No-start update...

[87M998X62]

Hey all,

I posted about my 87 M998 a while back regarding a no-start, and I hit another wall. Just a history of the trouble:

It ran fine years ago.. then slowly started having an issue where the starter would spin but it would retract the gear early and just free-spin. Then it would try to start intermittently, as if the starter was hitting like morse code (with the switch held on "Start"). Then it just got worse and worse, attempting to kick the starter once every few seconds or longer, on to nothing in the last couple of years...seemed like a connection was slowly getting worse.

Fast forward to today, when I decided to get back into the diagnosis. I was following the tech manual's procedure: no voltage at 74A on the starter, voltage was present at 14 on the neutral switch, 14B to pin A at body pcb harness had continuity, 74A to pin I on engine pcb harness had continuity, disconnected 2A from alternator and still no-crank. At this point, it says replace PCB. Another point to note, the "wait" light just stays on (rather dim) the whole time the switch is on run.

From what I've seen this isn't an inexpensive part, so does anyone have any other input on what else to potentially check before I have to spend that kind of money? Thanks in advance!!

 

[DREDnot]

Sure sounds like a start box to me.

Have you removed all the silicone globs that are covering all the cables and wiring connectors and cleaned all said connections? Under all that silicone is corrosion

 

[87M998X62]

So far the only silicone glob I have encountered was on the alternator, and everything looked ok. I went through and cleaned up a bunch of contact points a while ago.. no success.

 

[Mogman]

Have you tried shorting S and T on the diag port? this bypasses the PCB, if it does not crank then it is the starter, batteries or wiring.
S is wire #74 and T is 24V (battery)
Make sure you are shorting CAPITAL S and T, there are also lower case S and T on that plug.
There are connections both neg and positive on both sides of the battery box, many find issues with connections to the negative side shunt in the battery box.
Also have you had the batteries actually load tested?

 

[87M998X62]

I haven't tried the short yet, no. Thanks! As far as the batteries, I had them load tested maybe a year ago and I keep them charged up periodically with a slow charger. Also, I already cleaned up the connections in/around the battery box. Power is flowing, just not the way I need it to! I'll try the short trick when I get back to it next weekend.

In the unfortunate event that the PCB is actually shot, does anyone have a good replacement? I'd probably end up doing that and a grounding harness...I don't want to throw too much money at this thing above and beyond what I'm in it for already, and if you can even find replacements they seem to be $800-$1000...

 

[Mullaney]

I haven't tried the short yet, no. Thanks! As far as the batteries, I had them load tested maybe a year ago and I keep them charged up periodically with a slow charger. Also, I already cleaned up the connections in/around the battery box. Power is flowing, just not the way I need it to! I'll try the short trick when I get back to it next weekend.

In the unfortunate event that the PCB is actually shot, does anyone have a good replacement? I'd probably end up doing that and a grounding harness...I don't want to throw too much money at this thing above and beyond what I'm in it for already, and if you can even find replacements they seem to be $800-$1000...

.
Me personally, I wouldn't spend the money for a "grounding harness". They more often than not they don't solve your problem. Going through every connection with a wire brush and applying a bit of anti-oxidant paste will do more to solve your problems than anything else you can do.

The frame of the truck doesn't act as a ground. Every connection has a ground wire for lighting... The grounds need to be cleaned and pasted just like the "supply" side of the wiring.

BY THE WAY: You might want to disconnect the batteries before you start working on the wires.

 

[Bulldogger]

Have you tried shorting S and T on the diag port? this bypasses the PCB, if it does not crank then it is the starter, batteries or wiring.
S is wire #74 and T is 24V (battery)
Make sure you are shorting CAPITAL S and T, there are also lower case S and T on that plug.
There are connections both neg and positive on both sides of the battery box, many find issues with connections to the negative side shunt in the battery box.
Also have you had the batteries actually load tested?

Plus 1 on the outside connections of the battery box. Each post that the battery cables connect to on the INSIDE of the battery compartment usually has an equivalent post in the OUTSIDE of the compartment, out in the elements. That post was loose on my HMMWV, until I realized it existed.
Best of luck!

BDGR

 

[Bulldogger]

I haven't tried the short yet, no. Thanks! As far as the batteries, I had them load tested maybe a year ago and I keep them charged up periodically with a slow charger. Also, I already cleaned up the connections in/around the battery box. Power is flowing, just not the way I need it to! I'll try the short trick when I get back to it next weekend.

In the unfortunate event that the PCB is actually shot, does anyone have a good replacement? I'd probably end up doing that and a grounding harness...I don't want to throw too much money at this thing above and beyond what I'm in it for already, and if you can even find replacements they seem to be $800-$1000...

The PCB bypass to manual glow plug control is a well-established mod on this site. Our colleague TOBASH has a great sticky post about how to readily convert your Smart box into a Dumb box that is MUCH less likely to ever cause problems. CAMOtek also sells an already converted box. It's about the same $$ as a new Smart box, but has the reliability and simplicity desired.
BDGR

 

[TOBASH]

Thanks BullDogger:

My signature line contains the link to PCB and such.

I encourage members to DIY. If they PM me I can also help them obtain an affordable option.

 

[juanprado]

Load testing the batteries a year ago is almost like infinity in time.....

Harbor freight makes a good carbon pile tester that is reliable and cheap plus old school.

Make sure batteries are fully charged @ 12.6 V before load testing.

100 Amp, 6/12V Battery Load Tester

Amazing deals on this 100 Amp 6/12V Battery Load Tester at Harbor Freight. Quality tools & low prices.

www.harborfreight.com