7.4 v8 engine backfireing

Need a little more info.....has anything changed lately? Have you changed plugs or adjusted the timing? Has the boat overheated?
Don
 
mick dolan said:
Hi All I have a 1989 340 sundancer when she gets she starts popping on 1 engine anyone any idea what could be problem Mick Dolan:smt038
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Is it popping back through the intake or out the exhaust?

Does it happen when cold, hot or all the time?

If intake, could be lean & be a carb issue. Like some debris in the idle circuit. If efi, then could be a clogged or sticking injector. Could be bad plug wire or bad dist cap. Or ... sticking intake valve or broken valve spring.

If exhaust, its prob bad plug wire or bad dist cap. Or ... sticking exhaust valve or broken valve spring.

Either way, you can locate which cylinder by doing a compression test if it is a mechanical issue. You can look at the plugs at the same time. A good visual inspection of the entire ignition system from the coil, dist, plugs & wires. Don't forget about the connectors too.

Good luck & lmk if you need any other info. I rebuild engines for a living & have done many 7.4l engines.

Greg
 
Hi Don seems to happen after engine heats up maybe 40 minutes and stops when when you bring the revs back from 3500 revs to 2000revs thanks for the reply Mick
 
In addition to what has already been posted a weak or a broken valve spring or a bad cam lobe will cause this. Now all you have to do is figure out which one is the problem. Good luck.
 
similar problem with mine, same conditions. Finally found a defective trigger sensor in the distributor. You could actually see a little blown up capacitor on the sensor module.
 
I has a similar problem on my 4.3L engine, and it was a shorted spark plug... I would start with the easy things first and change your plugs...
 
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