Lean at WOT???

[iowackers]

2000 GMC Sierra ext. cab 4X4. 6" lift with 35" tires. Dynatech SupermaXX long tube headers, hi flow cats and Y, and Gibson cat back. Crane 212/218-.531 lift cam installed a year ago. Cold air intake. Tuned ECU from Nelson. Truck is running crappy at WOT. Feels like plugged cats. As soon as you let up 1/4 throttle it takes off like a bat outta hell. Would not idle right so I opened the set screw a couple of turns. Seemed to help for a while, now is dying again when turning at idle. I bought a wideband O2 and at idle and cruise it reads good. 14.0-14.9. The problem is at WOT. It went to 19+ !!!. I have emailed Nelson and he said to check fuel pressure. At idle I have 53. I just borrowed a fuel pressure gage with a long hose to check at WOT. What should I read? The fuel filter was changed about 20,000 ago. Truck has 86,000 on it. Is the fuel pump the main suspect here? Nelson said he increased my fuel tables aroun 25% across the board. Could this have taxed the factory pump? If so, what is a good drop in replacement that won't break the bank? Sorry for all of the questions, just looking for a little guidance. If it wasn't 5 degrees here I would have checked the WOT fuel pressure already!!

Rubie

[tanz45]

There's the problem...lifted truck. [some lifted racists on here]

Has it only gotten bad as the temp dropped? Intake leak?

Just because you have good fuel pressure, clogged injector/injectors?

[Frenchy]

Temperature drop does have an affect, I've had to do some tweaking on mine. That drastic though I'd suspect a fuel delivery issue, if it is the pump the Walbro 255 is a popular drop in replacement. I want to say the part number is 340GSS but I'm probably wrong.

[iowackers]

It has done it since Sept. so the cold has not changed it. I am definately guessing fuel issue since I replaced a lot of these pumps when I was a GM tech. Any good sponsors on here to buy from? Hopefully it gets nice soon so I can check it out. Too bad I can't take it with me to Texas next week!! I am sure the weather there will be much better.
tanz45 - At least my Trans Am sits on the ground. I love them lifted or slammed as long as they are done right!
Rubie

[pl4yboy]

Nelson sells the drop in GSS340 Walbro 255 you need.

[Paulster2]

Only two things it could be IMHO and both pertain to fuel.
1) Injector size
2) Fuel pump not keeping up

You need to check to see what your injectors are doing and make sure you haven't maxed them out (I doubt you have). Secondly, check to make sure you have the fuel pressure you need at WOT. You can check this by attaching a fuel pressure gauge at the Schraeder valve and placing it in a position OUTSIDE OF THE CAB where you can see it while driving. Check to see if you start losing fuel pressure at WOT. If so, I bet it's your pump.

Just some suggestions, but do as much diagnostics as you can do before you start replacing parts. Gunna save you a bunch of money in the long run.

[sprayedenali]

Only two things it could be IMHO and both pertain to fuel.
1) Injector size
2) Fuel pump not keeping up

You need to check to see what your injectors are doing and make sure you haven't maxed them out (I doubt you have). Secondly, check to make sure you have the fuel pressure you need at WOT. You can check this by attaching a fuel pressure gauge at the Schraeder valve and placing it in a position OUTSIDE OF THE CAB where you can see it while driving. Check to see if you start losing fuel pressure at WOT. If so, I bet it's your pump.

Just some suggestions, but do as much diagnostics as you can do before you start replacing parts. Gunna save you a bunch of money in the long run.

a friend of mine has a stock fuel pump and 28lb (maybe 32, cant remember) injectors supporting well over 500whp FWIW...

[chvy=power]

hook the fuel pressure gauge up and run it up to the windshield and shut the hood till it latches but not all the way. that way you can see the fuel pressure at WOT while your goin down the road. And if your running that lean be careful at high rpm its not good on the motor

[iowackers]

Finally went for a ride today with the fuel pressure gauge. 50 psi at idle. Very responsive with throttle movement. WOT was 58 psi. Truck still feels weak and at 5000rpm it dropped out and went really lean again (19.2 AFR) No codes. I have gotten 1 or 2 O2 codes in the last couple years, but that is all. Any ideas? Check injector duty cycle next?

[pl4yboy]

Finally went for a ride today with the fuel pressure gauge. 50 psi at idle. Very responsive with throttle movement. WOT was 58 psi. Truck still feels weak and at 5000rpm it dropped out and went really lean again (19.2 AFR) No codes. I have gotten 1 or 2 O2 codes in the last couple years, but that is all. Any ideas? Check injector duty cycle next?

Yes. IDC next. It may not show a clogged one though.