STRANGe ISSUE

[davetheslyrt]

Ok so I have 2000 NBS with 176,000 miles, whenever the gas gauge gets below 1/4 tank the SES light comes on and the engine starts to run poorly, It throws lean Right and Lean left codes. Once the tank is filled up the light goes away after about 3 miles and the performance returns.

Ok, so Is it the fuel pump or the intake gaskets? I am thinking fuel pump as it auto corrects after filling.

thank you in advance for all the help.

davetheslyrt

 

[TheFuzz]

I've never seen a fuel pump issue that manifests like that, but it certainly could be going out. Based on the symptoms, I'd agree that it's probably the pump...I can't imagine it's a gasket issue since the problem isn't constant. Have you ever replaced the fuel pump before? If it's the original OEM pump then I'd say it's definitely done its duty and is due for a replacement. How about your fuel filter, when was the last time you replaced it? Since both banks are getting starved for fuel then the problem is obviously upstream. Filter could be clogged, combined with a weak fuel pump, resulting in spotty fueling when the tank gets low.

 

[Perrin]

Doesn't that pump sit in a tray? Have you been over any huge bump lately? My first reaction is maybe the pump came loose and is floating in the tank, sucking air when the level get low enough.

 

[gitrduun]

Perrin it would take quite a jolt, it's held in by two rings

 

[davetheslyrt]

Well changed the fuel filter to a wx, the old farm had around 25k. Was full of black crap and now the truck runs better than when this started. Will see what happens when the tank gets close to empty.

Thanks for the advice.

 

[TheFuzz]

Great to hear, and glad to help!

 

[Z-56 Hoe]

Well? Hope that fix's it BTW

 

[southboundchicken]

with the mileage you have on it i would say its quite possibly a series of issues all of which were mentioned earlier. its almost a guarantee your manifold gasket is leaking if its the original seems like every truck i've seen this is a common weak link then the fuel pump is probably getting a little weak too and of course if your filters dirty that aint helping the situation at all

 

[Bossy70]

Yeh, hopefully the fuel filter fixes the problem. That is the smart first thing to change.

If it doesnt fix it, the problem is probably the fuel pump getting weak. I have seen weak/old fuel pumps cause engines to run bad when the tank gets low. I have even seen a weak fuel pump cause the engine to hickup/shutoff when rounding corners.

 

[TheFuzz]

That's what happened to mine on the way out to Cali a couple years ago. Last leg of the trip about an hour from Oceanside with 1/4 tank left or so. Super hot day, going up and down the hills on 15 and the truck nearly crapped out. Took it to north county GMC and they said the fuel pump was pretty much gone. Hooray for extended warranties.

I also wouldn't go as far as saying every truck will have manifold gasket issues. Mine was fine at 124K when I sold it.