First two hours of runtime on a rebuild (Street RV/268, bored 20over) were fine. Everything seemed great! Sent it to the exhaust shop to upgrade stock exhaust to a 2" pipe to the new cat, 2.25" from cat to new Flowmaster and 2.25" to the stock exit location... now it's got a miss.

Is it a timing issue?

Ideas?

 

Did you check your timing?

 

yes you may need to advance the timing more because now that you have that much less back-pressure because of the new exhaust your probably loosing a little fuel out the exhaust valve during overlap and it could be causing a miss.

 

5deg BTDC for Cali emissions. Needs to be advanced, now that I passed smog, methinks. I think I need to crank the idle a bit, too.

 

Engine cold or hot?
Did you plug in the O2 sensors properly?

 

Both hot and cold. O2 sensors correct, thought the upstream one is new. Passed emissions flawlessly (props to Engnbldr), just need to fine tune, I believe. I'll post results as I get to tinkering.

 

Does it ping when there's a load on the engine or at open throttle? THen your timing is too far advanced. 5* is factory spec, and all that advancing it to 8* did for me was make the engine ping.

If your timing is too far retarded, the engine will feel gutless at higher rpm.

 

It does ping under load! How can that be the result of being too far advanced at 5 degrees?? (That's an honest question, not sarcasm)

I would have assumed it would need the timing more advanced with the mods. Seems to be what others here have done. APalmer (above) posted about it being not advanced enough. Anyone with thoughts please chime in. I'm no expert at this timing stuff...

 

Move it backwards and see what happens