Not firing on two cylinders

Hello all. I just joined this site. I am looking forward to reading the posts. I have a 78 CJ 5 I just bought. Don't know what all previous owner did to vehicle/engine. It has a Mallory unilite distributor. It is running, but it will not fire on number 5 & 7 cylinders. Sparks a couple of times when it first turns over but nothing after that. I have replaced distributor cap, rotor button, plugs, and plug wires. Still no fire in 5 & 7. I don't know much about electronic coils and distributors. Why is it not firing on those two cylinders but is firing on the rest? Thanks in advance for any info/suggestions.

 

Check plugs and plug wires. If it is a spark problem, it could also be a cap cross firing.

 

Thanks mrhp. I replaced cap and button because I thought there may be cross firing. Also replaced wires. When I pull the wire out of the dist cap while running, there is no spark in either cylinder.

 

5 and 7 are right next to each other in the engines firing order (18436572) and on the engine itself. Try switching the plug wires at the plugs, they could have been put on backwards. Both those cylinders not firing would make one hell of a miss, how does it run otherwise?

 

Thanks jinpdx, It runs ok, other than the miss, and drives, just doesn't have much power. I did switch those two wires but no change. The problem is that when I pull a plug wire and put an old plug on it grounded to the engine, there is no spark except when it first starts turning over, then no more spark. I will try to separate the wires as far as I can today. I guess I am just not holding my mouth right. Thanks for the input. Jerry

 

If you have the Safe Guard Control Unit, do you have it set for 8 cylinders? s3=1 s4=1 for 8 cyl. s3=0 s4=1 for 6 cyl? IIRC s2 should be down. The =0 is a down position. HTH.

 

Walt, Thanks for the response. I have no idea if I a Safe Guard Control Unit or not. How can I tell. I know nothing about it. Just bought this Jeep and don't know what the previous owner(s) did to it. Anyway, thanks for the info. Jerry

 

Morning, I finally figured it out. The Mallory ditributor was malfunctioning. I put a stock distributor and coil in it and everything worked fine. I intend to take the Mallory apart and see if it can be fixed.