ONAN MDJE breakdown- need troubleshooting help

[Genevatexan]

Our ONAN 7.5 MDJE suddenly started blowing black smoke and spewing diesel fuel into the water yesterday. It continued to run, but we shut it down within 10 seconds. Initial concerns are possibly one cylinder dead-heading, or other serious failure. This is a very old unit leaving us the dilemma: Repair or replace. Can someone give us some direction on best approach to trouble-shooting? Much appreciated, GT

 

[rsmith]

The injectors are easy to pull. Crank it over and put your thumb over the hole see if you have compression

 

[Canuck Dennis]

Check for fuel in the oil pan, usually would turn to mayonnaise color

 

[TopHattandTails]

Replace it. It will eat you alive trying to keep it alive... Year after year you will feed that monster!

 

[Genevatexan]

There is a 2007 Cummins Onan MDKBK 9.0 Quiet Diesel in Ebay for $5K, new old stock. Never run. Very fair on price but it runs a 28 volt alternator and a 24 volt starter. After talking to Southern Plains Cummins they said the 24 volt unit cannot be modified to 12 volt, which is our config. I think their defense was that the circuit board and fuel injection were dedicated 24 volt and so just changing the starter would not make it functional. Btw, we dont use an alternator on the current Onan, since it uses the engine batteries the engines are charging those batteries in the current config. Can anyone confirm that this generator cannot be simply converted to 12 volt?

http://www.ebay.com/itm/290942332800?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Agreed that maintenance on the old one is expensive. Water pump was something like $300.

GT

 

[Genevatexan]

Gone now. Maybe posting that wasn't so sharp.

 

[Genevatexan]

So to complete this thread, here is what happened> removed injectors and tested on bench: all good. Turned over motor, good compression. checked oil, low and dirty, but not contaminated in any way. Checked coolant, full, not contaminated. Started engine again, huge black cloud for 5-8 seconds, then grey smoke, then second cylinder picked up, now running smooth. Apparently carbon buildup so big it broke loose, fouled second cylinder, black smoke pouring out of exhaust, unburned fuel slick on surface first time. Now carbon cleared, engine running smoother than ever. No damage. That's as best as we can figure. The MDJE lives to fight another day.

 

[TROUBLE]

How come i am never that lucky. Great news

Art

 

[RT46]

I have never been that lucky either!

That would have been a $10k new unit for me.


Genev,
you should play the lottery, now!