Paging Dr Ronmar, etc

[Third From Texas]

2008 A1R

Dash is going tits up. Speedo, 12v gauge, oil psi all blink out to zero (Low Oil dummy comes on). Fuel, 24v and air readings normal. Then I hit a little bump and Check Trans light comes on, then goes off, then all gauges come back to life. No funny noises, smoke, smells, etc.

I pulled over and of course there is no catastrophic oil dump, all fluids at normal level.

I'm suspecting a simple short but I'm worried about driving the truck home.

I *have* to tow my other LMTV with this truck to the local PD for a VIN inspection tomorrow,

HALP


"Never trust your gauges. The dash is a lie...."

 

[Third From Texas]

Seeing no oil on the ground, my first fear was oil pump failure, but she's running smooth.

I think it's just a short...

 

[TomTime]

That’s good, no bad issues! Maybe a loose connection or loose wire.
I hope you make it to your appointment.
Good luck!

 

[Keith Knight]

For it to affect multiple things it’s usually a common ground that is probably loose some where. Hard to find intermittent problems like that.

 

[Third From Texas]

For it to affect multiple things it’s usually a common ground that is probably loose some where. Hard to find intermittent problems like that.

Rgr that. I was just in panic mode.

Drove home once I was confident it was all just false positives. No issue other than the short.

I don't have much choice in the morning (only opportunity to get the vin checked before the new year and that truck needs to be off to it's new home before then). I don't see it harming anything at this point.

 

[Ronmar]

Well a few of those originate in the data bus. I would check the connections around the gauge controller on the bulkhead in front of your left shin when seated…. Also check the 12/24V supply connections over in/under the power panel. I would also look back at the LBCD connections between spare and air filter.

bounce followed by symptom change screams loose connection to me…

 

[chucky]

YEA!! JUST START ADDING GROUNDS !! everywhere panel to cab/cab to frame/ frame to ground on 12v /frame to ground on 24v and if that truck is like an AO the power distribution box under the hydralic pump those post corrode like a crazy, its the box that protects from putting jumper cables on wrong all the 12 and 24 run back to the battery box and its hard to get the nuts off of those rusty studs with out breaking one off if you do dont fret you can just put all the 12v togeather and put all the 24 togeather you just have no protection if you hook up cables wrong when mine showed its ass i was driving and the trans kept kicking out then re-engageing i just knew it was going to tear something up and it was the bottom stud rusty and loose as hell arking when you moved the cables by hand or hit bumps look there first i bet its all corroded

 

[chucky]

This is the box and its stood up on end and what it is 24 from batt to say the bottom studd goes thru some kind of circut in the box and comes out on the next stud above it and that cable goes on to the alt/cab and the same on the other 2 studs 12 in from battery out the other stud to alt/cab

 

[Third From Texas]

YEA!! JUST START ADDING GROUNDS !! everywhere panel to cab/cab to frame/ frame to ground on 12v /frame to ground on 24v and if that truck is like an AO the power distribution box under the hydralic pump those post corrode like a bastard its the box that protects from putting jumper cables on wrong all the 12 and 24 run back to the battery box and its hard to get the nuts off of those rusty studs with out breaking one off if you do dont fret you can just put all the 12v togeather and put all the 24 togeather you just have no protection if you hook up cables wrong when mine showed its ass i was driving and the trans kept kicking out then re-engageing i just knew it was going to tear something up and it was the bottom stud rusty and loose as hell arking when you moved the cables by hand or hit bumps look there first i bet its all corroded

I grew up around boats and every darned thing has to have it's own ground (same with fiberglass Corvettes).

 

[GeneralDisorder]

Since all the gauges are driven by the MMDC - I would start with the connections there as Ronmar mentioned. My truck had a bad pressure transducer inside the MMDC and I opened it up and replaced it with one from another MMDC (that also had a bad pressure transducer).

Another knowledgeable owner told me that the connections to the MMDC can be problematic and he was going to make a support bracket to keep the wiring harness weight from causing issues.

When I opened up mine I noted that the connection pins are quite bulky - I doubt they would have solder joint problems but I suppose it's possible. They can be re-flowed if you remove the back cover.

On mine I put inline desiccant / particulate filters for the on-board transducers. I suspect that moisture and rust probably kills them. One of the MMDC's I got used only had 136 miles on it. And of the three I have tested (including mine) all have had one pressure transducer failure and no other issues.

From what I understand the engine could care less about the gauges being operational so if this is a wiring or MMDC problem you should be fine to drive it.

A "short" would blow fuses. This is probably a poor connection or an "open".

The "polarity protection box" on the A1 trucks was replaced with the Load Battery Control Device - which performs the same functions and then some, but I also had REALLY nasty studs on mine - especially the lowest stud. Looked like mud wasps built a nest there.

Rick

 

[Ronmar]

This is the box and its stood up on end and what it is 24 from batt to say the bottom studd goes thru some kind of circut in the box and comes out on the next stud above it and that cable goes on to the alt/cab and the same on the other 2 studs 12 in from battery out the other stud to alt/cabView attachment 852556

The battery and alt are connected to the same terminal for both the 12 and 24v sections of the polarity box. The output to the cab/power panel is on the other terminal. The battery and alt need to be on the same terminal otherwise the power from the alt cannot get back thru the diode to charge the battery

 

[chucky]

The battery and alt are connected to the same terminal for both the 12 and 24v sections of the polarity box. The output to the cab/power panel is on the other terminal. The battery and alt need to be on the same terminal otherwise the power from the alt cannot get back thru the diode to charge the battery

So the battery cables are direct from alt to batteries just hingeing at the same stud on the polarity box but seperated in 12 on one end 24 on the other and the other 2 studs are 12/24 to cab copy that ! Thanks

 

[chucky]

I grew up around boats and every damned thing has to have it's own ground (same with fiberglass Corvettes).

When i first landed on this site everybody kept telling me the same thing ground ground ground so i did it and worked out that about the time my power issue while driving was that bottom stud on the polarity box being so corroded and rusty so it all got taken care or at the same time .

 

[BERZERKER888]

can the polarity box be bypassed or removed?

 

[GeneralDisorder]

can the polarity box be bypassed or removed?

Sure - just hook the 12v sides together on the same stud, and the 24v sides together on the same stud. Bypassed.

Rick

 

[Third From Texas]

OK, so while awaiting local PD to do the vin check on the other truck I took the time and popped open the driverside kick panel. I re-seated any connections I found and...the issue seems resolve.

Yeah!

Thanks all.

 

[Suprman]

Under the breaker panel is a grouped ground on the passenger side dash handle bolt. Thats known to be a problem sometimes. Take apart and clean.

 

[Third From Texas]

Revisiting this:

While troubleshooting months ago, I poked around the dash and the usual suspects. Everything I checked that should be grounded, was grounded. One thing I had done was disconnect the CTIS controller. I was unable to replicate the issue I was having (the gauges and dummy lights blinking in and out or functionality). Until...I hooked the CTIS controller back up. At that point, I might drive 5-10 minutes before the short reoccurs. I can replicate the issue now by hooking up the controller and starting the truck up then driving a bit.

I'm wondering if the ground wire that secures at the base of the controller has a short back in the harness. And to top it off, the controller is now in "all five lights solid" mode (it was 100% functional before I removed it).

So the issue first appeared soon after I had removed the controller to paint the heater panel ands now I'm convinced it's related. The truck drives for weeks with no issue if the controller is disconnected. And the issue reappears as soon as the controller is reconnected.

Of course, A1R means no proper TM. I know that the controller is different on the A1R but that's about all I know....

 

[GeneralDisorder]

I would monitor the supply voltage to the MMDC using both power and ground from it's harness for my gauge. If that looks normal I would scope the power (+7v) and data lines to the instruments and see what I could discern from that.

The gauges you note are "blinking out" have no connections except to the MMDC itself (2001A - Instrument Data, 2002A - Instrument Power +7v, 3004A - Instrument Ground) and a single wire from the lighting circuits for illumination (1908A - Light +12v).

The only possibilities I see are:

1. Low/dirty power or poor ground to the MMDC = bad data being fed to the instrument bus.

2. Some kind of interference on the J1587 data bus. MMDC and CTIS are both on this bus.

3. MMDC itself has problems - can't see how this would relate to the CTIS but they are near enough - could the harness being plugged in or not change the strain on the MMDC connectors?

 

[coachgeo]

I would monitor the supply voltage to the MMDC .....

MMDC ??

Metal Marking Device Controller?
Monkey Mash Dog Collar?
My Mother Despises Congress?