89 350TBI low end loss of power

[Vinny1050]

Can drive an hour going easy no problem. Once I hit an on-ramp and hammer it like 3k plus rpm the engine loses power under 2k rpm.
Acceleration from a stop is jumpy but not miss fire jumps. Feels like a starved fuel system getting a surge of fuel jump. No shakes, pops, smoke, or total loss of fire just a steady bog any throttle and the engine stays steady where it’s at. Give it little throttle to get 2200 1-2 shift and once it hits 2k the engine jumps back to life then loses it at the low rpm. Idle is normal and Revs to the moon in park.

Power braked to get the stumble in the garage for some testing, fuel looks normal no drips or cutout as far as I can tell also don’t have a good meter to test pressure but got 11psi to injectors with a buddies tool.
Sprayed water on headers and all same temp.

Seems like issue persists all day until I start it the following morning then I’m back to normal until I hit that on-ramp again.

I’m running no o2 so I’m in a preset loop I think.

New egr valve and tested unhooked with same results

New distributor, icm, wires, coil.

Cleaned and replaced every ground in sight.

New gaskets and filters on throttle body and injectors.

Maf and tps voltage tested fine

No vacuum leaks.

Engine and harness are very old but I have gone through and re-pinned most engine bay connectors.

Im hoping someone on here can help me here how would a loss of fuel bog me down at low rpm but still rev high no problem. I’ve changed everything spark related besides the ecu

 

[Wes Harden]

Backed up exhaust

 

[Vinny1050]

Backed up exhaust

Should have added that I have dual long tubes with an H and single chambers. Nothing backed up there

 

[Blue85]

11psi is within spec, but is that sitting at idle or while it's under load?

Why not run an O2?

 

[Vinny1050]

11psi is within spec, but is that sitting at idle or while it's under load?

Why not run an O2?

That was at idle. I was considering adding a gauge inline to check at any point when symptoms arise but didn’t have the right adapters and clamps on hand so left it.

I was considering welding a nut for a heated o2. I didn’t because the truck was running okay as is.

I am also building an ls for this truck so most of the money right now is going towards that

 

[Blue85]

It's kind of silly to run TBI without an O2 sensor.

 

[Vinny1050]

It's kind of silly to run TBI without an O2 sensor.

You are right but for my purpose it ran fine on the preset tune. This is a 86 k10 someone had done an awful tbi swap into.
In 6 months I've already rebuilt the 700r4 and fed up with this jack shit wiring so I bought the 5.3.

Just trying to make it last until I’m ready.

 

[Wes Harden]

another possibility has occurred to me. something in the tank blocking the fuel pick up when hard accell? Maybe the fuel well basket is loose ? had an s10 suv at the shop would back up all day, stall going forward. Loos basket in tank.

 

[Vinny1050]

another possibility has occurred to me. something in the tank blocking the fuel pick up when hard accell? Maybe the fuel well basket is loose ? had an s10 suv at the shop would back up all day, stall going forward. Loos basket in tank.

When we get some good weather I am going to try dropping the tank. Previous owner said he put a new pump but the filter was full of some gray sediment so I’m sure pump is dirty.

 

[Vinny1050]

Can drive an hour going easy no problem. Once I hit an on-ramp and hammer it like 3k plus rpm the engine loses power under 2k rpm.
Acceleration from a stop is jumpy but not miss fire jumps. Feels like a starved fuel system getting a surge of fuel jump. No shakes, pops, smoke, or total loss of fire just a steady bog any throttle and the engine stays steady where it’s at. Give it little throttle to get 2200 1-2 shift and once it hits 2k the engine jumps back to life then loses it at the low rpm. Idle is normal and Revs to the moon in park.

Power braked to get the stumble in the garage for some testing, fuel looks normal no drips or cutout as far as I can tell also don’t have a good meter to test pressure but got 11psi to injectors with a buddies tool.
Sprayed water on headers and all same temp.

Seems like issue persists all day until I start it the following morning then I’m back to normal until I hit that on-ramp again.

I’m running no o2 so I’m in a preset loop I think.

New egr valve and tested unhooked with same results

New distributor, icm, wires, coil.

Cleaned and replaced every ground in sight.

New gaskets and filters on throttle body and injectors.

Maf and tps voltage tested fine

No vacuum leaks.

Engine and harness are very old but I have gone through and re-pinned most engine bay connectors.

Im hoping someone on here can help me here how would a loss of fuel bog me down at low rpm but still rev high no problem. I’ve changed everything spark related besides the ecu

I may have figured it out.

Ground connecting engine to frame was broken I must have overlooked it. Getting check engine while symptoms present.

Jumped pins for codes 13 (o2) and 43 (esc circuit)

Turns out my new knock sensor connector the pin pushed itself in far enough to lose contact with the sensor. Rigged it for a test and couldn’t get symptoms again.

From some research it looks like the ECU will do a ESC test. Changing timing and conditions to try and force feedback from the sensor.

Going back to Falmouth in a few weeks so we will see if that long ride brings the problem back.