Engine not running right!!

[Desertdogs]

Okay, this one is a stumper. Decided to go to boards to see if anyone can figure this out. Please read thoroughly the details, we've gone on a few wild goose hunts already. Engine starts, but runs rough, as it appears to be firing only on cylinders 4,6,7,8.

Engine was pulled out of a 2003 Z-28, LS1 w/32K miles on it, fresh out of the car. Excellent condition, and owner is known, so no funny business.

Engine has brand new sensors everywhere, and for 24X reluctor. Changed out oil pump and timing chain to SLP enhanced pol pump and double roller chain and gears. Followed instructions to the letter as for TDC and lining everything up.

Inspected engine while oil pan and front cover was off, everything was clean, no bad marks on cylinder walls or anything. Everything re-installed according to Chevy instructions (I've built numerous bikes, off road machines, and do my own work on my street vehicles, so I'm careful)

Computer's a MEFI 4B, and plug n play harness from CBM; and was sent back for checking last week, everything about harness and computer passed.

Injectors were cleaned and balanced professionally, and just pulled them all to make sure none were stuck, all are good.

Checked all wiring, voltage, everything is in correct place and working. Coils are brand new as well, all are working.

Fuel is pumping at 55psig, cam and crank sensor are in correct spots. Unplugging MAP has no change.

So we are stumped..any ideas?

[pajeff02]

Unplugging the MAP or the MAF? Unplugging the MAF will make it default to speed density.

Can you scan it for codes? I am not familiar with a "MEFI 4B" but assume it has some sort of base tune pre-loaded for the engine? Have you pulled plugs to verify spark?

[SMWS6TA]

checked the #2 injector?

[Naaman]

What's special about the #2 injector?

It's not firing on half the cylinders? A bunch of bad plugs?

Waiting to see what this turns out to be...

[0rion]

What vehicle did the engine come out of? I'm sure that's a typo since there was no 2003 Z-28. I'm not familiar with that ecm either but does it require a case learn procedure?

[jb3golf]

Did you check for codes and do you have a live data scanner? That would help....fuel...compression...air..spark....knock them out one by one....

[jb3golf]

Also what kind of deal did you get the engine for? If it was an amazing price...There may be a reason for it....just saying...no disrespect to the seller....did you see and hear it running in the seller's vehicle before you took delivery?

[bisogun35]

wish you success

[cammed goat]

I am not familiar with MEFI 4B either, but I am tempted to say your issue is wiring related. If the engine is good, and you went over it properly, sounds wiring related. Possibly a bad ground/damaged harness somewhere or maybe you're missing a harness or something isn't connected or connected correctly.

[35th-ANV-SS]

What vehicle did the engine come out of? I'm sure that's a typo since there was no 2003 Z-28

This is the first thing I noticed.