What did you do with your GMT400 today...or yesterday....

[Big T]

Did you try a screwdriver or jumper wire?

Is the exciter wire, purple?

Are you getting power to the exciter wire?


Do you have a load tester?

Check both batteries?

Check at the end of the cable going to the starter?

Purple to relay has power. If we jump the incoming purple power to the the outgoing purple to the starter, we do not get the starter to run. Need to confirm continuity on the purple wire to the starter.

No load tester. Did check battery voltage and got 12.5 at both.

Reportedly AAA has located a tow for us. Will have it towed to our place and continue the troubleshooting there.

 

[Big T]

 

[dbrannon79]

at first glance my first thought was why he had to pull the tire to r & r the starter but then remembered the bracket at the rear of the starter is a pia to get at with the tire in place! get one of those "lone wolf 2000's" trigger style remote starter buttons so when something like this happens you can for the most part bypass the starter trigger wire.

I wonder if the manifold got to the wires going to the starter

 

[Big T]

at first glance my first thought was why he had to pull the tire to r & r the starter but then remembered the bracket at the rear of the starter is a pia to get at with the tire in place! get one of those "lone wolf 2000's" trigger style remote starter buttons so when something like this happens you can for the most part bypass the starter trigger wire.

I wonder if the manifold got to the wires going to the starter

It’s all about the access.

Thinking the same on the manifold cooking the wire. Same result with two starters, has to be in the wiring to the starter. So the strategy is to get it to our place and work on it there.

 

[snarl95]

Corrosion of the cables at the battery?

 

[Big T]

Corrosion of the cables at the battery?

We believe the purple exciter wire. Tow truck driver stuck a socket extension in there, hit some wire and starter jumped. We’ll go through it tomorrow.

 

[Big T]

 

[Big T]

Inspired by the view, Paveltolz sent me this picture:




For ease of work, we parked Paveltolz’s truck in front of the garage.

 

[Paveltolz]

Parked the truck in what has to be a subdivision of Shangrila. Yes, this place does exist and pictures do not do the house, the area or the views justice but, boy do we still try to capture them.






When invited to visit, take my advice (even if you have to get towed here), don’t delay, BigT and his dear wife are wonderful people and excellent hosts.

The truck. I may have found the right solution.


Seriously. I don’t know what has gone wonky but, trouble shooting rules out the Starter Relay BUT:
There is no power going down stream from the relay on the exciter (purple) wire to the starter to from the relay’s pin B-7 when the key is turned to START.
We jumped the pins at the starter from A9 (battery power, hot at all times) to B7 (purple exciter wire) and still, no power to the starter.
Voltage at B9 (hot on start only) checks out when the key is placed in Start or Crank.
Ground pin A7 is also good.
All fuses in the Under Hood box are good as is the ‘crank’ fuse in the Instrument Panel fuse box.

On inspecting the starter and the 00 battery to starter connection it looks like I’m in contact with the heat shield which bears out when our tow truck driver did his checks and kicked the starter over (starter is probably good then). Can’t see the Exciter Wire connection so that will have to be inspected to see if I bogarted that up too. Still doesn’t explain why the symptoms with both starters are the same unless its just one of the PavelTolz things where a part decided this is as far down the road of life expectancy it is going to go. Like suddenly losing oil on a back road.

Shout out to AAA’s Gary of Drummond MT who lived less than 5 minutes from where we stopped…in Drummond MT. It took AAA’s dispatch over an hour to figure out they had a guy in this small town (so no shout outs to dispatch) but, once he did get the word it didn’t take him long to come get us at the gas station across from the “Used Cow Lot.”

 

[Paveltolz]

Under Hood Pin outs for the starter relay for those who want to play along. Hint, this would be the view if you were looking at the bottom of the box.

 

[ak diesel driver]

Might check out the nbus on the transmission. Not sure if that acronym is right lol

 

[Glagulator]

If B9 is hot in crank then the park/neutral switch on the trans is OK.
I have repaired 2 trucks in the past with starter problems due to the
PPL crank wire being shorted down behind the starter.
One was a short to ground, easy to fix.
The other was a short to the glow plug wires, that got exciting for the owner.
The PPL wire @ B7 from the relay goes straight to the starter
with no other connections.

 

[Paveltolz]

If B9 is hot in crank then the park/neutral switch on the trans is OK.
I have repaired 2 trucks in the past with starter problems due to the
PPL crank wire being shorted down behind the starter.
One was a short to ground, easy to fix.
The other was a short to the glow plug wires, that got exciting for the owner.
The PPL wire @ B7 from the relay goes straight to the starter
with no other connections.

Neutral Safety Switch info is very good to know as that was another concern. Who knows what evil learns in the hearts of electrical systems.
With the battery lead to starter disconnected, I need to confirm the status of the Purple exciter wire, Ensure it isn’t broke / open between starter and B7and also that there’s no contact at the heat shield with any of the wires and then move forward from there.

We’ve been greeted by a nice, short duration, morning rain shower that has moved on. Will start checking things in this much less stressful environment as soon as the light gets better.

 

[jrsavoie]

Not sure I understand correctly.

Did you have power to the purple wire, at the relay, with the key in the start position?

Did you have power to the relay exciter wire, with the key in the start position?

 

[Paveltolz]

Not sure I understand correctly.

Did you have power to the purple wire, at the relay, with the key in the start position?

Did you have power to the relay exciter wire, with the key in the start position?

With reference to the Relay in the Under Hood Fuse box.
The relay is clicking and I’ve swapped in a known good relay from BigT’s ‘not a donor car yet’ suburban. It also clicks but, that’s the only life sign we have.

With the Starter Relay removed, Yes, I have power to the relay’s connector at B9 with the key in the start position. 12+ v. (supposedly, this wire is supposedly purple too).

There is no power getting to the starter on the Exciter/Purple wire which runs from B7 to the starter. Regardless, Key in Start or, with relay removed, jumping power to B7 from A9 (power from battery).

 

[jrsavoie]

With reference to the Relay in the Under Hood Fuse box.
The relay is clicking and I’ve swapped in a known good relay from BigT’s ‘not a donor car yet’ suburban. It also clicks but, that’s the only life sign we have.

With the Starter Relay removed, Yes, I have power to the relay’s connector at B9 with the key in the start position. 12+ v. (supposedly, this wire is supposedly purple too).

There is no power getting to the starter on the Exciter/Purple wire which runs from B7 to the starter. Regardless, Key in Start or, with relay removed, jumping power to B7 from A9 (power from battery).

The way that wire was routed through the big loom, I left it & ran a new 10 ga purple high temp wire from start to finish.

It was easier and faster than trying to run it like the oem.

I used the tiny corrugated tubing over the wire and followed the original route.

 

[Big T]

Purple exciter wire to the starter is good and getting 12v at the starter when attempting to start. Back to diagnosing.

 

[jrsavoie]

Doesn't make sense.

If the starter cranks when the starter solenoid is jumped with a screwdriver. Then it should crank with the purple wire powered.

Can you load test the purple wire?

It may read voltage but not carry enough amps to work.

If it has one tiny strand of wire left, it will read voltage. But might not work for the solenoid.

Maybe check ohms from one end of the purple wire to the other.

Not being an electrical guru. I'm not sure I explained that properly.


I think Marty suggested trying an emergency push button start.

 

[Big T]

Doesn't make sense.

If the starter cranks when the starter solenoid is jumped with a screwdriver. Then it should crank with the purple wire powered.

Can you load test the purple wire?

It may read voltage but not carry enough amps to work.

If it has one tiny strand of wire left, it will read voltage. But might not work for the solenoid.

Maybe check ohms from one end of the purple wire to the other.

Not being an electrical guru. I'm not sure I explained that properly.


I think Marty suggested trying an emergency push button start.

Found a small nick in the insulation of the purple wire down by the starter.

Do not have a load tester.

Weather is perfect for working on trucks:

 

[ak diesel driver]

Take a separate wire and run from the battery to the purple terminal on the starter to test the selenoid. Depending on what he touched with the screwdriver doesn't prove the starter is working properly