Truck stumbles when shut off

[Hoosierlong90]

As title says. 94 tbi 350.
Checked fuel pump
Replaced fuel filter
Changed icm twice
Checked fuel regulator diaphram
Checked everything ig ignition I can think of
Timing checked
Timing advance works
Truck hesitates when I take off and 4th gear cruise.
Weird problem to me.

Is there a relay that will cause ignition problems that I'm experiencing?

Any help is appreciated!

 

[Schurkey]

As title says.

I don't know what "stumbles" when shut off means.

Run-on when shut off is generally due to one of three things.
1. Idle speed too high
2. MSD or other spark-box needs a corrective diode spliced into the alternator wiring
3. The idle speed is too high...check it again.

94 tbi 350.

Truck hesitates when I take off and 4th gear cruise.

What is the fuel pressure under load? You seem to have already inspected cap, rotor, plug wires and spark plugs. Verify EGR operation, PCV system, and the heated-air intake on the air cleaner snorkel.

Will the ignition coil reliably fire a spark-tester calibrated for HEI?

Connect a scan tool, verify ALL the sensors and computer outputs. Check the fuel trims, and knock-sensor/ignition retard.

 

[Hoosierlong90]

I don't know what "stumbles" when shut off means.

Run-on when shut off is generally due to one of three things.
1. Idle speed too high
2. MSD or other spark-box needs a corrective diode spliced into the alternator wiring
3. The idle speed is too high...check it again.


What is the fuel pressure under load? You seem to have already inspected cap, rotor, plug wires and spark plugs. Verify EGR operation, PCV system, and the heated-air intake on the air cleaner snorkel.

Will the ignition coil reliably fire a spark-tester calibrated for HEI?

Connect a scan tool, verify ALL the sensors and computer outputs. Check the fuel trims, and knock-sensor/ignition retard.

It sorta diesels when I turn the key off. It goes 2 more revolutions, clunky clunk! I noticed iac error on the scanner last night. I'll swap it out and see what happens.

It has ran great the last year the way it's set up, so I don't know. It almost seems like it misses till I give it a bit more throttle, then it feels normal. At idle it shakes.

Hoping the iac is the culprit.

 

[Hoosierlong90]

I don't know what "stumbles" when shut off means.

Run-on when shut off is generally due to one of three things.
1. Idle speed too high
2. MSD or other spark-box needs a corrective diode spliced into the alternator wiring
3. The idle speed is too high...check it again.


What is the fuel pressure under load? You seem to have already inspected cap, rotor, plug wires and spark plugs. Verify EGR operation, PCV system, and the heated-air intake on the air cleaner snorkel.

Will the ignition coil reliably fire a spark-tester calibrated for HEI?

Connect a scan tool, verify ALL the sensors and computer outputs. Check the fuel trims, and knock-sensor/ignition retard.

 

[95burban]

Could possibly be pre ignition. Have you done a tune up lately? Is there a lot of carbon on the plugs? If so I would start with ice cold water and start pouring it down the throttle body at a high rpm.

 

[Hoosierlong90]

Could possibly be pre ignition. Have you done a tune up lately? Is there a lot of carbon on the plugs? If so I would start with ice cold water and start pouring it down the throttle body at a high rpm.

Motors 1 year old.

 

[Schurkey]

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THAT can't be good. I think you need to make plans for replacement. Probably an entire distributor, mainshafts are hard to come by, now.

But I'd still check the idle speed.

 

[Hoosierlong90]

I

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THAT can't be good. I think you need to make plans for replacement. Probably an entire distributor, mainshafts are hard to come by, now.

But I'd still check the idle speed.

Idle speed is good in tune and at idle. I think I'll try a different distributor just to see what happens.

Fingers crossed!!!

 

[Hoosierlong90]

You must be registered for see images attach

THAT can't be good. I think you need to make plans for replacement. Probably an entire distributor, mainshafts are hard to come by, now.

But I'd still check the idle speed.

Update! I figured it out Schurkey, it was the intake manifold gaskets. Replaced them and it's back to running smooth. Thanks for the insight and help!