Riddle me this... hot start 'N dies, miss / cut out only in summer

[alpinecrick]

Starts right up when cold and runs excellent all winter long and short trips around town. smooth and powerful from idle to redline.

The problem is during summer after a 60+ mile highway drive, It will run great the initial drive until shutoff. When trying to restart it cranks a bit longer, fires, revs up (as usual) then dies. Have to crank awhile and manually give it throttle so it stays running. Will run slightly rough from idle to redline, cuts out if you mash the gas or even smooth gentle throttle inputs. Definitely a miss like electrical or no fuel? Once you let it cool down for at least an hour, it fires up, revs, idles fine.

This was a once a year random problem only with the hard starts when warm. This year is the first time it has missed or cut out throughout the RPM range after a heat soaked hot start

NO Service Engine Soon light.

What do you think the problem is?

Anyone experience something similar?

97 K1500 Vortec 5.7 Black Bear Tune. 210k miles
original poppet spider fuel injection
Fuel pump (2nd time) replaced 30k miles ago with Delphi pump along with new fuel filter
New plugs, cap, rotor, wires 20k miles ago
New Bosh O2 sensors (all 4) 20k miles ago
New high flow catalytic converters 20k miles ago
Engine grounds are clean

if you haven't replaced your fuel filter since the new pump I would start there.

 

[97K1500Silverado]

Can’t find my damn Bluetooth scanner so will have to get another on order.

 

[97K1500Silverado]

Sticking EGR valve that is almost closed but stuck just open enough to drop vacuum and cause hard start (low vacuum) and low speed skip with no codes. HTH

Interesting, but yesterday it cut out briefly in the high rpm range at 3.5k about 3/4 throttle. This was when hot.

From a cold start it ran great from idle to redline without any cutouts or rough spots.

 

[97K1500Silverado]

if you haven't replaced your fuel filter since the new pump I would start there.

I may have replaced it once since the pump but it’s easy and cheap enough to do so will get one on order. [emoji106]

 

[97K1500Silverado]

You can check the relay by seeing if another one in the underhood fuse panel has the same pins. Swap them and see if the problem persists. If that's it, a new relay is under 30 bucks IIRC. Replaced it and starter relay on my Burb but not sure if either was really bad. Both were likely the original ones though so after 20 years probably due for replacement. My other 99 Burb had fuel injection work done years ago; I think the fuel pressure regulator was one thing changed. The spider upgrade wasn't available then, so I know 2 separate injectors were bad and replaced. Also upper manifold. Seems like the bill was around a grand.

The stock setup is 2 fuel injectors which sit above the spider poppet valve injection. Correct?

I found other relays that look the same in the fuse box but the fuel pump relay has more pins than the others. May get a replacement.

 

[97K1500Silverado]

I scanned for codes. Nothing stored.

I looked at the Ignition Control Module. It looks original. I may replace it.

Acdelco 19352931 $100
Delphi DS10039 $78

Will prob go acdelco. Hopefully it comes with dielectric grease. Looks like you reuse your old heat sink.

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[SAATR]

I scanned for codes. Nothing stored.

I looked at the Ignition Control Module. It looks original. I may replace it.

Acdelco 19352931 $100
Delphi DS10039 $78

Will prob go acdelco. Hopefully it comes with dielectric grease. Looks like you reuse your old heat sink.

You must be registered for see images attach

That's heat sink compound, not dielectric grease. Heat sink compound is thermally conductive, dielectric grease is resistant to heat and electrical conduction. If you want the module to have the same long, happy life, use heat sink compound.

That said, if you believe the ICM is the issue, test it. Run the engine and use a hair dryer or heat gun to warm it up. See if your problem comes back when the module gets hot. Be careful, especially with a heat gun! You can overheat and kill the module this way. Better to have an infrared thermometer handy to keep an eye on the temp. Figure that it sees whatever the air temp coming off the radiator is under operation, probably 150 to 190 degrees. If it doesn't act up with raised temperature, it likely isn't the problem.

 

[alpinecrick]

96K1500,
I think the ICM requires heat sink paste on the back of the module. If I understand what you’re saying, I wasn’t aware dialectic grease would be a substitute?

 

[alpinecrick]

SAATR beat me to it......

 

[97K1500Silverado]

That's heat sink compound, not dielectric grease. Heat sink compound is thermally conductive, dielectric grease is resistant to heat and electrical conduction. If you want the module to have the same long, happy life, use heat sink compound.

That said, if you believe the ICM is the issue, test it. Run the engine and use a hair dryer or heat gun to warm it up. See if your problem comes back when the module gets hot. Be careful, especially with a heat gun! You can overheat and kill the module this way. Better to have an infrared thermometer handy to keep an eye on the temp. Figure that it sees whatever the air temp coming off the radiator is under operation, probably 150 to 190 degrees. If it doesn't act up with raised temperature, it likely isn't the problem.

Good idea on how to test.
My luck I’d prob end up killing it.

I’m just going to replace it.

Ordered a oem acdelco from rockauto

I have computer CPU thermal grease so will use that if the part doesn’t come with it.

Looks like just get it snug as it’s easy to over tighten and possible damage it.

I recently did distributer cap, rotor, plugs, wires, coil. So the ICM will round out the ignition system refresh.