MEP-952B Starting Issue

[bohunk]

I can only get my 952B to start if when cranking using the starting motor I push down on the 'thingy' (technical term) that is supposed to be pushed down when starting using the manual hand crank. The manuals seem to indicate the only time that is necessary is when trying to start using hand crank. Mine fires & runs sweet but ONLY if I push that 'thingy' down while cranking it over... otherwise... nada. Anybody know if that is the way it is supposed to be?

 

[Suprman]

The plunger thingy? That's the fuel solenoid. If you don't have an external power source you have to manually push it down until the unit starts running and making its own power.

 

[bohunk]

Well Suprman, I didn't have the exact NATO connector but I did apply external 24v to the connector and a proper ground. When I attempt to start the unit the fuel pump hums (another technical term) and the unit will turn over very quickly, but will not start until I manually depress that "start/hold solenoid" (got that terminology from the FM) then it starts immediately. I think that solenoid should automatically latch if & when the unit is started by using either the 'local' or 'remote' panel. It only makes sense that in the heat of battle somebody should NOT have to open the cover and manually depress that solenoid. I just want somebody to confirm that is how it should work. IF... that is correct then I know I have a bad solenoid and need to set to work attempting to source one. AND... I really want it to work as I described because I don't want to get up in the middle of the night and go out and depress that 'thingy' just to get it to start... I think it SHOULD latch on its own if attempting to start it with starter motor. The manual clearly states one has to depress it using 'right hand' while turning the manual crank with the left hand. It doesn't address that solenoid when starting electrically... leading me to again believe it should latch automatically.

 

[Suprman]

Yup if 24v is used to start it the solenoid should activate. If you are hand cranking it you have to push it down manually.

 

[DieselGenAC]

The controls should activate that solenoid. As far as I could tell from the brief time I had the covers open on one, there are controls inside the main control panel and in a black box on top of the engine near the air filter cover. Its called a preheat module according to the TM (item 14 on page 1-7 in the TM at the link below). A voltage regulator sits somewhere on or near the alternator but I doubt any controls run through it.

http://www.liberatedmanuals.com/TM-9-6115-664-13-and-P.pdf

Does the solenoid hold after the unit starts? In one of the schematics (page 421), I see a HOLD and a PULL going to J11 for the run solenoid and it looks like they both come from the preheat module. See if you get any voltage to that solenoid at those two wires. I have seen a couple dual stage solenoids that have a higher power winding to move the solenoid and a lower draw coil to hold so the pull wire might have power for only a few seconds during startup. If the pull or hold voltage isn't there, I bet the preheat module is bad. If you have pull and hold voltage, the solenoid is bad. There is always a chance that a connection or a wire is bad so you should pierce insulation near the source (preheat module) to check voltage to be sure.

 

[bohunk]

Thanks for the trouble shooting hints DieselGenAC. I am on to other projects at the moment... when I circle back around to this I will let you know what I found.