8v92 DDEC II ECM Needed

stevet903 · August 22, 2010, 07:36:41 PM

This one has me stumped and has put me to the side of the road a couple of times. I have an 1989 XL with an 8v92, DDEC II. 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, and the power resumes like nothing happened. No smoke when this happens. This used to happen occasionally, and only when the cruise control was on. Now it happens with cruise or normal driving. Mostly on the highway, and seems to be happening more often. It also seems to happen after 4-5 hours of driving in hot weather (mid 90's). Today, it kept happening when I lifted out of the throttle and it would only run at about 15 mph. Pulled over, shutdown and restarted, wiggled the ECM wires to see if I could make it happen again (no change), and it ran fine for another hour until the next stop.

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. I've tightened all connections on the front and back junction panels. It happens if you start from the front or use the rear start switch.

I figured that since it looks like the light sequence that happens when you start the engine, I replaced all the relays in the ignition and engine run circuits, and replaced the rear start switch. Figured I couldn't go wrong with those, seeing as it is 21 years old. No change though, still have the problem. Engine runs great otherwise. Any one ever have this happen to them and know of the fix? My gut feeling is that the ECM has a heat soak issue, since this only happens after driving for a while and only in hot weather. Anyone have a 8v92 ECM for sale? The part number would be a 7570050-141 or 7570050-154.

Steve

hargreaves · August 22, 2010, 09:44:36 PM

Steve, just because you have good voltage at the ECM does'nt mean the connection is good. The injector drivers in the ECM require a bit of current. I would check the fuses that power the ECM. Also check the grounds.

If you can get a spare power connector for the ECM you can make up a Jumper. put some alligator clips on the ends and hook it up to a spare battery, drive it for a while and see if the problem goes away.

A lot of ECM problems revolve around the power source and the fuses.

belfert · August 23, 2010, 04:37:13 AM

Check for any possible inline fuses. I think Ace found some in his DDEC wiring that were causing problems. The fuse connections could be corroded.

There are often DDECs on Ebay for sale if you really need one.

robertglines1 · August 23, 2010, 04:49:33 AM

I have a 89 XL like yours..the only ecm problems I had is a bad 12 volt switch localed next to the vanner in the rear curbside bay ceiling..also one battery went weak on 12 volt feed for ecm and dropped the voltage bellow the 11.7 volt required...if head lights go out also sounds like the 12 volt feed . Also ck grounds where they are welded to frame...there isn't any thing that would make heat build up in front lower compartment with your Ecm relay? just a few thoughts.Please post outcome...Bob after thought..front rear start selector switch located in/on side of rear junction box...contacts do fail or get corroded in old switches...

blue_goose · August 23, 2010, 05:09:43 AM

I had the same type of problem with mine and was losing ground. Never a code when it happened, but would shut down and then restart when I came off the throttle.
Jack

Len Silva · August 23, 2010, 05:17:48 AM

I don't have the real time experience of others here, just electrical/electronics in general. , I agree with the others, an actual ECM problem would be the last thing on my list. Power and ground would be first, followed by bad or erroneous sensors.

Busted Knuckle · August 23, 2010, 06:46:35 AM

As Brian mentioned, Ace & I have both had problems with the ECM fuses!
I think Ace had a bad fuse that looked good, but I don't remember fer sure.

I know we had one that'd do almost just like yours but got so bad it wouldn't pick back up after letting off the throttle.
It was bad corrosion in the fuse holders in the battery compartment and if I shook those wires all would be fine for a while. I ended up replacing the fuse holders and never had a problem after that!

Also I have a rebuilt ECM on the shelf, bur don't remember what it cost.
I'll check the #'s and make sure it's the one you need and see what we paid for it, and reply back here.

BK

stevet903 · August 23, 2010, 06:02:49 PM

Thanks for the advice everyone. I spent most of today going through the battery connections, the grounds, and the power connections to the ECM. I cleaned all of the battery connections (24V system, 4 batteries, about 20 connections), as well as the entire power trail from the batteries to the ECM. FYI, this has circuit breakers for the ECM power and a fuse for the ignition wire circuit. Unfortunately, nothing that I saw looked corroded or even dirty enough to cause a problem, but I cleaned it all anyway. I figure it's cheaper than an ECM !! I'm heading west, in the St. Louis area, now, so we'll see if it continues to happen when we get on the road again on Thursday.

Steve

Sam 4106 · August 23, 2010, 06:41:28 PM

Does anyone know how many versions of the DDEC II ECM there are? Mine is 7570050-111. I have heard both 7570050-141 and 7570050-154 mentioned before and wonder if I have a really early version. I wonder if I upgraded to the later version if my performance would improve. I have been told that the PROM is all that needs to be changed for the upgrade. Anyone know for sure?
Thanks, Sam MC8

stevet903 · August 23, 2010, 07:20:51 PM

I could never find the answer to that question. I know there is a -051 (my original version) , a -131, a -141, and the final version, -154. I know the latest version gets the odometer working which helps if you have a silverleaf. If you want to do the upgrade, the kit from DD contains a new PROM and a piece to hold it down. The part number for this is R6171618 and costs about $100 with a $50 core charge. You need to remove the ECM from the engine and take the bottom cover off, without breaking all of the 15 or 20 year old little bolts off, which is easier said than done. I did it to get the Silverleaf to work, but didn't really notice any performance or driveability changes. Probably not worth it since you have a fairly late version.

Steve

Busted Knuckle · August 23, 2010, 08:36:50 PM

Quote from: stevet903 on August 23, 2010, 06:02:49 PM
Thanks for the advice everyone. I spent most of today going through the battery connections, the grounds, and the power connections to the ECM. I cleaned all of the battery connections (24V system, 4 batteries, about 20 connections), as well as the entire power trail from the batteries to the ECM. FYI, this has circuit breakers for the ECM power and a fuse for the ignition wire circuit. Unfortunately, nothing that I saw looked corroded or even dirty enough to cause a problem, but I cleaned it all anyway. I figure it's cheaper than an ECM !! I'm heading west, in the St. Louis area, now, so we'll see if it continues to happen when we get on the road again on Thursday.

Steve

Steve I don't know if I was clear enough on what the corroded fuse holders were for on our bus or not! They were the 2- 12V feeds for the fuel injectors if one of these goes dead the engine will run (barely) but have no power!

I ain't say'n yers don't have breakers, but it would be the first in that era I saw that did! (but then again my Prevost experience is not a lot either!!!!!!)

Good luck!

BK

rv_safetyman · August 23, 2010, 08:39:44 PM

Since I last talked to Sam, he has apparently had his ECM read by someone. His 111 version not only did not have distance (MPH, MPG, etc.) but it was also missing other data as well. That is the first time I have heard of things besides distance missing.

Along with Steve's solution, there is a DD upgrade kit to DDEC III. I think it is about $1k - 1.5K. Pretty expensive, but better than replacing a DDEC II with the same thing at a DD dealer. (If you can). I sure got bit trying to mix and match engines and ECMs. If you have to replace the unit, and you buy a used DDEC II ECM, be sure that you have it read and understand how it is set.

I am not sure how DD handles the upgrade. When I went from DDEC III to DDEC IV (only way to get J1939 for my transmission working), they simply off-loaded my DDEC III settings and installed time in the DDEC IV ECM. It might be possible to talk them into installing a higher HP setting in the new ECM. They are reluctant to do that within the same ECM (emission issues probably). However upgrading may make the HP increase possible.

BTW Sam, I got the returned VMSpc but have not had a chance to write the check. Currently away from the office for a day or two.

Jim

stevet903 · August 24, 2010, 05:37:50 AM

Jim - good to know on that version of the software. In Sam's case then, upgrading the PROM would be worthwhile to get the VMSpc data.

Bryce - I went over the electrical system with a fine toothed comb, tracing everything to the ECM. The injector power ends up on a six pin connector on the ECM - 4 12V and 2 ground. The 12V supply comes from the 12V battery terminal, through the 12V cut-off switch, to the rear 12V bus bar in the rear electrical compartment above the engine. It goes through two circuit breakers and out through a round connector on the right side of the electrical box. These two 12V feeds split into 4 in the harness on top of the engine just before the power connector. The two grounds are fed from the ground battery terminal to a ground stud on the bottom of the electrical compartment. The two grounds wires are connected to the ground stud, run through the same round connector on the side, through the engine harness to the power connector. The ignition wire power source is taken on a different 12V wire directly to the battery post - no switch - then through a 15A fuse in the rear electrical compartment. It then moves to the front of the bus, through a pair of circuit breakers in the lower compartment ATEC/DDEC junction box. There it provides power for the ATEC computer and becomes Prevost circuit 202, ignition power, which ends up as DDEC circuit 439. Hope this helps someone troubleshooting an XL sometime!!!

Steve

Busted Knuckle · August 24, 2010, 05:53:19 AM

Wow Steve nice job, good detail and very informative!

You definitely know a Prevost better then me!
Again, I'm more used to SETRA's and MCI's of which all of those did the same as your ATEC / Ign wire and come straight off the battery into an inline fuse holder then to the ECM for the 12V injector feeds.

Wish I could help more, but you've covered what I would have.

Might wanna go over to BNO and see if Pete can be off assistance! He is the DDEC guru!

BK

Sam 4106 · August 24, 2010, 06:26:02 AM

Hi Steve & Jim,
Thanks for the additional information. I called the local DD dealer and they wanted $125 for part # R6171618. I don't think the person I spoke with was very knowledgeable about DDEC II and didn't mention a core charge. I didn't have my ECM read, the number (7570050-111) was on a tag attached to the ECM.
I had a power to the ECM problem recently so I will share what I found. My 8V92TA DDEC II is a transplant into a "76 MC8 and the power to the ECM was provided through a relay between the batteries and the ECM. The contacts became corroded and made intermittent contact until they failed to make contact at all. I took that relay apart and the contacts didn't look bad but they wouldn't pass current. I removed that relay from the circuit because it wasn't shown on the schematic. The engine has started every time since. Steve, you mention a 12 volt disconnect in your wiring system, you may want to check the contacts in that disconnect. You may have the same intermittent problem I had. Just a thought.
Good luck, Sam MC8