5.3 Starts then Dies

[cpressler]

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

[5FDP]

You didn't fail the MAF sensor in the tune file and you didn't wire in a separate IAT sensor. The stock MAF is a 5 wire harness and within that harness is two wires for the IAT, you need to get that working.

Fail the MAF in the engine diag tab. Set the MAF fail high to 0hz and set all 3 MAF dtc's to MIL on first error.

The engine will run without the IAT but it won't run super well when it thinks it's at the north pole.

[cpressler]

003 P59 5_3L VATS Delete Flex Fuel MAF.hpt12-1-21 Log 1.hpl
Failed it but i read the DTC and nothing

[cpressler]

12-2-21 Log 1.hpl
I forgot i had a spare MAF laying around. Air temp is 63F in this log but it still starts then dies.

Any suggestions?

[5FDP]

You could try unfailing the MAF now that you have one.

Does the throttle blade move when you press the pedal?

[cpressler]

Thanks for the quick reply. i dont have a pedal the engine is just on a stand. Will it not idle without a pedal? All im trying to do is get a video of the thing running so i can sell it

[5FDP]

If it's a drive by wire, yeah you need a pedal.

It can't open the throttle blade without a pedal. No air, no go.

Maybe you can try holding the throttle blade open a tad to keep it running.

[blindsquirrel]

There are failsafes that will shut off spark and fuel if there are certain faults in the ETC system - like if the pedal goes missing.

[cpressler]

Looks like blind squirrels do get a nut. I feel stupid but thanks for the input, fired right up