I replaced a broken spring, put everything back together and it runs bad. Runs fine under normal driving, but bring up rpms under load and it backfires and runs horrible. I think I may have a collapsed lifter. Any input would be greatly appreciated!

UPDATE- Runs great in open loop. I changed the map sensor thinking that was the problem initially. It seems to run better with the MAF unplugged in closed loop, but not much better.

 

Take the heads off to see what damage is done.

That's the only way to really know..

 

Before you pull the heads, run a compression test on the cylinder w/ the failed spring and a few others for comparison. Should be within 10% of each other.

Disconnect the fuel pump, and hold the gas pedal at WOT during cranking.

Report back w/ findings...bad compression points to a damaged valve and/or piston, good compression points elsewhere.

 

PS: could be as simple as a damaged plug wire when you removed it...

 

update in original post