Need Help DDEC II

Sam 4106 · June 10, 2012, 07:19:27 AM

Hi all,

We are at a rest area just north of I-29 and Hwy 34 near Glenwood in western IA. We have an electrical problem with the DDEC II . It started with the cruise kicking out and progressed to not having any throttle. These problems are intermittent, but I don't feel comfortable continuing with this situation. Bus is a 1976 MCI 8, with 8V92 TA with DDEC II and 740 Allison transmission (non-electronic). Any guidance would be greatly appreciated.

Thanks
Sam

hargreaves · June 10, 2012, 08:03:45 AM

Does your bus have a throttle cutout when a door is open?. This could be the cause. Cheers Gerry

Brian Diehl · June 10, 2012, 08:07:08 AM

Sam,
Have you tried going through all the connectors from front to back disconnecting them and reconnecting them? Start with the wires feeding the front controls from the computer in the back. Then pull apart the connectors on the computer and re-seat them.

Just some ideas ...

rv_safetyman · June 10, 2012, 08:12:25 AM

Sam, sorry to hear about your issue.

I would give very strong odds that you have a computer electrical connector that needs to be cleaned/re-seated or a bad system ground. Like the later DDEC version, DDEC II uses wire 953 as the "ground" wire for all switches/controls. I don't think 953 is attached to the bus ground system, rather it is a DDEC system ground.

Try removing each plug from the ECM and then reattaching. Do it several times. If you have contact cleaner spray it on the connectors.

OOPS, Brian and I posted at the same time.

Jim

luvrbus · June 10, 2012, 08:14:37 AM

Probably dirt build up at the roller and rail on the TPS blow it with air then it should be good to go

Sam 4106 · June 10, 2012, 09:52:43 AM

Hi all,

Update: I found a couple of loose screws on a terminal block under the dash. I didn't think they were loose enough to cause a problem, but we decided to try again and within a short distance the throttle kicked out 3 times. After that it seemed to work fine for several miles around 1500 rpm. I increased the speed to about 1700 rpm and we traveled for 50 or 60 miles before the throttle started kicking out again. We were within sight of a Rest area when the engine stopped completely. After a minute or two, the bus restarted and we made it to the rest area. I have checked the connections in the rear electrical panel for the engine and found nothing loose or corroded. There are some other terminal blocks in the front electrical panel that I will check next. There are also some terminal blocks in a junction box on the right side of the engine that I will check.
I have checked the roller on the throttle. There is not any dirt built-up. The roller turns freely and there is no dirt on the pad. Thanks for all the help. I will update again if I find anything.

Thanks
Sam
PS: any other suggestions would be appreciated.

Sean · June 10, 2012, 11:44:15 AM

Quote from: Sam 4106 on June 10, 2012, 09:52:43 AM
... I have checked the connections in the rear electrical panel for the engine and found nothing loose or corroded. There are some other terminal blocks in the front electrical panel that I will check next.

Sam, the connections you need to check are at the DDEC unit itself, not in the electrical panel. The DDEC box is mounted to the top of the engine and should have a fuel line going to it (how the computer is cooled). There are two connectors on the side which are dogged down with 1/4" bolts. Loosen the bolts, pull each connector, clean with contact cleaner if you can, then reconnect and tighten the bolts.

-Sean
http://OurOdyssey.BlogSpot.com

hargreaves · June 10, 2012, 12:38:56 PM

The TPS could also be bad. Gerry

hargreaves · June 10, 2012, 12:45:43 PM

Did you check the connector coming from the TPS? Cheers , Gerry

Sam 4106 · June 10, 2012, 01:01:46 PM

Hi guys,

I removed all the connections from the ECM and saw no corrosion as well as checking all the connections that I could find. We drove another 20 or 30 miles without incident, but then had the same problem again. I can get the throttle to respond by letting up and reapplying it.We made it to another rest area (the only places we have computer Wi-Fi) I don't have any contact cleaner but we are only 10 miles from Sioux City,IA So I may be able to get some in the morning. I am going to remove the connectors Sean suggested again to see if we can get to a campground for the night. Wish us luck.

Gerry, yes I checked the connector at the TPS if that is the one at the throttle petal.

Thanks for the help, Sam

hargreaves · June 10, 2012, 01:06:24 PM

sounds more and more like you have a bad TPS sensor. Cheers Gerry.

luvrbus · June 10, 2012, 03:35:33 PM

Sam do you have a reader like a Pro/Link if the TPS is bad I seem to remember you need one to read the code 21 or 22 on a DDEC 11 it won't flash on a early model DDEC 11

stevet903 · June 11, 2012, 04:30:40 AM

I have the exact same problem on my DDEC II. After trying all of the suggestions here (and more), I finally found out what is going on - heat. Is it hotter than usual where you are traveling? Mind starts acting up when it is over 85 degrees out and it runs for a while (it usually takes a couple of hours). It seems that the ECM gets heat soaked and kicks it out of cruise control, and then doesn't respond to the throttle. After you pull over and it cools down it will run for a while again. To se if this is the problem, get a towel, soak it with water and put in on top of the ECM. I've found that it will run fine until the water evaporates, then it will act up again (just keep wetting the towel!!) Seems that the cure for this is a new ECM.....

Steve

PS, Make sure you don't have an exhaust leak in the area of the ECM that could be heating it up...

edroelle · June 11, 2012, 05:36:45 AM

I also had the same problem, but on a DDEC III. I limped to the Detroit Diesel shop in Canton, Ohio, where they could find no problem. So, I had them change the throttle position sensor. That problem has not reoccurred.

I also had other intermittent problems. As Sean suggested, I removed the connectors from the ECM and sprayed them with electrical contact cleaner. I also applied a SMALL amount of dielectric grease to the contacts. This corrected the intermittent problems completely.

The problem will get worst. If you have to be towed or pay a shop, it will be much more expensive than the $100 or so for a new TPS.

Good luck

Ed Roelle eight one zero, five one six, nine eight eight eight
Flint, MI

Sean · June 11, 2012, 09:33:02 AM

Quote from: luvrbus on June 10, 2012, 03:35:33 PM
Sam do you have a reader like a Pro/Link if the TPS is bad I seem to remember you need one to read the code 21 or 22 on a DDEC 11 it won't flash on a early model DDEC 11

FWIW, I have a DDEC reader and we're in the Sioux Falls area for a week or two. I'd be happy to lend it to you; it's a short drive from Sioux City.

-Sean
http://OurOdyssey.BlogSpot.com