Starting Issue

[HotRodTractor]

I have been attempting to track down a starting issue that I originally thought was a pair of weak batteries. When you turn the ignition on everything comes up just as it should, but the moment you move the ignition switch to "start" the starter solenoid engages and kills power to everything with that nice classic dead battery "click click click" - power to everything goes away with each click.

I started with the batteries and have subsequently went through every power wire and ground on the truck with no real results. I tested the starter thinking that it was possible that it was shorted and pulling large amounts of current. It tested good and pulled 130 amps unloaded. I haven't tested it loaded.

Now comes the odd part. If I put power to the starter relay directly from battery it turns the truck over very well. If I turn the ignition to run and then activate the starter directly from the battery the truck spins over and starts right up with zero issues. Once the truck is running I can't find any issues with anything.

If I unhook the starter solenoid wire and turn the key to start - obviously the truck doesn't start, but i also don't get any weird power draws.

Something goofy is going on and I am out of ideas. I can obviously do a couple of different things to keep from having to cross the starter, but I would like to figure out why I can't start the truck from the key switch and correct it.

 

[HotRodTractor]

No ideas?

 

[JoshH]

Bad ignition switch? :dontknow:

 

[HotRodTractor]

I've wondered if it was the switch.... but the starter relay does get power every time I turn the key, so that is why I keep dismissing the switch.... it seems to be doing its job, but when the relay pulls in, it loses power and then repeats the process of click click click.

 

[duratothemax]

The ignition switch sends a discrete signal to the ECM...then, once the ECM verifies that the engine isnt already running, and the trans is in park/neutral, the ECM applies +12v to the starter relay, which then causes current to flow to the solenoid, and then to the starter.

The ignition switch itself isnt directly connected to the starter or starter relay in any way on all 2003+ trucks.

Did you try a new starter relay?

FWIW, LBZ/LMM ECM applies +12v to the starter relay to trigger it, LB7/LLY ECM applies ground to the starter relay to trigger it.

 

[HotRodTractor]

The ignition switch sends a discrete signal to the ECM...then, once the ECM verifies that the engine isnt already running, and the trans is in park/neutral, the ECM applies +12v to the starter relay, which then causes current to flow to the solenoid, and then to the starter.

The ignition switch itself isnt directly connected to the starter or starter relay in any way on all 2003+ trucks.

Did you try a new starter relay?

FWIW, LBZ/LMM ECM applies +12v to the starter relay to trigger it, LB7/LLY ECM applies ground to the starter relay to trigger it.

I swapped it with one of the other relays in the fuse box with no change. In fact I have had everything out of that fuse box a couple of times now just trying to figure out if I have extra current draw somewhere that was drawing the battery down and that was when I started experimenting with the starter and realized that it wasn't dead batteries or a constant draw on the system - it was something else.

 

[Bustedknuckles]

The last time I had one that acted weird like that I just gave up and put a new starter on and it fixed it. The starter had even checked good

 

[HotRodTractor]

The last time I had one that acted weird like that I just gave up and put a new starter on and it fixed it. The starter had even checked good

I wonder if the starter solenoid is drawing too much current causing a voltage drop feeding the fuse box causing everything to go crazy?? I suppose that might be possible.....

I was debating on wiring in a relay down close to the starter and use the existing solenoid wiring to trigger the relay and see if that solves the problem at least temporarily....