Dies in gear when throttle applied

[92GMCK2500]

92 5.7L TBI, 7004r

Truck dies in gear when throttle is applied.

Diagnostics so far:
- fuel pressure tested.
- Reads consistently at 9.5 psi key on, engine off. Builds to 9.5psi then bleeds to zero in 1-2 seconds. Cycled several times, same result. Is this normal?
- Pump primes for 2 seconds with key on. Did not test fuel pump electrical because of this. Do I need to?
- Holds steady at 11 psi at idle in P or N & in gear. Any gear RD321.
- Stumbles and dies when throttle applied while in gear. Pressure flutters very slightly, approx 0.5 psi when this happens. Otherwise it holds at 11psi.
- Stumbles when first shifted into gear, at idle, (no throttle), but then recovers. Fuel pressure steady 11psi.
- Idle RPM reads 900 rpm on tach in P or N. Seems slightly high, suspect vacuum leak.
- Rpm Stumbles but then settles to 600 rpm on tach when put in gear.
- Ignition - ICM & Coil is new AC Del., plugs & wires reasonably new. Wires ohm'd to spec, plugs maybe oil fouled. Plan on cleaning today.
- New ish cap & rotor.
- Don't suspect ignition as truck idled for 20 mins, no stumbles/miss.
- Truck had code 32 for EGR, so I'll start there today following the service manual diagnostic flow chart.
- Gas is old, over a year, I am going to drain that.
- Fuel pressure regulator?
- EGR valve or solenoid?
- Vacuum leak? We tested by spraying carb cleaner over fittings with engine idling, no Stumbles apparent or heard. Suggestions for other methods??

Any help appreciated, thanks!

 

[Drunkcanuk]

92 5.7L TBI, 7004r

Truck dies in gear when throttle is applied.

Diagnostics so far:
- fuel pressure tested.
- Reads consistently at 9.5 psi key on, engine off. Builds to 9.5psi then bleeds to zero in 1-2 seconds. Cycled several times, same result. Is this normal?
- Pump primes for 2 seconds with key on. Did not test fuel pump electrical because of this. Do I need to?
- Holds steady at 11 psi at idle in P or N & in gear. Any gear RD321.
- Stumbles and dies when throttle applied while in gear. Pressure flutters very slightly, approx 0.5 psi when this happens. Otherwise it holds at 11psi.
- Stumbles when first shifted into gear, at idle, (no throttle), but then recovers. Fuel pressure steady 11psi.
- Idle RPM reads 900 rpm on tach in P or N. Seems slightly high, suspect vacuum leak.
- Rpm Stumbles but then settles to 600 rpm on tach when put in gear.
- Ignition - ICM & Coil is new AC Del., plugs & wires reasonably new. Wires ohm'd to spec, plugs maybe oil fouled. Plan on cleaning today.
- New ish cap & rotor.
- Don't suspect ignition as truck idled for 20 mins, no stumbles/miss.
- Truck had code 32 for EGR, so I'll start there today following the service manual diagnostic flow chart.
- Gas is old, over a year, I am going to drain that.
- Fuel pressure regulator?
- EGR valve or solenoid?
- Vacuum leak? We tested by spraying carb cleaner over fittings with engine idling, no Stumbles apparent or heard. Suggestions for other methods??

Any help appreciated, thanks!

How old is the fuel pump?
I ask this because I had pretty much same symptoms on my 91 years ago. Changed a few parts and nothing fixed it. Finally bit the bullet and dropped the tank.
The little rubber hose that connects the pump was full of holes. Enough gas to run but then under load would stumble.

 

[92GMCK2500]

Pump is old, not original but 10 years plus at a guess.

What was your fuel pressure?

Throttle in P or N it behaves normal. Throttle in gear, stumble then dies.

 

[Drunkcanuk]

Pump is old, not original but 10 years plus at a guess.

What was your fuel pressure?

Throttle in P or N it behaves normal. Throttle in gear, stumble then dies.

I didn't test fuel pressure, was just a parts cannon shooter at the time. LOL
When the pump was changed, did the little hose get changed? That's not "that long" ago, the hose should have been ethanol rated back then.
Ya, mine idled and revved up just fine, as soon as it had to drive under load, same symptoms.

Not saying it IS the hose, just one thing (the last thing anyone wants to do is drop a tank for a few inches of hose) it could be.

 

[Drunkcanuk]

Can you hear "bubbles" in the tank?
Another fella on here a while ago heard that, and it ended up being the hose.

 

[92GMCK2500]

I didn't test fuel pressure, was just a parts cannon shooter at the time. LOL
When the pump was changed, did the little hose get changed? That's not "that long" ago, the hose should have been ethanol rated back then.
Ya, mine idled and revved up just fine, as soon as it had to drive under load, same symptoms.

Not saying it IS the hose, just one thing (the last thing anyone wants to do is drop a tank for a few inches of hose) it could be.

Who knows about the hose. Before my time. Thanks. I'll keep that in mind.

I'll square away the 'air' & EGR side first and see where I land

 

[Drunkcanuk]

Who knows about the hose. Before my time. Thanks. I'll keep that in mind.

I'll square away the 'air' & EGR side first and see where I land

I don't blame you.... dropping the tank sucks!!!
Good luck

 

[Schurkey]

Connect a scan tool, look at the data stream. Verify ALL the sensors, especially coolant temp, TPS, and MAP.

 

[Schurkey]

- fuel pressure tested.
- Reads consistently at 9.5 psi key on, engine off. Builds to 9.5psi then bleeds to zero in 1-2 seconds. Cycled several times, same result. Is this normal?

Pressure seems a little low. Not holding pressure is totally normal on TBI.

- Pump primes for 2 seconds with key on. Did not test fuel pump electrical because of this. Do I need to?

The pump will "run" on less-than-optimum voltage. But it won't run RIGHT. Yes, I'd check the voltage near the pump, with the pump RUNNING. Also verify amperage draw of the pump, with the pump RUNNING.

- Holds steady at 11 psi at idle in P or N & in gear. Any gear RD321.

Seems reasonable. Most folks prefer to be at the high-end of spec (~13 psi) but you shouldn't have stalling problems at 11 psi.

Is your gauge accurate? How do you know?

- Stumbles and dies when throttle applied while in gear. Pressure flutters very slightly, approx 0.5 psi when this happens. Otherwise it holds at 11psi.
- Stumbles when first shifted into gear, at idle, (no throttle), but then recovers. Fuel pressure steady 11psi.

Pressure maybe varies when the engine stalls because the alternator quits charging, and the system voltage droops.

- Idle RPM reads 900 rpm on tach in P or N. Seems slightly high, suspect vacuum leak.
- Rpm Stumbles but then settles to 600 rpm on tach when put in gear.

You haven't dicked with the tamper-resistant base idle screw, have you?

- Truck had code 32 for EGR, so I'll start there today following the service manual diagnostic flow chart.

Wise.

- Gas is old, over a year, I am going to drain that.

Probably a waste of time and fuel.

 

[92GMCK2500]

Connect a scan tool, look at the data stream. Verify ALL the sensors, especially coolant temp, TPS, and MAP.

Yeah, thanks...
I have an old scan tool I picked up a while back, not sure of its capabilities. I do plan to connect it when time allows.
TPS was on my radar, I am familiar with the voltage test so I'll do it again.
Coolant & MAP are old and never been tested so I can check those too.