oh my god

ok this is gonna be a long story. i had a friend reuild an engine and put it in my 92 saturn and it was fine but a week or two went by and it started surging at idle and when i accelerated it would bog really bad so bad i couldnt pass a minivan. so we replaced damn near everything we could think of. that didnt work so we felt the exhaust suck back into the muffler and thought bad valves did a compresion test and all 4 cylinders were leaking. so a year goes by with me driving it this way. so now my friend has this new head and valves the head has been shaved, bored, port and polished all that good stuff. he puts it all back together and still does the same thing. he hooks up a scanner to it everything checks out but he notices that while accelerating it is pulling spark away. he checks coil packs, he checks knock sensors and has no idea what the hell is causing this. he suggests it could be the ecu. what do you guys think and if it is the ecu what the hell do i do with it. thanks

are any of the parts on it from a different year, like engine wise? cuz that could be throwin the ecu off, or you're right, the ecu could be junk, if so, replace it from a used parts yard or sumthin, i did the same (didn't have the same problem tho) and it works great. but if you have compression leaks, then thats not ecu related, hows the cylinder walls and all?

how much throttle was used on acceleration when it pulled spark?

also were the same head bolts used?

91 and 92 S-series used different crankshafts and are not compatible with other years, the toner ring for the crankshaft position sensor is 10 degrees of and the 91/92 PCMs are programed to match. therefore use a 93+ crankshaft with a 91/92 PCM or viseversa and your base spark timing will be off 10 degrees(advanced or retarded depending on which combonation, can't remember which is which) throw in the reading from the knock sensor and who knows how far your timing is off.

so what year was the donor engine? if the crank does not match the PCM there is no easy fix, ether the crankshaft or PCM/wiring harness needs swaped.