M923 Starter Issue

[fuzzytoaster]

Murphy came on a recovery with me this weekend when hitting a rough patch in a construction zone. The truck ran great but after we got home and I tried to start her again issues appeared. Initially engaging the starter resulted in the engine trying to turn over but it never got a full rotation. Letting the starter cool down I found the ground wire #94 that grounds the PCB box to have been disconnected. It looked as if the end nut on the starter was loosened enough for the main ground wire to lose enough contact so that the smaller wire #94 took the current and singed off. Fearing the worst I hit the TMs and searched the forum.

Having cleaned the starter contacts and verified the wiring I'm still having no luck. The M923 is slaved off a running M931 to avoid running the batteries down and I've got a confirmed 24V to the starter. The cleaning and tightening solved the wire #94 issue from smoking/burning again but she is not turning over. It's almost feels as if she isn't getting enough power to make a full rotation to start the engine but you decide from the video clip.

I looked at the PCB and went ahead and swapped a known good one from my M931. The original never clicked but this newer one clicks when the power is on (cant verify if it clicked on the m931). I had suspected a bad PCB initially as it was an older unit but the same issue still exists. It's a little bewildering..and I've even hit it with a hammer to make sure the starter isn't physically stuck, I've had that issue with an M35A2 before and it worked. Also the M923 has always started and ran great but that road patch was terrible. I ran out of time today to try and turn her over by hand, tomorrow I'll attempt it.

Video: http://youtu.be/tWQ9dXhrqjQ

 

[goldneagle]

I think you have a bad battery in the system. Since the starter is trying to turn the relay and solenoid are working. It is doing the same thing as it would with weak batteries. Another idea is to try jumping between the two large bolts on the solenoid and see if you get any faster speed out of the starter motor. If the starter motor spins fast then there might be an issue with the solenoid not making a good connection internally. You can try rigging a battery disconnect switch with heavy wires to the large terminals on the solenoid. Otherwise don't use a good screwdriver to jump them since some arcing may occur.

I just reread your post and remembered that my tractor mower had the same issue. I always thought the battery was too weak, or the wire feeding the stater was too thin... Ended up it was a bad starter. Once we replaced the stater the mower starts almost instantly!

 

[74M35A2]

I should have traded you a new starter for the LED lights!

The PCB is working since it will engage the starter. Measure battery voltage at the starter terminals where the battery cables connect to it. During an attempt to crank, battery voltage should not drop below 20V. If it stays at 20V or higher, then the starter is shot. If the voltage is less than 20V, then the batteries are weak, or the cables/connections are bad.

If a cable terminal was loose, it likely overheated the stud it was connected to, and possibly damaged something.

Measure voltage during cranking as a next step. Use the ground terminal connection
on the starter to have an accurate reference, not an engine ground.

 

[74M35A2]

I think you have a bad battery in the system. Since the starter is trying to turn the relay and solenoid are working. It is doing the same thing as it would with weak batteries. Another idea is to try jumping between the two large bolts on the solenoid and see if you get any faster speed out of the starter motor. If the starter motor spins fast then there might be an issue with the solenoid not making a good connection internally. You can try rigging a battery disconnect switch with heavy wires to the large terminals on the solenoid. Otherwise don't use a good screwdriver to jump them since some arcing may occur.

That starter can pull up to 1000 amps, so use something with an insulated handle if you are going to do this to keep from burning your hand (will likely get hot).

 

[goldneagle]

I should have traded you a new starter for the LED lights!

The PCB is working since it will engage the starter. Measure battery voltage at the starter terminals where the battery cables connect to it. During an attempt to crank, battery voltage should not drop below 20V. If it stays at 20V or higher, then the starter is shot. If the voltage is less than 20V, then the batteries are weak, or the cables/connections are bad.

If a cable terminal was loose, it likely overheated the stud it was connected to, and possibly damaged something.

Measure voltage during cranking as a next step. Use the ground terminal connection
on the starter to have an accurate reference, not an engine ground.

From what I can tell, on the M939 the ground goes from the battery to the starter then to the engine.

 

[davo727]

Did the whole truck get air on that rough spot?

 

[fuzzytoaster]

I think you have a bad battery in the system. Since the starter is trying to turn the relay and solenoid are working. It is doing the same thing as it would with weak batteries. Another idea is to try jumping between the two large bolts on the solenoid and see if you get any faster speed out of the starter motor. If the starter motor spins fast then there might be an issue with the solenoid not making a good connection internally. You can try rigging a battery disconnect switch with heavy wires to the large terminals on the solenoid. Otherwise don't use a good screwdriver to jump them since some arcing may occur.

I just reread your post and remembered that my tractor mower had the same issue. I always thought the battery was too weak, or the wire feeding the stater was too thin... Ended up it was a bad starter. Once we replaced the stater the mower starts almost instantly!

It very well could be a bad battery, all were showing between 12.8V-12.6V though they are revived "good old" 6TMFs . I did clean the battery contacts and double check their connections but I'll give it a shot tomorrow.

I should have traded you a new starter for the LED lights!

The PCB is working since it will engage the starter. Measure battery voltage at the starter terminals where the battery cables connect to it. During an attempt to crank, battery voltage should not drop below 20V. If it stays at 20V or higher, then the starter is shot. If the voltage is less than 20V, then the batteries are weak, or the cables/connections are bad.

If a cable terminal was loose, it likely overheated the stud it was connected to, and possibly damaged something.

Measure voltage during cranking as a next step. Use the ground terminal connection
on the starter to have an accurate reference, not an engine ground.

PM me again, my inbox was full earlier.

Did the whole truck get air on that rough spot?

The rear axle did I swear it, it even dislodged the holding pins for the tailgate and spilled my drink.

 

[jcappeljr]

I have some used working starters for sale.$175 each.250 cummins and 8.3s

 

[74M35A2]

Open circuit battery voltage means almost nothing. Best battery health indicator is to measure the voltage drop under load during cranking. From your YouTube video, it seems like bad batteries. The CCA rating of a battery is a measure of how much current the battery can put out for a specific time before dropping below a specific voltage. If you measure less than 20V at the starter during cranking, repeat the test measuring voltage at the battery terminals. If low there also during cranking (after fully charged), the batteries are shot. 12.8V or 1.26 specific gravity is a fully charged battery, but it still may not be healthy, check voltage under load.

I don't think batteries can really be rehabbed. Some people/devices/chemicals/charge methods are believed to break the sulfation build up, but at that point just go with 2 group 31's rated at 1000cca if you use it only in warm climates, or I'd go with 4 x 750cca if cold starting will occur.

Lower CCA batteries of equivalent size will last longer than a higher CCA battery due to plate thickness inside each cell. This is why a new Kenworth truck with an ISX engine uses 4 x 650cca group 31's, all in parallel, as a 12V system. Those batteries will last about 7 years operating outside of the warm engine compartment. A lower priced International with the same engine will use 3 x 1000cca batteries. Lower cost, yet lower life. The starter max draw is 2000 amps at -40 and 12V in that instance.

 

[goldneagle]

I just purchased one of these battery load tester. I would recommend you get one and test your batteries. This way you will know if they are good. Only $29.29

http://smile.amazon.com/gp/product/B000AMBOI0/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

 

[Scrounger]

[h=1]I would start with the basics. While you have the battery box open check the electrolyte levels. More on battery checking later. Then clean and check every battery connection. It only takes one loose cable to cause the problem that you are having. Then check the grounds, frame, engine and what not. Make sure the starter cables are tight. There are several ways to check batteries. I tend to use all of them. I use a Midtronices[FONT=&quot] [/FONT]MDX-P300 to see if there is an internal short. Then break out the Duo-Check and check the charge on each cell. After a full charge they get load tested with a carbon pile tester. That is 50% of rated capacity for fifteen seconds and the voltage can’t drop below 9.6 volts. If they pass they get recharged and installed. Since your starter is trying I tend to think there is something loose.[FONT=&quot][/FONT][/h]

 

[Wildchild467]

74M35A2 knows a bunch about starters, no doubt. A great resource! I have a newer style starter I am going to put on my deuce sometime just as soon as I get the other stuff on my "to-do" list done on it. I can't wait!

 

[Scar59]

Did the whole truck get air on that rough spot?

Rough roads and air time will bang up a marginal battery, load test each battery, one has a broken plate and will be open. PCB works if the starter is engaging.

 

[Jeepsinker]

Yep, load test each battery individually. You can also isolate each pair of batteries and try to start, but you only need to do that if you can't find a load tester.

 

[74M35A2]

This entry is an F up.

 

[74M35A2]

74M35A2 knows a bunch about starters, no doubt. A great resource! I have a newer style starter I am going to put on my deuce sometime just as soon as I get the other stuff on my "to-do" list done on it. I can't wait!

Working for an OE supplier of both automotive and MD/HD starters, and overseeing a HD starter warranty return division that does 100% warranty retention and analysis may have something to do with it.

Load banks work, but the vehicle starter itself is the perfect load bank. You can't get more of a representative load. Don't go and buy any testers to solve this. Follow this order, as compiled from all above input:

1. Make sure the electrolyte level in each battery cell is at least covering the plates. If not, add distilled water.
2. Fully charge the batteries. Doesn't matter how you do it, 24V off another MV for hours on end, or disconnect the series cable and use one/several 12V automotive charger(s) overnight. Fully charged should show 1.26 on specific gravity, or 12.8V per battery after removing the surface charge. Surface charge is the artificial open circuit voltage that will be present just after charging. It may be 13V or higher. Typically have to apply a load of several amps for 30 seconds to remove this useless charge and reveal the true charge level of the battery.
3. Measure battery voltage at the starter during a crank attempt. Repeat at the battery terminals. It should not drop below 20V when cranking or attempting to crank.
4. If and only if you can get a solid 20V to the starter during cranking or a cranking attempt, and after confirming the engine rotates freely as it should, can you blame the starter. The starter can't do what it is designed to if the power required is not delivered to it. Extended cranking with low batteries will cook a starter in a hurry, because a lot more time will be spent conducting hundreds of amps through each copper commutator section on the armature as the armature rotates much slower than it is supposed to. The higher the cranking speed, the shorter the time each segment is exposed to high current, the less heat that is built up in each segment, and the longer it will last. The brushes also become softer the hotter they are. Short bursts like he did in the YouTube video are OK. With only a little more battery charge, or jumping off a weak vehicle to where it can crank continuously, yet slowly, will kill a starter very quickly.

Hope this helps everybody.

 

[fuzzytoaster]

Sitrep:

Spent the day working out on the truck. I load tested each battery getting 12.6/12.8/12.0/11.8 respectively and used the slave off my running M931 to charge them and when attempting to crank. Trying to simplify the situation I completely removed all the 6TMFs and put in two recently new type 31's out of the M931 but still no luck at turning it over. I shot another video and I'm getting 25V to the starter but when cranking im dipping way below 20V hitting as low as 11V with the new pair of batteries. The battery terminals were cleaned and double checked, the starter ground wire cable was checked and got a little warm but nothing abnormal. The ground terminal on the starter itself spins when trying to tighten the bolt so.. but I now have clicking so I suppose that's progress.


http://youtu.be/c6D9hdU7J40

 

[Jeepsinker]

You have a bad cable then.

 

[fuzzytoaster]

You have a bad cable then.

Edited about starter ground terminal.

 

[74M35A2]

That clicking and the 11V sounds like dead batteries. There is not even enough power being supplied to hold the solenoid engaged against its internal spring. Your load test seems OK. Was the 11V drop measured at the starter? I am guessing so from the video. Repeat the test and measure the voltage at the battery end. If it stays much higher there, your problem is in the cables or their connections. How old are these batteries from their new date (not reman date)? Check all the connections after a few crank attempts, and feel if any are hot. If so, that will help to highlight the problem.