question concerning my engine swap and ecm/tcm communication

thomasinnv · April 14, 2018, 04:40:37 PM

I have spent hours poring over the schematics for both my bus and the donor bus getting ready for the engine swap. I have verified that all of the inputs and outputs between the ecm and the vehicle are on the same wires and pinout on both vehicles with one exception. the donor engine (2001 mci multi-plex system) communicates with the tcm via J1939 on wires 925 and 926. On my coach (1998 mci pre multi-plex hard wired) the ecm communicates with the tcm via J1708 on wires 900 and 901. My assumption is that there will be no issues because the ecm and tcm don't care what data bus they use to communicate on, so long as the communication is present. I don't think the ecm really cares what data bus it is using to talk to the tcm. I don't know enough about the ddec to make an educated guess though. Anyone with some knowledge or insite on the subject? Am I looking into the face of trouble?

thomasinnv · April 15, 2018, 08:11:33 AM

Nobody? I figured Clifford or Hardheadedken (i think that was his handle?) would have this one.

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buswarrior · April 15, 2018, 01:54:37 PM

Bill Gerrie maybe?

Weather is really bad all the way from the Gulf to above the Great Lakes all weekend.

Ice storms, rain, snow, repeat. Power off, trees down, shoveling the driveway...

Standby...

happy coaching!
buswarrior

luvrbus · April 15, 2018, 02:38:45 PM

I don't know about that one,it seems like the Data rate would be screwed up since the J1939 is so much faster than the J1708 and the J1708 is a 6 pin connector vs the 9 pin for the J1939, you might should call Ken or Jack ( bluegoose),Just a WAG I am thinking a TCM and a new harness may be in your future

thomasinnv · April 15, 2018, 03:08:40 PM

Quote from: luvrbus on April 15, 2018, 02:38:45 PM
I don't know about that one,it seems like the Data rate would be screwed up since the J1939 is so much faster than the J1708 and the J1708 is a 6 pin connector vs the 9 pin for the J1939, you might should call Ken or Jack ( bluegoose)

I understand the data rates are different, and you cannot combine J1708 and J1939 on the same bus, as they would not be able to talk to each other. Kinda like me trying to talk to a frenchy without knowing french. No comprende.

In this situation, both modules would be connected via their appropriate J1708 buses.

The schematic for my coach shows the ddl from the tcm (J1708) being hard wired directly to 900 & 901 on the ecm which is it's ddl (also J1708). The earlier B500 (up to around 2004/2005) were capable of using either J1708 or J1939 data buses. So...the ecm and tcm would be connected via the J1708 bus on both devices. I guess the question really is would the newer engine only try to communicate with the tcm via J1939 or would it accept communication via the J1708 bus? Would there be something in the design of the ddec to limit the tcm communication to one or the other, or does it listen for data on all active busses?

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luvrbus · April 15, 2018, 03:26:01 PM

Derrick,I didn't even try when I upgrade to the DDEC IV because my B500 is a retarder transmission and was told I needed the J1939 and harness I paid $250.00 for the TCM plus a 100 bucks for programing and 60 bucks for the harness.I figured what the hell it was cheaper than a oil change and John 316 paid 14k for the transmission and it has no miles on it

thomasinnv · April 15, 2018, 03:48:12 PM

Got my answer, I was finally able to talk to a guy at freightliner that knows ddec inside and out. It seems that both the ecm and the tcm have to be programmed for which buss to communicate on. Even though the new engine has J1708 active by default, it will be looking for the tcm on J1939 and if it doesn't find it there it thinks there isn't one. The tcm is currently setup to communicate on J1708 so even if I were to connect the 2 together via the J1939, same story there. If the engine is looking for the transmission on J1939 it won't find it. One or the other has to be re-programmed so they match. Simple solution is going to be to pull the ecm while the swap is taking place and take it to detroit and have them change the setting.

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luvrbus · April 15, 2018, 05:44:43 PM

That makes sense to me but I wanted a ECM and a TCM you could buy easy

thomasinnv · April 15, 2018, 07:24:17 PM

Ok I am losing faith in these schematics. The service manual on my bus specifically states for wtec installations with ddec connect the J1708 between the two, but I opened up the harness and the J1939 is in use. I think I'm just going to proceed with the swap and see how it plays out. If I run into a problem I will address it at that time. I also have conflicting documents from Allison. One says that wtec 3 used J1708 until 04/05 then they all went to J1939. The other Allison doc I have says ALL wtec 3 were J1939 so who knows. I'm done banging my head against the wall on this. I'm just going to proceed come what may. I'll let you know how it comes out.

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bobofthenorth · April 15, 2018, 08:55:39 PM

Didn't Jim Shepherd go through all this in great detail a few years ago? I think he'd be worth a phone call.

busfan · April 15, 2018, 10:10:59 PM

You could always do the light switch mod!

https://www.youtube.com/watch?v=ozbWf_QsPrw

luvrbus · April 16, 2018, 05:30:47 AM

Derrick, do you have the application manual those are the most helpful manuals I have when it comes to the electronics,it doses get confusing when trying to figure out who's responsibility it belongs to Allison,Detroit or the OEM good luck

thomasinnv · April 16, 2018, 07:19:48 AM

As far as the allison, I just have a couple of spec sheets with conflicting info. I had a full service manual a couple years ago but it's current location seems to be undiscoverable.

I do recall a couple guys on the board going thru some similar details concerning a B500 install a few years ago. The common outcome seemed to be the requirement for the J1939 communications. Since both engines were bolted to a B500 seems I shouldn't have an issue. I opened up the harness to the tcm and the J1939 data cable is installed with the 120 ohm resistor in place. I wouldn't think they would have went thru the trouble if it wasn't being used.

The schematics in my bus may just not be entirely accurate. Right in this year range they had some with ddec3 and some with ddec4, some with b500 and some with a few other trans.

I wish I had my usb link here, this mystery could be solved in about 5 minutes.

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luvrbus · April 16, 2018, 07:44:02 AM

Derrick, you don't need a service manual try and download the B500 application manual (Principal of Operation) it covers everything,if you still need one when I get home towards the end of the week you can use mine and make copies of what you need