1992 blazer will not restart hot.

351FUN

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Truck starts up cold perfectly, runs smooth, zero issues. Once you cut it off after its at operating temp it will not restart until it cools off. It cranks fine, the starter is turning fast and you can smell some gas so I think its getting fuel fine. I tried the coil and ignition module tonight with no change. I'm diagnosing blind right now because I don't have any of my tools, just a few I had left in the truck before I moved.
 

351FUN

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Check fuel pressure, might have a pump going bad. The coolant temp sensor will do this too if it is bad.
Pump is new and gives a solid 13 psi while running that never changes. Is this the coolant temp sensor by the thermostat? I believe that's new too but that doesn't mean its good these days.
 

east302

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On the vortec it’s by the thermostat (vs left cylinder head for temp gauge) so it’s probably near the same spot for yours.

Not sure about the TBI, but if you hold the gas down while cranking on a vortec it stops injector flow and can be a workaround for a flaky temperature sensor.

A scanner can tell you what the temperature readout of the sensor is. If it’s some oddball number then there’s a problem. There may be a way to check it by resistance values but I don’t remember for sure.
 

PlayingWithTBI

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There may be a way to check it by resistance values but I don’t remember for sure.
Yep, there's a couple ways.
1.) check resistance when the engine is cold, then warm it up and check again. This will give you a ballpark idea.
2.) Submerge the sensor in ice water and check it (s/b ~9600 Ohms @32°). Then stick it in boiling water (s/b ~185 @212°)

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A scanner is the easier way to go :waytogo:
 

351FUN

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Well I finally got back to working on it, it pissed me off enough I went and bought a Q60 and parked the blazer in the back lot for a bit. Swapped out the temperature sensor just because its so cheap, it ran great for a few trips and started right back up until this afternoon trying to leave work it would not start at all. Its over 90 out so the truck is pretty damn hot even without running, so it could still be a temperature thing. I don't have anywhere to do real diagnostics on it though and I'm out of ideas at this point.
 

Jeepwalker

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Did you say you tried a new ignition module? Have you verified there's a spark (insert spare spark plug) when the warm engine won't start? I guess narrow down if there's spark or not.

If there isn't any spark, what if you removed the module when the engine was hot and not starting, closed the hood (to keep the engine warm), ...let the module cool on it's own, or blow with a hair dryer (not heat, just air) ....and reinstall it after it's cooled? ...to see if the cooler module would start the vehicle. Maybe the module is on it's way out. Or maybe the coil is acting up (check connectors too).

Also, beneath the module in the distributoor is a pick-up coil, some small wires (that like to break after many miles). I think those were still on 92's. Someone correct me if I'm wrong. And then theres a cast metal 8-sided unit that spins by the pick-up coil. That metal ring cracked and broke on my truck. It would still run but like crap. The distributor needs to come out to check those. So check the coil first.

I'm just tossing out things that come to mind.....
 

wb292

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Anyone know what the cure was? I'm having the same issue on my 91 K1500 5.7. Starts and runs great when cold or cool. When I drive it home about 70 miles with the AC on, it won't restart for at least 30 min after shutting it off. I replaced the fuel pump relay and oil pressure sensor hoping it was not getting fuel. Short trips into town and back aren't an issue. It will start easily. I drive it about 140 miles a day and it otherwise runs great. The fuel pump is a Delphi and is about 9 months old. How would the water temp sensor keep it from hot starting as mentioned in a earlier post? I replaced it with a new one when I rebuilt the engine 2 years ago.
 

Schurkey

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Anyone know what the cure was? I'm having the same issue on my 91 K1500 5.7. Starts and runs great when cold or cool. When I drive it home about 70 miles with the AC on, it won't restart for at least 30 min after shutting it off.
Do you have spark when it won't restart hot?

Do you see fuel spraying from the injector(s) when it won't restart hot?

If you have no spark and no fuel, I'd be looking at the distributor including the magnet by the pickup coil.
 

wb292

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I was unable to check it out because it happened at the supermarket. I’m hoping I have Saturday free to run down the issue. Does anyone know how the coolant sensor could be a factor in this?
 
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