258 Help

Working on a customer's CJ5 with a 258. It idles fine, but when it is revved up, it pops out the exhaust and sometimes back through the intake. Also looses power when driving down the road. Swapped carbs and that didn't solve anything. It has a prestolite distributor with the factory electronic ignition and a new ignition control module. I'm thinking it is something with the ignition. I have checked timing and vacuum readings, which are all spot on. I have two other distributors, one is like what is in there and the other is an older points style. Ideas?

 

Humm, not sure but could the valve timing be off/ timing chain jumped one tooth? The ign can be adjusted to be in spec with the distributor and the valve timing still be late. just asking I may be way off here. .

 

Trigger wheel digging into the sensor ?

 

And with one of these you can save money on your next doctor appointment and do it yourself…

 

yeah... valves is what I'd check out. Have you had the valve cover off yet? Look for loose or bad rockers, bent pushrods, broken springs, etc.

 

Self colon scope.

 

Bad coil is also a possibility, also possibly clogged fuel filter, or failing fuel pump.

 

Agreed first thing that comes to my mind is a lean condition for some reason.

 

I suppose a check for excessive backlash could be done to see if the timing chain has a bunch of slack. Might check the TSM for the specs, no idea off hand what it should be but would think backlash would be not more than 2-3 degrees from crank to rotor.

 

I'm leaning towards a timing chain issue. Fuel system is all new. I swapped out distributors and that didn't help either. While adjusting the timing, I noticed the timing mark jumping around a few degrees. Vacuum gauge also jumped around. To me, this is indicating a valve timing issue.

 

I'm with you, just because.