Questions and Answers
Backfiring Jeep
Q. Have been restoring my Jeep for about 6 months now, and I have finally got to the part where it starts. I have got it to start but its not running very well, It's backfiring very bad. The number 8 cylinder isn't even firing and many misfires and the header of this cylinder barely gets hot. It don't have a problem idling after its warmed up. But I have found it backfires even worse under power, even just letting the clutch out in neutral. It's no where near drivable.
We have put all new plugs and wires in. It has a new Delco coil, new distributer cap and rotor. I don't think that any of the valves are sticking, could be wrong though. But I have tried to run some of that oil through it to free them up if it is the case, but it wasn't a help. It has a two barrel carb that has been recently rebuilt, so it should be clean. The motor has been sitting for about a year. I ran it through five gallons of gas at an idle trying to figure it out. Because of the fiberglass body we have had to put all new grounds to the frame and battery and I am almost positive that they are all good grounds, they're securely fastened and checked with a multi meter. I know that the firing sequence is correct, checked with the Chilton. And the timing has not been messed with. I need help bad. I am thinking it could have something to do with the ignition box? But they usual work or don't work. But when we grounded this box to the frame I noticed it sparked with the ignition turned on. I don't know what this means.
Year, make and model - 1975 Jeep, CJ-5
Engine size - 304 V8
Manual or automatic transmission - 3speed manual
Mileage - approx. 60,000
Carb or Fuel Injection - carb
ABS brakes - none
P/S - A/C - Cruise control - neither, manual steering
Rack and pinion steering - noBackground info:
new fiberglass tub, with hood, fenders and so on. Lots of new wiring. little motor work, with exception of headers and new Delco Coil.I hope that this info is enough for you to help me with a little trouble shooting.
Thank you for time and concern.
NoahA. There's not too much electrically that could be causing the problem. If it was an ignition related problem, it would not run at all. The only electrical reason one cylinder would not fire is a bad spark plug, a bad ignition wire or a bad distributor cap. Since you changed all of these things, I think we can rule that out as a cause. Just to make sure you do have spark, use a pair or spark plug wire pullers and pull off the wire from the plug. You should have a nice hot spark.
If that's so, then the problem is mechanical. You either have a bent or sticking valve. If the backfire is through the carb, you have a stuck intake valve. If it's from the exhaust, it's a stuck exhaust valve. It is also possible the valves are adjusted to tight, not allowing them to close completely. Check the Chilton manual for the adjustment procedure.
When the valves are adjusted correctly there should be a marked improvement in the way it runs.
Information provided courtesy of ALLDATA
