96 suburban stumbles

96 suburban k2500 454, startes great cold,...hard start warm,...stumbles at take off and under acc. load,...new plugs, wires, cap, rotor, new down stream o2, upstream o2 about 30k ago, help,...sounds like it is carburated and starving for air.

96 suburban k2500 454, startes great cold,...hard start warm,...stumbles at take off and under acc. load,...new plugs, wires, cap, rotor, new down stream o2, upstream o2 about 30k ago, help,...sounds like it is carburated and starving for air.

How is the fuel pressure?
Any codes or check engine lights?

How is the fuel pressure?
Any codes or check engine lights?

The fuel pressure is correct,...new fuel filter and fuel pump last 30days,...
no codes at all,...

Ac delco plugs and cap and rotor?
Have you run a full pressure test?
Is it losing spark when hot?
Any check engine lights?

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 61-63 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 56-63 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

Ran a full fuel test and all looks good,...was cincerned about regulator,...did make the mistake of not using ac delco,...waiting for motor
to cool now to change out plugs to ac delco,...no check engine light,...

Ac delco plugs and cap and rotor?
Have you run a full pressure test?
Is it losing spark when hot?
Any check engine lights?

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 61-63 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 56-63 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

What was your pressure readings?

Best to use ac delco?
What brand of plugs did you use?

I would get a scanner on it and check all sensor readings and for stored and history code.

Preasure reading are all with in the ranges you listed,...have scanned for codes and no codes stored,...have used scanner to drive test and see nothing abnormal,...


Ac delco plugs and cap and rotor?
Have you run a full pressure test?
Is it losing spark when hot?
Any check engine lights?

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 61-63 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 56-63 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

A friend had the same problem and it turned out to be a bad coil.
It would run great until the coil got hot from the engine's heat.
Also very hard or impossible to start once hot.

A friend had the same problem and it turned out to be a bad coil.
It would run great until the coil got hot from the engine's heat.
Also very hard or impossible to start once hot.

I seen the coil failure when it got hot ....that was 40yrs ago however..

I seen the coil failure when it got hot ....that was 40yrs ago however..

Yep, you're pretty close :wink:
Dodge W200 (M880) ex US Army 1977