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post #1 of (permalink) Old 11-13-2002, 12:30 PM
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two dead clinders at idle, but fine at higher rpm

My 151 currently idles quite rough, i know that`s a jeep thing, but mine is really rough. The strange thing is, that there is no signifcant change in rpmwhen you unplug the igniton wires from cylinder 2 and 3 . (Both have a spark). If you disconnect Nr. 1 and 4 the engine stumbles. If you increase rpm the engine smoothes out and all 4 cylinders seem to work fine. Right now i`m quite confused about the reason for these strange behaviour. Maybe the lifters fill only with increased oil pressure or do i have a vaccum leak in the manifold?

Any comments to this theory would really be appreciated

Thanks in advance

Momo

It`s getting f**ing cold in Austria right now.
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post #2 of (permalink) Old 11-13-2002, 12:55 PM
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Re: two dead clinders at idle, but fine at higher rpm

Blown head gasket between cylinders. Do a compression check.
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post #3 of (permalink) Old 11-13-2002, 01:00 PM
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Re: two dead clinders at idle, but fine at higher rpm

check your spark plug wires too.
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post #4 of (permalink) Old 11-13-2002, 01:10 PM
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Re: two dead clinders at idle, but fine at higher rpm

I haven`t done a compression check so far, but it accelerates without problems, so this would speak against a blown head gasket. The only problems is idle. I have replaced the igniton wires today.

Momo
post #5 of (permalink) Old 11-13-2002, 01:20 PM
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Re: two dead clinders at idle, but fine at higher rpm

Hey Momo, I just saw from your first post, you're in Austria! Where in Austria? End of January I'm heading over to Arlberg, Lech more specifically, for a little skiing!

brent
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post #6 of (permalink) Old 11-13-2002, 01:27 PM
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Re: two dead clinders at idle, but fine at higher rpm

Vienna. Lech is perfect for skiing you will definitly enjoy it.

Momo
post #7 of (permalink) Old 11-13-2002, 01:52 PM
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Re: two dead clinders at idle, but fine at higher rpm

If your jeeps ignition is DIS (distributerless) it may be a bad coil, cylinders 2-3 are companion cyls. Just a thought.
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post #8 of (permalink) Old 11-13-2002, 01:54 PM
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Re: two dead clinders at idle, but fine at higher rpm

Yep, been there about 10 times in the past fifteen years. my favorite place. Vienna is a gorgeuos city too. went there on Sports trips when I was in school in Holland.

back to your misfire problem:

how do your plugs look after idleing for a while? are you sure you've got spark at idle on 2 and 3? pull ne of the wires and hold it near a ground with a screw driver or something stuck in it to see if you can get a spark. one something like this I'd start at the distributor and make sure the cap is on straight and completly down. I screwed up one time and didn't put it back on completly straight and had similar problems. ended up with crossfiring under the cap. then after ruling out the cap, move to the wires making sure they are good (you said they were new) and that they were secure to the cap and the plugs. then make sure the plugs are good. If all that check out I'd move to a compression check.

brent
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post #9 of (permalink) Old 11-13-2002, 08:37 PM
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Re: two dead clinders at idle, but fine at higher rpm

Vacuum leak, somewhere between those 2 dead cyls. --
A classic symptom.

If it was a head gasket, you'd feel it at higher R's too.
If it was plug wires, a dead DIS coil, cap, switched wires,
crossfiring etc. it would also be there at higher speeds,
especially acceleration.

Generally a vacuum leak, hose, base/manifold gasket etc, is
a fixed leak size, doesn't get bigger with speed.
But, the total amount of air/fuel mixture does with speed.
So at idle the amount of fresh air getting in is a larger
percentage of the total than at higher speeds - thus why it's
most pronounced at idle.

Higher speeds its virtually overwhelmed by the volume of
correct mixture.

Spray a burnable carb cleaner, starting fluid, propane, etc
around the carb base gasket and any vacuum trees close by.
Should be an easy fix.

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post #10 of (permalink) Old 11-14-2002, 08:18 AM
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Re: two dead clinders at idle, but fine at higher rpm

just thinking,

what about a burnt valve?

clint
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