1995 k1500 issue

[Mark-DuCo]

So my truck started doing something weird for me the other day. It won't start after it gets warmed up.

Starts just fine cold, and runs great the entire time it is running until you shut it off. Once it is shut off it won't start for a good 30 minutes of cooling off. It will crank away, but not fire. I did manage to get it restarted right away with some ether the other day, which leads me to believe it is a fuel issue, not air or spark.

It almost seems like it could be vapor locking. But with the electric fuel pump in the tank, I didn't think that would be the case. I certainly could be wrong though. I would think if my fuel pump was going out, it would have trouble starting all the time and would run poorly.

Im kind of stuck at this point, maybe Ingo can help before I have my local mechanic work on it.

 

[Jaybird1980]

Do you have a spark checker? The starting on SF could be a fluke.

I would check for spark when it is not starting. If it has spark, check the shrader valve on the fuel line and see if you have sufficient pressure.

If no spark I would check the cap and rotor, if nothing visually bad then I would lean towards Ignition Control Module
If no fuel or weak fuel I would lean to Fuel Pump relay.

These are just guesses at common failures I've seen. A fuel pump can be intermittent when it starts failing as well. Some testing would help narrow down your issue.

 

[Ark]

Cranks away vigorously? No fire at all?

Multiport or TBI?

Failing temp sensors sending a bad signal can cause different behavior between hot and cold. Like, it's hot, but reading -20F so it floods with fuel and won't start. Temp sensor for the engine and temp sensor for the dash gauge are often different.

You could try cranking with the throttle pinned open, Google says that'll reduce cranking fuel because the computer thinks you're clearing a flood condition.

Or just throw a temp sensor at it and check the wiring, they're cheap and easy. Also try leaving the key in RUN for several seconds before cranking, to spool up the fuel pressure. If it's a two wire sensor, you could unplug it and crank, then short it with a jumper and crank. If one works, it's the sensor.

Cranking rules out starter and firing on ether rules out air and spark. Either mix problem or fuel supply problem.

 

[printcraft]

Fuel pressure check, cap rotor check.

 

[Mark-DuCo]

Cranks away vigorously? No fire at all?

Multiport or TBI?

Failing temp sensors sending a bad signal can cause different behavior between hot and cold. Like, it's hot, but reading -20F so it floods with fuel and won't start. Temp sensor for the engine and temp sensor for the dash gauge are often different.

You could try cranking with the throttle pinned open, Google says that'll reduce cranking fuel because the computer thinks you're clearing a flood condition.

Or just throw a temp sensor at it and check the wiring, they're cheap and easy. Also try leaving the key in RUN for several seconds before cranking, to spool up the fuel pressure. If it's a two wire sensor, you could unplug it and crank, then short it with a jumper and crank. If one works, it's the sensor.

Cranking rules out starter and firing on ether rules out air and spark. Either mix problem or fuel supply problem.

It is a 350 TBI. It just cranks, doesnt even attempt to fire unless you shoot some ether in. I have tried with the throttle open to no effect.

 

[Mark-DuCo]

Do you have a spark checker? The starting on SF could be a fluke.

I would check for spark when it is not starting. If it has spark, check the shrader valve on the fuel line and see if you have sufficient pressure.

If no spark I would check the cap and rotor, if nothing visually bad then I would lean towards Ignition Control Module
If no fuel or weak fuel I would lean to Fuel Pump relay.

These are just guesses at common failures I've seen. A fuel pump can be intermittent when it starts failing as well. Some testing would help narrow down your issue.

After talking to some other people, I am leaning towards the Ignition control module, apparently it is fairly common in this truck for it to act up when it gets hot. The new ones even come with some sort of thermal barrier paste to try and help is what I was told.

 

[Jaybird1980]

After talking to some other people, I am leaning towards the Ignition control module, apparently it is fairly common in this truck for it to act up when it gets hot. The new ones even come with some sort of thermal barrier paste to try and help is what I was told.

Yeah it's pretty common, but so is a failing fuel pump relay. If you have a spark checker available it will help narrow it down.
A volt meter will also be able to rule out the fuel pump relay, it's real easy to get to, should be on the passenger side firewall.

It sounds stupid to say, but may sure you check while it's in failure mode.

 

[Mark-DuCo]

Yeah it's pretty common, but so is a failing fuel pump relay. If you have a spark checker available it will help narrow it down.
A volt meter will also be able to rule out the fuel pump relay, it's real easy to get to, should be on the passenger side firewall.

It sounds stupid to say, but may sure you check while it's in failure mode.

I've got a multi meter so I will check when I get home to rule out the fuel pump relay before trying a new ICM.

 

[Jaybird1980]

I've got a multi meter so I will check when I get home to rule out the fuel pump relay before trying a new ICM.

If it is the ICM make sure to clean the mounting surface good and use the grease that is with it

 

[Ark]

It is a 350 TBI. It just cranks, doesnt even attempt to fire unless you shoot some ether in. I have tried with the throttle open to no effect.

Hmm, usually a totally whacked out mixture will at least sputter and attempt to fire.

Ignition control module having thermal failure is a good theory, especially with a bulletin or known issue, but I wonder why it only manifests on starting and not simply when it gets hot.

Sounds like a nice checklist of things to inspect and test.

 

[Brad69]

Did it fire on starting fluid?

If so it’s a fuel supply issue relay or pump I would do both.

But you being from Ferdinand are probably a skinflint !

 

[rem788]

Are you sure it is TBI? GM stopped using TBI in the late 80's early 90's. I suspect it is central port injection. It uses a single injector with 8 tubes that have poppet valves at the ends to deliver fuel at the intake valve. These systems required a minimum fuel pressure of 55 psi to open the poppet valves, anything less would result in no start, mainly when cold but also when hot. Starting with ether ( not a good idea, carb cleaner is a little safer) indicates it is not ignition. You most likely have a fuel delivery problem. First check should be fuel pressure. If is truly a TBI, pressure should be around 13 psi (there is no schrader valve on the TBI systems, you must tee into the fuel line), central port injection must be 55 psi or higher. If the fuel pressure is correct, in my experience the TBI injectors rarely failed, the central port injectors failed so often GM built a replacement injector system. As others have stated, incorrect sensor readings could also be the cause. An inexpensive scanner which can display live sensor data could help quickly determine if there is an incorrect sensor reading. Good luck

 

[BR8818]

Are you sure it is TBI? GM stopped using TBI in the late 80's early 90's. I suspect it is central port injection. It uses a single injector with 8 tubes that have poppet valves at the ends to deliver fuel at the intake valve. These systems required a minimum fuel pressure of 55 psi to open the poppet valves, anything less would result in no start, mainly when cold but also when hot. Starting with ether ( not a good idea, carb cleaner is a little safer) indicates it is not ignition. You most likely have a fuel delivery problem. First check should be fuel pressure. If is truly a TBI, pressure should be around 13 psi (there is no schrader valve on the TBI systems, you must tee into the fuel line), central port injection must be 55 psi or higher. If the fuel pressure is correct, in my experience the TBI injectors rarely failed, the central port injectors failed so often GM built a replacement injector system. As others have stated, incorrect sensor readings could also be the cause. An inexpensive scanner which can display live sensor data could help quickly determine if there is an incorrect sensor reading. Good luck

1995 was the last year for throttle body injection.

 

[BR8818]

Even if it runs on either it could still be the icm, the icm also triggers the ecm for injector pulse.

 

[rem788]

"icm also triggers the ecm for injector pulse." Correct. In my experience it was rare for the icm to lose the signal to the ecm while maintaining spark. The quick check to see if the ecm is receiving the signal from the icm is to crank the engine and then see if the fuel pump continues running for 2 seconds after you stop cranking. If the pump runs, this indicates the ecm is receiving the signal, if not the ecm may not be receiving the signal.