MEP-804a preheat

[calucyk]

New to the forum. Bought first military generator. Excellent machine. Ran load bank last weekend. Machine ran at 61amps comfortably.

This forum has been extremely resourceful. TM’s equally helpful.

That said, I have a question regarding preheat. When I turn S1 to preheat, the starter engages and the engine starts. The couple of times I tested preheat, the temperature was 60 degrees or higher. I was expecting no starter engagement or engine start, just silence while the glow plugs warm. Further, turning to start position should engage the starter and engine start. Does all MEP-804a generators operate like this?

thanks in advance. Tony

 

[DieselAddict]

Welcome to the forum!

The starter shouldn't engage in preheat. I recommend taking the TM and going over the wiring on S1 to make sure someone didn't put a wire in the wrong place. When you take a look at the switch you'll see plenty of extra terminals where someone can put a wire that shouldn't be there.

 

[calucyk]

Welcome to the forum!

The starter shouldn't engage in preheat. I recommend taking the TM and going over the wiring on S1 to make sure someone didn't put a wire in the wrong place. When you take a look at the switch you'll see plenty of extra terminals where someone can put a wire that shouldn't be there.

Roger that. Per the TM schematic, locations 2, 4, 6, and 8 are hot. On mine, 4 and 8 are bridged and have wires on them. Need to trace those wires to their end points. On the other side of S1 is 1, 3, 5, and 7. 1 and 7 are bridged with a diode - need to check direction, but as I read the schematic, the starter would not operate in the S1 start position, if the diode is reversed. Mine works, so diode must be in correct direction. 1, 3, 5, and 7 each have a wire. Need to trace those to their end points.

Anything sound off based on above?

Thanks, Tony

 

[kloppk]

My money is on the diode CR5 is reversed on S1.
The striped end of CR5 should be connected to terminal 1 of S1.
The non striped end of CR5 should be connected to terminal 7 of S1.

 

[calucyk]

My money is on the diode CR5 is reversed on S1.
The striped end of CR5 should be connected to terminal 1 of S1.
The non stiped end of CR5 should be connected to terminal 7 of S1.

thanks for the quick response. Will look it over tomorrow during daylight. Thanks again, Tony

 

[Guyfang]

Attachment is for the S1 wire hook up.

 

[calucyk]

​	​	S1 Switch​	​	​
From​	Wire #​	Switch contact #​	​	Wire #	From
J6-23​	139C​	1 2​	​	136D​	CB1-1​
TB6-4​	137N​	3 4​	​	136C​	P4-4​
J7-8​	118B​	5 6​	​	136B​	S2-2​
TB5-14​	140A​	7 8​	​	136A​	J3-U​
​	​	CR4 diode is mounted between terminals 1 and 7. The Positive side is attached to terminal 7.​	​	​
​	​	​	​

Thanks Guyfang. Very helpful. Once the rain stops, I will verify S1 wiring and then report my findings (and most likely success). Thanks, Tony

 

[Guyfang]

Do not forget to TEST the diode.

 

[calucyk]

Thanks Guyfang. Very helpful. Once the rain stops, I will verify S1 wiring and then report my findings (and most likely success). Thanks, Tony

Guyfang, I compared your chart wire numbers and termination points to the TM schematic PDF posted here ( (2) All the TM's you need to work on the MEP-804A | SteelSoldiers ). See page 21. The wire numbers and termination points do not match. Is it possible the schematics posted at the link above do not apply to my machine? I can't rule out I'm reading this wrong. Any advice before I start moving my S1 wires to match either schematic?

 

[calucyk]

Attachment is for the S1 wire hook up.

Guyfang, I compared your chart wire numbers and termination points to the TM schematic PDF posted here ( (2) All the TM's you need to work on the MEP-804A | SteelSoldiers ). See page 21. The wire numbers and termination points do not match. Is it possible the schematics posted at the link above do not apply to my machine? I can't rule out I'm reading this wrong. Any advice before I start moving my S1 wires to match either schematic?

 

[Guyfang]

You are right! Wrong picture. I was having problems coping and grabbed the wrong switch. Sorry. Here is right out of the book.

 

[calucyk]

You are right! Wrong picture. I was having problems coping and grabbed the wrong switch. Sorry. Here is right out of the book.

View attachment 849659

No worries. Thanks for confirming. Appreciate all the help. Rain is supposed to end around noon, so I can report back my findings/results soon. Thanks again, Tony

 

[calucyk]

You are right! Wrong picture. I was having problems coping and grabbed the wrong switch. Sorry. Here is right out of the book.

View attachment 849659

Problem solved. Wires 172A and 190A were reversed; 172A was on S1 7 and 190A on S1 1.

Last question related to glow plugs and the original problem. When I move S1 to the preheat position, it initially makes a click sound. It sounds like two energized points closing. Is it normal in preheat to make an initial (low) click sound? Thanks again, Tony

 

[kloppk]

When you move S1 to PREHEAT a contactor (relay) closes sending power to the glow plugs. That's the click/clunk you hear.

 

[calucyk]

When you move S1 to PREHEAT a contactor (relay) closes sending power to the glow plugs. That's the click/clunk you hear.

Perfect and thank you. Tony