97 5.0 vortec backfiring through exhaust

[Slimpickens]

Well I'm trying to help a buddy out. His truck just started running like crap. Popping and backfiring through the exhaust.

New dizzy 4 months old
New cap. 4 months old
New rotor 4 months old
New plugs and wires 4 months
New crank sensor 3 months
Fuel psi 60lbs
55lbs running
Inspected spider and all looks fine. No shiney spots from fuel dripping or fuel seepage.
Throwing cam crank correlation code
Showing missfire cylinder 7
Truck has 260k miles all original.
Tested
Maf
Ignition coil... Yes both sides
Ignition control module.
It wasn't throwing the cam/crank
Correlation code until it started running like carp.

Any help is appreciated.
I'm hitting a wall here.
Thanks
Leo

 

[michael hurd]

Was the timing offset set correctly?

You may have a timing chain issue.

 

[Slimpickens]

Honestly have no idea if it was offset correctly. I asked him about the distributor and he said he wasn't sure what they did at the shop.
I've thought about the timing chain too. He is prettymuch tapped out at the moment. I've got about 5 hours in the truck for him. Checking this and that. In about ready to tell him to take it to a shop... I really want to help him, but it may be more involved than what I can do for him.

 

[someotherguy]

The P1345 is only going to crop up if the distributor wasn't set correctly, or if it's badly worn. Thing is, it will still run relatively normal even with the distributor WAY out, even up to 20 degrees off. (been there, done that.)

For the misfire code and backfiring, my first suspect would be the cap, even though it's only a few months old. Especially if it's a parts house/generic type cap. Get an AC Delco or Delphi cap and try that. Also be sure that in all the tinkering that nobody gets the wires on wrong. In a hurry it can be easy to overlook that they're not in exactly sequential order; the terminals are numbered to help prevent this.

Richard

 

[Slimpickens]

Richard, The first thing I did was try a different cap. Made no change. On another note I pulled #7 spark plug wire it made no change in idle quality.

 

[superdave]

I'm with Richard on checking the wires first. I take a silver sharpie and write the number on the boot at each end of each wire just as a crutch. It's almost sounding like a timing chain, jumped timing issue. At 260k miles, it could have a lot of slop.

Did all the problems start 4 months ago when the work was done, or did it run fine and just start this recently?

 

[Slimpickens]

Superdave,
I've verified the wires 3 times to be honest. 4months ago he called me for a no start issue. I couldn't honestly say what it was doing when he had the dizz, plugs, and wires replaced. The backfiring is a new issue.
Also I pulled the crank sensor just to see if maybe for some odd reason it was messed up physically. I found 3 tiny lines scratched if you will on the face of the pick up. So I'm thinking that could be from timing chain slack. I would think it would only be one Mark from the reluctor if it were to make contact....
Any thoughts,