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Thread Title:

8v92 DDEC II Problem

Created On Saturday June 19, 2010 14:06

stevet903

Posts: 5
Joined: Sep 2009

Saturday June 19, 2010 14:06

This one has me stumped and has put me to the side of the road a couple of times. I have an 1989 8v92, DDEC II, in a Prevost bus. Once in a while, the SEL, CEL, and Cruise control lights come on while driving down the road. The bus loses power, but the lights go out if you lift out of the throttle, the lights go out, and the power resumes like nothing happened. No smoke when this happens. This used to happen occasionally when the cruise was on, now it happens with cruise or normal driving. Mostly on the highway, and seems to be happening more often. Also seems to happen after hours of driving in hot weather (low 90's). It does not throw a code. I have done the wiggle test and got nothing, voltages at the ECM are good. No bent pins, and I used some contact cleaner on the ECM plugs/terminals with no change. Engine runs great otherwise. Any suggestions?

Thanks
Steve

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GoneFishen

Posts: 1325
Joined: Jan 2007

Saturday June 19, 2010 19:08

The older DDEC 2 ecm's had a problem with 'throttle drop out'. What was generally done was upgrade to the DDEC 2 prom chip which changes to same DDEC 2 but software level upgraded to 121. The last software went to 141/ Getting a new chip and installing it in the back of the ecm and then having the ecm reprogrammed will generally fix this isssue. Make sure that the ecm you have also has the plastic triangle to hold the new prom chip is place. If this does not correct the problem a reman ecm will fix the issue.

-------------------------
DDA tech for 30 years,all 2 cycle,series 60,50 mbe also.
1995 F250, 191k mi.
Lost Wages, Nv

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stevet903

Posts: 5
Joined: Sep 2009

Saturday June 19, 2010 19:21
It has the latest prom in it with the 154 software, and the plastic triangle.... Anything else to try before a reman ECM? Thanks for your help!! Steve

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GoneFishen

Posts: 1325
Joined: Jan 2007

Sunday June 20, 2010 10:22
Test ecm. ------------------------- DDA tech for 30 years,all 2 cycle,series 60,50 mbe also. 1995 F250, 191k mi. Lost Wages, Nv

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JoeZ

Posts: 938
Joined: Dec 2008

Sunday June 20, 2010 16:05

Several times on older Prevost Motorhomes I have found problems in the ignition switch, foot pedal or the wiring going to the back. The power drops off and the ECM does a self test and the engine goes into a "limp mode." The CEL,SEL,Cruise and Engine Brake lights come on for a few seconds and then everything resumes as normal.

-------------------------
One of the last 2 Stroke mechanics left.
44 years in the business and worked on everything from 53 series to 149 series. Winding it down now...time to move on.

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GoneFishen

Posts: 1325
Joined: Jan 2007

Monday June 21, 2010 21:35
Joe has brought an interesting idea, get a v/o meter and install the probes into the ign. wire. test drive with a helper and watch the voltage to the 439 circuit. Any drop or loss to this circuit will reset as he has said. ------------------------- DDA tech for 30 years,all 2 cycle,series 60,50 mbe also. 1995 F250, 191k mi. Lost Wages, Nv

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stevet903

Posts: 5
Joined: Sep 2009

Monday October 25, 2010 22:31

I went through the electrical system with a fine toothed comb, focusing on the ignition circuit. I found nothing, but cleaned connections and replaced relays just to be safe with no change. I then did the same on the power side with no change. I saw that the power connection to the ECM had some wire splices in it and was wrapped in tape, and didn't touch it - but I bought a new power connector, pins and wire and built a new one. This weekend I finally got around to pulling the old one out - guess what I found? There were two splices after the factory splice in the wiring harness. Each was barely soldered, covered with loose fitting heat shrink and all filled with green corrosion. I also found what I hope to be the problem - one side of the 12V wires going to one bank of injectors had both wires almost corroded through, outside of the heat shrink, green with corrosion, and held together with a couple of strands of wire. One broke when I took the tape off of the outside, and the other broke with a gentle wiggle. I replaced the connector with the new one. I haven't had the chance to run it long enough to tell if this was the fix, but I am hopeful. Thanks for the suggestions - I should have pulled the tape apart long ago just to see what was under it, but ...... Live and learn. Steve

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