[BusNit]

I have been going through a stack of repair receipts on my coach. Previous owner had the ECU replaced a couple of months prior to my purchase. On the W.W. Williams invoice it shows the ECU as a DDEC IV. It shows pre 98 series 60 programing. How can I tell if that is the case? They paid $4600+ for the ECU swap and programming. I do know when I plug in my VMSpec dongle to the DDEC port up front, it gets power but no communication.  (So this is a two question post)

[MrE]

My assumption would be that W.W. Williams changed the ECU programming from a pre-98 series 60 to programming for an 8V92. I would try plugging your VMSpec dongle into a DDEC port in the engine compartment. CANbus isn't rocket science, you have a positive, negative, CANbus high, and CANbus low that will feed all the information to your VMSpec.

If your engine compartment DDEC port works, you will only need to run a twisted pair for the CAN high and CAN low to get your driver's compartment DDEC port to work. You already have the positive and negative connection, just missing the communication. Pin-outs are easily found with an internet search.

[BusNit]

Thanks Jon. Where do I find the engine connector? I looked but haven't seen it. My coach is at a repair shop so I can't do much until I get it back. I do know that the coach sat alot at the previous owners covered storage facility. (He owned the facility) Curious why an ECU would fail and how I can prevent a future wallet wiping action! Complaint was he had no throttle and had Detroit tech come out to the storage yard, swap out filters with no luck in getting it to run. Had it towed to Phoenix W.W. Williams in April of 2021

[encantotom]

There is no decision port in the engine compartment on your coach. The vms pc should work using the rectangular plug ip front. Make sure you have the communications set up right on it

Tom

[MrE]

So I did some further internet sleuthing into your problem. I have additional questions;
1. Has VMSpec ever worked in your coach?
2. Did the coach ever run properly after the ECM was changed?

Your engine originally came with a DDEC III ECM and there are known issues replacing the DDEC III ECM with a DDEC IV ECM. GOING FROM A DDEC III TO DDEC IV ECM?

Here is a link to the DDEC IV APPLICATION AND INSTALLATION MANUAL on the WOG forum. There is way more information in the 749 page pdf than you'll ever need but it should give you the information needed to diagnose your DDEC diagnostic port you're using for your VMSpec.

This is an image of the connector guide from the Silverleaf website. 

[BusNit]

Thanks Jon! I will look into the socket once I get the coach back. (in about a month!). Bus ran great and still does. VMspec never connected to the app or showed not found. I'm not sure which DDEC it is supposed to be other than the II. Engine I believe is a 1991 build. I do have a handheld MPSI scanner but never tried connecting it. Regarding the DDEC ECU, would W.W. Williams be able to tell me exactly? it was repaired/flashed at the DD in Phoenix. I can bring them the receipt.

[MrE]

My SWAG (scientific wild ass guess) inclines me to believe that when W.W. Williams replaced the ECM, they failed to correctly connect the CAN high and CAN low wires from your DDEC port to the new ECM.

[encantotom]

simon, i have a scanner that works up to ddec2 i believe. would have to see if it does ddec3.

tom

[Richard]

Like Tom said. Think horses not zebras when you hear hoof beats. The vmspc is picky on baud rates and usb port when setting it up. Get those wrong and it will not communicate with the ecm.