Need help from DDEC/ATEC integration guru

[Sean]

Well, I've just come out of the Detroit/Allison shop, troubleshooting a TPS problem (turns out to be a bad wire, which we're going to have to disassemble half the bus to replace).  While we were there, though, with the ECM out (and replaced, during the troubleshooting process), I worked on an old problem that has been with us since we bought the bus.

The issue is that my DDEC-II ECM has no idea how fast I'm going.  This isn't really a big deal, in that it does not affect operation of the engine or the coach.  The built-in cruise control feature, for example, works just fine most of the time, based solely on engine RPM.  It's a nuisance, though, because it means that my fancy SilverLeaf VMS engine display can not provide me some of the most basic and useful information: MPG, distance-to-empty, trip computer, and total engine miles.

Way back in the beginning of our history with this coach, I ran the troubleshooting procedure for this all the way down to the step that said "Replace ECM."  I stopped there, because ~$2K for an ECM was too much to fix a problem that only affects a cab display.

Well, the ECM has now been replaced, and the problem is still there.

I'm stuck now, because the next logical step is to replace the "Maximum Feature Throttle Interface," which is the black box that connects the DDEC-II ECM to the ATEC-1 ECU.  This interface is not provided by either Detroit or Allison -- it is the responsibility of the "Vehicle Manufacturer," who, in my case, is out of business.  The actual black box was made by KDS Controls of Madison Heights, MI, but I have no part number for them to track down, nor do they deal with individual operators.

I also have no real evidence that there is anything wrong with this box.  It seems to be doing the rest of its job just fine, translating the TPS signal from the DDEC into a TPS signal usable by the ATEC.

So here's where I am at, and any help or suggestions would be appreciated:

I have traced ATEC signal wire 205 (output shaft speed) from the ECU to the interface module, and the wiring checks out.  I have traced DDEC signal wires 903 and 557 (VSS open-collector and VSS return) from the interface module to the DDEC ECM and these wires also check out.

I don't have a scope, without which I am not sure how I can verify that the speed signal from the ATEC is actually present on wire 205 (suggestions welcome).  I'm also not certain what the open-collector output from the interface module should look like in order to be the expected input to the VSS pins on the DDEC, or how to test for this without a scope.  My DVM does tell me that pin 903 (VSS open collector) is putting out 5 volts from the ECM when the ignition is on (about the same as the signal voltage supply for all the three-wire pot-type sensors).

Incidentally, the "schematic" for the Maximum Feature Throttle Interface is on page 3-27 of the Allison CEC-1 troubleshooting manual.

Any thoughts?

-Sean
http://ourodyssey.blogspot.com

[Sammy]

Sean, check wires 113 and 112 on Pins M1 and L1 respectively (ATEC)-J1B connector
These are the wires that carry the output speed signal from the sensor on the trans to the ATEC ECU.
Check troubleshooting procedure for Atec code 22, this will give you a resistance value to look for also.
You need to check if ATEC "sees" the VSS - use a ProLink.
You can also use the DDEC 2 troubleshooting chart for Code 54.
Start with these checks, let us know how you make out.
Sammy 

[RTS/Daytona]

Sean

On The DDEC end

I Think your going after the wrong VSS wire

I believe DDEC 903 is a "open collector - DRIVER circuit - meant to DRIVE an electronic speedo

and

DDEC - 556 pin (E-2) Vechicle speed + and
DDEC - 557 pin (E-3) Vechicle speed -
are the actual wires from the atec tranny speed sensor

556 and 557 are usually used for cruise control input 

Pete RTS/Daytona

see my other responses on the BNO board

[NJT 5573]

Sean, About a year ago the kids spilled pop in my shift selector pad. $1700 @ DD. I found a rebuilder in Mn. that sent me one next day air for $200. (rebuilt). They have everything  I can think of for DDEC/ATEC. Looms, ECM,s etc. They treated me very well. Trouble shot some of my parts for me no charge etc. I'd be shocked if they don't have the part you may need. Their name is General Diesel Electronics, the phone is 2182624553,  I dealt with Randy. When he found out that I was a bus nut and not a truck shop he sent me a free Allison manual to help me sort things out. He even paid the postage. Go figure.

[Sean]

OK, responding to several here --

Sammy:

I've run the complete troubleshooting for DDEC code 54, that's what led me to the "Replace ECM" step, which did not fix the issue.  This procedure assumes you have a mechanical speed input, which I don't -- it's a black box between the DDEC and ATEC.    So I can't do the step "Replace VSS sensor," at least not unless I find another black box.

I will check wires 112 and 113 as you suggest, but I'm wondering how the ATEC could work properly without seeing this input.  I have no "Check Transmission" light lit on the ATEC, and a code reader on the ATEC shows no codes.  Wouldn't a failure in this input generate a code in the ATEC?

Pete:

My DDEC manual shows that 557 is the VSS return, and 556 is the signal wire for "standard" VSS sensors, and 903 is the wire for "Open Collector" type senders.  The documentation in the ATEC manual for the Maximum Feature Throttle Interface says it is an Open Collector signal and is to be connected to wire 903.  Could this be in error?

I will go read your other posts next...

NJT:

I will give Randy a call, it's worth a shot.  Nobody at Detroit or Allison can help with this box, as it is OEM-supplied (in my case, Neoplan USA in Lamar, Colorado, now out of business).

Thanks everyone.  Keep those helpful hints rolling in.

-Sean

[RTS/Daytona]

Sean

I'm just an novice at this DDEC / ATEC stuff

I believe the only thing that the ATEC tranny ECM needs/wants is TPS input -

I believe one functions of your black box (and the only function of my style Black Box)
  is to isolate and perhaps modify the DDEC - TPS signal and connect it to the ATEC

I NOW believe that your DDEC OPEN COLLECTOR speed input - is truely an alternate way
  to input speed signal - but it's input would most likely be a 0 to 5 volt pulse -
  unlike the VSS signal from a magnetic pickup on the ATEC - that type of signal is a sine wave
  that goes both positive and negative  - I would further quess that your Multi Layer Black box
  prehaps takes your ATEC sine waves and converts it to positive only pulses

If your main purpose/problem is to give a speed signal to your DDEC so that you can get
that very useful info to your Silverleaf  (GLASS DASH) - then perhaps you can - wire your
ATEC 16 pulse per rev sensor to the DDEC VSS ports and use a PROLINK to switch your DDEC
from tack input cruise to VSS input cruise ??

Pete RTS/Daytona

Perhaps you can bounce this off the Allison Tech ??

[Sean]

Thanks, everyone, for the follow-up.

Here's where I am now at:

I spent a little more time with the black box.  The frequency-to-voltage converter chip, it turns out, is counting tach pulses from DDEC wire 505, and turning them into an on/off signal (not sure at what rev, though, without scoping it) to be fed into the ATEC on wire 222.  This wire is used by the ATEC to inhibit certain shift ranges at certain engine RPM.

Wire 908 from the DDEC, which is a pulse width signal that carries the TPS value, is merely fed through a set of resistors and diodes directly to the ATEC on wires 106A, 104, and 124.

That leaves my problem area, which is wire 205 coming out of the ATEC.  This is a square-wave pulse, 16 pulses per rev, representing the output shaft speed.

Incredibly, the black box does nothing at all with this signal except pass it directly to the DDEC on BOTH wires 557 and 903.  And herein, I think, lies my problem.  I can't see how the DDEC will get any speed information at all if both of the sensor wires are shorted to each other, no matter what signal from the ATEC is tied to them.

So here's my new question:  From the open-collector circuit diagram in the DDEC book, it looks like 903 and 556 should be tied together, and the speed input should then come in on 557.  Should I just disconnect 903 from the interface and see if it works?  Will the DDEC pick up a pulse from the ATEC without a dedicated signal return path?

I definitely need to find a Pro-Link to do any further testing...

-Sean

[Sammy]

Sean, the ATEC  ECU and the DDEC  ECM should be checked with a ProLink - you can see all the parameters.
Where are you located?
You can send me an e-mail if you prefer.
Sammy 

[Sean]

Sammy,

Just to be clear, we've checked all the parameters in both the ATEC and DDEC with a reader when we were at Williams.  Also, I can see all the DDEC information on my VMS.  I need the Pro-Link to change the VSS Enable parameter, in order to test my work.  Until I fix this, I need to keep VSS disabled, otherwise I get a Check Engine and no cruise.  So for each potential fix I try, I need to enable VSS to see if it worked, and then disable it again if it doesn't.

Incidentally, the readers have been of little help here, because the problem appears to be in this mysterious interface module.

We are in the Tucson, AZ area right now.

-Sean

[Sammy]

Sean, I am in NY. I would have liked to offer some assistance.
I have a ProLink and all software needed to troubleshoot.
I have scanned some info that might help you and would be willing to e-mail it to you if you'd like.
It's an Adobe .pdf file.
It's a description of how the interface works - from a service manual.
I'm still doing more homework on this for you. I had Prevost coaches in the fleet I worked with that had DDEC 2 and ATEC, just gotta find the right diagram.
Send me an e-mail, I'll send you the file.
Sammy 

[Sean]

Sammy,

Thanks.  I sent an email to the addy in your profile.

I'll wait until I hear from you, but, based on all the advice I've seen so far, it looks like my 205 wire is simply hooked to the wrong DDEC wire in the module -- should be 556, not 557 and 903.

-Sean

[Sean]

Well, here's the final answer:

The tailshaft output speed signal comes out of the ATEC on wire 205, and this is to be connected directly to BOTH wire 903 and wire 556 on the DDEC-II.  557 is to be left unconnected.

In my case, my 556 and 557 wires were shorted together someplace in the harness.  I could not find where -- it's buried someplace deep in the coach.  However, simply clipping 557 back at the ECM solved it, and my VSS input is now working perfectly.

My next challenge is to figure out why, now that the speed signal is working right, my SilverLeaf VMS200 is still not showing mileage accruing on the trip meter.  (Engine hours are also not incrementing, so something else is amiss.)

Thanks, everyone, for all the help, and especially Sammy, who sent me copies of the relevant electrical print pages from, ahem, an unnamed coach builder, which ultimately led to the final solution.

-Sean

[Sammy]

Sean, very happy to hear your problem is solved, glad to have been able to help.
Regards,
Sammy 

[H3Jim]

Sean, I found the tech guys at Silverleaf to be very responsive to helping figure out why mine was not working correctly.  They even did a software patch and sent it to me. It turns out my "older" engine had slightly different pulses than teh solftware was looking for. I acced their help through the help board on their website - and the tech guys monitor it closely.  Good luck, its a really nice piece of sofware.