No Spark when hot
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No Spark when hot
I have a '93 7.5l super duty with a no-spark problem. If I shut it down after reaching operating temp I lose spark. I have already replaced the coil, ICM and ignition circuit relay. When I turn on the ignition and hear the relay actuate the engine starts fine if the relay doesn't click, I have no spark. I am concerned at this point it might be the ECM but don't see how engine temp could affect the computer? I'm also wondering if the PIP sensor and PCM can be ruled out since the relay energises both? I hate to keep throwing parts at it.
Any insights are greatly appreciated.
Any insights are greatly appreciated.
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From: Kentucky
If the fuel pump relay doesn't kick in it could be the PCM. The other thought is a weak connection on the PCM relay mucking things up. Check for good battery power at pins 37 and 57 on the PCM connector with the key ON.
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Thanks for the suggestions guys, I'll check it out. I've been through the entire wiring harness with dialectric grease but need to find out exactly where the good people from Winnibago hid the PCM before I can check for voltage.
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my problem continues
I've run more tests and can't figure this out: I ran both the key on engine off and engine running tests with no faults at all, I get a 111 code after both. I even ran the WOT dynamic test and didn't get any codes. After shutting the engine down it wouldn't restart so I figured I'd try to run the engine off test again and I couldn't get the test to initiate? I'm hoping this might clue someone in on what might be happening. I don't have the service manual for electrical distribution - only body, chasis, and drivetrain so I'm making many assumptions on what takes place when the key is turned. The relay I hear click when it starts is the fuel pump relay? (rla 2005 said) this same relay actuates when I start the KOEO test. I still haven't been able to find the PCM on this thing and need to scoure my service books for more info on what it looks like and where its located.
This is really annoying me!
This is really annoying me!
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From: Easton,Ks
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From: Easton,Ks
That would be a F53.
I have one just like it.
The PCM Computer is right in front of the Brake Pedal.
I have one just like it.
The PCM Computer is right in front of the Brake Pedal.
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Ahhh, now I get it. I was thinking the ECM and PCM were to different modules, you're saying they are one and the same.
Assuming I get voltage at pins 37 and 57, then what? The computer has an intermittant problem only when hot? That wouldn't be good, I've been quoted $269 for a new one.
Assuming I get voltage at pins 37 and 57, then what? The computer has an intermittant problem only when hot? That wouldn't be good, I've been quoted $269 for a new one.
Fleet Owner
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From: Easton,Ks
Then check for good grounds on pin #40 & 60.
Make sure you have a good PCM Relay on the relay box in front of and to the left (drivers) of the radiator.
Others have been known to do that.
Just for my information what color was the ICM (TFI) that you took out and what color was the one you put back in?
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From: Easton,Ks
By the way this does not sound like a computer or Ignition system problem.
Sound more like you losing power to the PCM Power relay and that would mean the problem is in the Ignition Switch, its plug or the wiring before or after the switch.
If you unplug the computer and it still has no spark then the problem is not the computer.
Sound more like you losing power to the PCM Power relay and that would mean the problem is in the Ignition Switch, its plug or the wiring before or after the switch.
If you unplug the computer and it still has no spark then the problem is not the computer.
Post Fiend
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From: McKenzie River
I had a 302 in Mustang that ran fantastic until it got to operating temp on the freeway, then it would shut down just like you turned off the key (usually at 70mph in the fast lane during heavy traffic) then re-start normally in half an hour and repeat the cycle. After throwing almost a whole new ign. system at it, I found the culprit.............the contact on top the rotor would tweak away from the cap when it got hot and shut the car down, cost $2.79...........Might be worth checking out.
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Both the old and new ICM were grey if I remember correctly. I did replace one relay of the two, located in a black plactic housing mounted right above the radiator, drivers side. Is this the PCM relay or a fuel pump or something else? when this rely doesn't engage, that's when I lose spark. I can work the ignition switch off and on until I hear that relay actuate, then she starts right up. If this relay is feeding power TO the PCM then at least I know the computer isn't the problem.
I also don't understand "If you unplug the computer and it still has no spark then the problem is not the computer" How could it ever have spark with the ECM unplugged?
I also don't understand "If you unplug the computer and it still has no spark then the problem is not the computer" How could it ever have spark with the ECM unplugged?