Question93 gmc 1/2 ton ext. cab 350 stalls unpredictably and for no apparent reason. Have changed fuel pump, fuel filter. ignition coil, distributor and rotor even tried another ecm still stalls. When stalled, no fuel is present at the throttle body injectors. After waiting a couple hours it will start up ok.
sometimes it will run a long time and next time will stall right away. Fuel pump (even after changing) seems to run a long time (9-10 sec) when turning the key on 1/2 way is this normal or a symptom of the underlying problem? I had a mechanic put it on a scanner and no codes showed up, only thing strange was scanner showed that vehicle was in back up fuel mode. I appreciate any advice>
AnswerYou FOUND your answer being that that you stated:
" scanner showed that vehicle was in back up fuel mode.....
Normally the fuel pump should initially run for only 2 seconds and then stop on pre-start.
Possible causes:
1. Faulty fuel pump relay and or wiring from ecm to relay or from relay to fuel pump.
2. Leaking fuel pressure regulator.
What appears to be happening is that you are losing fuel pressure thus causing your hard start problem.
Put a fuel pressure gage on the fuel rail so you can monitor the fuel pressure all the time. I have a 10' long fuel line on my gage so I can put the gage on the seat next to me while I drive the vehicle so I can monitor the fuel pressure for testing purposes ONLY.
When it WON'T start what are you losing, Fuel or ignition to the spark plugs ?.
Hint: Although highly dangerous, When you have this NO START condition, spray a little starting fluid in the intake and see IF the engine TRIES to start.
let me know.
autohelp
