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Hello, My first C4, several other generations I'm new to C4's 1992 Base LT1 won't start after the engine is up to operating temp. Starts great when cool and runs great till I turn it off, I come back a couple minuets later and it cranks just fine but won't start. If I sit and wait about 10 minuets then it will start and run great again.
I've done some diagnostics, and I don't want to throw money at it unless I know that a part really needs to be replaced. This is what I have so far.
Fuel pressure at 40 and holds when turned off
Fuel pressure 40 when key on, drops to 38 when running, increases to 42 when revved up. Seems to operate and hold pressure ok
Engine oil on dipstick smells a bit like fuel, but pressure holds when turned off
Injectors are original and they All ohm to about 13ohms both cold and hot
Possible other causes:
Injector leak even thought pressure holds?
Fuel Pressure Regulator even though pressure seems to operate correctly?
Ignition Control Module?
Coil?
Opti Spark?
Temp Sensor of some sort?
ECM?
If anyone has seen this type of condition I'd love to know what fixed it.
Out of the bluer I'd say distributor, have your buddy hold a wire whilst you crank it. Think mines going I loose power a lot when hot. Something with non bosch modules or something?
Getting a service manual and following the diagnostic steps will help narrow it down a lot.
Does it die when hot?
Something to try with your ECM under the hood. When it won't start, put an ice pack on top of the ECM let it sit on it for 10 minutes. Try to start. I say this because when my 93 did this and I tried this it would start right up.....pointing to the solder joints inside the computer getting touchy when it gets hot.
Getting a service manual and following the diagnostic steps will help narrow it down a lot.
Does it die when hot?
Something to try with your ECM under the hood. When it won't start, put an ice pack on top of the ECM let it sit on it for 10 minutes. Try to start. I say this because when my 93 did this and I tried this it would start right up.....pointing to the solder joints inside the computer getting touchy when it gets hot.
No, the engine never dies and runs great. Just won't start again till you let it sit for 10 minuets or so.
You can pull the vacuum line to the fuel pressure regulator and check for a gas smell or actual gas in the line. If so you need a new regulator. Gas smell in oil, I think that you have a leaking injector.
The fuel pressure holds while the engine is off, that rules out a fuel leak flooding the car when it is off and sitting. I would check for spark, when you crank the car do you get spark out of the ignition coil?
I would start with the ICM. It is attached to a finned heat sink which is bolted to the cylinder head. The heat sink can get quite dirty and greasy which decreases its ability to cool the ICM. There is also supposed to be a thin layer of thermal paste between the ICM and heat sink - like the stuff used for computer CPUs. This tends to dry out after time, which can also cause the ICM to overheat.
Try cleaning the heat sink and applying new thermal paste. Also make sure the cylinder head mounting surface is clean.
It could be that the ICM is getting heat soaked after the car is shut down and the cylinder head heats up when coolant stops flowing through it.
The fuel pressure holds while the engine is off, that rules out a fuel leak flooding the car when it is off and sitting. I would check for spark, when you crank the car do you get spark out of the ignition coil?
I have not yet checked for spark during the non-starting episodes. What is the best way to test for spark at the coil ?
I would start with the ICM. It is attached to a finned heat sink which is bolted to the cylinder head. The heat sink can get quite dirty and greasy which decreases its ability to cool the ICM. There is also supposed to be a thin layer of thermal paste between the ICM and heat sink - like the stuff used for computer CPUs. This tends to dry out after time, which can also cause the ICM to overheat.
Try cleaning the heat sink and applying new thermal paste. Also make sure the cylinder head mounting surface is clean.
It could be that the ICM is getting heat soaked after the car is shut down and the cylinder head heats up when coolant stops flowing through it.
I can check the ICM for contact and paste, however when I turn the engine off when warm and it won't restart until I wait about 10 minuets. I would not think that the ICM would 1, get too hot to start within that 10 minuets and 2, cool enough to start after the 10 minuet wait...
No, the engine never dies and runs great. Just won't start again till you let it sit for 10 minuets or so.
I have a 92 also. Mine was doing the same thing. As stated above ecu warms, up won't restart. Runs great ,won't die. Just would not restart. Easy check. When car won't restart check ecu . Warm normal,hot to touch no good.
I have a 92 also. Mine was doing the same thing. As stated above ecu warms, up won't restart. Runs great ,won't die. Just would not restart. Easy check. When car won't restart check ecu . Warm normal,hot to touch no good.
Thanks, that seems easy enough, I'll check it. What was your fix for that?
I have not yet checked for spark during the non-starting episodes. What is the best way to test for spark at the coil ?
Pull the coil wire and locate it close to a ground and see if it throughs a spark to ground. You could also get a different wire and spark plug run the new wire up to the manifold and lay a spark plug in the intake, that would allow you to crank the car and see if it has spark.
Well I'm back on the quest to solve the "Non-Start when Hot" problem on 92 LT1
Not leaky Injectors because I replaced them. Injectors were relatively cheap and I kind of wanted to do them anyway so I put in Bosch 111 from FIC. However my problem persisted.
Engine cranks over well but will not fire or start
It's Not a spark problem, lots of spark during a Not-start episode.
Seems more like a fuel starvation issue because if I spray carb cleaner into the PCV Hose the engine will fire up then then quickly die when that spray us used up.
Something is telling the injectors Not to open and allow fuel to flow into manifold
OR
There is no fuel pressure which would allow the injectors to flow fuel
Has someone said coolant temp sensor already? If the signal is bad / implausible, it makes too rich mixture that are hard to start the engine. Easy to diagnose, just measure the resistance on cold and hot (wishfully measure near ECU connector so you test the wiring as well). Or try with the connector removed (it should fallback to the default temp). There are might be multiple sensors (coolant, intake air), I'd check everyone by trying without a connector
Well I'm back on the quest to solve the "Non-Start when Hot" problem on 92 LT1
Not leaky Injectors because I replaced them. Injectors were relatively cheap and I kind of wanted to do them anyway so I put in Bosch 111 from FIC. However my problem persisted.
Engine cranks over well but will not fire or start
It's Not a spark problem, lots of spark during a Not-start episode.
Seems more like a fuel starvation issue because if I spray carb cleaner into the PCV Hose the engine will fire up then then quickly die when that spray us used up.
Something is telling the injectors Not to open and allow fuel to flow into manifold
OR
There is no fuel pressure which would allow the injectors to flow fuel
Still Seeking...
Did you ever solve it?? Watching how low my oil pressure drops, I'm wondering if it might be low viscosity oil, not making the 4 psig pressure switch.
Did you ever solve it?? Watching how low my oil pressure drops, I'm wondering if it might be low viscosity oil, not making the 4 psig pressure switch.
I did solve the mystery, it was not low oil pressure. It was a faulty ECM under the hood by the battery. The test went like this. Put a plastic Ice Pack on top of the ECM and secured with a couple of bungee cords, started the car when cold and it starts just fine, drive around a little bit till engine gets warm. Turn off the engine and then attempt to start again, it starts right up, repeat a few more times and it starts Every time while the ice pack is on the ECM. REMOVE the ice pack, drive a couple of miles, turn off the engine while warm and boom, No Start!! Lots of cranking but no start!! Put the ice pack back on, let it cool down and it starts up again.
The ECM is located under the hood near the battery and it gets hot and when its old it malfunctions and tells the fuel injectors Do Not Open, thus no fuel.
I took off the ECM and sent it off to be rebuilt, I think it's the solder connections that go bad in these things. Got it back and it's been great ever since. GM may have corrected this by 94 but it's common in 90-92.
I did solve the mystery, it was not low oil pressure. It was a faulty ECM under the hood by the battery. The test went like this. Put a plastic Ice Pack on top of the ECM and secured with a couple of bungee cords, started the car when cold and it starts just fine, drive around a little bit till engine gets warm. Turn off the engine and then attempt to start again, it starts right up, repeat a few more times and it starts Every time while the ice pack is on the ECM. REMOVE the ice pack, drive a couple of miles, turn off the engine while warm and boom, No Start!! Lots of cranking but no start!! Put the ice pack back on, let it cool down and it starts up again.
The ECM is located under the hood near the battery and it gets hot and when its old it malfunctions and tells the fuel injectors Do Not Open, thus no fuel.
I took off the ECM and sent it off to be rebuilt, I think it's the solder connections that go bad in these things. Got it back and it's been great ever since. GM may have corrected this by 94 but it's common in 90-92.
Thanks, that's a lot of help. I might pull the ECM and resolder it myself. I've done it with old ham radio stuff.
92 LT1 No start when warm/hot ??
