Rebuilt engine, won't start.
 

I just reinstalled the engine in my 96, it turns over but won't start. It has spark to the plugs, has 43 lbs. fuel pressure. I took a lot of care to make sure I reinstalled the opti correctly. When it's turning over it will backfire from the exhaust and the intake which seems like a timing problem. Plug wires are all in the correct order. I haven't touched the opti. It ran good before, I just took it off and put it back on. Any ideas ? I'm hoping I'm missing something simple.

Any ideas?

If you are sure the timing chain and Opti were installed right my first guess would be valve lash too tight.

I don't think the valves are too tight but it's easy enough to back them off before I tear into the opti. I'm afraid I must have messed up installing the opti.

What if the water pump is out of the car and the ECT sensor is not connected? Would this would cause the PCM to read -40 for coolant temp by an open circuit correct? If thats the case then it would be dumping too much fuel and preventing the engine from firing?

it is possible you didn't get the cam dowel in the right Opti position.

Did the opti push on easily and was it completely flush with the block before you put the 3 bolts that hold it on?

backfire at random does often mean a opti issue not being positioned right

with that said incorrect valve lash also as noted

I installed the Opti with him and it did pop on easily, we lined the opti up with the cam dowel, gently guided it into position and a gentle tap and it popped right into place. It was flush with the block once on, the holes for the opti bolts were in contact with their respective holes on the engine, we threaded them in, snugged them up individually and torqued them to their respective values (106 in-lb)

-16°C (max temp limit on ECM) does advance timing a bit (+8º). But I'm not sure that is the default for no ECT signal. You can try just plugging the sensor in so it can at least get ambient temp for spark timing.

Did you do any mods while you were rebuilding it? Did you adjust the tune for the mods? It still shouldn't backfire though.

During the install we replaced the stock cam with the Lt4 hotcam. We have a reprogrammed computer but havent yet installed it, we figured we could atleast verify that the engine runs. It ran on the old computer fine so we figured it would atleast fire on the old one.

It runs. Re- adjusted the valves and it fired right up.
I sure screwed that up. Thanks for your help everyone.