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Author Topic: Engine dies @ 60 lbs  (Read 2447 times)
berrybus
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« on: November 11, 2006, 05:26:43 PM »

We have a MCI 9, with a detroit 318 engine and two months ago we pressure washed and degreased engine and compartment.  We had not  started the engine until today.  Upon starting the engine, the engines starts fine until air pressure reaches 60 lbs.  Then it dies and will not restart until pressure goes back below 60 lbs.  Any suggestions that may help me correct this problem would be greatly appreciated.

And also, I noticed on some of the questions, a "new" shows up...how do I do this on my messages?

Thanks
Jim Berry
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Tim Strommen
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« Reply #1 on: November 11, 2006, 05:38:00 PM »

Sounds like you may have washed out a wire to the shut-down circuit.  On my rig, there is a skinner valve attached to the back of a short-throw air-cylinder which pushes the shutdown valve.

As the bus airs up, if the valve is in its shutdown state (unpowered), it allows air pressure to the cylinder and pushes the fuel shut-off lever to "stop".  After I had my bus pressur washed the front engine controls didn't work (had to start the bus from the back to get it off the washing stand).  I found that in the process of washing the engine I had washed of the insulation from a few brittle wires and they had popped the breaker to the front controls.

Based on this, I'd recommend that you start by looking at the shut-down circuit, and take measurments from the solenoid to the driver's seat to find your problem.

Cheers!

-Tim
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DrivingMissLazy
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« Reply #2 on: November 11, 2006, 06:03:29 PM »

And also, I noticed on some of the questions, a "new" shows up...how do I do this on my messages?
Thanks
Jim Berry

New shows up on other peoples posts that you are looking at. Not on your own for you. It shows up new on everybody elses screen for your new post.
Richard.
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« Reply #3 on: November 12, 2006, 12:19:24 AM »

I've seen this problem arise many times after pressure washing. Usually it self heals when the water dries out of the solenoid on the back bulkhead that feeds the "skinner valve" or sometimes it's as simple as the rear shut down switch got bumped into the shut down position. And of course it could also be the wiring insulation/shorting situtation as described above! BK  Grin
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berrybus
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« Reply #4 on: November 12, 2006, 07:21:41 AM »

where is the skinner valve ? and where is the solenoid on the back bulkhead ? thanks jim
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gumpy
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« Reply #5 on: November 12, 2006, 08:04:03 AM »

It's definitely the safety shutdown system, or the stop switch on the rear control panel.

Check the switch first. make sure it's in the run position.

The safety shutdown is composed of a low oil presure switch which is down by the frame on the drivers side, and two temp stats, one in each thermostat housing on either side of the engine. There might also be a low coolant senor in your reserve tank above the fans.

If the switch is in the run position and it won't run, start removing the wires from the t-stats and oil pressure switch, one at a time till it will run. These switches ground the wires when activated, so removing them will allow the bus to run.

craig
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Craig Shepard
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DrivingMissLazy
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« Reply #6 on: November 12, 2006, 09:07:48 AM »

If the switch is in the run position and it won't run, start removing the wires from the t-stats and oil pressure switch, one at a time till it will run. These switches ground the wires when activated, so removing them will allow the bus to run.
craig

iI think I would remove all the safety shutdown wires first and then re-connect till the engine quits. This would save on starter wear and battery run down.
Richard
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« Reply #7 on: November 12, 2006, 09:41:47 AM »

I had to bypass my shutdown circuits several months back. The old relays in there were sending false signals. One of these days I might get around to troubleshooting it, but the telltales still work and I monitor gauges religiously whilst driving.

Sometimes these shutdowns could shut you down at the most inopertune time! I might risk a blown head or low oil damage to get her somewhere safe if I was in the center lane pulling the Grapevine... or in the middle of a downtown six-lane rush hour when the shutdown pulls the rack. Just imagine...

Especially if it was a false alarm!

Just some thoughts,
Brian B.
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Brian Brown
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« Reply #8 on: November 12, 2006, 10:12:11 AM »

I had to bypass my shutdown circuits several months back. The old relays in there were sending false signals. One of these days I might get around to troubleshooting it, but the telltales still work and I monitor gauges religiously whilst driving.

Sometimes these shutdowns could shut you down at the most inopertune time! I might risk a blown head or low oil damage to get her somewhere safe if I was in the center lane pulling the Grapevine... or in the middle of a downtown six-lane rush hour when the shutdown pulls the rack. Just imagine...

Especially if it was a false alarm!

Just some thoughts,
Brian B.

My 4104 is not equipped with a shut down circuit. However, the schematic shows it as an option.  Included in this circuit is a "Shutdown Over-rule" switch. It only allows engine operation in first gear.

I think the Series 60 and other electronic engines have a similar feature but with their deep memory, it's use will probably void any warranty.

Len
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« Reply #9 on: November 12, 2006, 04:29:13 PM »

where is the skinner valve ? and where is the solenoid on the back bulkhead ? thanks jim

If you're running a DD 6V92 or 8V92, it's at the top of the engine towards the front of the block.  On a rear engine T-drive, this will be the part towards the back of the bus (it should be the same side as the belts).  Generally the fuel shutdown lever is around the throttle lever.  The skinner valvle can be attached to the shutdown cylinder or remotely located.  Instead of running all over the electrical system first - I'd verify that the shutdown lever is being actuated (sounds like it is, but just make certain...) - then find out why.

It's fairly likely that you've narrowed down the cause of the problem (you say it started when you washed down the engine compartment).  You probably want to start with major components that are around the engine (ground points, power distribution, relays, breakers, etc...).

Do you have a service guide for your rig yet?  It'll make a big differrence while tracing out wires and process control (i.e. the shutdown circuit).

Cheers!

-Tim
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« Reply #10 on: November 12, 2006, 07:41:43 PM »

Len,

I think all 4104s have a switch on a rear panel for shutdown. This is actually a convenience for mechanics to use along with a starter switch and another switch that shuts off the starter solenoid for safety. These four switches(One is a bay light) are all on a small panel at the top right side of the engine bay, very hard to see.

The circuit you described is probably the one that shuts down the engine because of low oil pressure or engine overheating. This is the purpose of  the "Shutdown Over-rule" switch.
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Len Silva
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« Reply #11 on: November 13, 2006, 06:13:14 AM »

Len,

I think all 4104s have a switch on a rear panel for shutdown. This is actually a convenience for mechanics to use along with a starter switch and another switch that shuts off the starter solenoid for safety. These four switches(One is a bay light) are all on a small panel at the top right side of the engine bay, very hard to see.

The circuit you described is probably the one that shuts down the engine because of low oil pressure or engine overheating. This is the purpose of  the "Shutdown Over-rule" switch.
Yes, that's exactly what I was talking about, responding to Brian's message.
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« Reply #12 on: November 13, 2006, 11:39:15 AM »

I was told by a very wise old diesel mechanic.  NEVER PRESSURE WASH YOUR ENGINE UNLESS YOU ARE ENTERING A CAR SHOW OR SOMETHING...  No good can come of squirting 2000 psi of pressurized water at electrical components, etc... Tongue

I know some of you will probably howl with laughter at this, but I used to work on the wash rack my freshman year of college.  We used very high pressure water and steam cleaners.  We washed everything except the driver's butt.  However, the only engines we ever washed or steamed off were engines that were out of the trucks and about to be torn into. 

Jimmy
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berrybus
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« Reply #13 on: November 13, 2006, 06:34:35 PM »

thanks fellows .i still cant figure it out . what could make it shut down at 60lbs consistantly? thanks jim
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« Reply #14 on: November 13, 2006, 07:04:42 PM »

Hey there, These folks are right, There are three switches in the raer that will shut you down. I don't type fast enough to explain all. I have owned 5 MCIs If you want to call my cell I will take you through it. Charlie 678-612-2170 www.beatenbo.com
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gumpy
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« Reply #15 on: November 13, 2006, 07:36:55 PM »

thanks fellows .i still cant figure it out . what could make it shut down at 60lbs consistantly? thanks jim

Go back and read my post above.

It's shutting down normally. If you watch your shutdown cylinder as the pressure comes up, you''ll see it activate and activate
the fuel cutoff lever. The solenoids are spring loaded, and they won't overcome the spring until the pressure reaches around 60 psi.

It's either the rear control switch is in the off position, or it's one or more of the safety shutdown system sensors related to low oil pressure, high temp, or low water level.

Do you have a manual?  Look at the safety shutdown electrical schematic.

By the way, if you air the bus up with shop air, it won't start at all, or, more likely, it'll start and die when you release the start button.

You didn't say what you've done to find the problem. It' working the way it's supposed to. Troubleshoot as indicated above.


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Craig Shepard
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« Reply #16 on: November 13, 2006, 09:24:33 PM »

Jim, the auxiliary air system is probably the source of the air for the air shutdown solenoid. Since no air is passed from the primary air system unltil the minimum pressure valve is overcome (about 65 psi on ours), no shutdown occurs until that pressure is reached. When that pressure is reached, the pressure stops rising on the primary side while the auxiliary side catches up. Then, they rise together.

After the air in the auxiliary system bleeds off, the solenoid relaxes, opening the rack.

What can be humorous is that you can have just one air leak, the solenoid itself, and it will cause all of the symptoms that you are getting.

Good luck on finding your leaks and the cause of the shutdowns.

Tom Caffrey
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gumpy
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« Reply #17 on: November 14, 2006, 04:58:40 AM »

Jim, the auxiliary air system is probably the source of the air for the air shutdown solenoid. Since no air is passed from the primary air system unltil the minimum pressure valve is overcome (about 65 psi on ours), no shutdown occurs until that pressure is reached. When that pressure is reached, the pressure stops rising on the primary side while the auxiliary side catches up. Then, they rise together.

Yeah, that's a better explaination why it happens always at 60 psi. I like that better than my spring theory  Cheesy

Quote
What can be humorous is that you can have just one air leak, the solenoid itself, and it will cause all of the symptoms that you are getting.

An air leak is not causing the problem. That's an electrical problem.

Most all air systems leak down, and what Tom said is true in that once the bus shuts down at 60 psi, it will not take long for the pressure to drop back below the magic 60 psi again, and the whole thing starts over next time you start the bus.

The problem is electrical.

« Last Edit: November 14, 2006, 06:40:11 AM by gumpy » Logged

Craig Shepard
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« Reply #18 on: November 14, 2006, 06:19:31 AM »

Craig is correct... the problem is electrical. Something, a bad sender or relay, is tripping the shutdown circuit. Unless you really do have low oil pressure (possible) or high water temp (impossible on a cold start).

If you can find the shutdown relay, you can readily bypass it to begin your troubleshooting.

HTH,
Brian B.
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Brian Brown
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