fire67bird

I've got a junk yard 5.3 from a wrecked 2002 Suburban that is backfiring thru the exhaust when I try to start it. It will turn over and run for a second but then dies. I used HP tuners to turn off the VATS and have a stand alone program running it. Does anyone know what could be causing the backfire? The engine is on a homemade run stand with the O2 sensors connected with open pipes and the MAF sensor was plugged in but laying on the ground.

94LTZ

iTrader: (5)

Are you using the harness and ecu from the same vehicle? If so are any of the wires going to the crank sensor damaged?

wayfastwhitey08

over fueling?

too much pre-load on the valvetrain?

stretched timing chain?

bad coil causing unburnt fuel to be pushed into the exhaust and ignited?

fire67bird

94LTZ - yes I'm using the harness/ECU that came with the engine. The crank position sensor was what I originally suspected when it had a no start condition. Found less than 1 volt there but no obvious issue. Then I noticed that the CAM position sensor wires were bare going into the sensor. Fixed that and the voltage at the crank position sensor went up to 12.

wayfast - I think you are correct. I had poured some gas into the intake to see if it would fire off because many have reported stuck injectors on these junkyard engines. I got it started and let it run for a min. to get the extra gas burned off. Hopefully that was all that it was.

Thanks for the help.

wayfastwhitey08

good deal.