M998 Electrical Woes

[Jon0249]

I've been having some nagging problems with Gunny (my '90 M99. Voltage gauge has been inconsistent and erratic, usually charging, but at times over- or under-charging. So upon inspection, I observed a crack in the VR potting material. I put off swapping the voltage regulator until my batteries were dead. Put new batteries in, and initially, turning on the ignition produced a clicking noise in the ESS box. Subsequently, no click, but also no glow plug light. And no glow plug. Late summer in Texas allows me to start it, but not for long.

I took every precaution to not fry the box, which I just purchased to replace the burnt up original unit. Any ideas what I'm up against?

 

[BLK HMMWV]

sure your new batteries fully charged.
All the grounds good and tight.
You disconnected batteries before changing out ESS?
All the connections tight?
You change out box with same kind you removed?

 

[Katavic918]

Also low batteries are murder on electronics.

 

[papakb]

It would be helpful to know what alternator/regulator you have in your truck. Troubleshooting is different for different models of A/Rs. Pictures would be even better!

Warm weather tells the EESS box that glow plug activity isn't necessary. Something to be aware of because it's the way the system was designed, it's not a problem. Now if it still does it when it's cold you have issues.

 

[Jon0249]

I swapped boxes several months ago - it had been working perfectly since. But batteries were low when I experienced the failure. New batteries are charged, connections tight, did everything I was supposed to. If low voltage is bad on the box, that has to be it. Any ideas if the damage is visible? Potential for repair? Another $700 is a tough pill to swallow.

 

[Jon0249]

When the old batteries were on their last leg, starting it would produce a clicking sound, like one of the relays in the box not getting enough juice. Since I replaced the batteries, I don't get the clicking sound, but neither do I get any solenoid/relay click at all. I haven't gotten a glow plug light, and was only able to start when ambient temp was 70+. If it is the box, is there a way to test it?

In addition, since I replaced the voltage regulator, the volt meter has never been out of the yellow range. I have not put a meter on it, but I don't have a good feeling about it.

I removed the KDS box - which replaced an older version - and found no visible evidence of board component failure, but that doesn't really mean much. I'm getting really tired of dealing with all these electrical problems, and I'm pretty sure I'm not alone.

 

[Jon0249]

I do not have the heavy duty alternator - believe mine is a 60-amp. Warm weather allowed starting - I started having these specific issues before it got cold, but now our 70-degree days are gone for a while here in Texas. Because I'm not getting a relay click from the box, but starter is engaging, I'm guessing the box is wasted. If so, would that affect the new voltage regulator that isn't getting out of the yellow zone on the volt meter?

 

[Jon0249]

So instead of a steady glow plug light, I get a single flash after turning on the ignition. Starter engages, just no glow.

 

[riderdan]

So that (single ready light blink) is the way my truck has always worked if it's warm enough not to need to preheat the glow plugs. In the summer, or in the winter if I have the block heater plugged in, just a single blink and then it starts right up. When it's cold, the light illuminates until the plugs have been preheated and then turns off.

I suspect that either your box is working as designed or--if it's cold but you still just get one blink--there's something wrong with the circuit that tells the system to preheat glow plugs.

 

[DREDnot]

Im with riderdan… sounds like maybe the temp unit for the glow plugs is bad, or mismatched to the new control box?
There are certain TSUs that don't work with certain boxes. I believe older style TSU/GPCs don't work with newer style boxes

 

[Bulldogger]

Once you get it started, you should adjust the voltage regulator on the new alternator, it's in the TM and not hard. Just be careful, as you can easily slip with the screwdriver when removing the cover to access the port for the rheostat on the regulator.

It's not good to run the truck extended period with the voltage in the yellow, if indeed it was low. But that's behind us now.

Bulldogger

 

[papakb]

I always use a small phillips head screwdriver when adjusting the regulators because they tend to self center in the potentiometer. Remember to disconnect the batteries before you start working around the alternator. The power lead from the battery to the 60A alternator is an 8 gauge wire and it's capable of supplying beau-coup power that will burn things up if shorted and spacing around the alternator connector cover is tight.

A good safe place to read the output voltage to the batteries is on pins V (+) & Y or W (-) of the STE/ICE connector beside the shifter.