low compression

[aholland]

I have a 78 CJ5 w/ AMC 360. I have changed ignition module, coil, wires, plugs , dist cap.
after chasing this all down and trying to eliminate why it was backfiring thru the carb.
Would a distributor make this backfire and have low compression In the # 5 cylinder?
Compression test was at 95 on #5 and 135-140 on the others.
after all the wiring this jeep started and ran fine for a minute. then shut it off and restarted it ad now its spitting and sputtering.
my other question would be the ballast resistor, does it need to be installed with a coil that says no ballast resistor? and does that mean it internal in the coil?
please help

 

[JPNinPA]

A distributor will not cause low compression.
Low compression can cause backfiring.
A stuck or burnt valve will give low compression and backfire. Redo compression with a tsp of oil in each cylinder. This is called a wet compression test. It helps delineate between a leak at the piston vs the head. If your compression doesn’t get drastically better the leak is in the head.


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[Gennybro]

Cool info man, thankyou.

 

[Gennybro]

Should he let it run for a minute before doing the test?

 

[JPNinPA]

Not necessary. Just be sure the battery is charged maybe even connect a charger up with a 30-40 A capability to support the start. You want the same speed start each cylinder.
As always safety first.
Be sure coil is disconnected so no stray spark and pull the fuel pump fuse so there is no gas.


Regards,
JPNinPA

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