my truck runs very rough at start up when it is cold outside, sounds like it has a hugh cam. if you hit the accelerator at this time it starts backfiring out the exhaust, this last about a min then starts idling fine. NO check engine light comes on. i also have another problem durning hard acceleration the engine act to me like it is either getting too much gas or not enough, as soon as you back off the accelerator it crisps back up like normal. sometimes durning the hard accelerator it backfires through the throttle body and through a knock sensor code. just to throw it out there the truck smells like it runs rich at an idle. i have changed all of the electric components on the engine from a donor engine.
it has 12psi fuel pressure at an idle. been fighting this since i got the truck and put the engine in it 2 years ago, the guy i got it from said it ran good when he quit driving it. he quit driving it because the bottom end of the engine was knocking. the truck set for 5-7 years before i got it. any help would be nice thanks trav

 

I'm fairly new to TBI and no expert but I've rehabilitated two recently; an 87 GMC 5.7 and a 1990 7.4. One common failure is the coolant temperature sensor that tells the ECM what temp the engine is a startup (NOT the temp sending unit in the head). It can be in a range that isn't good but not bad enough to trip an engine code. Also on the list is the MAP sensor and the EGR valve. These are cheap parts, easy to test and replace.

 

ya those have crossed my mind as well, the donor parts i swaped with was in a good running truck before the engine was pulled. so i assume (we know what that means) they are good. thanks for the advice i think i will start with a NEW map sensor and go from there. thanks again