The question is does the ECM need to know you are trying to start the engine or can I abandon the stand alone harness start wires and do my own start circuit?
Stand alone ECM need start circuit?
- Thread starter Mogman
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What are you trying to accomplish? Why not just use the existing start system? Have you looked at the wiring diagram for your truck? They're available at https://www.gmupfitter.com/pages/body-builder-manuals There is a very good section in the ELECTRICAL MANUAL explaining how the starting system works, what the inputs and connections are, etc.
Because I want to, I did not ask if I SHOULD, I asked if I COULD..the batteries are under the passenger seat and I already have primary leads going from the dash panel to the battery box in the custom body harness, it would be a very simple solution to add a start relay in the battery box that is only about 18" from the starter. this is a HMMWV conversion. I already have relays for 12V run, 12V acc and 24V acc in the battery box, the idea is to only have relay power running through the ignition switch limiting total load on the ignition switch to under 2A, also because it only takes about 10 seconds to remove the passenger seat it makes troubleshooting issues much easier as a HMMWV is definitely 50lb of crap stuffed into a 5lb bag and that was BEFORE the conversion it is also designed like no other vehicle out there adding to the difficulty of a conversion like this, this is a picture of the relay section of the battery box under the passenger seat.
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Are you looking to bypass the ECU for starting, as in the ignition switch will hit a relay and engage the starter solenoid directly?
I am not sure if the LMM cares or not, but one reason not to do that is you eliminate a couple subtle but important features:
I am not sure if the LMM cares or not, but one reason not to do that is you eliminate a couple subtle but important features:
- Starter disable while running (you could then hit start and grind the starter if the engine was running already, or hold the key on and the starter would stay engaged once the engine started -- the ECU prevents both of these from happening normally)
- Starter overheat protection (ECU limits cranking duration to ~15 seconds per attempt)
Thanks for the heads up, don't think that is going to be a problem though as I am not an idiot... also there is no way one could get confused and think a HMMWV was not running when it actually is..
If you really wanted to, yes it is doable. The ecm just needs to see the ignition in the run position. You can jump the starter solenoid manually and the engine will start. If I'm not mistaken, the ecm is just looking for the appropriate cam/crank sensor signals and the voltage at the ignition circuit. If all it good it fires the injectors. If the cam/crank signal is not present, it just sits and waits for them. If you were strong enough, you could trun it over by hand and it would start as long as the other items checked out