Vortec 305 running super lean

[nauju]

I have a 1998 gmc sierra with the 305 vortec and it is running very lean on both banks, I have changed the oxygen sensors, fuel injectors, intake manifold gaskets, fuel pump, fuel filter, mass air flow sensor, crank position sensor,egr valve,spark plugs and wires and the distributor and it is still running very lean I have also checked for vacuum leaks and there are none anyone know what can it be?

 

[ralmo94]

What does it do in open Loop with fuel trims reset? Also, how do you know it's lean, fuel trims, wideband, ect? Has anything changed between it running normal and lean? Does it do ok in speed density with MAF unplugged?

 

[Schurkey]

What are the misfire counts for each cylinder?

What is the fuel pressure under load?

How old are the intake manifold-to-cylinder head gaskets?

Does the engine run different if you pinch each one of the vacuum hoses (one at a time)?

 

[nauju]

What does it do in open Loop with fuel trims reset? Also, how do you know it's lean, fuel trims, wideband, ect? Has anything changed between it running normal and lean? Does it do ok in speed density with MAF unplugged?

What does it do in open Loop with fuel trims reset? Also, how do you know it's lean, fuel trims, wideband, ect? Has anything changed between it running normal and lean? Does it do ok in speed density with MAF unplugged?

It runs fine when it’s cold or after it has been sitting for a few hours, after it warms up it has a fuel trim of 30-40% on bank 1 and 20-30 on bank 2.I unplugged the maf and it makes it run richer but it still runs the same. What’ll do is after you’ve been driving it for a good while the truck will start to bog down and it doesn’t want to accelerate anymore I have to pull over and shut it off and let it sit for 5-10 minutes before it’ll start to run enough for it to accelerate then after awhile it’ll do the same and I have to pull over again and again

 

[nauju]

What are the misfire counts for each cylinder?

What is the fuel pressure under load?

How old are the intake manifold-to-cylinder head gaskets?

Does the engine run different if you pinch each one of the vacuum hoses (one at a time)?

It actually doesn’t have any misfire counts which I find strange.fuel pressure under load is 58.I just replaced the manifold to cylinder head gaskets.it doesn’t run different when the lines are pinched.

 

[ralmo94]

I would recommend as a diagnosis step, reset trims by unhooking bat power, and unplug o2's. Take it for a spin with o2's unplugged. If it runs fine that way, next to explore is why the o2's read lean, could be circuitry, exhaust leak, or even aftermarket o2 sensors. They don't always read the correct scale.
Have you monitored O2 voltage?

Have you checked spark plugs for color?

 

[ralmo94]

It actually doesn’t have any misfire counts which I find strange.

On my 454 misfire monitor was off factory stock. Don't know if they did that on 305 also, but could explain that if they did.

 

[nauju]

I would recommend as a diagnosis step, reset trims by unhooking bat power, and unplug o2's. Take it for a spin with o2's unplugged. If it runs fine that way, next to explore is why the o2's read lean, could be circuitry, exhaust leak, or even aftermarket o2 sensors. They don't always read the correct scale.
Have you monitored O2 voltage?

Have you checked spark plugs for color?

I disconnected the o2 sensors and it runs the same. Spark plugs definitely look like they’re running lean.

 

[ralmo94]

Have you checked the charcoal canister hose, and pcv?

 

[nauju]

Have you checked the charcoal canister hose, and pcv?

Yes I have