I rebuilt a 5.3 LS and its currently on the stand but wont run. It will fire right up on the push button starter then dies like VATS is still on. The donor engine is out of a flex fuel 2003 Yukon Flex Fuel (DBW) and the PCM P59 is from a 2003 Silverado (DBW) non Flex Fuel. I have verified that there is 58 psi at the rail before cranking and pressure drops slightly ~55psi once it turns over. Seems to have spark until it turns off and ive increased the injector flow rate for the flex fuel injectors. Not sure if it matters but power goes through the stock fuse block to power the PCM. The only codes that popped up was stuff that wasnt hooked up like EVAP, O2s, MAF and Transmission
I plugged up all the vacuum ports not connected in the intake
Hoping someone with more experience on here can help me get this running so i can sell it
Thanks in advance