Engine Run-On
Thread Starter
Joined: Jan 2006
Posts: 6,670
Likes: 6
From: Concord, CA
Engine Run-On Strange happening that started this morning. My 71 Nova LS1 swap, which has been no problem for since it has been on the road for almost two years...
Would not turn off with the key now. On start up, I noticed that the pump prime would not turn off (1-3 sec) after priming, but keep running.
On turning off the key. It would take about 2-4 sec to stop running. Fuel pressure is still at 58psi. so, running out of fuel is not killing the engine.
Heading to the drags tonight, need to fix it quick. Any suggestions, I wonder if the Alternator is back feeding and causing the run-on ?
Just asking for some suggestions on what to check... in a bind to resolve and don't have the time to fish around.
Thanks..
BC
Would not turn off with the key now. On start up, I noticed that the pump prime would not turn off (1-3 sec) after priming, but keep running.
On turning off the key. It would take about 2-4 sec to stop running. Fuel pressure is still at 58psi. so, running out of fuel is not killing the engine.
Heading to the drags tonight, need to fix it quick. Any suggestions, I wonder if the Alternator is back feeding and causing the run-on ?
Just asking for some suggestions on what to check... in a bind to resolve and don't have the time to fish around.
Thanks..
BC
Is it just the engine, or do you still have radio or other accessories when you turn the key off? Need to isolate to the engine harness/PCM by verifying ignition/BAT voltage at the PCM connector with key on/key off. Looks like blue 20 and 57 are BAT voltage, blue 19 is ignition.
Thread Starter
Joined: Jan 2006
Posts: 6,670
Likes: 6
From: Concord, CA
Didn't have anytime to problem solve, got in and drove to work.. turned it off.... and to my surprise... it kept running..
Will see if I can check fuses and relays.. that are related to the PCM,....
thanks for the response..
BC
Will see if I can check fuses and relays.. that are related to the PCM,....
thanks for the response..
BC
Thread Starter
Joined: Jan 2006
Posts: 6,670
Likes: 6
From: Concord, CA
Well... Not sure is going on.. but after a few full throttle blasts down Sonoma Raceway... all has returned to normal. ???? I will find some time to check over my wiring and such.. oh well..
BTW.. 12.869 at 108.97
Best ET = 12.869 backed by a 12.993
Best trap speed = 109.97
Rt = -0.212
60' = 1.934
This with street tires.
BTW.. 12.869 at 108.97
Best ET = 12.869 backed by a 12.993
Best trap speed = 109.97
Rt = -0.212
60' = 1.934
This with street tires.
I thought about it a little more. The fuel pump prime run-on suggests that the PCM thinks the engine is starting or running. I'm not certain which sensor tells the computer that the engine is running vs. the key on/not starting (assuming crank position?), but it appears that either the PCM A) isn't getting a signal to shut off the engine (switched input or sensor), or B) refuses to shut off the engine (aka bad computer).
You might want to poke around the tuning section to see if you can find out the PCM start/run logic.
ETA: Nice numbers! That thing runs strong.
You might want to poke around the tuning section to see if you can find out the PCM start/run logic.
ETA: Nice numbers! That thing runs strong.
Last edited by hookemdevils22; Oct 21, 2016 at 05:36 PM.
Thread Starter
Joined: Jan 2006
Posts: 6,670
Likes: 6
From: Concord, CA
Hook... Yeah.. I figured something was not shutting down the signal to the Fuel relay signal. Or my power relay panel that controls the power to the PCM and IGN devices had a sticking power relay or power was cross feeding to keep power flowing ??..
But the problem came and left without reason ?...
thanks for responding.. will have to change the plugs before I go next time... might cut a few 10's off... LOL
BC
But the problem came and left without reason ?...
thanks for responding.. will have to change the plugs before I go next time... might cut a few 10's off... LOL
BC
are you using the original ign switch? my '66 c-10 started doing that occasionally. the brass contacts had eroded and dusted the switchplate making it conductive in every position.
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Thread Starter
Joined: Jan 2006
Posts: 6,670
Likes: 6
From: Concord, CA
Clint.. will do.. I have had the Nova outside in the side yard for the past few month while I was using the garage for working on the old Farm Truck. Could be due to the SF areas cool and moist nights (fog) that the switch is now acting up.
But it is back inside now...
BC
But it is back inside now...
BC
On The Tree
Joined: Feb 2014
Posts: 157
Likes: 3
doesn't ECM need to see a crank signal to make pump run continuesly?(sp) maybe stray voltage in harness
Other than that a stuck or sticking power/ign relay now unstuck/unsticking due to vibration from running car hard? as well as everything drying out with lots of racing heat/hotsoak.
Just random thoughts
Other than that a stuck or sticking power/ign relay now unstuck/unsticking due to vibration from running car hard? as well as everything drying out with lots of racing heat/hotsoak.
Just random thoughts