LMTV wont start

[Crazyls2]

Good afternoon folks, first please let me apologize in advance if this is here somewhere already. I did a couple of searches with no luck.

I thought my truck had low batteries because it seems to drain them after sitting for more than a month. I took out my batteries and verified they are good then topped them off before putting them back in the truck. Once back in the truck I press the red start button and i hear relays clicking but the starter doesn't turn.

I checked the relays the cab, they seem to be working as intended.
Put a meter on the starter solenoid and I see 24vdc when I press the starter button.

I have had the plug on the transmission controller come loose before so I pulled the dash apart to make sure they were secure and they are.

Any of you guys have any suggestions as to what I might try next? I have tried going through the TM but couldn't find the troubleshooting tree for starting.

Would greatly appreciate any help you can provide

Sean

 

[Crazyls2]

This is my third day of work trying to get my truck back to life...... after countless hours I took my frustration out on the rebuilt starter and it started

 

[Mullaney]

This is my third day of work trying to get my truck back to life...... after countless hours I took my frustration out on the rebuilt starter and it started

.
These trucks in their native form with 4 batteries and the 100 amp alternator just aren't happy sitting around. They have a vampire drain and if they sit for more than two weeks - you will need to charge them.

I'm assuming that "taking out frustration" means that you gave the starter a "Love Tap" or two?

The ground runs through the alternator to the frame. Removing that connection, cleaning it really well and applying some anti-oxidizing paste could help. Cleaning the electrical box under the spare tire is another place that needs the same care. DISCONNECTING THE BATTERIES first will be safer than smoking your truck.

 

[Ronmar]

Multi-Clicking relays/solenoids is classic bad connection. A weak connection will pass full voltage untill you try and pull current thru it. Most likley spots as mentioned are the polarity box and shunt behind cab between airfilter and spare, as those are out in the weather...

The main vehicle ground is a strap between starter case to drivers frame. It needs to be clean and solid or things go wonky. You were working on tge starter right?

On an A0 ground goes from battery, thru the shunt to the starter motor housing. Starter to frame via strap. Passenger frame up to cab and cab to X3 ground point in power panel. The alt ground runs to passenger frame and back thru the starter ground pathway to the batteries...

 

[Crazyls2]

.
These trucks in their native form with 4 batteries and the 100 amp alternator just aren't happy sitting around. They have a vampire drain and if they sit for more than two weeks - you will need to charge them.

I'm assuming that "taking out frustration" means that you gave the starter a "Love Tap" or two?

The ground runs through the alternator to the frame. Removing that connection, cleaning it really well and applying some anti-oxidizing paste could help. Cleaning the electrical box under the spare tire is another place that needs the same care. DISCONNECTING THE BATTERIES first will be safer than smoking your truck.

I have cleaned the ground strap and connection but not the other areas mentioned. I will look into it but I do think in the short term, I am just going to disconnect the batteries if I think k it will sit for a while.

Yup, the love tap is what I meant. After a few motivational taps she fired off.

 

[Ronmar]

The vampire load on the A0 is from the transmission. You can pull CB22 to remove that current draw...

 

[Klaus]

I am having the same problem. Charged batteries, verified at 12.8 V on back 2 and 12.2 V on front 2. Was running fine until I shut it off and tried cranking it again. Truck has been sitting awhile while I figured out my brakes problem... I get dash lights when I turn on Main Power, but when I push the Start button it the lights flash on and off and I get that loud clickety-click repeatadly. Starter now won't turn over.

So I shut it off and back on but without trying to start it I pushed the Up and Down arrows on the TPSS and saw "d" then "1" and finally "-". The transmission appears to be in neutral and I don't see any circuit breakers tripped. Not sure what to try next. Odd that it started fine after charging the batteries, but not a second time, right away.

Any advice would be much appreciated!

 

[GeneralDisorder]

I am having the same problem. Charged batteries, verified at 12.8 V on back 2 and 12.2 V on front 2. Was running fine until I shut it off and tried cranking it again. Truck has been sitting awhile while I figured out my brakes problem... I get dash lights when I turn on Main Power, but when I push the Start button it the lights flash on and off and I get that loud clickety-click repeatadly. Starter now won't turn over.

So I shut it off and back on but without trying to start it I pushed the Up and Down arrows on the TPSS and saw "d" then "1" and finally "-". The transmission appears to be in neutral and I don't see any circuit breakers tripped. Not sure what to try next. Odd that it started fine after charging the batteries, but not a second time, right away.

Any advice would be much appreciated!

Did you test the batteries with them disconnected? 12.2v is ~40% discharged or one bad battery - probably can't deliver full amps.

You have classic symptoms of discharged battery or bad cell (if those readings were with batteries in parallel).

Remove batteries from truck. Fully charge AND TEST batteries with load tester. Reinstall on truck.

 

[Ronmar]

What year/model truck?

Rule #1 voltage is NOT good unless tested good UNDER LOAD!

do you have a voltmeter? If not get one and measure the power at the batteries when you push the start button. It should drop no lower than about 10-11v

if that is OK, measure voltage at the 12 and 24v battery power test points in the cab power panel, also while pushing the start button.

i expect at some point, you will find the voltage falling drastically in conjunction with the pulsing you are experiencing. This by the way is a classic bad conne tion bad battery scenario. static voltage is felt equally throughout a circuit regardless of the circuit resistance. Resistance resists the flow of current so as soon as you try and pull current theu a circuit the resistance in the circuit causes a voltage drop. Like a garden hose, you turn on the faucet and open the nozzle at the end of the hose, you have a good spray(pressure and flow). Now close the nozzle and kink the hose somewhere. Again open the nozzle and you will have a brief high pressure(voltage) spray and then the spray will fall off to near zero. The kink is resisting flow and causing the voltage to drop at the nozzle.

this situation will cause relays to pull in briefly till the voltage drops and their field collapses. This causes voltage to spike again pulling in the relay that causes another voltage drop releasing the coil and starting the cycle over and over again untill you release the button.

if the voltage under load drops at the battery as General alluded to, the batts are the issue.

if the voltage pulses at the power panel test points, look to the polarity box connections. This is a common failure point, they are out in the weather inboard of the spare tire and tend to corrode…

 

[Klaus]

The readings were taken with them installed and hooked up as per the TM. I will remove them, charge again, retest and see if that improves the situation.

Thanks!

 

[Ronmar]

The readings were taken with them installed and hooked up as per the TM. I will remove them, charge again, retest and see if that improves the situation.

Thanks!

Just measuring with a meter is not a real test. You must test with load applied…

 

[Klaus]

What year/model truck?

Rule #1 voltage is NOT good unless tested good UNDER LOAD!

do you have a voltmeter? If not get one and measure the power at the batteries when you push the start button. It should drop no lower than about 10-11v

if that is OK, measure voltage at the 12 and 24v battery power test points in the cab power panel, also while pushing the start button.

i expect at some point, you will find the voltage falling drastically in conjunction with the pulsing you are experiencing. This by the way is a classic bad conne tion bad battery scenario. static voltage is felt equally throughout a circuit regardless of the circuit resistance. Resistance resists the flow of current so as soon as you try and pull current theu a circuit the resistance in the circuit causes a voltage drop. Like a garden hose, you turn on the faucet and open the nozzle at the end of the hose, you have a good spray(pressure and flow). Now close the nozzle and kink the hose somewhere. Again open the nozzle and you will have a brief high pressure(voltage) spray and then the spray will fall off to near zero. The kink is resisting flow and causing the voltage to drop at the nozzle.

this situation will cause relays to pull in briefly till the voltage drops and their field collapses. This causes voltage to spike again pulling in the relay that causes another voltage drop releasing the coil and starting the cycle over and over again untill you release the button.

if the voltage under load drops at the battery as General alluded to, the batts are the issue.

if the voltage pulses at the power panel test points, look to the polarity box connections. This is a common failure point, they are out in the weather inboard of the spare tire and tend to corrode…

it is a 1998 M1078A0. Thanks for the detailed explanation! It greatly helps, where the TM did not. I have yet to look at the polarity box. But now thanks to you and the General, I have a plan. I have a voltmeter and a battery tester. The charger I have is one from PulseTech.

 

[Ronmar]

While you are messing with it, pick your best 2 batteries and only hook up those 2 in series(keep one inner and one outer battery/remove the forward two or the rear two) Four 120AH batteries series parallel(240AH) is way too much for the 50/50 alternator to charge properly, and a horrible load for it If they are discharged. Cat specced a pair of group 31’s(100AH) for the equipment that uses these engines… 100AH is a good match for the alternator.

have had th