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Old 05-29-2021, 07:19 PM   #1
Mini-Skoolie
 
Join Date: Oct 2017
Location: Bellingham Washington
Posts: 32
Year: 2005
Coachwork: Thomas
Chassis: Freightliner
Engine: 6.4 liter Mercedes MBE 900
Rated Cap: 48 passenger
MBE 906 won't start

My bus is a 2005 Freightliner/Thomas dognose with a MBE 906. It cranks well, but WILL NOT start. I bought it in August 2017, sight unseen from Govdeals.com auction, and drove it from Attalla Alabama to my home in Bellingham WA. It ran perfectly the entire way. I haven't driven it very much, only one 500 mile trip in 2019, and just to take it out now and then for some "exercise". But it has always started easily and run well. I moved it about a month ago. I finally have the build complete enough to use, but last week when I went to start it, It just wouldn't. It cranks, but doesn't even TRY to fire.

Thinking it's lost prime, I opened up the filter housings on the engine, and there were some little black specks in the pre-filter screen bowl, though the screen was not at all clogged, nor was the actual filter in the adjacent housing.

I made a trip down to Freightliner in Mount Vernon WA and got new filters, including a new fuel/water separator and bowl. There, a guy in the service dept. overheard the parts guy and me talking, and suggested that the source of the black particles might be deteriorating hoses. So, I got another fuel hose made to replace the one between the water separator and the pre-filter screen.

So I replaced all the filters, and the hose, filled the filter housings, and still, crank, no start. I pressurized the fuel tank with air, no help. I even pulled up the floor over the fuel tank access opening (REALLY glad I provided access to that) and checked the fuel pickup tube. It's ok.

Reading some stuff here, and elsewhere on the internet, I thought the engine-mounted fuel pump must've failed, so I coughed up the bucks and got a new one. I installed it yesterday, and after putting everything back together, NO START. No sputtering, nothing, just cranking. Ugh.

I've been working on cars and trucks my whole life, but this is my first diesel, and I'm stumped. I've checked the dash readout, no codes.

It seems that fuel is getting through the pump, since the main filter is (I think) down stream of the pump. What would keep fuel from getting to the unit pumps (injectors)? Or if the fuel is getting to the unit pumps, what's keeping them from working?

This engine has a crank position sensor, and a camshaft position sensor. I don't know how to test either of those things.

Anyone have some suggestions?

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Old 05-29-2021, 08:40 PM   #2
Bus Crazy
 
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Join Date: Dec 2015
Location: pa
Posts: 2,135
Year: 98
Coachwork: 1. Corbeil & 2. Thomas
Chassis: 1 ford e350 2 mercedes
Engine: 7.3 powerstroke & MBE906
You do not talk about what you tested. The Mercedes has specific section on fuel pressure, fuel quantity.
Did you follow those procedures ..BEFORE..you spent the money and changed the fuel pump?

Pressuring the tank provides no help with bleeding the fuel system since the diesel return line is pressurized as well

Did you read the mbe906 manual about bleeding the fuel system..very specific..
You can crank a long long..long..long time before you have bled the system.. you risk starter damage and waste of battery longevity.

Yes it can be your crank sensor ..or any of the other 4 critical sensors..or a broken computer..
Start with the things you can test and let us know what and how you tested.

Good luck,
Johan
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Old 05-30-2021, 01:45 PM   #3
Mini-Skoolie
 
Join Date: Oct 2017
Location: Bellingham Washington
Posts: 32
Year: 2005
Coachwork: Thomas
Chassis: Freightliner
Engine: 6.4 liter Mercedes MBE 900
Rated Cap: 48 passenger
MBE 906 won't start

Thanks, Joeblack5.
I have acquired a "copy" of the 1869 page MBE 906 manual. There are some tests that can be performed on the fuel system. Some require that the engine be running, and all require tools I don't have.

I notice that many of the entries only indicate how to remove and replace items. For example, there's no info on testing a crank or cam sensor, just "replace the sensor if it becomes inoperable".

After scouring the Fuel System section, I can't find any procedure written for bleeding the fuel system. In the section titled MBE 906 Owner's Manual, I found a short section on priming the system. Basically, "work the hand pump (doesn't have one) and crank the engine for 30 seconds max at a time, with a 2 minute wait between attempts. Engine should start within 6 attempts."

Testing: So far, testing has been just checking things. The fuel lines from the tank have proved clear, the filters are new and are filled with fuel, the hoses are full of fuel, fuel is getting through the pump to the main filter(the housing is completely full when checked).

I have not found a procedure for checking the unit pumps electrically. Also, I'm working alone, so I cannot turn the key and be under the hood at the same time.

I've found nothing indicating whether it is ok to bleed the fittings on the lines AFTER the unit pumps. Only that there is a special socket for the injectors. In your opinion, is that a useful thing to do?

The manual says to check that the crank and cam sensors are pushed fully into their holes. I haven't checked that, but I'm wondering how would they get dislodged from their holes while the vehicle is stationary?

Engine oil is full. Coolant level is full. Batteries are charged. I was unable to get to the crank position sensor last night. I'll try again today. Perhaps I'll find it.

Things are a little more difficult for me these days, since I had a stroke in mid-2020. Working on things is good therapy, except for the frustration factor. Bus ran fine one day, then not at all the next. I'd much rather be putting the finishing touches on the interior build, than messing around with this.
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Old 05-30-2021, 07:21 PM   #4
Bus Geek
 
Join Date: May 2009
Location: Columbus Ohio
Posts: 14,857
Year: 1991
Coachwork: Carpenter
Chassis: International 3800
Engine: DTA360 / MT643
Rated Cap: 7 Row Handicap
alot of thigns can happen when a bus is stationary.. connections can corrode.. rodents can chew wires.. i would most definitely make sure the cam and crank sensors are in their holes.. and unplug / replug the wires to them as well..



also see if there is a procedure for reading the codes on the LCD panel of the instrument cluster.. i know there is for the CAT based freightliner dashboards so im guessing you also can for the MBE906.. computer codes can help determine what sensor the engine doesnt read correctly (if any)


Tools are one of those things worth looking into.. I have a whole garage full of them.. often boiught because something didnt work and I needed it fixed.. *BUT* there also comes a time when its worth not buying the special tools but is worth hiring a mobile rig to come out and look at it and run their diagnostic computer on it.. I dont have the mercedes software or id send it to you..
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Old 05-31-2021, 12:17 AM   #5
Mini-Skoolie
 
Join Date: Oct 2017
Location: Bellingham Washington
Posts: 32
Year: 2005
Coachwork: Thomas
Chassis: Freightliner
Engine: 6.4 liter Mercedes MBE 900
Rated Cap: 48 passenger
MBE 906 won't start

Thanks, Cadillac Kid. I didn't have the energy today to muck around under a bus. As for codes, I WISH there were some codes. I have used the procedure listed in the MBE 906 "code book", and there are none.

This episode has caused me to get the MBE 906 engine manual (1869 pages), the Freightliner FS-65 chassis manual (1158 pages), and the fault code manual (only 108 pages). I've always gotten the shop manual for any vehicles I've owned, and remember when they were a 2 inch thick book for $35.00 (seemed astronomical back in the day).

This vehicle has an insane level of complication, and I literally know nothing about the electronic control systems that run it. Perhaps tomorrow I'll be able to find the crank and cam sensors.

So here's this question: would a malfunctioning sensor cause the injector (unit) pumps to completely stop providing fuel?
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Old 05-31-2021, 06:03 AM   #6
Bus Geek
 
Join Date: May 2009
Location: Columbus Ohio
Posts: 14,857
Year: 1991
Coachwork: Carpenter
Chassis: International 3800
Engine: DTA360 / MT643
Rated Cap: 7 Row Handicap
its most surely possible for the computer to deny sending fuel to the injectors.. moist often there is some type of code when it doesnt, however i know on the navistar engines they will crank / no-start from a failed Crank sensor and not set a code.


some of the MBE engines came with air intake pre-heaters, if the weather is cool and that fails I might expect to see some white smoke while cranking..


if it were mine (and I didnt have the ability to "obtain" the Merc software) then id probably want to follow the fuel pressure test procedures in the book to make sure the system is truly primed up.. the easiest and most likely scenerio for an engine to not-start after it sat for a while is,


1. rodents nested in the air intake and clogged it up.. (easily checked by looking in the air filter box)


2. the fuel system lost its prime


3. the fuel got old and clogged the filters .. but usually that happens after it runs for a short time (couple hundred miles)(you changed the filters)


4. Dead or weak batteries


im only giving general ideas as i dont own an MBE, joeblack is one id definitely pay attention to, he knows diesels and takes the time to learn how his vehicles function
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Old 05-31-2021, 10:41 AM   #7
Bus Crazy
 
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Join Date: Dec 2015
Location: pa
Posts: 2,135
Year: 98
Coachwork: 1. Corbeil & 2. Thomas
Chassis: 1 ford e350 2 mercedes
Engine: 7.3 powerstroke & MBE906
Sorry to hammer on ths.. did you verify flow wth out bubbles and pressure at the return line of the fuel injectors.
attached manual, look at diagram paragraph 15-page 25 somewher in line B.
If you are by your self you likely have to make a remote starter switch to look at flow and pressure and take all precautions if it accidentally starts up,



good luck,
Johan
Attached Files
File Type: pdf mbe900-05a-1 trouble shooting repair manual.pdf (1.14 MB, 8 views)
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Old 05-31-2021, 11:01 AM   #8
Skoolie
 
Join Date: Oct 2018
Location: Central Alabama
Posts: 203
Year: 1998
Coachwork: Blue Bird
Chassis: TC/2000
Engine: 5.9 Cummins 12-valve
Rated Cap: 1
MBE900 or 906? Post is different from registry. Does it matter?
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Old 05-31-2021, 11:03 AM   #9
Bus Crazy
 
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Join Date: Dec 2015
Location: pa
Posts: 2,135
Year: 98
Coachwork: 1. Corbeil & 2. Thomas
Chassis: 1 ford e350 2 mercedes
Engine: 7.3 powerstroke & MBE906
No difference in the manual as far as I know.. MBE 900 is a series of motors.
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Old 05-31-2021, 08:18 PM   #10
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Location: mid Mo.
Posts: 422
Year: 1976
Coachwork: bluebird
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A friend of mine always unhooked his batteries and brought them into his shop to stay charged all winter. He couldn't get it started one spring and had to call in re-enforcements, problem was ECM wire fell down behind the frame and he didn't hook it up to battery terminal. Did you unhooked your batteries and miss place anything?
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Old 06-05-2021, 05:56 PM   #11
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Location: Calgary, Alberta
Posts: 366
Year: 2001
Coachwork: Thomas
Engine: Cummins ISC 260HP/660Q/MD3060 6spd
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Any luck getting it started yet? I don't know that engine at all but I almost bought a bus with one a few years ago but ended up with something else.

Only suggestion I have is not likely but it is possible - Try charging up your batteries completely because sometimes they can put out enough power to crank the engine but not for the computers to get it going. Also check the voltage to make sure they're up to par.

I had a 2004 Ford 6.0 a while back that would crank no start every once in a while, usually at the least opportune time; I would crank and crank and usually after a battery recharge or two and some prayers and waiting it would finally go. I don't believe it made any codes but when the third shop wanted to replace the cam shaft position sensor I said that's not the problem so they dug deeper and found the cam shaft position sensor wire had a loose part.
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Old 06-09-2021, 11:32 PM   #12
Mini-Skoolie
 
Join Date: Oct 2017
Location: Bellingham Washington
Posts: 32
Year: 2005
Coachwork: Thomas
Chassis: Freightliner
Engine: 6.4 liter Mercedes MBE 900
Rated Cap: 48 passenger
MBE 906 won't start

Thanks, all.
"Miles" the bus went to the truck hospital last week on a hook. I was unable to find the problem. Word is, the injector leak return line was broken between 5 and 6, and had been fixed with a piece of hose. The "fix" had to have been done by the school district in Alabama in 2017 at the latest. I've driven it 4000 miles since then without issue. Anyway, Good Sam towed it, and Valley Freightliner is fixing it. Gonna be $1900 to have them fix it, but the fuel system test gauge and fittings kit was $1000.
At least I have the manuals now. All 3000+ pages.
Again, thanks.
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Old 06-12-2021, 11:27 AM   #13
Bus Crazy
 
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Join Date: Dec 2015
Location: pa
Posts: 2,135
Year: 98
Coachwork: 1. Corbeil & 2. Thomas
Chassis: 1 ford e350 2 mercedes
Engine: 7.3 powerstroke & MBE906
Oh man, sorry to hear about the troubles, thanks for letting us know the outcome. Would you have been able to notice a fuel leak if you would have looked between cyl. 5 and 6?

Johan
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Old 06-12-2021, 11:14 PM   #14
Mini-Skoolie
 
Join Date: Oct 2017
Location: Bellingham Washington
Posts: 32
Year: 2005
Coachwork: Thomas
Chassis: Freightliner
Engine: 6.4 liter Mercedes MBE 900
Rated Cap: 48 passenger
MBE 906 won't start

Again, thanks for your help, Johan. It's not likely I would have seen the broken line, or the repair, since I did not take apart the engine. Also I didn't have the shop gear that was used to troubleshoot the fuel system, or to prime it. The mechanic had to use ether to get it started, then he found the leak with it running.
At my age and level of relative infirmity (still recovering from a stroke) it may be time to phase out mechanic work. I did a brake repair a couple of months ago on my Suzuki Vitara, and it was much more difficult than it really should have been.
This fix was within the budget, and done by a good shop. I'm happy to have the bus back. On with life.
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