Intermittent misfire that I’ve been chasing for months out of guesses

[9er9er10]

I have a 1992 Ford Ranger XLT 4.0 manual 4 x 4. When I first bought the truck, I noticed that it would throw a code for a moment and misfire and then go away as I did maintenance on it. It would just disappear however it did not after a month or so of owning the truck the misfire got worse and for an entire month didn’t go away. I took it to a shop and when I dropped it off, the misfire disappeared, except for when the engine got up to engine temperature and then it went into a closed loop at this point, I have replaced the MAF sensor and idle control valve with new to me sensors, I’ve replaced the cam control sensor. I’ve listened to the injectors and it sounds like they’re all firing except for one that I couldn’t get to. Fuel pressure was good to the rail, except I don’t think I ever checked it while it was misfiring I attempted to test the coil pack, and everything was within spec. I thought it could be the coolant temperature sensor but I don’t see how that could cause an intermittent misfire

 

[JoshT]

I'm not at all saying that it is your problem, but my 4.0 would run like that when it had a bad head gasket.

I'd recommend a compression and leak down test. A quick check you could do at home is the "radiator glove test." It won't catch everything, but can be an instant red flag if it doesn't pass.

Again I recommend the tests, not just ripping off the head and changing gaskets. The test is pretty much just labor involved. Start firing the parts cannon and you are liable to cause more problems than you fix. Same goes for "new to me" sensors if you don't have first hand experience how they were functioning before you installed them.

 

[RangerNumber3]

Sounds like a bad plug wire. Open the hood in the dark with the engine running and see if one wires is arcing. My two cents.

 

[MaicoDoug]

Isolate the ignition issues. Hate to admit this, but the 4.0 access to the spark plugs is all but impossible making me do stupid things in attempt to R&R the plugs. After a complete set installed for the first time in my life I had compressed the ground strap onto the electrode. I would have never guessed that I ever did. But I did. Finally realized that working from beneath was a good idea on this engine.

So out they all came for inspection. Not to mention the sorry condition of the spark plug threads which required a back & forth action to save them during removal & installation. Aluminum debris (from the heads) was the first thing I noticed, and after that the collapsed electrode. So all in all it was successful, however flipping sockets, with 1/8 turn increments, removing the transmission dipstick and other things. All because I wanted to change spark plugs and after the initial attempt ended up with a misfire. So far the iridium plugs are working no issues after 20kmi. R&R'ed the ignition coils/wires as well. Double check what you have first, combustion gasses test in the cooling water will tell you about the headgasket. A night time (dark) looking for a spark test should tell you if you have a spark misfire, also listening to your AM radio in the truck during the misfire will indicate the noise possibly.

For me, when I throw parts at an engine I start with the most prescribed methods. Intermittent problems- situations are the toughest to pin down. Ignition systems never get any better with age, I would start with all fresh ignition components, coils, wires & plugs. Clean, clean, clean. Including any magnetic sensors around the crank with a damp cloth. Do this yourself if possible.

 

[9er9er10]

I'm not at all saying that it is your problem, but my 4.0 would run like that when it had a bad head gasket.

I'd recommend a compression and leak down test. A quick check you could do at home is the "radiator glove test." It won't catch everything, but can be an instant red flag if it doesn't pass.

Again I recommend the tests, not just ripping off the head and changing gaskets. The test is pretty much just labor involved. Start firing the parts cannon and you are liable to cause more problems than you fix. Same goes for "new to me" sensors if you don't have first hand experience how they were functioning before you installed them.

Thank you very much for your response however when I bought the truck, I did a compression test on it and all the cylinders are good except for the back left which I couldn’t get to do the space requirements so maybe I can check that one again

 

[9er9er10]

Sounds like a bad plug wire. Open the hood in the dark with the engine running and see if one wires is arcing. My two cents.

I also put new spark plug wires

 

[mikkelstuff]

You did replace the cam shaft synchronizer right?

 

[9er9er10]

Yup

 

[9er9er10]

Isolate the ignition issues. Hate to admit this, but the 4.0 access to the spark plugs is all but impossible making me do stupid things in attempt to R&R the plugs. After a complete set installed for the first time in my life I had compressed the ground strap onto the electrode. I would have never guessed that I ever did. But I did. Finally realized that working from beneath was a good idea on this engine.

So out they all came for inspection. Not to mention the sorry condition of the spark plug threads which required a back & forth action to save them during removal & installation. Aluminum debris (from the heads) was the first thing I noticed, and after that the collapsed electrode. So all in all it was successful, however flipping sockets, with 1/8 turn increments, removing the transmission dipstick and other things. All because I wanted to change spark plugs and after the initial attempt ended up with a misfire. So far the iridium plugs are working no issues after 20kmi. R&R'ed the ignition coils/wires as well. Double check what you have first, combustion gasses test in the cooling water will tell you about the headgasket. A night time (dark) looking for a spark test should tell you if you have a spark misfire, also listening to your AM radio in the truck during the misfire will indicate the noise possibly.

For me, when I throw parts at an engine I start with the most prescribed methods. Intermittent problems- situations are the toughest to pin down. Ignition systems never get any better with age, I would start with all fresh ignition components, coils, wires & plugs. Clean, clean, clean. Including any magnetic sensors around the crank with a damp cloth. Do this yourself if possible.

What are magnetic sensors around crank?

 

[MaicoDoug]

9er9er10- Sometimes there is a crank ignition sensor (or other) sensor that collects metallic debris from being close to the road. Can't remember how the 4.0 ignition is triggered, but if there is one down there, often the signal can be corrupted by metallic debris.

Coil packs are next.....?