My 92 f150 4x4 5.0 runs great until engine warms up then the engine misses and transmission will shift early please help thanks

265

Asked by Apr 12, 2014 at 02:14 PM about the 1992 Ford F-150 XLT Lariat 4WD LB

Question type: Maintenance & Repair

13 Answers

1,150

It is very common for electronics to malfunction when they warm up. Have you had it scanned for codes?. With the trans acting up as well as the engine running bad it sounds like the PCM. Injectors, spark, and trans shift solonoids are all controlled by the PCM

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265

Thanks is the pcm the ignition control module where would I locate the pcm thanks

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265

I took it too a ford dealership where I had talked to someone that said I would get a printout of all the codes but since my truck is nothing stock he was more concerned about other issues and told me I couldn't get a printout of the codes and there was too many for him to write down kinda wasted $90 if you ask me but what do you do

265

I did have the ignition module tested at another parts store where it was tested and passed the test on their machine twice but I am open for any ideas thank you very much all help is greatly appreciated...

20,130

Sounds like you have an ignition problem (electrical) and the failure is due to a heat issue. The PCM could be good and sending info to the tranny to shift while the engine is not capable of handling the load due to the miss.

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265

That could be very true thanks Oj I know while its missing I can put the truck in neutral or park and the miss goes away and revs and runs great till I put it in gear.

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265

Also when I bought the truck it was running like this and noticed the oxygen sensor was unplugged so I plugged it back in but no change in how it runs. I took it to a dealer to have a diagnostic test done but they didn't give me the printout of codes said their machine couldn't print them out. The dealership guy said that my dual exhaust with only one oxygen sensor is one of the problems since the original owners put a dual exhaust and headers on it instead of the original single exhaust.

20,130

Not completely familiar with your make and model of vehicle, especially when modifications were made all over the place. A miss under load could indicate a timing issue. Does your vehicle have a distributor, or is the ignition electronic? Are all cylinders firing at idle? You have to check as it can be hard to tell by eye or ear with some engines. If you have a distributor make sure the vacuum line (if it has one) is not leaking. When you step on the gas of an engine with a vacuum advance, it looses vacuum and the timing is advanced, usually via a spring.

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20,130

Keep in mind if the engine runs well in park or neutral it is basically free spinning with no load. Domestic auto engines also require some back pressure to perform properly. I suspect the modifications to the engine and exhaust were not accompanied with the proper adjustments/replacement of parts to the electronic system on the vehicle. You may be well served if there is a "speed shop" in your area where someone versed in engine modifications can make the proper corrections. Unplugging the oxygen sensor is neither a fix or adjustment.

20,130

Since the engine was modified check the simple things first. Are all the spark plug wires in good shape. Check each one and make sure they are not resting or touching something like the AC accumulator. Check the woring hornace from the PCM for frayed wires or a previously removed clamp/standoff which was not replaced. electronic components can give you fits. They normally read ohms or resistance signal being received. If a wire is partially grounding itself it will throw off a lot of things,

265

Actually the only modifications were just going from a single exhaust or factory exhaust to headers with duals sorry to not describe better. The motor is a 5.0 efi I'm guessing electronic ignition since it has the newer style fuel injectors but not completely sure thanks

265

OK oj I have installed new plug wires and plugs I have looked through out the truck for any loose or frayed wires but haven't found any and corrected any loose connections

685

What transmission do you have? If it is a E4OD, "it is computer controlled." You will have to post codes. You can run a self check yourself on the PCM with out going to the dealer to get the codes. With out more information I could name off a dozen issues that might be effecting it.

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