large split in the muffler and backfiring.

[nothinbutroad]

so i finally got my truck up and running, but on the test drive there was a loud back fire, driving back home it kept back firing, several times idling at lights and about 5-8 back fires upon accel before i reach 25 mph. i also noticed a huge power loss. checked under the car and theres a large split in the side of the muffler. is the muffler causing the back fire or is something else in the engine causing the backfire that blew the muffler? I dont wanna replace the muffler and blow a hole in the new 1.

Ps. before i replaced the 02, map, maf and replaced some vacuum lines, it was running rich and black smoke was pouring out. after replacing all that it runs fine(no smoke) but now i have back fire and a hole in the muffler.

pps. driving up hill there was an insane amount of back firing, and down hill there were none at all.

 

[arco777]

Sounds like excessive fuel is getting dumped into the exhaust. One cylinder may not be firing. Check your plugs and see if any look unusual.

Have you pulled codes? Check KOEO and KOER and see if you get anything.

A backfire is probably what blew the muffler apart, by the way.

 

[Dan Whitaker]

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A backfire is probably what blew the muffler apart, by the way.

Yep because all a backfire is, is a small explosion. You didn't mess with your timing did you? That can cause a backfire.

 

[arco777]

Didn't think timing was adjustable on an OHV, short of pulling the SPOUT connector which would retard it.

 

[nothinbutroad]

11 koeo, 22 koer, ran a smoke test, no leaks. i didn't touch the timing but i think it may be off. i know the first and loudest backfire blew the muffler. what I'm trying to figure out is all these smaller backfires. when i changed the spark plugs i mixed up cylinders 5 and 6 when i attached the wires so when i started the engine it backfired loud, so i think i could have screwed up the timing.or even damaged a cylinder? everythings running fine now except the backfire and powerloss. if i replace the muffler and its still backfiring will i blow another 1?

 

[colintrax]

Could be a stuck open exhaust valve allowing the air/fuel mixture to leave the chamber before it sparks. Have you done a leak down test or compression test?

 

[arco777]

11 koeo, 22 koer, ran a smoke test, no leaks. i didn't touch the timing but i think it may be off. i know the first and loudest backfire blew the muffler. what I'm trying to figure out is all these smaller backfires. when i changed the spark plugs i mixed up cylinders 5 and 6 when i attached the wires so when i started the engine it backfired loud, so i think i could have screwed up the timing.or even damaged a cylinder? everythings running fine now except the backfire and powerloss. if i replace the muffler and its still backfiring will i blow another 1?

Just did the research and timing is not adjustable on the 4.0L OHV. The crank position sensor signal would most likely be either correct or not signalling at all so doubt it is half-bad.

You can't damage a cylinder from a backfire. Double check your firing orders though.

Check your fuel pressure at the rail, and check that the fuel pressure regulator and injectors are holding pressure when the key is turned back off. A stuck injector or malfunctioning FPR could be dumping too much fuel.

Did you ever compare your spark plugs?

Code 22 indicates MAP/BAP sensor issue, by the way. Check that out as well.

 

[nothinbutroad]

brand new map sensor, reset the continuous codes. i stopped getting a 22 with the koeo, but still getting a 22 koer. ya i compared my sparkplugs to the old ones, same exact ones, i gapped them all at .54. one of my customers at work suggested a compression test so ill check that out next. could hooking it up in the wrong firing order damage a piston or valve? i got the correct firing order now but maybe that tweaked a valve and is keeping it open?

 

[nothinbutroad]

if the valve is stuck open, how do i fix it? i noticed it only back fires in drive, idling in park it does not.

 

[arco777]

I don't think you have a damaged valve but you can find out by doing a compression and leakdown test.