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I have own a 78 CJ5 since 1984 it has a stock 304 engine with around 82k miles.
For a while now whenever I drive specially on a long drive on the highway it stars backfiring and it seems like is not getting enough fuel in the carburetor, after the engine cools off for a little the problem goes away.
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Have you checked your carburetor gasket are you heading leaking air any wear near the exhaust headers or near your exhaust pipes try checking around your carburetor and near your head gaskets with an accelerint like carburetor cleaner if there a leak any were you will hear motor rev up while running back firing use my means there is to much pressure in the exhaust you might have a valve sticking
This is an example of the issue I’m having
Yesterday I took a 25 mile drive, I was on the expressway for about 30 minutes doing 50 to 55 miles an hour when the issue started. It starts by what it feels like no fuel is getting to the carburetor and as I press on the pedal it backfires I pulled over waited a couple of minutes and I drove off but I had to drive for a short distance at low-speed cause it felt like the carburetor was flooding, On the way back I drove through the local streets all the way doing 30 35 40 stopping at lights etc, and I made it home with no issues whatsoever.
Sounds like your carberator needs an adjustment if your spraying more fuel then the engine can handle it could cause extreme amounts of exhaust gas which is to much for the exhaust pipe to handle which could be were the backfiring at higher rpms and higher speeds try to slow the fuel down by adjusting your carberator
I have replaced the following:
Carburetor
Fuel pump
Fuel filter
Fuel sending unit
Electronic Ignition
Distributor cap and rotor
Spark plugs and wires
Muffler (removed catalytic)
The timing is on, no vacuum problems
I am not just throwing parts at it, trust me I have tried to diagnose this problem for a while now, every time I changed a part I would test drive it to see if that part fix the problem.
This only happens while driving for a while at high speed, it does not happen if I’m driving around the neighborhood, that’s why I mention that the problem starts after the engine reaches a certain temperature.
Don’t know what else to do.Just a few thoughts …
Have you done a complete leak down and compression test on the engine?
Have you tried re-jetting your carb?
Have you attempted to vary the spark plug gap.
Or switch temperature range of your plugs.compression test was fine, so is the carburetor and spark plugs
You must have misread what I was inquiring about …
Let me try again..Have you tried re-jetting your carb?
Have you attempted to vary the spark plug gap.
Or switch temperature range of your plugs.
Yes the only thing I haven’t done is change temperature of the plug, but I’ve had this jeep since 1984 and I have always use NGK GR4 spark plugs with no problems, about the carburetor, it has a Motorcraft 2100 which I have also replaced a couple of times in the past with no problems
Nightflyr is asking if you have tried changing the spark plug gaps manual seeing if that helps and the list of parts you said you had replaced sounds like your just throwing parts at the truck why did you remove the catalytic converter that could be why is backfiring the catalytic converter is on the truck for a reason did you remove it because it was bad
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