Intermittent starting gremlin driving me NUTS

[mckee1710]

1997 K1500 pickup, 5.7 Vortec, 66k miles. Very intermittent stumble on start up. When it does occur, the starter sounds high pitched, almost like its turning over faster than normal. The engine stumbles for a second or two, misfire like, then reaches idle RPM. ONLY occurs on a re-start when the engine is warm, never on a cold start. No CEL, no codes per scanner. Fuel pressure tests within spec. Truck starts/runs flawlessly otherwise. This issue has persisted for over a year and is continually driving me crazy, mainly bc it’s so sporadic.

Recent maintenance/new parts that have had no effect:
-new battery
-Fuel pump/sending unit (spectra)
-fuel filter (ACDelco)
-full ign tune-up plugs, wires, coil, cap, rotor (all ACDelco)
-intake manifold gaskets (FelPro)
-crank position sensor (Delphi)
-coolant temp sensor (Delphi)
-MPFI swap (ACDelco)

anyone with a similar issue or ideas to test? It’s such a minor thing, I know, but its really starting to drive me nuts. Thanks in advance.

 

[delta_p]

I know it only has 66K on it and you changed many things that should have fixed it, but can you pull the distributor and just look over the gear teeth for any wear or vertical play of the shaft. I have a '96 with 163K and I had this slight stumble every so often at idle, never threw a code, and it always started and ran great. It was consistent though. I decided to put a new distributor in. I noticed on the old one, some teeth looked a little worn, not really too bad though, and the shaft was pretty rusted up and it didn't spin as free in the bushings as the new one. The new distributor got rid of the stumble.

 

[mckee1710]

I know it only has 66K on it and you changed many things that should have fixed it, but can you pull the distributor and just look over the gear teeth for any wear or vertical play of the shaft. I have a '96 with 163K and I had this slight stumble every so often at idle, never threw a code, and it always started and ran great. It was consistent though. I decided to put a new distributor in. I noticed on the old one, some teeth looked a little worn, not really too bad though, and the shaft was pretty rusted up and it didn't spin as free in the bushings as the new one. The new distributor got rid of the stumble.

I recently pulled the distributor as part of the intake gasket job and didn’t see any wear on the gears. Didn’t check for play in the shaft though. I’ll definitely keep it in mind, thanks

 

[mckee1710]

It seems to be engine temp related, last few days have been relatively cold here, stumble hasn't occurred once...

 

[JohnDenver]

I had a somewhat similar starting issue, though not exactly the same, and the problem was that the starter wiring was run by the exhaust manifold (or some hot exhaust part) and the wiring started to short out. Eventually it just cranked continually and fried it—luckily I was already at the shop for an unrelated issue!

 

[Erik the Awful]

Bendix not kicking out fast enough?

 

[mckee1710]

Bendix not kicking out fast enough?

Is there a way to test it? Maybe I should pull the starter and inspect it...

 

[Erik the Awful]

If the sound of the starter running fast is after you let up on the key, then there's your test, R&R the starter.

 

[mckee1710]

Alternator died about a week ago, replaced with new (not reman) AC Delco professional. Charging properly. No effect on starting issue.

Inspected starter and from what I researched it was the 24-year old OE Delco Remy. Pinion gear had some serious wear. Replaced with new (not reman) AC Delco professional, gear redux w/ OE heat shield over solenoid. Turns over strong, but STILL the issue persists. Only when warm.

Could it be either the ICM or TPS? Kinda tired of parts swapping but it seems near-impossible to diagnose such an intermittent issue...

 

[Erik the Awful]

Wow, sorry that I wasn't helpful on that one. How did the ring gear look when you had the starter out? Does the starter need a shim under it?

I know starter shims were a common thing back in the day, but I thought they had the machine tolerances sorted when they produced GMT400s.