So far that's the only viable explanation I have left. I bought the car with a DOHC ZC that was misfiring really bad (not drivable, wouldn't rev past 2k). Get it home, find out several of the rockers had popped off. Put them back in, worked fine. Drive around a bit for short trips, still good. Come back the next day, misfiring pretty bad. Didn't think to look I was short on time. Go down the road, stops running. Rockers popped off and happened to knock the keepers off and dropped a valve. Replaced with a known good running ZC (ran fine for me for over 10k). Put in car, ran well. Again, come back later, misfire. Now, I had found large chunks of the cat in the tailpipe, so I figured it was a plugged up exhaust. Took it down and got a brand new exhaust header back. Put 50 miles on it yesterday and ran well (no long stops, 40ish of that was highway driving to and from muffler shop). Get up this morning, misfire. Pushed the rockers back on and test drove good. Went 10 miles to my gf's house. Sat for 20 minutes, went to Subway and back no problems. Sat for 3 hours and again, misfire. Left it there will go back tomorrow and repair. I have no idea what's causing this. No exhaust obstructions, no codes, no abnormal engine noises when running, no overheating. Only clues I have to work with are that it only happens when the car sits for a while, and that it's happened in this one car with two different engines. When I put the rockers back in, it runs great, no smoke. Valve lash is perfect, oil is fresh and contains no coolant, coolant contains no oil, cam timing is perfect and ignition timing is 15 advanced. Anyone ever see something like this?

 

wtf?? sounds like either the car doesn't lik zc's, some one is messing w your car, or it's got a bad vibration in the motor and is causing the nuts on the rocker arms to come loose. have you tried using teflon locking nuts?

 

I doubt someone is following me doing this . The adjuster nuts on the rockers never come loose, so I have no idea what's forcing them out. There's no noticable vibration when driving it with all rockers in place. No backfires, no issues at all when driving after I fix it, but it always shoots at least one loose after it sits and I go back to start it. I can't remember on the old motor, but on this one, it only shoots intake rockers so far. Could it be an injector or manifold issue? Not sure what though. It's got a new fuel pump and filter, and full of fresh gas

 

Wow that's really weird. Im gonna have to go with someones messing w/ your car heh. There's really no reason for a rocker to pop off after sitting. especially on two different motors.

 

did u swap in a complete zc or just the block, pistons, crank ect....?

 

It was a complete assembled motor that I had been using in another car for 10k with no issues. Only things I swapped from the previous motor were the intake manifold, injectors, and distributor. Everything else was from the other car. I also swapped the fuel pump from the old car onto this one. I wiped out the runners before I put the manifold on and it looked fine. Could some sort of fuel issue cause this?

 

Bump

 

maybe it's the manifold that's causing the problem
you said your motor didnt cause any problems until you used the old manifold, dizzy and whatnot...have you tried troubleshooting the things you swapped from the old motor??

just my .02...thats what i would do if it kept having those problems...

 

im with him some one has to be messing with you