8V92 DDEC1

[PCC]

I am the slave to my 8th coach; a 1988 Prevost with 8V92 DDEC1.

New engine has 40K on it, and after driving it for a few months, it developed a hiccup, like a sensor shutting the engine down for less than a second, but only at idle.

Then one day I left the batteries on overnight, and had to recharge the batteries. Started the engine and no hiccup, until I closed the battery drawer.

I shut the engine down, and re-opened the battery drawer to find that the 12v cable had been installed leaving the terminal the wwrng way, and the wire had been rubbed raw against the stainless steel framework and shorted out. (Left a 2" hole in the frame)

So I corrected that problem, and now it will not start at all.

Could that short have damaged the DDEC1 ECM? They tell me that those units are like a tank, but I cannot find anything else that would cause the coach not to start.

The ECM is a very old model; can it be replaced with a later/different version?

When I began trouble-shooting the no start, I did find the breaker (5A) to the ECM was tripped. I reset that, but it still will not start.

I have done too much work on this coach to stop now, so I hope to get some ideas. This is a new one on me, but then, in this realm, isn't every day a day of discovery !!!

[luvrbus]

Check your ground and power supply for 11.5 volts probaby just a fuse and you can upgrade to a later DDEC if you choose 



good luck

[robertglines1]

check to see if the breaker is bad jump around it temporary..I have a 89 pre 8V92.... Also ck to see at least 24 volts on batteries..also inside the passanger side rear bay on frame rail there are another set of breakers just before your 12volt or dedec controll switch....I have forgotten to turn this switch on before and the engine will crank but won' start.Also the control box located in the same area bolted to the ceiling has a reset button it...You can go to prevost coach and download a wiring diagram to your coach .....need serial # last 4or 5 numbers I think. Good luck..let me know what you find.....ck rear front start position on your rear junction box.

[PCC]

Thank you for your responses. I have the wiring diagram, and have spoken with mechanics, and Detroit Diesel, and everyone is purplexed by this.

All voltages are all good, so am I understanding that these ECM units and the EDU, are reasonably fireproof? If so, what else could shut down the system?

Anyone's thoughts.

Thank you

[luvrbus]

Have you checked to be sure that the engine is getting fuel

[Busted Knuckle]

PCC,
There should be 2 wires going from just 1 battery (12 V) for the ECM.
More than once on MCI's & Setra's I have found the inline fuse holders on these wires to be bad.
I've seen them badly corroded and not making contact, wire broken in the hard plastic and so on. I'd temp bypass the inline fuse and try it.

I saw you mentioned a breaker, I'm not that familiar with Prevost. It could be they have a breaker instead of inline fuses. If that is the case I'd bypass the breaker. If it works you know where the  problem is.

Maybe some of our DDEC wiring gurus can chime in and help with post #'s etc and you could go straight from the battery to the correct posts on the DDEC. If it then started work yer way along the path til you find yer short.
FWIW  BK  

[Busted Knuckle]

Have you checked to be sure that the engine is getting fuel

Good point also Clifford!  
  BK 

[PCC]

Thank you for the fuel suggestion. I have a friend coming by to be sure that the fuel tank, while not empty, is not leaning forward sufficient to move the fuel away from the pick-up; it is a kneeling coach.

I understand that the fuel is used for balast, and so a minimum of 5" in the tank is required, or the sensor will shut down the engine, and the tank sits over the front axles.

I love converting coaches, but these mechanical dilemas sometime get the best of me. Gald I can come here and ask my questions of those who have been here before.

Thank you

[PCC]

Another issue with my coach is the DDEC DDL terminal does not have any data wiring, so the tester simply read "No Data"

Does anyone know which terminals from the ECM are for data, so I can wire these terminals to the DDL connector for testing?

The data is supposed to appear on DDL terminals J & K, and these terminals have no wires at all !!

Thank you Prevost - DD instructed them to install these wires, obviously after my coach was built !

[expressbus]

PCC,

I have a Prevost but have not encountered your problem. Now having said that I can tell you I did have an experience with the coach not starting. Someone mentioned the front/rear start toggle and button. I was doing work in the engine bay and did not want to go into the coach and start it then come back out, then go back in. you get the picture. Well I flipped the toggle on the outside right hand of the 24 volt cabinet in the engine bay to rear start. The push button worked just fine and when I was finished doing the work, which was cleaning the oil off the fan blades, but that is another story, the engine would not fire from inside the coach. I too was very perplexed as to what I had done. Turns out the toggle switch, in the adverse environment it lives in will actually get dirt, oil, corrision you name the method of losing contact between the blades and it can be found in the engine bay. Cheap way to fix it is to throw the toggle bottom to top back and forth several times. This usually cleans the contacts enough to get you back in business again. Hey, if nothing else you are not out any money for having tried it.

Saw you had to charge the batteries. It is also possible reading the voltage at the batteries is not giving you the information you need, in fact it may be misleading you. Battery voltage needs to be tested under load to determine if the battery is good or bad. You could be seeing a high enough voltage with a volt/ohm meter that you conclude the battery is good but have insufficient voltage to crank the engine. I also think there is a voltage below which the DDEC I will shut down so no harm comes to engine or transmission. That bears checking because I do not have DDEC I in my coach.

[PCC]

Voltage sensor??

So when I first tried to start it, with low voltage, it would have shut down. After I re-charged the batteries, and had enough voltage, does it reset itself?

I know it spins well now, and starts on ether.

I have so many more ideas now - I needed something to do on Monday !!

Thank you

[rv_safetyman]

Pete Papas was kind enough to send me this information:

[gyrocrasher]

Voltage sensor??

So when I first tried to start it, with low voltage, it would have shut down. After I re-charged the batteries, and had enough voltage, does it reset itself?

I know it spins well now, and starts on ether.

I have so many more ideas now - I needed something to do on Monday !!

Thank you

Forgive me if I am being obtuse; but if it starts on ether, does that not indicate a fuel problem?
Mitch

[PCC]

Yes, Mitch - It is either fuel, or ECM - Wish I could be sure, so I am going to check fuel first, though with a voltage problem, like the ECM shuts down and does not reset, the engine will get no fuel.

So I keep eliminating the possibilities.

[robertglines1]

with my 89 prev it is very sensitive to water level and oil level both will keep you from starting.will turn over and not start..again if you find the problem please post'