-and-Vacuum-Tester-62637.html

 

[nyceguy01]

I have the same guage and it was showing in the lower portion of the "normal" green area so it looks like I may have said 16 and meant 18..lol

After the new Pump and Spider I installed last night. its running great.
I put another 200 miles on it today with no codes so Im hoping its good to go.
The Mv on the O2 still shows lower on bank 1 but the fuel trims look OK and it hasnt thrown a code yet.

Gonna put some more miles on it while I wait for the new ECM and y-pipe to arrive and go from there.

I also get to swap out a brake line tomorrow after work, on the way home my driver front line rubbed the tire and died..lol
It was uneventful so I limped it the 2 miles home using the park brake and got it in the shop.

 

[stutaeng]

You should be okay. It seems like driving these truck 30-40 miles on these trucks for codes to show up.

I'm glad you found the problem!

 

[AK49BWL]

The Mv on the O2 still shows lower on bank 1 but the fuel trims look OK and it hasnt thrown a code yet.

On my 97 350 (and my 03 4.3 even), my two banks are NEVER in sync... 1 is always leaner than 2, usually about 4-6% difference. Never could figure it out, and since the programming options for these PCMs (even the 0411 swap) don't allow you to change the fueling per-bank, I think we're kind of stuck with it. My personal guess is it's because of the exhaust system, and the fact that the two sides are not equal length. But that's just off my head, no research I just programmed the VE for the middle ground so now LTFT 1 commands about 2% and LTFT 2 commands about -2. It works.

 

[nyceguy01]

Dammit...lol
Im back.

Has been running great till this morning.
Got the lean codes and rough running now along with a surging idle...

Fuel pressure is low. 30-32 psi.. It has a new delphi pump and upgraded spider already from a couple weeks ago... UGH...

Whats the best way to check each ? Id dont want to pull the plenum off if I dont have to...

 

[Tominator]

Hey, any luck with this? I’ve had similar problems with mine after intake manifold gaskets and spider mpfi upgrade. Still showing lean and random misfire. It’s a work in progress and likely has vacuum leaks I’m trying to find. But, I also pulled out the new spark plugs and they’re all fouled from overfueling. Maybe go there?