Problems

[big_o7]

I have a 94 ranger with 267,458 miles on it.....here is my issue, the thing is missing and back firing through the entire rpm range until the truck has run at about 2200rpms for 15miles, then it tunes out, so far i have checked the tightness of the intake manifold, (upper and lower), i also replaced the PCV, as well as sparkplugs. i also checked the wires. i have also replaced the MAF sensor....I dont have any ideas and i need to get my truck working before long, its not a daily driver for now but ill need it occassionally and i dont want to drive it with its problems......I think that it probably has as vaccum problem, or a sticking valve. any help would be appreciated, thanks.......

 

[woodyedmiston]

Hmmm? Are you losing any coolant? I'm thinking of a minor crack in one of the cylinder heads - maybe it goes away as it gets hot because cylinder temp will burn off that small amount of water.

On the other hand backfiring suggests other problems. Have you considered a PM to MAKG?

 

[MAKG]

Backfiring? Doesn't sound good.

I'd try a leakdown test, and run the self tests (looking for a CAMP complaint). And measure ignition timing (base and advanced). Something is firing the spark with a valve open.

 

[Evan]

I had a similar problem after I had rebuilt my 4.0. The problem was a leaky injector. There is a waste spark on the exhaust stroke, and it was igniting fuel that was leaking in, resulting in a backfire. After some driving and engine warmup, the injector would stop sticking and the problem would go away, until the next cold start.

EDIT: Hmmmm. My waste spark explanation actually doesn't make sense, but the symptoms were very similar to yours and the problem was a leaky injector on #4.

 

[big_o7]

I have determined that the problem is not electrical, other than the fuel injector leak,(i dont know how to test for that.) I think that i have narrowed it down to 2 possibles. either a broken of weak valve spring, or the time chain has skipped a gear, or is just wore and needs replaced....are there any easy ways to check spring tension.....