1994 4.0 ohv will not run when heat soaked

cardana24 · May 1, 2017

Hey guys,
This problem has been hard for me to troubleshoot because it has only happened to me twice in the last year. I am not sure if I am loosing spark or fuel because when I test things the truck is running fine. Basically this has happened to me twice, it has been on the two hottest days that I have driven the truck for more than a half an hour. I will drive the truck for at least thirty minutes, everything is running fine. I will go into a store come back out to the truck half an hour later...start the truck, it will sputter and die. Pushing the gas pedal makes it run worse. I can normally re start the truck but its just dies quickly again. Once the truck cools off it runs fine again. Does anyone have experience with this? I have replaced my MAF, spark plugs and wires, and the ignition coil looks newer too. None of these things changed this problem. I looked around on google and it seems that some times the fuel pump relay can cause a problem like this, or the ignition module. Any advice?

BlackBII · May 1, 2017

The fuel pump is a simple electric motor, and when they get too hot they won't run. They are normally cooled by the gas in the tank but if the temp of the gas in the tank is quite warm then it won't have much cooling effect.

The next time this happens turn the key on but don't start the truck. When the key is first turned on, you should be able to hear the fuel pump turn on to prime the system.

chewy012 · May 1, 2017

This sounds similar to an issue I've been chasing for a year now on my '92 ohv. I've replaced every sensor, and checked everything I could think of, to no avail.

Mine occurs coming off the highway and sitting at a stop light too long, it just start sputtering and die. Have to sit for like 5 minutes, then it's good again. It started out only in hot days, but now it seems to just be random.

Hope you find an answer, cause I haven't haha.

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chewy012 · May 1, 2017

Although, I have not checked the fuel pump relay... I have a few laying around. I'll let you know if it makes a difference.

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cardana24 · May 1, 2017

BlackBII said:
The fuel pump is a simple electric motor, and when they get too hot they won't run. They are normally cooled by the gas in the tank but if the temp of the gas in the tank is quite warm then it won't have much cooling effect.

The next time this happens turn the key on but don't start the truck. When the key is first turned on, you should be able to hear the fuel pump turn on to prime the system.

I can't really do that because even when the truck is running well
My fuel pump does not come on until I am cranking the truck. I never hear it hum with just the key on

RonD · May 1, 2017

cardana24 said:
I can't really do that because even when the truck is running well
My fuel pump does not come on until I am cranking the truck. I never hear it hum with just the key on

Not possible, fuel pump can't run while starter motor is on, voltage is to low, under 10volts while starter is drawing power, and usually power is cut off in any case, key turned to START cuts power to most systems(except spark) so starter gets all possible voltage.

Ford computers power up fuel pump for 2 seconds each time key is turned on.
So turn key on and off as many times as needed, if don't hear the HUMMMM of the pump then replace the pump or you have a wiring issue.
This has been the same on all Fords, and all Ford Rangers since 1983, first computers

chewy012 · May 1, 2017

I just snagged a relay, $18 at o'reilly... You should see if you can find a better deal. I hate to say it, I read an exploder forum that said fuel pump relay sometime causes intermittent failure. I'll let you know if it helps me.

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cardana24 · May 2, 2017

RonD said:
Not possible, fuel pump can't run while starter motor is on, voltage is to low, under 10volts while starter is drawing power, and usually power is cut off in any case, key turned to START cuts power to most systems(except spark) so starter gets all possible voltage.

Ford computers power up fuel pump for 2 seconds each time key is turned on.
So turn key on and off as many times as needed, if don't hear the HUMMMM of the pump then replace the pump or you have a wiring issue.
This has been the same on all Fords, and all Ford Rangers since 1983, first computers

I am just saying I do not hear it run...that's all. I will try to listen a little harder next time I'm in the truck.

chewy012 said:
I just snagged a relay, $18 at o'reilly... You should see if you can find a better deal. I hate to say it, I read an exploder forum that said fuel pump relay sometime causes intermittent failure. I'll let you know if it helps me.

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Yeah, I will order one online. Let me know if the relay fixes/helps your problem.

chewy012 · May 2, 2017

Will do, might take a few days as it's intermittent.

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chewy012 · May 4, 2017

Tank and a half down, and it's running good. No CEL, no stall, first week without either in months. I feel good about it.

.... Until next week when it starts up again haha.

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msubully82 · May 10, 2017

I had a similar problem. When hot, for instance after filling up at a gas station, the engine would occasionally crank but not fire. Wait a minute or so, and it fired right up. Replaced the relay and never had the problem again. I hope the relay fixed yours too.

Now, I notice the sound of the fuel pump running for a couple of seconds when I turn on the key to the ON position.

cardana24 · May 11, 2017

msubully82 said:
I had a similar problem. When hot, for instance after filling up at a gas station, the engine would occasionally crank but not fire. Wait a minute or so, and it fired right up. Replaced the relay and never had the problem again. I hope the relay fixed yours too.

Now, I notice the sound of the fuel pump running for a couple of seconds when I turn on the key to the ON position.

Yeah, I hope so too. I replaced the fuel pump relay with a non oem relay so we will see.

The problem that you are describing is not exactly like what I am experiencing. It sounds like yours will not start when you were experiencing the failure. Mine will normally restart, but run very poorly (undividable). It will usually die with in 5-10 seconds of running very poorly. When I try to give it throttle it makes it die even quicker. Do these engines have a cold start or ilde air control valve? I am wondering if that could possible be stuck open. Would that cause the symptoms that I am experiencing? It's hard for me to troubleshoot because I do not drive the truck often and I have only experienced this twice in the year that I have owned the truck.

msubully82 · May 12, 2017

Correct, mine would not start - not even fire at all. Yours does not sound like the relay. They do have an idle air control valve, but I'm not real sure what the failure symptoms are. Mine actually wanders up and down at idle when cold, but never stalls. It doesn't do it when warmed up. I am wondering if the IAC is related to that.

Also see the very recent thread about my intermittent MAF sensor issue.

lil_Blue_Ford · May 14, 2017

Have you checked the fuel pressure? I had a problem with my one Ranger where it wouldn't start warm, but you could hear the pump running. Turns out the pump was putting out less than half of the pressure it should, thus the pump was bad.

Also, when was the last time the fuel filter was changed? That can have a big impact on fuel delivery.

As far as the IAC goes, with the engine running at idle, gently tap on it with a wrench or small hammer. If that changes the idle, the IAC is probably sticking. If you unplug the IAC at idle, the RPMs should drop and it should idle low or die. If it stays the same or goes higher, you either have a bad IAC or a vacuum leak or both.

To test the MAF, unplug it while it's running. It will run rough and throw a CEL, but if it becomes more driveable, then the MAF is likely bad.

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1994 4.0 ohv will not run when heat soaked

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