Working on the M1078 LMTV

[Lmtv772]

...

 

[DanM7890]

Where is this connection located?

 

[NDT]

Where is this connection located?

Behind the dashboard, the Allison harness has a branch that leads to the instrument cluster. The connector in my hand is on the Stewart and Stevenson-supplied half of the connection. I believe this is the feed for the speedometer and who knows what else.


I have fondled most of the rest of the harness from instrument panel to transmission and there are no obvious cuts, wear points, etc. The Allison controller rebuilder, who is obviously extremely knowledgeable, knew from my picture of the burned board that that part of the board controls the "N" solenoid. So I still need to ohm out the N solenoid in the tranny before I feel even remotely comfortable installing a new controller. I will also ohm out ALL the harness wires looking for shorts to ground. This will be easy, as there is a bulkhead connector right at the transmission.

 

[Suprman]

Interesting. I had a wtec3 give me a solenoid shorted error. It takes a measurement before actuating.

 

[NDT]

More diagnostics today while Newark Electronics ships AMP connector parts to fix the connector mentioned previously. At the transmission, there is a large bulkhead connector. I disconnected it and ohmed out each pin to ground, both going to the transmission and the chassis harness. There was no continuity, which is interesting, as I was expecting the solenoids in the transmission to show some resistance. But I know no coils are shorted to ground.

 

[NDT]

Suprman has discussed this before, here are some pictures of the troublesome thermal switch on the starter. Mark's truck has a new starter, and the leads for the no longer present thermal switch were hanging loose, which raised alarm bells at first. After inspection of my truck with OEM starter, it was apparent what the wires were for. I taped them up real good.

 

[NDT]

While the cab was raised for harness inspection, I thought it would be a good time to install the new voltage regulator. NOT! The newer Niehoff N4307 regulator is not backwards compatible with the OEM N1506-1 alternator. My truck has the newer N1511 alternator, and the N4307 is what is on it.

 

[Lmtv772]

...

 

[tennmogger]

More diagnostics today while Newark Electronics ships AMP connector parts to fix the connector mentioned previously. At the transmission, there is a large bulkhead connector. I disconnected it and ohmed out each pin to ground, both going to the transmission and the chassis harness. There was no continuity, which is interesting, as I was expecting the solenoids in the transmission to show some resistance. But I know no coils are shorted to ground.[/QUOTE

Having no continuity through control solenoids to ground is probably ok. I'm guessing, but it's common to not switch the power to any solenoids but to ground them to turn them on. That is done so that supply voltage does not have to be routed through all wires associated with solenoid control. The control switch defines which solenoid gets grounded, not powered. The reason for this is to avoid having a bundle of hot wires looking for mischief. A bundle of potentially grounded wires is much easier to maintain.

If that's the case, your metering at the trans connector would be looking at the 'bottom' (low side) of the solenoid coil, which is not grounded, and you don't see continuity to anything through the coil because the power is off (so no connection to the 'high side').

Metering at the cable connector would be looking for a grounded point coming from a control switch, which is not activated (so not grounded).

YMMV

Bob

 

[DanM7890]

I wish I had someone like you up here to help me get mine running. I received the title today but the truck is still sitting. I have no time to get into it

 

[mkcoen]

I wish I had someone like you up here to help me get mine running. I received the title today but the truck is still sitting. I have no time to get into it

You just made the perfect argument as to why you should move to Texas!

 

[NDT]

Believe me, having time to work on this is a rare gift due to the slump in the oil and gas industry.
Studied the WTEC ii manual provided by mkcoen. What a huge aid that is. I now know all the solenoids are indeed isolated fron ground, switched on the high and liow side, and should be around 3 ohms. Values of 1-2 ohms will burn out the driver as we have in this case. Direct shorts or opens will cause the controller to fault and display error codes, as suprman had suggested.

 

[DanM7890]

I work for a valve and instrument distributer so I know what you mean. We don't have much oil here but we do have a lot of LNG stations.

Keep up the good work I can't wait to see a video of it running.

 

[NDT]

All transmission solenoids in spec!! 3 ohms at transmission, 4 ohms with chassis harness. Whew! Trans does not have a burned solenoid. Starting to think the ecu was having a bad day.

 

[mkcoen]

All transmission solenoids in spec!! 3 ohms at transmission, 4 ohms with chassis harness. Whew! Trans does not have a burned solenoid. Starting to think the ecu was having a bad day.

Wow! Check sheet and everything. So where am I taking you to lunch? Papadeux's or Ruth's Chris Steak House?

Still working on the regulator but may be found.

 

[NDT]

Come get this thing. Mission accomplished.

 

[aleigh]

Nice work guys

 

[mkcoen]

Lucky NDTs positive additude far outweighed my negitive one. Life seems a whole lot brighter now.

 

[tennmogger]

Way to go!!

 

[Tinwoodsman]

Talk about staying focused. Great job.