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Author Topic: 8V92 won't start  (Read 3953 times)
Merlin
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« on: March 03, 2011, 12:50:04 PM »

Any suggestions to point me in the right direction on this vexing situation?  Here are the facts:
(1) engine has been running great nearly every day for several months ... started every time in about 1/4 turn with pre-heating
(2) aired up the bus with aux compressor as I normally do, bags were up and bus was level
(3) turned the key ... zilch ...
(4) tried the rear start switch and button ... zilch
(5) not a groan or any indication that the starter was trying to turn
(6) batteries are new (four months ago), and all cables are clean, tight and connections are well protected with Vaseline
(7) voltmeter tells me there is nearly 25 volts across the four batteries
(Cool batteries have always been connected to a battery minder that is claimed to keep them "stirred up"
(9) bus was properly shut down in neutral (Allison 5 speed), and air brake applied, tag axle down
(10) to be sure there is air in the system in case the aux compressor somehow did not get air to the controls in the engine compartment, I used an air hose to fill the rear air tank.  It seemed to be up, but just in case I did it manually.

Now what?

Starter solenoid problem?  If so how do I test it or better yet how to jump around it without frying myself or something else of value?

I'm writting this from an RV park in Alabama where there is no panic to get the problem cured but sooner or later, I think my wife would like to get on the road again.

We phoned the road service insurance people this morning and they promptly sent out a little guy in a pick-up with a tiny 12v battery to "jump start" the bus.  Sigh ...   Even after my careful explanation of the situation and the fact that the bus is 24v.  The perplexed road service guy was kind enough to give me a phone number of a fellow who might know something about 8V92's.  This is comforting ... especially the "might" part.

Such is the tale of bus ownership, I guess.
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eddiepotts
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« Reply #1 on: March 03, 2011, 01:47:13 PM »

I know this is the silly point but you did not say anything about checking the main power switch. Somebody may be playing a joke on you. If your not getting any noise from the solenoid you need to see if getting power to it when you push the starter button. If not trace it back to the batteries and find the disconnect. If getting power to it then you can bet the solenoid is not kicking in. Tap it with something and try again while tapping.
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« Reply #2 on: March 03, 2011, 01:48:45 PM »

Do you have voltage at the starter? Do you have voltage at the engine master switch? Are you DDEC?. Fuses? Battery master switch? Sorry for the generalities, that is where I started when it happened to us...Cable
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Ed Hackenbruch
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« Reply #3 on: March 03, 2011, 01:50:17 PM »

Also move your gearshift lever back and forth a bit. Sometimes mine looks like it is in neutral but is just a hair off and the bus won't fire.
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« Reply #4 on: March 03, 2011, 01:54:47 PM »

In my bus there is a relay that switches power to the solenoid.  It's in engine bay electrical panel.  I don't know what bus you have so no idea where yours might be.

I would at least try jumping positive voltage to the activate terminal on the starter solenoid to see if the starter motor works.  If it does, start working backwards from there.  basically to that relay, then to the rear starter switch, etc.

Brian
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« Reply #5 on: March 03, 2011, 04:17:47 PM »

ck neutral switch on side of trans that wire has broken on my 1978 MCI   also in top front box under drivers window there should be a solenoid (like the old ford type) that supplies power when switch is turned on to big delivery post. should click when you move switch and have power to both sides.
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Van
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« Reply #6 on: March 03, 2011, 04:20:11 PM »

Chasis to starter grounds Huh
« Last Edit: March 03, 2011, 06:11:36 PM by van » Logged

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papatony
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« Reply #7 on: March 03, 2011, 05:00:09 PM »

what year and make bus
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white-eagle
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« Reply #8 on: March 03, 2011, 05:19:33 PM »

same thing happened last year with ours.  i started it up and moved it back under the shade at walmart.  20 min later when fran arrived with the groceries, it wouldn't start.  Tried all the tricks, then called Coachnet.  Lakeland's Central Florida Bus (at my suggestion to Coachnet) showed up in about 1/2 hour and put in rebuilt started after testing a few things also.  and life was good again.
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Tom
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Cary and Don
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« Reply #9 on: March 03, 2011, 06:02:15 PM »

We had a similar thing that went on for awhile.  It would start just fine one time and not the next,  usually when the engine was hot.  Turned out the wire that went from the relay on the bulk head to the starter solenoid  was bad.  Easy fix,  just took forever to figure it out.

Don and Cary
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chart1
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« Reply #10 on: March 03, 2011, 06:13:55 PM »

1.need to check voltage 2 turn the key while moving shifter back in forth slowly in the nuetral position. If there is power at the starter you should hear some kind of clicking if you have voltage. If it is the neutral saftey switch you will not hear anything.
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« Reply #11 on: March 03, 2011, 06:14:48 PM »

where are you in Alabama.
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gus
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« Reply #12 on: March 03, 2011, 07:22:40 PM »

You need to start at the starter and work forward.

You also need to let us know what bus and engine you have.

Starter relays seem to be the most common problem. As posted already, this is in addition to the starter solenoid. If the relay fails everything fails. You can jump across its terminals to find out quickly if it has failed.
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chart1
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« Reply #13 on: March 03, 2011, 07:27:44 PM »

Yes a big heavy duty screw driver is the perfect testing tool if you have voltage at the solenoid.
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« Reply #14 on: March 03, 2011, 07:35:35 PM »

No clicking and good  voltage check the small wire at the bottom of the solenoid it is supposed to be hot when the stater button is pressed they are bad about coming lose or breaking just another place for you to check


good luck
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Charley Davidson
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« Reply #15 on: March 03, 2011, 08:45:37 PM »

How long you been sitting? If you don't have fuel pressure the starter will not work, check all the simple easy to get to stuff.
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chart1
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« Reply #16 on: March 03, 2011, 08:51:01 PM »

How does fuel pressure have anything to do with the starter turning over?
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Charley Davidson
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« Reply #17 on: March 03, 2011, 09:02:29 PM »

How does fuel pressure have anything to do with the starter turning over?

There's a switch at the front fuel filter (front meaning the one towards the front of the bus) that will not let electricity to the starter if there is no fuel pressure
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thomasinnv
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« Reply #18 on: March 03, 2011, 10:23:10 PM »

chart1, I could be wrong here but I think you have it backwards.  the fuel pressure sensor dis-engages the starter when fuel pressure IS present to keep the starter from grinding teeth once the engine starts.  this is how the start button override works when you hold the button down to move the bus off the road when the emergency shut down will not allow it to keep running on its own.  I suppose however that a FAULTY fuel pressure sensor could cause the starter to not engage.
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« Reply #19 on: March 04, 2011, 06:30:47 AM »

Really confused!!
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1976 MCI 8
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Merlin
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« Reply #20 on: March 04, 2011, 06:47:48 AM »

Thanks friends for the replies and suggestions.  Here is a brief listing of the info that I did not initially provide:

Engine is an 8V92T (silver, non-DDEC)
Allison 5sp automatic
1985 Prevost
Parked at Rainbow Plantation RV Park, near Summerdale, AL
Engine has been idle for 7 days
There are no electrical wires to either fuel filter housing meaning no pressure cut-off switch
Good voltage (25 VDC) present at right lug of starter solenoid when master battery switch is ON
Transmission is in neutral as indicated by the little light on the shifter control panel
Starter solenoid wiring looks to be in good condition, all wires are fairly new and no corrosion is evident

Today I have a diesel mechanic coming by that is familiar with "the old stuff" like two stokes.  After being tossed from one phone operator to another for half of yesterday, I finally was able to speak to this fellow who is a hold-over from the old days when diesel engines actually sounded good.

The suggestions on this board (all of them) are very appreciated.  All are common sense and armed with that advice I will sort through the easy stuff myself before the old diesel mechanic arrives.  Last resort is of course a big hammer applied to the solenoid to wake it up, or possibly totally destroy it.  In that case the diesel mechanic will have something expensive to add to his bill.

A side note here is the timing of this "event".  A dozen admirers were watching us methodically (looking like professional RVers) ready the bus for pulling out of the park.  Wife was all decked out in her baseball cap, wrap-around sun glasses, and two-way headset ready to guide me out of the parking spot.  Dead silence ... as the audience listened for the vaunted big diesel sound ... still dead silence.  Geesh, can't an embarrassing moment like this happen with no witnesses?
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« Reply #21 on: March 04, 2011, 07:02:12 AM »

Merlin,
The front/rear start toggle switch in the rear electrical box above the engine is notorious for failure, but that is usually after it has been disturbed. Just a thought.
And it seems this kind of thing only happens with a bunch of looky lews around.
George
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George & Debi
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papatony
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« Reply #22 on: March 04, 2011, 08:02:00 AM »

    I would get some one to start it while you are at the solenoid to see if there is power coming from the neutral switch on the tyranny
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Charley Davidson
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« Reply #23 on: March 04, 2011, 08:53:29 AM »

I stand corrected on that switch, it keeps the starter from engaging and running while the bus is running/has fuel pressure bad case of memory failure, too bad I don't have a switch that keeps my mouth from engaging when my brain is not running Roll Eyes
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« Reply #24 on: March 04, 2011, 09:13:41 AM »

I hadn't posted a response because you said you had help on the way.  However, just in case that doesn't work out, you can try this.

If you can safely reach the solenoid with a screwdriver, you can short from the battery terminal to the small coil terminal.  Be extremely careful here as the bus may start right up.  Be sure that the trans is in neutral, the brakes are set, and that you can do this without getting tangled up in belts or fans.
This will bypass any safety switches in your system, so be very careful not to get hurt.

You know that you have good battery at the solenoid, so that if it turns over at all using this method, you have likely ruled out the starter or solenoid.  That leave an electrical problem which is very hard to solve from a distance with a good schematic.
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Merlin
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« Reply #25 on: March 04, 2011, 01:58:45 PM »

Success !!

We back tracked from the batteries ... starter ... and wiring in the rear junction box.  All good.  For whatever reason the bus would now start from the rear starter switch.  Can't understand why because we did nothing to change things except for many "switch flippings" and wire tracing.  Anyhow it started on the typical 1/4 turn.

Now the tracing was focused on the front junction panel and the run/start relay.  It is good.  Wire from front to rear beginning at this junction box is continuous.  Good signal on the tester.  OK ... now the wire from front starter to the front relay ... also good.

Beginning to sweat at this point because we were running out of things to trace.  Final is the thing we should have checked first, and that is the front starter switch itself.  Position 1 is good, and momentary position 2 does not pass the test. 

Embarrassing, eh?  Now I can phone Prevost to get a new keyed start switch or just go to NAPA and pick up an exact replacement which is the same as a garden tractor keyed start switch.  Why can't a Prevost bus have something more impressive than a Briggs & Stratton key?

End of saga.  If only all bus problems were so easy to solve although when old bessy fails to wake up it feels like a major problem.  Could have been worse.  We could have been at a truck stop fuel island when it failed to start.

Thanks again for all the words of advice.

Merlin & Cyndy
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« Reply #26 on: March 04, 2011, 02:57:31 PM »

  Why can't a Prevost bus have something more impressive than a Briggs & Stratton key?
Merlin & Cyndy

I bet they charge for it as if were the key to Fort Knox gold vault

glad it was simple, it usually is as was my problem.
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« Reply #27 on: March 04, 2011, 03:22:06 PM »


...  A dozen admirers were watching us methodically (looking like professional RVers) ready the bus for pulling out of the park.  

Well there's your problem!!!  Roll Eyes
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Craig Shepard
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« Reply #28 on: March 04, 2011, 03:26:38 PM »

I stand corrected on that switch, it keeps the starter from engaging and running while the bus is running/has fuel pressure bad case of memory failure, too bad I don't have a switch that keeps my mouth from engaging when my brain is not running Roll Eyes

I was going to correct you on this, but I see you realized your mistake already. 

It's a common misconception that the fuel pressure switch keeps the bus from starting. It's true, that it disengages the started AFTER the bus starts and builds
fuel pressure. It's part of the safety shutdown system, and is what allows the driver to override the shutdown by holding in the starter button. It's also necessary with a properly functioning
safety shutdown system because without it, the bus will shut down until oil pressure is built up. That's why you have to hold the button in until the oil pressure light goes out on the dash. Of course
that only works if you have air pressure in the tanks.

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Craig Shepard
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