4.2L power loss - JeepForum.com

 
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post #1 of 12 Old 05-08-2006, 09:34 PM Thread Starter
COSourdough
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4.2L power loss

Well, I was really impressed with my Jeep, she was running great and had plenty of power since I got the stallin at stoplights issues fixed. Not sure how this fits in, but since I filled up the other day, she seems to have about as much pick-up as when I had the 3.07s in. It's got 4.10 now. Runs smooth, no missing, just no acceleration, and it doesn't want to rev as high. I took off the air cleaner today and noticed a bhit more blow by than I've noticed before, but I don't think that has anything to do with it being sluggish.

It also "diesels" a bit afte I shut it off (which I guess is timing?) but it was doing that when it had pep also. I'm hoping it has something to do with this tank of gas, or the moist weather we've had tsince I filled it. Doesn't sputter or stall, just gutless...Thoughts?

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post #2 of 12 Old 05-09-2006, 05:34 PM Thread Starter
COSourdough
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I squirted a buncha carb cleaner in it while it was runnin last night, hoping for the cheep easy fix...Nope. still gutless today.
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post #3 of 12 Old 05-09-2006, 05:42 PM
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Quote:
Originally Posted by COSourdough
Well, I was really impressed with my Jeep, she was running great and had plenty of power since I got the stallin at stoplights issues fixed. Not sure how this fits in, but since I filled up the other day, she seems to have about as much pick-up as when I had the 3.07s in. It's got 4.10 now. Runs smooth, no missing, just no acceleration, and it doesn't want to rev as high. I took off the air cleaner today and noticed a bhit more blow by than I've noticed before, but I don't think that has anything to do with it being sluggish.

It also "diesels" a bit afte I shut it off (which I guess is timing?) but it was doing that when it had pep also. I'm hoping it has something to do with this tank of gas, or the moist weather we've had tsince I filled it. Doesn't sputter or stall, just gutless...Thoughts?
Timing?
Have you checked all the basics? Timing, wires, fouled plugs, clogged high speed jets? Mine had all the symptoms yours does. I changed the plugs and wires and did a serious flush of the carb (after doing a .040 venturi tube boring) Now it does something it has never done since I bought it..Spins tires off a light
Rattles like a happy baby so until I replace the timing chain I'm not going to do too much hot rodding.
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post #4 of 12 Old 05-09-2006, 05:58 PM
Bobbywolf
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Timing is pretty easy to play with. Just loosen the nut under the distributer a bit, and adjust back and forth, taking it for a spin after each adjustment. Find a happy medium where it idles well, and has the best power without pinging.
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post #5 of 12 Old 05-09-2006, 09:17 PM Thread Starter
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Yeah, I had a '73 Chevy truck many years ago that I had to adjust the timing on quite frequently, so I have the gist of the "field expedient" method without using a light. I know the timing's off (or at least I assume that's what causes the dieseling, but it was doing that before this recent loss of power too, so I'm not sure it's the fix. Either way, I gfuess I need to adjust it, then go from there.
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post #6 of 12 Old 05-10-2006, 10:24 PM Thread Starter
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OK, now tonite I finished mounting the towbar brackets and as I was hooking the Jeep to the truck to check things out, it died. I slipped the clutch a little to check if the T-case was in neutral (it wasn't) and it just died...wouldn't start again. I cranked on it for awhile, then just left it there. went back out awhile later and it fired right up...

Is this all timing, ignition, carb or what?
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post #7 of 12 Old 05-11-2006, 08:53 AM
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Are you sure it didn't flood when you were trying to restart it? If everything is setup right mine will fire right up with no throttle, just turn the key, when it's warm.

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post #8 of 12 Old 05-11-2006, 08:55 PM Thread Starter
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Well, I just adjusted the timing and set the idle back down (it was at 13-1400 to keep it running). Seems a bit better, but I might need to tweak the timing a little more. I have to drive it a bit to see if that was the problem.
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post #9 of 12 Old 05-11-2006, 09:48 PM
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Plugged cat?
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post #10 of 12 Old 05-11-2006, 10:59 PM
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Chances are its still the timming and the idle, your just going to have the tweak it for a bit, mine was doing the same thing last week.

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post #11 of 12 Old 05-13-2006, 01:44 PM Thread Starter
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ALso found I have a bit of oil in the air cleaner, coming from that filter toward the rear (not sure what it's called. I replaced the air filter to see if the excess oil on the filter might be restricting airflow, but no noticeable change. PCV looked OK to me, but I baought another and put it on, just in case. The thing seems to run okay downhill or flat, but has no power to maintain speed going uphill. I'm gonna fart around with the timing again in a little bit. I got a new cap, rotor, plugs and wires (not installed yet), but I don't think they're the problem, we replaced all that when I first got the thing about 2 years (about 10.00 miles) ago. A buddy thinks just from hearing about it, hasn't actually ridden in or seen it) it could be the coil? I think that was replaced shortly before I bought it thopugh, because there was a used coil in the obligatory box o' parts that comes with a used Jeep.

Suggestions?
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post #12 of 12 Old 05-13-2006, 04:51 PM
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vaccume leak, I had the same problem with my 4.2. Check all the hoses and mating surfaces. The vaccume leak will cause the power valve not to kick in as fast as it should, and it will result in poor acceleration, stalling, not starting, rough idle, etc.... You might just need a new carb, it sugests in the haynes manual to replace the carter bbd every 50,000 miles. I converted to an MC2150 and am much happyer with my jeep

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