I have owned this truck for about a year, when we first picked it up it was running ...ok, I figured a little tune up maybe some sensor replacements I could get it running well again, well it worked until recently. The engine went from running good to stuttering and stumbling.
The first couple times this happened my son was able to make it stop just by unplugging the #3 spark plug wire at both ends then plugging it back in..when he told me this I thought no way, a spark plug wire is just a means of getting the current from the distributor too the plug it has no effect on any thing else. But I thought what ever, as long as it's running for him that’s cool.
Well the problem kept happening more and more until it wouldn't go away. I started to think what is the deal with the spark plug wire? Why was it working to fix the problem? then it came to me INDUCTION he was probably getting current bleeding out of the spark plug cable and it was effecting some sensor through the wiring. I told him to take all the wires off and remove the cap and rotor so we could re-route them, we inspected the cap it was pretty well burnt at the contacts and I could see trails in the dust on the inside of the cap so I figured it might be part of the problem we replaced it put it all back together started it up ran like a charm a little rich at first then we let it sit there and run for about 30 minutes sounded sweet, revved nicely so we though COOL done deal (obviously all the sensors, computer, injectors etc were operating properly at this time) we shut it off went to re-start about 10 minutes later and it's right back to running crappy.
We had the timing light out already so we went along and clamped the pick up on each plug wire they all had a spark, so the plugs are getting spark. I listened to the injectors with the stethoscope and there all ticking away. I thought just because they are all ticking doesn't tell me that they are getting fuel so we pulled one of the plugs it smelled like gas so we put it back in started the engine and started pulling spark plug wires off to see if what effect it had, we were able to pull off all the drivers side wires with no change and the number three wire on the passenger side (the furthest one back ) so the motor was running on the first two cylinders on the passenger side.. We recently timed it at 10 degrees btdc (spout disconnected) we also checked the fuel pressure it's all good. So what is up with this thing? I have already changed out most sensors except the MAP, computer and the distributor and all related to it.
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First, I would check all of the engine harness wiring connections to ensure they are all good - especially all of the ground straps, etc. After that, I would get a code reader or use the test light / voltmeter method to check for error/diagnostic codes. I prefer a code reader, because you can do all the tests (including cylinder balance test) easier. Then, I would check the coil to make sure it's good. Then, do a resistance check on all the plug wires, including the coil wire. Might not be a bad idea to put all new plugs in (again), as you may have some that are bad. You could have a faulting TFI module or a bad pickup / stator in the distributor. Something is causing it to spark erraticallly (for lack of better explanation or words). May want to pull the distributor cap off and see if it's like the old one already. Also a good idea to do a compression test, leakdown test, cooling system pressure test, etc etc etc. Worst case is the engine is worn out and requires rebuild or a new short block.

 

Sorry to bring back a dead thread - but I am having nearly the exact same issue, and it is driving me insane! Any ideas?

 

rotate all your plug wires 1 space over clockwise on the distributor. i had this exact same thing happen to me. for some reason everything jumped 1 spot. trying to time it made it worse. the only way to fix it that i can think of would be to pull the distributor and and reset everything. but yeah move every wire over one spot and truck still running just fine. and im not the only one who's had this happen to. only takes a minute so try it. on mine it was running only on the number 2 and 5 cylinders.