Please don't hate me because I have a motorhome ;)
My '94 Vogue with Cummins 8.3 300 mechanical and Allison MD3060 trans.
The trans has a "service indicator" showing and a fault code of 66 which is serial communications failure. I had the local Allison shop look at it and they said it was not seeing the TPS.
I only have a barebones and barely readable schematic on this orphan coach and cannot determine how all the components wire together so I can do some trouble shooting. I am not about to pay Allison $90.00/hour to trace wiring harnesses around the coach.
I bought the Allison Service manual but it does not cover the electronics at all.
Because it is a mechanical engine, there is a VIM (vehicle interface module) between the TPS and the ECU. I don't know if there is anything else in the circuit.
So, what Allison docs cover the connections between these devices? I don't want to spend more money on a book that doesn't tell me what I need.
The trans works OK the way it is but it runs on it's own default setup. It won't go into 6th until I get over 65 MPH and there is some "flare" in the 4-5 shift on a hard pull. I'm hoping that getting this corrected might help my mileage.
Thanks for any help,
Len
Len,
A wild guess is that you have a sensor failure on the engine that detects engine rpm. The transmission needs to know
how fast the engine is running to know how to shift properly. Probably is located on the back of the bellhousing at the top and senses the ring gear passing the pickup. Otherwise may be on the injection pump drive gear housing.
I had the same problem on my Isuzu, The tranny wouldn't shift correctly and lockup right. The engine rpm switch sensor was bad. Luckily that only cost me $65 to fix and save a $7,000 transmission repair that wouldn't have made any difference.
Like I said, Just a wild shot.. Good Luck....
Len,
With the information that you have provided, the first thing that I would do is to run a resistance test on the TPS. I would do this with an analog meter to be certain that there are no skips (digital meters can have a hard time picking this up). If that checks out and all connections look okay I would try to get some documentation about the VIM. If you can't find out what signal the VIM should be sending or what signal the ECU is looking for you are dead in the water. I will look in some of my service manuals tomorrow to see if I can find out what the tranny wants to see on that input.
hth, Tq
Len,
Try these steps first:
Disconnect all your battery cable connections. Leave them disconnected for a minute or two, re-connect and test it.
Check all trans harness connections that you can see, make sure they're clean and secure. Check for damaged pins too.
Check the same for the engine TPS.
I have the troubleshooting manual that you are looking for.
Send me a copy of your motorhome schematic if possible - Adobe .pdf
I'll be glad to help you.
Let me know how you make out.
Sammy
If the trans operates off the engine ECM/TPS (assuming engine control) then the engine ECM would set a code also.
If the code is showing a TPS fault, that'd be the first thing I'd look at...not sure about a trans TPS, but as others have stated, the TPS is probably not too expensive, and easy to check for faults....if you know the range of resistance. If it's mounted on the engine or under the drivers floor, it may be weathered and failing. The wiring connectors near, and connected to, the TPS would be a good place to start your search too.
I would think (this can be dangerous) that the TPS would be easy to find and rule out.....if the throttle is a TPS controlled unit, and the engine runs OK....Major Bummer. I defer to Sammy and Torq. Gonna get more tedious. ;) This is a SWAG, but if the engine is mechanical (this may not be what you mean by "mechanical), where is the TPS for the trans? Is it on the engine or mounted near the accel pedal...or is there a mechanical link between the engine and trans (like a "kickdown cable"), with the TPS in the trans..or on the side of the trans?
If your throttle linkage is a rod, cable, or some sort of non-TPS gizmo? Could the coach have a TPS for the trans only stuck onto a link in the throttle linkage? If you have a "fly by wire" engine with an ECM and com-link between the engine and the trans....good luck, the problem could be wiring...
Post what you find...JR
Thanks folks,
The engine is mechanical (non-electronic) The TPS is cable operated from the governor and mounted on the engine. It appears clean and mechanically functional. I don't know what resistance to expect and haven't yet checked that.
Sammy, I am a retired telco engineer and somewhat knowledgeable in systems wiring. This is the worst schematic I have ever seen. The entire coach and chassis with every possible option (including 3 different engine/trans) is on one sheet, reduced to B size and a tenth generation copy at that. Even with a magnifying glass, I can't read most of the pin outs.
The wiring harness on this coach also appears to include every option. There are several unused connectors here and there but few readable labels.
I'm also not sure how the ECU gets the road speed info. The schematic looks like it comes from the speedo sensor on the LF wheel but the Allison books shows on in the rear of the trans. Not really a problem because road speed seems to work OK.
Torquester, Documentation on the VIM is just what I'm looking for. Is the VIM typically provided by Allison or a third party? I haven't even found it yet, though I think it's up front under the television. I have to tear half the coach apart to get to it. (I can see the ECU under there but haven't gotten to where I actually put my hands on it.
So, that's what I'm looking for; typical resistance readings for the TPS, typical wiring from the TPS to the VIM to the ECU.
Any help is greatly appreciated.
Len
Len, check your e-mail, I sent you some info.
Let me know if there's anything else I can check for you.
VIM is sometimes incorporated into the OEM vehicle wiring - not always in a separate black box.
Best of luck with your repair.
Sammy 8)
Len - not trying to be a smart a$$ - but just a reminder that well over half of these type failures posted on the boards end up being corrosion, cracked or broken pins, harnesses, etc. - I'm sure you've already checked, but I just couldn't help the reminder after reading "I had the local Allison shop look at it and they said it was not seeing the TPS." - HTH
AS full disclosure I'll admit this month to the following errors this month alone:
1) replaced garbage disposal and forgot to drill dishwasher plug!
2) replaced water heater - shut off breaker at panel and my W/H miser switch (belt and suspenders) - switched only the breaker - no hot water - took me a few hours to figure that one out - DUH!
Len,
The resistance range for the TPS could be just about anything. I wouldn't be to concerned about the actual values at this point. I would just get a min. and max. reading and make sure that the entire sweep is linear (watch for glitches). If you could get this reading at the input connector to the VIM it will help rule out connections and cable to that point.
It would be my guess that the VIM is a not supplied by Allison. Let us know when you get to the VIM as to what it says on it (make, model, etc.). With the information that we have that is about all I can help with right now. Standing by.
p.s. If this was a bus, we wouldn't be having these problems now, would we? ::)
I'm learning a lot which means now I know less that I did before. A kind gent from the Diesel RV board sent me the entire troubleshooting manual and I have a better feel for it now. I think I was mistaken in believing that the VIM had something to do with the problem. Now I see that the TPS does not go through the VIM and may not even be the problem. I was only going by what the Allison tech told me.
Now it looks to me that code 66 is a serial communications interface problem but this is a mechanical engine. What would the SCI connect to?
The diagram just shows a twisted pair going into thin air.
Could it be that the ECU just needs to "be told" that there is no serial connection with this engine? Or is there some other device somewhere to simulate the serial connection?
I'll do some more digging after Christmas.
Thanks again,
Len
OK guys, I'm making a little progress but still need some help.
Sammy was kind enough to send me the TS info for fault code 66 and I now have the whole book.
The problem now is that the Vehicle Interface Wiring (VIW) connector does not go anywhere and never has. It's just coiled up at the trans ECU.
I talked to the Allison folks in Ocala, FL but not much help over the phone.
BTW the tech did tell me to cut the ground wire (wire 144) to the ECU, said it was a mod from many years ago. I did that but no joy. Hope he is right.
Anyway, it seems to me that since Vogue did not connect this cable to anything that there is probably a way to tell the trans that there is no serial connection to the engine.
Any more ideas??
Thanks,
Len