496 no start issue

[chartersj]

Bad ground

That's what it seems. When the black/yellow leaves the relay, it goes through the shift switch, changes color to yellow/orange, and goes into the computer. And I still get continuity through the shift switch. I have also jumpered the switch out so I don't see it being that.

 

[chartersj]

[IMG2=JSON]{"data-align":"none","data-size":"full","src":"https:\/\/i.ibb.co\/G9yYY4H\/Untitledse.jpg"**[/IMG2]click to enlarge

This diagram would be for 2005 and earlier 496s with the 10 pin harness. From what I have read they changed the harness in 2006 when they went to a 14 pin harness and relay for the starter.

 

[chartersj]

I had my mechanic buddy come over last night to see what he thought. After going through what I had already done and doing some more trouble shooting/ testing, he thinks its something to do with the ground for the computer. It seems the relay gets its ground through the computer, and the computer is not grounding the black/yellow to the relay to operate for some reason. We put a jumper from one of the rear motor stud ground to the relay ground (black/yellow) and then the motor would roll over with the key. I kept the computer unplugged for this test just to be safe, so we didn't try to start the engine this way. Everything seems to point to the computer, or the computer is not liking what it sees and will not ground the black/yellow to roll the motor.

 

[chartersj]

I have a bit more information for those interested. At the starter relay, I have 7.15volts when I measure across the relay from the yellow/black(starts out as yellow/red from key) to black/yellow. When I measure from yellow/black to battery ground I get 12.2 volts. Then when I measure voltage from battery ground to black/yellow, I get 4.99 volts at key on and key start. That would explain only getting 7.1 volts across the solenoid. Why would I be getting 5 volts on the black/yellow? I know the sensors run on 5 volts off the motor. Do I have a shorted sensor? But then why does the other 3 relays all operate fine and no fault codes?

 

[alldodge]

Guessing, but the blk/yel goes to ECM and the ECM is what applies the ground. With the ECM not applying a ground but having something like a floating ground from a transistor or such, there is a resistive kind of ground or floating. This is why your seeing power on it because power goes thru the relay coil (which is also resistive)

 

[chartersj]

Guessing, but the blk/yel goes to ECM and the ECM is what applies the ground. With the ECM not applying a ground but having something like a floating ground from a transistor or such, there is a resistive kind of ground or floating. This is why your seeing power on it because power goes thru the relay coil (which is also resistive)

That does make sense. I just thought it was strange it was the same voltage as the sensors. I guess I would have to measure what the sensors are getting exactly and see the difference. I'm not totally convinced something is wrong with the computer But I'm not sure what else it could be at this point

 

[Bt Doctur]

Does the starter turn if hot wired? If yes, wire in a slave or relay and wire in a ground

 

[chartersj]

Does the starter turn if hot wired? If yes, wire in a slave or relay and wire in a ground

Yep it will if I cross the relay or add a jumper from ground to the relay ground.
That's a good idea, and I may end up doing that at least to try to start the motor to see if any fault codes will generate while running.
It seems odd that the relay needs the key turned to start to put 12 volts to the relay AND computer needs to apply ground to the other side both at the same time to operate the relay.

 

[Bt Doctur]

relay or slave I can find no mention of an ecm providing a ground. The only other diagram has the solenoid/relay connection going thru the neutral safety at the control box and to ground.

 

[chartersj]

relay or slave I can find no mention of an ecm providing a ground. The only other diagram has the solenoid/relay connection going thru the neutral safety at the control box and to ground.

Ok yeah well at this point i think it's my only option to try it to see if I can get the motor to start and see how it runs

 

[chartersj]

I was in my garage and came across the smart craft harness that I unplugged and set aside when I pulled the motor last fall. It connects on the top of the motor and splits into a few plugs but none are connected to anything. I thought to myself I may as well just try it even though I had no thought it would change anything and sure enough she rolled over lol. Primed the fuel injectors and fired right up. Feel a bit stupid but what a relief!!

 

[alldodge]

Cool, a good think to know early on. It should have a termination resistor inside the connectors, even the ones not used. With the cable disconnected, the CAN buss is not able to talk fully with the ECM, or at least my thought on it

 

[chartersj]

Cool, a good think to know early on. It should have a termination resistor inside the connectors, even the ones not used. With the cable disconnected, the CAN buss is not able to talk fully with the ECM, or at least my thought on it

You must be right. There is something in that harness it must be looking for. That is why I thought it would be a good idea to take it off because each end doesn't have a plug and it wasn't feeding anything...or so I thought lol