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Miss fire/ low power/ dead cylinder?

Mean Green

Mean Green

Basic User
City
edinburg
State
tx
After a long battle with body work, I'm finally getting around to the mechanics... I'm not very familiar with the 4.2 but it seems that I'm down a cylinder... Cylinder 6 has 120 compression, spark but when I pull the plug wire it does not seem to effect idle at all... I pulled the valve cover off, and both valves open and close and both springs look good... Any ideas? Like I say, I'm not familiar at all with cjs, but it just seems to accelerate very poorly and has little power at all, which kind of led me to this conclusion... Thanks in advance
 
DirtyB

DirtyB

Crazy Cajun
Lifetime Member
City
Port Allen
State
LA
Compression seems oK, maybe a little low. I'd expect closer to 140, but a better test is to check cylinder compression relative to each other. You just don't want to see one cylinder significantly lower than the others.

It is odd that you don't notice a "stumbling" when you pull the wire.

Maybe timing is off?
 
J

jammer1

Scrambler Junkie
Lifetime Member
City
Maple Hts.
State
Oh
What did the spark plug look like, is it light tan, black or oil covered. If you take the plug wire off and put a bolt in the plug end. Turn the engine over with the bolt about 1/8" from metal ground and see if you get a spark. You could have a bad plug or plug wire. Or if oil fouled it could be valve seals or rings.
 
Mean Green

Mean Green

Basic User
City
edinburg
State
tx
As far as compression goes, the rest of the cylinders range from 130-145... I know 120 is a bit low, but it should be enough to fire... I installed new plugs, the old ones looked great except for cyl 6... It looked clean like it wasn't firing at all... I swapped the cap, rotor and wires and coil just because it needed them, but it didn't seem to help... I'm going to keep digging today
 
Mean Green

Mean Green

Basic User
City
edinburg
State
tx
the wires and firing order are all in check, I'm just wondering if the low compression could be the issue... It sounds like a 8n tractor at idle but cleans up a bit under acceleration... It has factory rear gears (something high I'm sure) and with the 33 inch tires, it won't hardly break 45 mph... With the t5, 4th and 5th gear are useless... It's probably time for a long lock but I was hoping to avoid it
 
Mean Green

Mean Green

Basic User
City
edinburg
State
tx
I know you guys like pics, not much to see but #6 plug is obviously different
 

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J

jammer1

Scrambler Junkie
Lifetime Member
City
Maple Hts.
State
Oh
Plugs look good, maybe a little lean. It must be firing otherwise it would be have unburnt gas (similar to a fuel fowled plug). I would ask if the plugs getting a spark but I can't imagine it as clean as it is if it wasn't.
 
Mean Green

Mean Green

Basic User
City
edinburg
State
tx
I don't know, I'm at a loss... It may be firing and burning the fuel, but that cylinder isn't producing any power... I can drive it around with the wire off and it runs the same. I bought the scrambler this way, not knowing how a 258 was supposed to run/sound... I'm starting to lean towards cyl head or gasket issues... It has a weber dgav33b carb on it, and it's in need of a rebuild as well
 
8

82cj7

Legacy Registered User
City
indianapolis
State
in
Does idle sound different when you rotate the distributor? Possibly the distributor was removed and not placed back in correctly.
 
Mean Green

Mean Green

Basic User
City
edinburg
State
tx
I don't think the timing is an issue, I checked it and it was ok... I'm not sure where to go from here other than a longblock... I had the rear main off recently and the main bearing are into the brass, so it's pretty tired regardless
 
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