8V Won't Fire

[Will Garner]

OK, here is the sequence of events. We went to SC on 22 Oct. Great trip. Filled up at Jack's in Lancaster SC. I've gotten diesel there before no problem. Run home was uneventful. Cleaned coach and put it back in the bus barn. On the 29th October pulled the bus out to put a pick-up truck inside the barn too. Pulled the coach back in. Yesterday I went over to the bus barn to dump the fresh water tank and winterize the water lines and traps. I needed to pull the coach out of the barn to do that so unplugged, got in and turned the ignition key. The engine cranked just fine. It made some whitish smoke as is normal when it first fires, but would not start. I tried several times, same result. I even tried using ether in the little ether cup, same result - smoke but no fire.

Today I'm taking the DDEC I-II code reader (thanks Ray and Tom) with me to see if there is a code showing. I may have a set of fuel filters so they will get changed too, even though they were changed in September 2011. I'll also be looking at any wiring that may have been vandalised by little four legged varmints.

What I need to know is what others have found to be a solution to their problem when encountering a "cranky" 8V? Remember, the fuel tank is full.

As always, any guidance from members of this group is more than welcome.

[JIM CHALOUPKA]

All I can add Will is my experience with the series 60 which might be totally different with an 8v. My fuel lines on the suction side deteriorated to the point of sicking air, thus NO START. Being you have mechanical injectors might make things different.

Spray your fuel lines with brake degreaser to bone dry and if they discolor/darken you have a leak, even though you find no diesel on the ground.

JIM :)

[Will Garner]

Jim,

Thanks for the insight. I always check the floor of the barn after backing out. The only fluid I ever found, actually my grandson found, was power steering fluid. There is a nasty little o-ring lower curbside flywheel end of engine that is notorious for leajing every 2-3 years. I'll clean the fuel lines as suggested and see what happens.

[truk4u]

Will,

Try starting it manually from the rear.

[Woody]

Check the 12V DC switch which supplys 12V DC to the DDEC.

[JIM CHALOUPKA]

Disconnect and reconnect the DDEC connectors to be sure of a proper connection.

[gmcbuffalo]

Do you have a emergency shutdown switch that maybe flipped, if you have one it should be on the dash. I don't remember if Prevosts have them. I had a GMC4107 and if the switch was tripped it acted just like the situation you discribe.

[AmeriStar]

Check the shutdown solinoid. If the arm is stuck out, no fuel is allowed into the motor.

[rahangman]

Kevin, if no fuel is allowed into the motor (makes sense) then why the puff of white smoke?

[gmcbuffalo]

Fuel is getting in just not air. The Shutdown close the air intake.

[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!

[Will Garner]

Paul,

I'm a very happy camper that only a relay was causing the problem. The NAPA replacement number for the relay is AR394.

I wish I was on the road. I retired and the wnet back to work for a PEF the following Monday. Hunny Do list was way to long!

Thanks all for your guidance on my problem.

[BoaterAl]

Will
Were they able to cross ref your defective relay using the NAPA interchange data base ?

[rahangman]

Got a part # to share, Cousin of my, 90???? I have had to replace both starting solenoids as they tend to get HOT then freeze up...Yup, carry a spare one of them too.

[Coloradobus]

AR-394 is the part number from Will's post #21 above, Our Napa carries them at about $26 and some change.

[rahangman]

Will.....is that an "extended use" solenoid? I can't think of the other name.

[Will Garner]

Rodger,

Its a simple old electro-mechanical relay. Activates with a 24V input and closes a circuit that outputs 12V. That is about the extent of my knowledge on relays, this one specifically. Now if I could just get those dang toad taillights to keep working ....

[rahangman]

You have trouble keeping your toad tail lights working....too? It seems about everyother trip I wind up redoing mine. I have gone to the process of running seperate wires from front to back, completely isolating the Jeep system, by boring holes in bottom of taillight assy and using seperate bulbs, no diodes or anything. Still have to play with it though. Sheeesh as if the bus doesn't keep me busy.

[Will Garner]

Rodger,

Roger That.

Mine are wired separately from the toad's regular light system. Two new bulbs in holes drilled through inside of taillight housing. New wiring all the way back to the connector on the tow plate. Mine my go for several trips, no problem. Then the next trip out, no taillights. Brake lights work fine. Turn signals work fine. The center relay of the five relays in the CC electrical box is always the one that is causing the problem, or maybe suffering from a feedback problem from another source. Of course if that is the case why do the taillights work at all after changing out the relay.

I've been thinking of taking out the CC electrical box and replacing it and everything in it with new stuff. That would include sockets for the relays instead of individual wires to each of the contact posts and a connector between the Prevost 24V panel wires and the CC panel wires. All that is holding me back is my profound ability to make sparks fly when doing electrical work!

[rahangman]

Will, well, pardner, good thinking. I had a thought brought to my mind from Branson Motor Coach, they suggested running a dedicated ground wire though my homemade harness instead of relying on a ground at the installed aux light bulb. Soon to happen. Should be simple even for me. No sparks today.

[gmcbuffalo]

Will being that you have individual wires to the terminals on the relays. Have you check the voltage to make sure the wires are on the right posts and their are no shorts.

[Will Garner]

Greg,

I've not checked as extensively as I should have. In order to get to the terminals on the relay one has to be flexible like a beer soaked pretzel. I'm not that flexible. That is the primary reason I've been considering a total new box with relay sockets instead of relays screwed to the top of the box with with individual wires to each relay post. In fact just getting the wires back onto the posts is a challenge since CC did not leave any slack in the wires.

The first relay that failed was in fact the wrong voltage. It burned out. I replaced it with the correct relay and it worked for one summer. Next spring, relay no workie. Winter is coming so there will be time to chase down these little problems. I've got the meters just have not had the time.

Hope all is well with you and Huong.

[mike kerley]

Guys, I curious as to where this "box" is located. My toad relays are in the bottom of the Prevost electrical panel in the rear compartment. I also battle with toad lights and its usually one of those relays that is sticking. I'm thinking of changing them out with something heavier duty as well. It never ends!