Problem with 94 Ranger 4.0

[kinny]

Three years ago I overheated my engine at 128k and decided to rebuild it. Now the truck has about 134k on it. Since then I've tried to iron little bugs out including a slight but persistent miss on acceleration. A couple of weeks ago it started running really rough, like one cylinder wasn't firing. After testing that all 6 plugs were firing I pulled the plugs. The number 2 plug was burnt worse than any plug I've ever seen and covered with oil. The tip and even pieces of the center insulator were gone. A compression test shows zero psi in that cylinder. I'm guessing preignition and that I now have piston and/or valve damage. The check engine light did come on but went out and there were no codes thrown when I checked with the OBD1 reader.

Now I have to decide whether to rebuild or scrap the truck. It's a factory lifted 4x4 and in very good shape and I hate to lose what I've put into it. If I do rebuild the engine again, I need to ensure this doesn't happen again. One of the things I discovered last year while trying to pinpoint the miss is one pin on the TPS that is supposed to have 5 volts had zero volts, which is supposed to get from the PCM. So I figured it needed a new PCM. I had been procrastinating on this as it's hard to get to and I just didn't want to deal with it. If this was causing bad timing it doesn't seem like the OBD1 was much use on this truck.

Any ideas on what caused this and what would you do if it was your truck?

 

[Uncle Gump]

I'm not positive... but that Toyota badge could very well be the entire problem.

Have you ran a compression test? Dry vs. Wet?

If it was a ring... you would probably leave a small smoke trail. If the other plugs look good... most likely a valve guide.

I would like to see some pictures of the factory lift. The only one I'm aware of was on the STX... not sure but I don't think that was even an option in 94.

And... welcome to TRS. I'm sure others will chime in with thoughts...