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Discussion Starter #1
Still working on the '92: 2.5 engine with a 5 speed manual transmission. I"m getting an intermittent misfire under load with some hesitation on acceleration typically in the 60-70mph range (I see it most often when merging on the interstate). Anecdotally, I think I'm seeing it more-frequently in circumstances when the humidity is very high or when it is raining--making me think I've got cracked wiring insulation somewhere.

I'm going to do some maintainance today, and the tune-up I've been putting off til I could "find time". I suspect new cap/rotor/wires/plugs may correct the misfire. Are there other likely causes I should be checking?

Thanks!
 

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Discussion Starter #2
Got as far as the plugs. Plugs were all finger tight. I'm guessing no one told the PO he needed to gap the plugs, because after a quick pass with a wire toothbrush, the gap on all of them was in the neighborhood of .080". Gapped the plugs to .038". No more intermittent misfire, no hesitation on acceleration.

Pretty sure I knocked a vac line loose (or cracked one). Idle climbs then drops almost to stall, then repeats. Saturday, or the next day I get home before dark, I'll take a look at that.
 

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B4U Task Force Admin
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Is .038 what it calls for??...sounds like an odd number.
 

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My notes from the manual say "most plugs" for the '92 should be set at .035"-.040". Spec that year was .060" as I recall, some kind of smog reduction scheme. I have no idea why the PO set the gaps so wide (.080" by my field measurement).

I wound up checking the plugs while stuck in a parking lot waiting for a friend. Didn't have a spark plug tool in my bag, but I found an old coil spring in my tool bag with wire that mic'd at .038"--so that's what I set it at. Response at highway speeds is significantly improved, I want to run a tank of gas to see what it does to MPG. When I get time to change the wires, rotor, cap, etc I'll probably throw in a new set of plugs, although these were in remarkably good condition.
 

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the new guy
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hunting idle now? normally a vacuum leak, as you noted
 

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hunting idle now? normally a vacuum leak, as you noted
Yeah, but it can be fun. I was sitting at a light this morning, listening to it climb and drop, when I heard a rumble matching it. A guy had pulled up next to me in a '59-'60 Impala Coupe, thought I wanted to race! I hollered back that I just had a vac leak, and he was disappointed.
 

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Still working on the '92: 2.5 engine with a 5 speed manual transmission. I"m getting an intermittent misfire under load with some hesitation on acceleration typically in the 60-70mph range (I see it most often when merging on the interstate). Anecdotally, I think I'm seeing it more-frequently in circumstances when the humidity is very high or when it is raining--making me think I've got cracked wiring insulation somewhere.

I'm going to do some maintainance today, and the tune-up I've been putting off til I could "find time". I suspect new cap/rotor/wires/plugs may correct the misfire. Are there other likely causes I should be checking?

Thanks!
I’ve had my 2.5 idle all over the place changed almost every part on the motor just trying to figure it out
Now after all these parts l have finally found the problem
My timing gears broke going down the interstate
I have learned that once the teeth start chipping away the motor will rough idle until starts warming up then it will run without a problem until l turn it off then restart
All this time the service engine light came on and off the real problem was the gears which the computer can’t tell you
Wish l knew this before l spent hundreds of dollars trying to fix this problem
Cap wires plugs coil fuel pump fuel filter throttle positioning sensor map sensor air mixture sensor
Vacuum lines
All this was a waste of dollars
Check Your Timing Gears First
 

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Been there Done it
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There's only 4 of em, put in new ones.
 

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the new guy
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well, look at it more positively. now you know you won't have trouble from those parts for a good while now
 
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