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Old 11-17-2019, 04:23 PM   #1
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08 Diplomat won't start

2008 Monaco Diplomat with 400 ISL.
Ran fine 4 weeks ago ended a 3500 mile trip in NE Tennessee, ready to leave for Florida and all loaded but she will not start, spins over like normal but will not fire up. There had been several nights in the low 20's so I plugged in the block heater the night before. Thinking fuel might have gelled I bought both fuel filters, prefilled both with a mix of fresh diesel and 911 fuel treatment. Still no start. The Medallion gauge normally will display "engine not running" when I turn the key to on and do not start it, but now it is displaying "engine comm failure".
Took the ECM off and had Cummins Knoxville connect on the bench, they are able to communicate with it and determined there were no fault codes.
Pulled both ECM fuses and I do not get any voltage to the hot side of the fuses. I do not have schematics for my coach so am stuck.
Need assistance or suggestions.
Thanks
Dan Brinson
2008 Monaco Diplomat 40PDQ
ISL 400
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Old 11-17-2019, 04:35 PM   #2
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You don't have a engine start / stop switch in the engine compartment do you?
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Old 11-17-2019, 05:46 PM   #3
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I've never been able to find rear a start switch in the engine compartment
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Old 11-17-2019, 06:05 PM   #4
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https://www.amazon.com/Tracer-Circui...NsaWNrPXRydWU=

You can get these at Lowes etc. Put the signal transmitter on the "hot side" of the fuse and then use the sniffer to chase the wires down.

Open your rear run panel and look for any blown fuses there.
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Old 11-17-2019, 07:39 PM   #5
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Does the wait to start light come on?
If not there is a engine/ignition relay that turns on the lift pump.
It won't start if the lift pump doesn't prime the system. The relay also sends a signal to the ECM
I fought mine for a long time before I found the relay.
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Old 11-17-2019, 08:52 PM   #6
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When you turn the key on, but before you turn it far enough to engage the starter, you should hear a noticeable humming sound for about 20-30 seconds coming from the engine compartment area. Are you hearing that?
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Old 11-18-2019, 03:00 PM   #7
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X2 on the above^^^. I would think on a 08 inside the rear run box (take the cover off) you have a pair of switches for starting back there. On that board are 2 fuses and the R one is for your lift pump.
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Old 11-18-2019, 06:37 PM   #8
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Originally Posted by Ivylog View Post
X2 on the above^^^. I would think on a 08 inside the rear run box (take the cover off) you have a pair of switches for starting back there. On that board are 2 fuses and the R one is for your lift pump.
I don't think the diplomats came with a rear start, I could be wrong though. It's a rear radiator so I don't know where you'd mount it. OP says he hasn't been able to find it. I'm not familiar enough with the Dips to know where they put the electrical.
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Old 11-19-2019, 06:02 AM   #9
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Quote:
Originally Posted by danbrinson View Post
2008 Monaco Diplomat with 400 ISL.
Ran fine 4 weeks ago ended a 3500 mile trip in NE Tennessee, ready to leave for Florida and all loaded but she will not start, spins over like normal but will not fire up. There had been several nights in the low 20's
Do you see any smoke in the tail pipe? Just wondering if the injectors are firing but the engine is too cold (or fuel issue) so it wont start.

If you are seeing some smoke that would indicate the ECM is firing the injectors but possibly the intake grid heater is not working.
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Old 11-20-2019, 07:01 AM   #10
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My 2008 Endeavor is the sister ship of the Diplomat and it does NOT have a rear start panel.

There are a lot of interlock systems in the darn thing. For example, if the transmission ECM which is located in the front run panel in the outside compartment below the driver, fails you will have all kinds of issues.

MY transmission ECM got wet from water entry from the hole at the top of the comparment. This was a self inflicted wound and not a factory fault.

The slide outs have interlock cutouts as well. What a pain with poor documentation.
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Old 11-20-2019, 10:13 AM   #11
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When a diesel spins but doesn't start you can usually find a fuel problem .


IMHO the easiest place to start is fuel filters .



Have you done anything recently to the fuel system , filters etc ?


I would replace both fuel filters , do them one at a time .
Pull the filter , look for any evidence of black goo ( algae ) or any other
trash that shouldn't be in the fuel system , it may be right on top , easy to see.

In your case I suggest you get a gal of clean diesel to 1st fill the new filters .


As stated you should hear the lift pump run when you turn the key to on .
You may need to go to the back of the coach or at least open the door
to hear the pump running .
My pump is loud enough so I can hear it while in the drivers seat .
This is all with the key on before starting the engine .


Good luck hope you get it running soon .
Let us know the outcome .


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Old 11-20-2019, 11:46 AM   #12
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All,

OP posted the same question over on the Cummin's section. Apparently he's not getting power to the ECM, but doesn't know why.
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Old 11-20-2019, 09:17 PM   #13
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If you recently returned from a long drive, it should not be the filters. If the batteries are not at full charge it may not turn over fast enough to start. Just a thought
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Old 11-21-2019, 07:07 AM   #14
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Quote:
Originally Posted by windsorbill View Post
All,

OP posted the same question over on the Cummin's section. Apparently he's not getting power to the ECM, but doesn't know why.

With that info he should look at the chassis batteries .
The ecm gets power from its own dedicated wire , usually coming directly
from the battery positive post .
An in line fuse is somewher in that wire

The wire can be accidentally left off
or corrode and then fall off .
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