92 5.7 random dies at idle

[jess t]

Hey all diagnosticians, my 92 C1500 5.7 throttle body 350 randomly dies at idle. New plugs, cap, rotor, pickup coil, ignition module (2) hasn't fixed it. Code 32 is only code and I know the EGR isn't randomly sticking open and killing it because it will come down to idle and run smooth as silk then randomly (not every time) start intermittingly missing, then die. Starts right back up and runs great the rest of the time, but will randomly do the same thing again, but not in any discernible pattern. I did not change the rotor shaft in the distributor and am thinking I may have a cracked magnet there, any thoughts?

Jess in ky

 

[PlayingWithTBI]

How's your ignition coil? Spray some water on it, not the wires, while idling and see if it stumbles. If that's good get a scam tool so you can see the data stream.

 

[jess t]

I wondered about the coil, but I have had the hood up while it was having one of it's missing fits, looking for arcing and there isn't ANY. None around any secondary ignition parts, even the coil. I haven't tried spraying water on the coil, but will do that. Also tried wiggling the wiring harnesses but cannot make it miss when it isn't. I've replaced the IAC motor and cleaned the throttle body passage and throttle blades, no difference. Thanks for offering suggestions. jt

 

[Schurkey]

randomly (not every time) start intermittingly missing, then die. Starts right back up and runs great the rest of the time, but will randomly do the same thing again, but not in any discernible pattern. I did not change the rotor shaft in the distributor and am thinking I may have a cracked magnet there, any thoughts?

My '88 K1500 had a high-speed misfire. Gradually and progressively got worse, would sometimes stall at idle.

Eventually stalled, would not re-start.

Cracked magnets on distributor shaft. GM dealership replaced the distributor mainshaft and the distributor-to-coil wire harness. Perfect ever since.

It'd be worth checking fuel pressure, too. Does the pump prime? Do you have fuel spray when the truck won't re-start?

Ignition coils can short internally, no visible arc. Verify by connecting a spark-tester calibrated for HEI. If it won't reliably fire the spark-tester, the coil is toast.

 

[MBski]

Here's another thought...Does it flood when it stalls? As recent as last week, my brother believes he's finally found the problem with my 93 5.7L TBI. It would stall/no restart and in the worst possible locations. Eventually it would restart but that was usually after it was unloaded from the tow truck.

Last week it finally failed in the driveway so we were able to put an old GM Tech 2 scanner on the ODB1 port and noticed the fuel trims, fuel/air ratio and Engine Coolant Temperature were going crazy. And it turns out the engine would flood once you dropped into gear. Apparently the PCM was reading a random minus freezing temps (here in sunny Florida) and telling the injectors to dump a lot more fuel than needed. The culprit seems to have been the ECT sensor on the top of the engine. The one thing we never realized is sensor is not the same one that feeds the temp gauge on the dash so this wasn't immediately obvious.

The computer seems to be re-learning on the first few test runs so it will take a few weeks before we're confident that was it. I just happened across the thread and although your issue sounds different, it might provide another angle for you to look at.

 

[stutaeng]

Here's another thought...Does it flood when it stalls? As recent as last week, my brother believes he's finally found the problem with my 93 5.7L TBI. It would stall/no restart and in the worst possible locations. Eventually it would restart but that was usually after it was unloaded from the tow truck.

Last week it finally failed in the driveway so we were able to put an old GM Tech 2 scanner on the ODB1 port and noticed the fuel trims, fuel/air ratio and Engine Coolant Temperature were going crazy. And it turns out the engine would flood once you dropped into gear. Apparently the PCM was reading a random minus freezing temps (here in sunny Florida) and telling the injectors to dump a lot more fuel than needed. The culprit seems to have been the ECT sensor on the top of the engine. The one thing we never realized is sensor is not the same one that feeds the temp gauge on the dash so this wasn't immediately obvious.

The computer seems to be re-learning on the first few test runs so it will take a few weeks before we're confident that was it. I just happened across the thread and although your issue sounds different, it might provide another angle for you to look at.

Wow, thanks for the information! And great diagnostic!

I didn't even know the TBIs had this information such as fuel trims available. There's a few guys running those GM Tech 2 scanners here. My brother daily drives a TBI, and I sometimes help him if has issues with diagnostics, but don't know a whole lot on them.

I've asked the question before as to why these GM trucks have 2 coolant temp senders. On my 00 5.7 my guage reads 1/4 mark, but the ECU is reading 190F. Chased my tail trying to get the instrument cluster to register correct, even changed the sender by the head. Finally, blamed the cluster and gave up.

BTW, The Haynes manual has a table of temperature vs. resistance for those temp. senders. Can't remember if they are only for the Vortec though. I remember checking mine with a DVOM and a heat gun, but of course, it tested okay.

But in neither your case and my case, I see absolutely no reason to have 2 sources of temperature, LOL. Maybe the sender by the head as always been there and when they went to a computer setup, they just decided to add another temp sender? If so, that was brilliant!

On a side note, I was driving my wife's '13 Town and Country yesterday and the $$$ light came on. When I got home I hooked up my scanner and it said something-thermostat. I looked at the freeze frame and the ECU has way more information than my 99-06 trucks, such as run time. I hypothesized, that if the temperature does not come up to operating temperature after a certain time or run or drive time, the ECU is programed to throw a CEL light. The ECT was 160F per the data. And I did realize then that the heater didn't seem as toasty as usual...