LOUD exhaust backfire after head/cam install....????

[1quick]

I dont see changing the compression being the reason it wont idle, yeah the tune wont be spot on but it should idle

 

[phat_ridegt]

im aware of the compression and valve changes....once i had it running for a minute or two it seems ives got a single cylinder misfire i need to tend to first. i am going to get a base tune in it as well and go from there

 

[1quick]

who's truck? lets throw a turbo in there before the exhaust goes on lol

 

[bikrboy128]

Put something on after the headers. I found out the hard way you need at least "10 of tubing after the o2 sensors or they read the air coming in the other way. It ran fine for a min. Took it to the track and barely got it off the trailer. It would idle fine around like 1-1300 anything over it was shit and if I let off it would die. Put the mid pipe on and all was right in the world.

this is what i was thinking. are the upstream O2s at the very end of the headers? it could be reading the outside air making the PCM think the exhaust is extremely lean (making it dump a retarded amount of fuel).

 

[SMR#002]

Check to make sure you don't have a cracked plug and that the plug wires are on tight. Did a header install on my Camaro and it was backfiring loud as shit until I started reving it turned out that a plug wire was loose

 

[phat_ridegt]

ive got a misfire on number 6. using the tech2, holding it at 2000 rpms number 6 is dead. changed coil, plug wire, good compression, no cylinder leakage no valve train noise. same injectors and intake that were on the truck previously. fml!

it runs fine above 1300 rpms, but when it goes to idle it backfires and stalls. im going to get the exhaust mated up before i do anything else and go from there. a cam shouldnt show up at a single cylinder misfire should it?????

 

[phat_ridegt]

also, ive never degree'd a cam, but i shouldnt be having these issues with it installed straight up....correct?

 

[Gone_2022]

also, ive never degree'd a cam, but i shouldnt be having these issues with it installed straight up....correct?

Well degreeing a cam is simply finding the best place where the valves open and close.... Depending on the cam card and what is already cut into it. I am honestly not sure if you set it straight up if it would affect anything. But with everything that was done to the engine it could be affecting it. Especially with the change in compression along with the different size valves and the different cam.

More than likely it is the open headers causing the issue. Magnified by the fact that the car is probably dumping fuel due to the head and cam swap. It is trying to compensate for everything Uve thrown at it.

 

[GearsForYourRears]

Did you change the plug? Misfire will dump lots of fuel and BOOM! Swap the coil to a different cylinder, the wire to a different cylinder, and the plug to.a third different cylinder. Then use the tech2 to.see if and where the misfire moves to.

 

[GearsForYourRears]

If you still have the misfire in the same cylinder, check the wiring to the coil.

 

[phat_ridegt]

Did all that. I'm going to swap the injector and coil wiring Monday. It has good spark though.

 

[School Boy]

After trying all of that it, it sounds like a cam or crank sensor problem.

 

[Xfirez51]

Well degreeing a cam is simply finding the best place where the valves open and close.... Depending on the cam card and what is already cut into it. I am honestly not sure if you set it straight up if it would affect anything. But with everything that was done to the engine it could be affecting it. Especially with the change in compression along with the different size valves and the different cam.

More than likely it is the open headers causing the issue. Magnified by the fact that the car is probably dumping fuel due to the head and cam swap. It is trying to compensate for everything Uve thrown at it.

Not likely that this is going closed loop. Certainly not at initial startup and probably not because of the open header. So O2s not having any affect on tune.
Base fueling tables would need to be trimmed, or use the CTS v AFR TABLES and the open header needs to be addressed. Any changes to the injectors on this build? fuel Pressure?

 

[phat_ridegt]

Has good fuel pressure the truck ran great before I swapped the motor so I highly doubt its got a bad injector or coil. Ive never seen a cmp or ckp issue cause a single cylinder misfire though

 

[Turbocharged400sbc]

single broken binary tooth on the ckp? did the jy motor have a cracked cover/etc?

 

[Xfirez51]

Has good fuel pressure the truck ran great before I swapped the motor so I highly doubt its got a bad injector or coil. Ive never seen a cmp or ckp issue cause a single cylinder misfire though

Wondering if perhaps FP had changed in which case fueling would be off due to different Pulse Constant.

 

[Turbocharged400sbc]

you do a leakdown yet?

edit:
its starting to sound like a possible bent exhaust valve?

 

[phat_ridegt]

Yah no leakage. I dunno wtf is up

 

[Gone_2022]

If it has no leakage and good spark then it's a fuel issue in the cylinder. Can only be a few different things and it sounds like your narrowing it down

 

[phat_ridegt]

So after putting about 20hrs into this truck trying to figure it out its fixed. ended up finding out i had the coil wiring backwards on the right bank fml lol. i didnt think it would fit incorrectly but apparently i was wrong lol. truck runs great going to be heading to speedinc soon for a tune. thanks for the help guys

 

[Eagle]

That'll do it! Good job getting it sorted!

 

[1quick]

nice

 

[boostedguy05]

glad it was something simple.

 

[Xfirez51]

So after putting about 20hrs into this truck trying to figure it out its fixed. ended up finding out i had the coil wiring backwards on the right bank fml lol. i didnt think it would fit incorrectly but apparently i was wrong lol. truck runs great going to be heading to speedinc soon for a tune. thanks for the help guys

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