92 Prevost DDEC 2

[gyoder]

can a bad ECU in a ATEC Allison transmission keep a 8V92 DDEC II in a 1992 Prevost from starting,
   I am working on a coach for a friend, he put batteries on it and crossed the terminals, it has not started since, it will turn over but not start, someone told me the transmission will keep it from starting,, we pulled the codes from the ECM and it is not setting any codes, it is communicating good, I don't have a card to read the ECU of the transmission,,,,,,,, i am at my end with this thing

[luvrbus]

2 fuses 1 from each head check those

[gyoder]

I have looked for those 2 fuses and looked in the book, can you give me a clue to where they may be?

[dickegler]

I have a 92 prevost and the ddec fuses are located in the rear electrical junction box above the engine.  They are resettable circuit breakers.

[Ace]

Mine are located right on top of the start batteries. One for each head of injectors.
Problem is, I had one blown and mine still started! Didn't run for crap but it still started! Doubt those two fuses are your problem. There are other circuit breakers but each coach location is different such as XL,  le mirage, and H


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[robertglines1]

See you are new to board. The more you share the more people will answer. general location and first name would be start. prevostcar web site:  go to wiring diagrams: from your serial number use last letter and last 4 digits =will give you diagram specific to your coach.  More info better from you the better.   Bob

[luvrbus]

If it is turning over as you say the transmission has nothing to do with it, you have no power to the injectors is the problem could be a bad sensor by pass each sensor and see if it fires are you sure the guy hooked the leads up after changing batteries ? 
Those are 12v only if he gave it a 24v jolt then it will be the fuses

[gyoder]

I finally found the in-line fuses above the batteries, they are good, there is good voltage coming to the ECM, we pulled the codes out of it and all is good, its not setting a code.
this coach has 82,000 on it and it hasn't cranked since 08, the gentleman that owns it isn't able to drive anymore, he had a guy put batteries on it and he put one battery on backwards causing a reverse voltage spike and it hasn't hit a lick since. I called a ECM place and he told me that an ECM can communicate but still not send power to the injectors.

I am an eagle owner, i built mine from scratch in the late 90s and have put 300,000 miles on it, it is a model 05 1969, this is my first experience working with a DDEC

[robertglines1]

ck this: curb side rear bay, see if there is a separate switch on the ceiling that needs to be turned on also. Also a reset button on it.  Also ck fuel pressure switch left rear side of engine for loose wire.  Also low coolant will let it crank but not start. Level must be above level of sensor located thru and above left rear engine door-look up.  ???orignal seated coach?? converter??  xl??   ck fuse holders for corrosion.   Bob

[PCC]

It is possible that the ECM can fail, preventing the engine from starting.

It happened to me, so, after checking fuses, and power to the ECM was able to rule out everything else, and it was the ECM.

[stevet903]

Turn the key on, do the Check Engine and Stop engine lights come on for about 10 seconds and then go off?  When it stops, is the stop engine light on?  If they come on and go out, it means that you have power to the DDEC system, and there are no codes.  If the lights stay on for 20 or 30 sec and then go out, you have a historical code.   If the stop engine light is on when it stops (or it doesn't start and the light is on), the DDEC system has shut it down.  There are three things that will shut you down -
Code 43, Low Coolant, Code 44, Oil or coolant high temperature,  or code 45, Low oil pressure.
The transmission ECU should not affect the ability of the engine to start.

Do you get any smoke while cranking?  If it hasn't run since 2008, I'd put new filters on and be sure they are full of fuel and the engine is primed. 

[expressbus]

Going to the bus barn this afternoon. I'll take a picture of a relay that kept mine from starting spring a year ago. The engine would turn over and produce whitish smoke but would not fire. The relay (mechanical) is inside the large electrical box attached at the rear of the engine bay. It is on the left hand side of the box in a row of relays. On mine it was the center relay that a friend tapped while I was turning the engine over and it fired right up.

I'm hoping that is the problem with the coach you are looking at but I can't say a gentle persuasion tap will free your stuck relay. You might have to get a new one from NAPA.

[Ace]

Ok great, you found the two fuses laying on top if the batteries and you say they are good! How did you check them? If you made the mistake I made by merely looking at them, then please take a volt meter and on top of each fuse there are test holes where you can check to see if  voltage is in fact crossing the fuse. Mine looked good but one fuse was blown and looking at it I couldn't tell because the break was way down below the bottom and very very hard to see! Check them with a volt meter to absolutely sure!


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[expressbus]

gyoder,

Here are two pictures taken this afternoon at the bus barn. One shows two relays, the other the location of the relays. The relay in the black plastic case is the one that was keeping my 8V92 from starting spring one year ago. The relay in the metal case is an original relay since they supposedly do not come with a metal case anymore. The relays are inexpensive and available from NAPA and most likely other parts houses. Having experienced the condition you speak about when the coach sat for 4-6 weeks I'm thinking that the coach you are looking at could easily have a hung relay. I was told they control something to do with the setting of the fuel racks timing but don't hold me to that.

Just sayin' ...

[wg4t50]

In our experience, not DDEC, but Cummins electronic engine and control systems, when someone connects the DC reversed, you will have at least blown fuse, smoked diodes, and from there is get real costly.  As said, don't know the DDEC, but other computers do not like reversed DC, also most likely took out the battery belt driven alternator too.
ALways fun and expensive games when you see things arcing
Dave M