Loss of power on acceleration when warm, backfires a lot.
 

I have an 87 Suburban with a 6.0 LQ4.
For a while now, when the motor is warmed up, when I go to accelerate sometimes it will bog down and not want to move. When this happens it backfires like crazy, and if I keep the accelerator pedal pressed once the RPMs finally get up the truck will accelerate and get up to speed.
When I did the swap 5 years and 16,000 miles ago I replaced the spark plugs, plug wires, fuel filter, ignition coils, and MAF sensor. I did not replace the fuel injectors. I have a fuel gauge mounted to my fuel rail that shows a constant 58 psi at idle. I do not have any check engine lights or any stored codes.

Any Ideas where to start?

Re: Loss of power on acceleration when warm, backfires a lot.
 

Sounds a lot like a fuel pressure problem. I would hook up the gauge and check pressure while under load if possible. Maybe change the fuel filter if it hasn't been changed in a while.

Re: Loss of power on acceleration when warm, backfires a lot.
 

Not sure why you aren't getting any codes. Running that poorly should trigger some response from the computer.

My truck with 5.3Vortec motor was running like crap for a while, including some back firing and very rough idle and poor throttle. The only codes I was getting was lean condition on the left bank. I tried a few basic tune things to no avail.

One day I decided to take off the bracket that holds the coils on the left side just to clean things up and inspect the coils. I had already installed new plugs and wires.

One of the coils was cracked on the bottom side and could not be seen unless it was removed. I had some spares so I changed out the coil and it runs perfectly again.

Re: Loss of power on acceleration when warm, backfires a lot.
 

Do you have a way to see which cylinders are misfiring if they are misfiring?
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Re: Loss of power on acceleration when warm, backfires a lot.
 

Update:
Since I started the thread I have replaced the Camshaft position sensor, Crank sensor, and MAP sensor as these were all not replaced 5 years ago when I did the swap. Did not change anything.
I never did have a ck engine light until two weeks ago I got P0175 rich on bank 2. Cleared the code came back a few days later.
I have a constant 58 psi fuel pressure at idle.
It seemed to only do this when under load and when the engine was warm.
Even worse with the AC on.
Then I replaced the Mass air flow sensor and still no change.
Two days ago I replaced the spark plugs and plug wires again (were replaced when I did the swap 5 years ago).
Now it seems like it is fixed. I have driven it about 60 miles and seems like the problem was solved.
When I inspected the plugs they weren't fouled out/black and all 8 looked the same.

If it comes back I will keep everyone posted.
Thanks for the help.

Re: Loss of power on acceleration when warm, backfires a lot.
 

dont you just hate chasing a problem...then find its something simple

Re: Loss of power on acceleration when warm, backfires a lot.
 

Man I do, as long as the problem doesn't come back.
My next two steps were to replace the throttle body, as I was thinking the Throttle position sensor was the problem.
If that didn't fix it, I was going to pull the motor and fully build it and make it a beast.