5 ton M923A1 starting issue, again

[Goliath P. Jones]

So I went to start up the M939 today and it was a little slow turning over, I stopped and tried a few times. Eventually it started turning over quicker but was cold and didn’t want to start. I pushed the cold start button for the three seconds as the directions indicated to do. It continued to turn over with no start. So I stopped cranking it over not wanting to burn up the starter, tried again and now no cranking, just a clunky clicking noise and nothing. I charged up the batteries thinking it might help it to turn over. Both batteries charged up and now it’s still not turning over, just the same clunk sound. The gauges move when the battery switch is engaged, parking break buzzer comes on as well as the abs light. I’m not sure what to try next, I’m leaning towards the starter being the issue as it’s not the first time it was slow to turn over. Any thoughts on what to try to further diagnose the problem before pulling the heavy beast of the starter out and having it tested and or rebuilt? Thanks in advance for any help and advice.

 

[juanprado]

Load test batteries 1st before doing anything if charged.
If not bring up to proper voltage before load test.

 

[Goliath P. Jones]

Load test batteries 1st before doing anything if charged.
If not bring up to proper voltage before load test.

What would be the proper way to load test them? I have a voltage meter, would I just test each battery separately to verify voltage or would I test them while hooked up in series? I’m not very familiar with the proper procedure to test 24 volt systems. Thanks.

 

[Mullaney]

What would be the proper way to load test them? I have a voltage meter, would I just test each battery separately to verify voltage or would I test them while hooked up in series? I’m not very familiar with the proper procedure to test 24 volt systems. Thanks.

.
It is a ROYAL PAIN, but with your cell phone camera - take a dozen pictures of the battery box from every conceivable angle. BE SURE that every battery gets its own picture. Then take a picture of the entire box. If you can't tell what is positive and negative, get yourself some tape and mark the ends of the cables...

Then comes the pain. Take out a battery or two (or more) and haul them to a battery shop or a starter or alternator shop. Have them test the batteries with a VAT meter. They can load test and also test with a bulb type tester - looking for a dead cell. Charging the battery (each are now 12 volts that way) might show smoke of you have a dead cell too...

That way you can break it down into individual components and not be concerned about 12v compared to 24v. Hopefully that makes sense?

 

[kendelrio]

You may want to check and see if its your "starting" solenoid in your PCB. I had several of the same issues before mine went kaput.

There is an easy way to check...

Zip tie your fuel shutoff solenoid back, swing your fuel shutoff valve into the "run" position, unscrew the power cable from the PCB, on the face of the connector are 2 big wire holes. Short those two together with a big wire, turn your batteries and start switch to the "On" and "Run" positions, then short your starter at the starter on the posts.

If it fires right up, it's your PCB. the rebuild is easy.

Here are some threads to help:

PCB rebuild thread

Here is the YouTube video from Wes explaining how to do what I described.

 

[Goliath P. Jones]

You may want to check and see if its your "starting" solenoid in your PCB. I had several of the same issues before mine went kaput.

There is an easy way to check...

Zip tie your fuel shutoff solenoid back, swing your fuel shutoff valve into the "run" position, unscree the power cable from the PCB, on the face of the connector are 2 big wire holes. Short those two together with a big wire, turn your batteries and start switch to the "On" and "Run" positions, then short your starter at the starter on the posts.

If it fires right up, it's your PCB. the rebuild is easy.

Here are some threads to help:

PCB rebuild thread

Here is the YouTube video from Wes explaining how to do what I described.

I really hope it’s not the PCB as I literally just replaced it a few months ago with one from Boyce equipment, a brand new unit. But I will definitely check it out to be sure. Thanks.

 

[Goliath P. Jones]

.
It is a ROYAL PAIN, but with your cell phone camera - take a dozen pictures of the battery box from every conceivable angle. BE SURE that every battery gets its own picture. Then take a picture of the entire box. If you can't tell what is positive and negative, get yourself some tape and mark the ends of the cables...

Then comes the pain. Take out a battery or two (or more) and haul them to a battery shop or a starter or alternator shop. Have them test the batteries with a VAT meter. They can load test and also test with a bulb type tester - looking for a dead cell. Charging the battery (each are now 12 volts that way) might show smoke of you have a dead cell too...

That way you can break it down into individual components and not be concerned about 12v compared to 24v. Hopefully that makes sense?

Fortunately it’s been converted to a two battery system. I’m really hoping it’s just a low battery issue as they are less than a year old. The last owner replaced them before I bought it, they are 950 cca. I will disconnect them and put them back on the charger overnight and be sure they are fully up and then run them down to the local parts store as they do all the battery, alternator and starter testing. I really appreciate all the advice, it’s frustrating to say the least when you go to fire up the thing and it doesn’t want to start. I was going to take it for it’s monthly cruise. I started it right up two weeks ago with zero issues. The joys of of big toys. Lol.

 

[juanprado]

I use a harbor freight

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

Northern tool also sells digital one

 

[Goliath P. Jones]

I use a harbor freight

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

Northern tool also sells digital one

I checked my local harbor freight website and they have the tester in stock for $20. I’ll go get one tomorrow and test them disconnected in the truck. I may have the shop test them as well just to verify them, especially if they test damaged or anything. Thanks for the link on the tester.

 

[Monkeyboyarmy]

Those 250 Cummins are cold blooded. They rarely start without starting fluid below 50 degrees unless they are turning pretty fast. Just a note, the ether does not work until the start switch is in the "start" position. So if just hit the button before turning it to start, it didn't get any ether. A lot of times I would just spray it into the intake stack although it takes a while for it to travel through all of the ducting and filter etc.

 

[Goliath P. Jones]

Those 250 Cummins are cold blooded. They rarely start without starting fluid below 50 degrees unless they are turning pretty fast. Just a note, the ether does not work until the start switch is in the "start" position. So if just hit the button before turning it to start, it didn't get any ether. A lot of times I would just spray it into the intake stack although it takes a while for it to travel through all of the ducting and filter etc.

I’m still trying to get it to turn over, batteries are deep charged. I have not had a chance to get a load test done yet or pick up a testing unit as I have not been able to get into town yet. Been waiting for a freight company to show up to deliver my new hay spear attachments. I was talking with my dad about the issues and he said the same thing about the ether needed to cold start them as he drove them regularly in the military and said that half of the rigs in the line up wouldn’t start or even turn over on cold days and they always had to have ether sprayed down the intake. I’ll let you know when I get the batteries tested, I really hope they are the problem over the starter.

 

[Goliath P. Jones]

Finally got a load tester for the truck batteries and even after over eight hours of charging they are both still very weak. So I’m going to pull them out and take them to a battery shop and see if they can do a very deep charge on them or verify if they are just no good at which point I will have to replace them both with some bigger CCA batteries, get a float charger set up on them as well as a block heater and replace the ether can on the cold start button system. Going into winter I definitely want to stay on top of it starting when I want it to or need it too. Quick question on the no starting issue. My brother In law mentioned something that I hadn’t even considered as a possibility for it not starting, he’s a mechanic at a local dealership and said he commonly runs into the problem of diesel trucks not starting or even turning over. Said it’s not uncommon that an injector sticks and fills a cylinder full of diesel and hydro locks and not allow the engine to be able to turn over. Looking at what it takes to remove injectors to try and clear the cylinder to see if it’s full isn’t something I want to tackle if I don’t have to. Is this something common to these engines? Could I test it if the deep charging or replacing the batteries doesn’t work by putting a socket and breaker bar on it to see if I can hand turn it and know it’s not hydro locked or is it too big of an engine to basically hand crank over? Thanks again for all the advice so far.

 

[charlesmann]

Maybe iv missed it. But did you try turning it over by hand using a ratchet and socket to determine if it hydalocked? That would be a less invasive method of determining a filled or partially filled cylinder. Also by turning it by hand, you can listen to the engine w/o the noise of the starter and be within earshot by the eng, instead of in the cab.

 

[Goliath P. Jones]

Maybe iv missed it. But did you try turning it over by hand using a ratchet and socket to determine if it hydalocked? That would be a less invasive method of determining a filled or partially filled cylinder. Also by turning it by hand, you can listen to the engine w/o the noise of the starter and be within earshot by the eng, instead of in the cab.

No, I haven’t tried turning it over by hand with a socket and ratchet yet. The starter isn’t turning over at all, it just makes a clinking sound when you engage the start switch. I hadn’t initially given any thought to a possible hydro lock situation until my brother in law mentioned the possibility. I wasn’t sure if a guy could hand turn a diesel engine as large as the 8.1 Cummins. But I will definitely try it tomorrow, after testing the batteries today with the load tester and them not showing but barely above bad, I am hoping they are the culprit, even though they aren’t more than a year old, as it’s the simplest repair.

 

[charlesmann]

I used use a turning tool that is inserted in the bellhousing and meshes with the flywheel ring gear. It was used to turn the eng by hand, mostly used for running the rocker arm rack or setting pump timing. I havent looked on these tcks to see if there is a hole for a turning tool, but if not, it can be turned at the harmonic balancer.

My son was dealing with starting issues and the starter just clicking on his 03 dodge with a 5.9. First thing i asked was if the batteries were charged, and he said “yes, they are brand new”, as was the starter. He took the hardest thing off, the starter, to get it checked and it came back good. Then it was his attitude of screw it, so i went to retrieve it and see him off on his deployment to okinawa. When i got the tck, first thing i did was multimeter it, and ea batt had 8 volts. It took diesels to jump it but at least it was determined it wasnt any other issues, except whatever is causing the batts to discharge.

Hopefully its just your batteries that finally gave up the goods.

 

[Goliath P. Jones]

Every other vehicle I’ve had to check if it wasn’t locked up I’ve used the harmonic balancer bolt with a socket and two foot breaker bar, and with the exception of some very large bore diesel tractor engines they all were able to be hand turned. I was unsure about the 8.1 as it’s a large engine, but certainly nothing ventured nothing gained. Worst case scenario it doesn’t turn over. I will try tomorrow and see what I get.

 

[charlesmann]

Every other vehicle I’ve had to check if it wasn’t locked up I’ve used the harmonic balancer bolt with a socket and two foot breaker bar, and with the exception of some very large bore diesel tractor engines they all were able to be hand turned. I was unsure about the 8.1 as it’s a large engine, but certainly nothing ventured nothing gained. Worst case scenario it doesn’t turn over. I will try tomorrow and see what I get.

The diesels i used to work on were the cat 3406 (14L), cummins n14 (14L) and mack engines. Before i purchased my turning tool, i would turn off the balancer.

I wouldnt think the 8.3 would be any harder to turn than the larger liter engines. Hopefully its just your batteries.

 

[Goliath P. Jones]

Well I know it’s been a bit since I last updated my progress on the starting issue. It was a combination of a couple things wrong with it. The batteries were bad, I replaced them, I charged them and load tested and they were shown to be dead, so with all the heavy rain, snow, etc it took a bit to get back to it. My son and did some testing to see if the starter was getting power to it. When it tested bad, we pulled the starter and I sent it to the rebuild shop, I got a call back a couple days later when he had a chance to open it up and look at it. The armatures had completely broken off. The shaft was just trashed and black carbon dust just poured out of it. It was not even able to be rebuilt. And as it was a prestolite he said wouldn’t even want it as a core return. I guess the Delco Remy is the better unit. Fortunately he had one new in stock and when I went down to pick it up he showed me the damage to the old unit. It was amazing that it had been starting at all in the past as I’m sure not all the damage was done at once. I guess it’s a testament to the military spec built stuff. Got the starter back in and batteries hooked up and it fired back up. Finally I can enjoy driving it again.

 

[Mullaney]

Well I know it’s been a bit since I last updated my progress on the starting issue. It was a combination of a couple things wrong with it. The batteries were bad, I replaced them, I charged them and load tested and they were shown to be dead, so with all the heavy rain, snow, etc it took a bit to get back to it. My son and did some testing to see if the starter was getting power to it. When it tested bad, we pulled the starter and I sent it to the rebuild shop, I got a call back a couple days later when he had a chance to open it up and look at it. The armatures had completely broken off. The shaft was just trashed and black carbon dust just poured out of it. It was not even able to be rebuilt. And as it was a prestolite he said wouldn’t even want it as a core return. I guess the Delco Remy is the better unit. Fortunately he had one new in stock and when I went down to pick it up he showed me the damage to the old unit. It was amazing that it had been starting at all in the past as I’m sure not all the damage was done at once. I guess it’s a testament to the military spec built stuff. Got the starter back in and batteries hooked up and it fired back up. Finally I can enjoy driving it again.

.
Congratulations!
A few bucks later and a little time invested, you have happiness.

 

[Goliath P. Jones]

.
Congratulations!
A few bucks later and a little time invested, you have happiness.

Yeah, fortunately my son works for a parts supply house and gets a pretty good discount on most things. The batteries that would have normally cost me $380 I got for a little over $200. The starter had I ordered it online from a military parts supplier was going for $450, but the local guy had it for $325. As the rebuild was quoted at $295 if it was doable, so definitely not too bad at all.