8V Won't Fire

[stevet903]

DDEC engines do not have an emergency shutdown switch or a shutdown solenoid - it's all controlled by the computer. First thing to check is to turn on the key and see if the check engine and stop engine lights come on. If they don't then you have a problem at the computer end - first thing to check is power. The 12V switch in the rear will need to be on - check the battery voltage at the 12V point - I think it has to be at least 10V for the computer to turn on. Sometimes if the Vanner is bad the 12V side of the battery runs down and the engine won't start - the starter runs on 24V and it will crank fine. If that's good then check the upper middle connector on the computer. It has 6 pins - the middle two are ground, and the outer pair on either side are 12V. Sometimes the pins get corroded.

If the check engine/stop engine lights go on, how long does it take for them to turn off? If it takes about 10 seconds, there are no codes. If it takes longer, then there is a historical code. If the lights stay on, you have an active code which may be preventing the engine from starting. The reader will tell you what it is. Many things can keep it from starting, probably the most common would be low coolant level. There are a variety of other sensors that could be bad as well.

Let us know what you find!!

[gmcbuffalo]

'If the check engine/stop engine lights go on, how long does it take for them to turn off? If it takes about 10 seconds, there are no codes. If it takes longer, then there is a historical code. If the lights stay on, you have an active code which may be preventing the engine from starting."
Good info Steve. If the sensors are stopping the engine from starting, will it still turn over?

[stevet903]

Yes, it will spin until you run the batteries dead. On a DDEC engine, the computer controls the injectors to get fuel into the cylinders - but you still need the mechanical end working. The fuel filters must be flowing, the fuel pump must be pumping, the lines must be solid with no leaks for the computer to do it's job.

[Will Garner]

Tom,

Did that one right away. Same result except now I was standing in the smoke field from trying to get it started!

Cough, cough ...

[Will Garner]

Steve,

Fortunately I installed an on board charger unit so I won't be having that problem. First thing I've got to check is that power is going through the circuit breakers to the DDEC II ECM. If the power is not going through then the breakers are either tripped (don't know where the rest buttons are) or they have failed completely. Since it smokes it is getting fuel - the old where there is smoke there is fire expression seems to apply here. I'm leaning to electrical since it went from fine when being put back into the barn to the next time trying to start it, not being fine (not starting). I had not noticed any reduction in performance on the last run. In fact it seemed to run better. That could have been since we left the 5,800 pound toad at home on that trip.

Anyway, I've noted your advice and will be checking all of it come Saturday.

Thanks,
Will

[Will Garner]

Greg,

Good to hear from you. The Check Engine light extinguishes in less than ten seconds. Its off before "Suzie" finishes her system checks. I read the codes and there were no reported active codes. I've never cleared the unit's memory so there are historic codes.

[Will Garner]

Jim,

I'll try unplugging the DDEC cables first. That sounds too easy to be the solution so I'll do it first. It is also easy to access. While it is unplugged I'll check for any corrosion on the connector pins that could be the culprit. Then I'll move on to the more difficult and challenging suggestions.

Thanks,
Will

[stevet903]

Be careful not to break the clip off of the top of the connector. A small flat bladed screwdriver inserted under the clip (90 degrees to the wire) is all it takes to release it as you pull it away from the computer. Flat, no need to pry up. The best way to do this is to take the injector connector off first (the one closest to you, looking at the computer), then insert the screwdriver further to take off the power connector. That way you are not trying to wedge the screwdriver in there over the injector connector. Ask me how I know this. On the other hand, even with a broken clip, it seems to stay connected with no problems....

[Will Garner]

I'm pleased to report the 8V is alive again. So what was the culprit. OK, I'll fess up, I did not do this alone. I called on some friends from the local equipment shop. After discussing the sequence of events I was asked to go into the coach and simply turn the ignition switch on - not try to start the engine. I thought, "Hey I can do that!" So I did. They asked me to do it a couple of times and I did. Then they asked me to try and start the engine. IT STARTED first try.

Now some of you may be asking what did they fix. Well technically nothing. What the one tech did was simply listen to what sounds there were in the engine bay when I had turned on the ignition switch. What he did was tap on one of two electro-mechanical relays. It seems that the relay was stuck and tapping on it freed it to operate normally. I got a replacement relay from NAPA and now have a spare on-board.

The relay for those of us with very experienced coaches, pre-digital multiplexing communications and solid state control boards, the relay is located at the upper left hand corner of the 24 Volt electrical cabinet mounted to the back wall of the engine bay. The bad relay has been there since the completion of the coach by Prevost in 1990. It was manufactured by Bosch in Germany.

To those who provided guidance and shared their experiences with 8V's I thank you. It really felt good to hear the sweet melody of an 8V coming back to life.

[phorner]

Will,

Glad to hear that you had a good outcome and an easy fix to your engine start problem. Sounds like you were right on the money when you first suspected an electrical component problem.

I'm sure it feels good to be back on the road!