[jjjacer]

This is a continuation on a previos thread Odd Behavior that i have but since it deals with a new set a problems and no one ever reads all the posts im posting the most relivent information in here.

After installing new engine into my car, it ran great, got it home 10miles later and let it sit about 2hrs. tried starting it again and now it misfires and backfires really bad, cant get over 2500rpms. if the rpms drop below 800 the car will backfire and stall out. only trouble codes are 12, 33, 21.

The only things i can think of are
HEP (origianal to this motor)
MAP (origianal to old motor)
Clogged CAT (origianal to old motor)

But with 3feet of snow on ground it will be hard to test the CAT as it will be a pain to remove right now. anyway of checking the other two or any thing else that can cause this.

 

[NAJ]

You need to be looking at all basics.
Fuel pressure/system holding pressure, secondary ignition, timing belt(3' of snow? ice/snow in the cover?). Broken/cracked vacuum line(s).
Checking a HEP on a vehicle that starts is difficult, all you can do is a wiggle test on the HEP wiring/connectors in an attempt to duplicate the problem.
MAP is easy, just be sure manifold vacuum is correct (16-20"HG) and that is what you are reading at the MAP sensor, then compare vacuum to voltage.
If you suspect a restricted exhaust remove the O2 sensor(leave the connector plugged in) and see if the problem disappears.That will relieve excess backpressure.
You also have a code 21 which is O2 sensor circuit, did the wires short out on the manifold/exhaust or short to each other?

 

[jjjacer]

got it running by removing the third spark plug wire and i got it to the repair shop, once the owner ran a few tests he removed the valve cover to find the 3rd cylinder rockers had fallen off. we believe when we first started the car there wasnt enough oil pressure and that caused the problem.