Strange starter behavour

[coachgeo]

Yes you would connect to the large + and - leads at the solenoid and the front of the starter motor where the main ground strap is located.

What general said IRT the load test. pushing the start button is a load test, just not a full capacity one, but it satisfies the basic requirement, "voltage is not good unless it is good while supplying a load"

If the voltage falls on its face when you push the start button(load test), you need to step back thru the circuit and see where it is dropping and either fix the bad connection or the bad battery. If it doesn't drop, it isn't being loaded which indicates a starter/solenoid not completing a circuit.

You can also help isolate a bad connection with the meter wired in parallel with the current path. Say one lead on the battery + and the other lead on the starter solenoid + and measure the voltage developed across the circuit resistance when you pull current, attempt to start... You can do the same thing on the ground path, battery - to starter motor ground point...

long test leads on one battery at one end and, volt meter on other. when hit red button (power on) the 1st of the the two battery (no 12v stuff on it/ older batt) dances between 12v and 10v when trying to start it. The 2cnd battery new in April (also 12v side) does same 12v-10v with occasional 4 & 5v hmmm. its a NEW larger battery

What is "on its face"? couple volts or half or more of volts?

Odd thing though is on first attempt at this... one clunk, as it tried to turn engine, then it started instantly like normal. ran it for about 10min checking stuff. shut it down. tried again several times.... same thing. clunk stop... clunk stop as you hold the red button. banged on parts of starter... no difference.

where does ground strap attach. so tight in there cant find it.

push of red button turns off the Trans keypad. Otherwise it looks normal

 

[coachgeo]

Bang bang bang of the starter? Add a big ground cable from the batts negative to a sanded spot on the main frame rail.

will shoot for getting a ground strap to add there. Maybe steal it off other LMTV alternator ground for now. Banged on it. No help

 

[Ronmar]

Well the trans display going dark indicates it is dropping voltage. Did you get a chance to check 24v at the cab test points while you pushed the start button. It also makes a difference where the leads are connected. IE, if you are connected to the battery clamp on the battery and not touching the actual post of the battery, a bad connection between clamp and post could be dropping all the voltage when you try and pull current from a good battery. for the battery volt drop test you want the test lead in contact with the lead posts on the battery...

I really should do a video on this some day...

 

[coachgeo]

Yes you would connect to the large + and - leads at the solenoid and the front of the starter motor where the main ground strap is located.

...

hmmmm... confused.. you say to attach 3 leads? (one each to large (+) and (-) ??* ) ... and third one at front of starter motor?

*I can look again but I think there is only one large one on solenoid as well as two small)

 

[coachgeo]

Well the trans display going dark indicates it is dropping voltage. Did you get a chance to check 24v at the cab test points while you pushed the start button. It also makes a difference where the leads are connected. IE, if you are connected to the battery clamp on the battery and not touching the actual post of the battery, a bad connection between clamp and post could be dropping all the voltage when you try and pull current from a good battery. for the battery volt drop test you want the test lead in contact with the lead posts on the battery...

that's what I was wondering about the volt drops. I was on terminals.

I will try to climb to the PDP for the test spots.... think with it tilted its not got the Passenger door above the huge mud puddle anymore LOL. really rather not climb thru cab while its tilted

 

[Ronmar]

hmmmm... confused.. you say to attach 3 leads? (one each to large (+) and (-) ??* ) ... and third one at front of starter motor?

*I can look again but I think there is only one large one on solenoid as well as two small)

Sorry, i got you confused with 2 different tests.

Lets just stick with voltage tests.

Test 1: 24V battery voltage at the + and - battery posts while you push start. Tests if battery can handle the load. Probably should NOT go below 10V

If not OK, work on getting a battery that will not fall on its face under load.
If OK, on to test 2.

Test 2: Repeat the 24V test at the cab PP test points. A bad connection at say the Polarity Protection Device could cause a drop at the PP which drops the trans and removes neutral start circuit. Since your trans display is going out when you push start, this sounds like a likely scenario.
If test 2 is not OK, move back thru the circuit toward the batteries(PPD?) and repeat the test, looking for a point where the voltage does not drop significantly more than the batteries do.

If test 2 is OK,

Test 3: repeat the 24v test at the starter solenoid(+) and motor(-) where the large gauge cables are connected.

Again, voltage falling on its face under load, work back toward the source to find where it is being lost under load. A bad connection at say the shunt, or even a bad battery post clamp or where the cable terminal is bolted to the post clamp, or a bad/corroded cable crimp...

you should at no time see less than ~3% less than the loaded battery voltage. IE: if the battery drops to 11.5/23V while cranking, the voltage at the end of the load path(starter and solenoid) should drop no more than 3%(~0.69V) from that source voltage due to circuit resistance.

 

[coachgeo]

Sorry, i got you confused with 2 different tests.

Lets just stick with voltage tests.

Test 1: 24V battery voltage at the + and - battery posts while you push start. Tests if battery can handle the load. Probably should NOT go below 10V

If not OK, work on getting a battery that will not fall on its face under load.
If OK, on to test 2.

Test 2: Repeat the 24V test at the cab PP test points. A bad connection at say the Polarity Protection Device could cause a drop at the PP which drops the trans and removes neutral start circuit. Since your trans display is going out when you push start, this sounds like a likely scenario.
If test 2 is not OK, move back thru the circuit toward the batteries(PPD?) and repeat the test, looking for a point where the voltage does not drop significantly more than the batteries do.

If test 2 is OK,

Test 3: repeat the 24v test at the starter solenoid(+) and motor(-) where the large gauge cables are connected.

Again, voltage falling on its face under load, work back toward the source to find where it is being lost under load. A bad connection at say the shunt, or even a bad battery post clamp or where the cable terminal is bolted to the post clamp, or a bad/corroded cable crimp...

you should at no time see less than ~3% less than the loaded battery voltage. IE: if the battery drops to 11.5/23V while cranking, the voltage at the end of the load path(starter and solenoid) should drop no more than 3%(~0.69V) from that source voltage due to circuit resistance.

For clarity/reminder how it is done: - to remove PPD you pull the 2 big leads (and there small one if present) off top post of PPD and attach those 2 instead to each other; bypassing PPD. Repeat for bottom most post's 2 leads . Correct?

Am forgetting What do you do with red capped ones on their own post? Doe those 2 tie to each other as well... orrr ??

 

[coachgeo]

Bang bang bang of the starter? Add a big ground cable from the batts negative to a sanded spot on the main frame rail.

is the solenoid on the "power steering bottle?" bracket on frame rail... one of them in the starter circuit?

 

[Suprman]

The main ground goes thru a current shunt the connections deteriorate add the new ground

 

[coachgeo]

is the solenoid on the "power steering bottle?" bracket on frame rail... one of them in the starter circuit?

appears so... if we (me and George Germann heavy repair) jump this solenoid....truck starts.

 

[coachgeo]

The main ground goes thru a current shunt the connections deteriorate add the new ground

will do. I know where the shunt is your speaking of. For the ground just pull it off Negatve of the 24v ground of the combined two battery. or any of the negatives between the pair? (im just running two batts)

 

[coachgeo]

so far PPD was bypassed by using the lugs on the PPD to bolt the lower 2 and its partner red one above it together onto one lug. Same for the upper 2 and its partner red. It started after that.... about 20 min later.... it went back to .... No change... still just clunk.

we chased voltage drop all over the place. Drops about everywhere. All testing was from his 24v jump pack to eliminate potential for it being one of my batteries was the issue.

again it starts via jumping the solenoid on the frame rail. What does that solenoid interrupt? is that how the Start inhibitor cuts out the start function? buttt.. coil in the solenoid tests as good

Tag Polarity Protection Device

 

[Ronmar]

so far PPD was bypassed by using the lugs on the PPD to bolt the lower 2 and its partner red one above it together onto one lug. Same for the upper 2 and its partner red. It started after that.... about 20 min later.... it went back to .... No change... still just clunk.

we chased voltage drop all over the place. Drops about everywhere. All testing was from his 24v jump pack to eliminate potential for it being one of my batteries was the issue.

again it starts via jumping the solenoid on the frame rail. What does that solenoid interrupt? is that how the Start inhibitor cuts out the start function? buttt.. coil in the solenoid tests as good

Tag Polarity Protection Device

The relay near the power steering is the aux start relay. This is the old school way of dealing with the flyback voltage from the start solenoid which is part of the starter where the + cable is attached. the aux relay closes a circuit and applies 24v to energize the solenoid on the starter.

Relay K1 in the power panel powers the aux start solenoid when it has what it needs to energize(ign power, neutral start and pushbutton circuits complete).

voltage drop testing is VERY straight forward and should not require anything else. You start at the batteries and if it falls flat there, then you deal with the batteries first… what do the batteries measure when you jump the aux relay? What does the voltage measure at the starter solenoid when you crank from the aux relay?

now if you are jumping the aux start relay and it cranks, you are bypassing most of the need for cab power. But you could still have a volt drop there that is killing the crank from the cab…

 

[coachgeo]

now if you are jumping the aux start relay and it cranks, you are bypassing most of the need for cab power. But you could still have a volt drop there that is killing the crank from the cab…

If I understand you right.. jumping the aux. starter will start it...... but I may still not have other well functioning stuff like transmission electronics turn signals, brake lights etc. ?

 

[Ronmar]

If I understand you right.. jumping the aux. starter will start it...... but I may still not have other well functioning stuff like transmission electronics turn signals, brake lights etc. ?

Correct, or those items may drop offline unexpectedly.
what did the 24V do at the cab test points while you pushed the start button?

the first issue I had with a LMTV was this one. Pushed the button and it went clunk, or clunk and click,click,click from the dash relays as long as the button was pressed. The load applied by the start switch and the circuitry it powered was enough to drop the voltage in the power panel low enough that the relays would relax, then pull in as the voltage spiked, then relax again as it fell… It was a bad connection at the polarity box, but the voltage was perfect at the test points until I pushed the start button…

 

[coachgeo]

Correct, or those items may drop offline unexpectedly.
what did the 24V do at the cab test points while you pushed the start button?

the first issue I had with a LMTV was this one. Pushed the button and it went clunk, or clunk and click,click,click from the dash relays as long as the button was pressed. The load applied by the start switch and the circuitry it powered was enough to drop the voltage in the power panel low enough that the relays would relax, then pull in as the voltage spiked, then relax again as it fell… It was a bad connection at the polarity box, but the voltage was perfect at the test points until I pushed the start button…

same as you describe above. Yesterday, we combined all the lines at the polarity box using the box's studs to combine them. at first that made a change... 20 mins later.. it all returned back to clunk

 

[coachgeo]

@Suprman @Ronmar @GeneralDisorder added-ish a ground to chassis as a test (ground vice gripped to cleaned spot on chasssis) no go... still clunks.

 

[Ronmar]

So do you see a volt drop in the cab during the clunk?

 

[coachgeo]

So do you see a volt drop in the cab during the clunk?

yes if I recall right. we saw it everywhere from just after battery all the way forward. Hence why bypassed the PPD.

Tag Polarity Protection

 

[GeneralDisorder]

yes if I recall right. we saw it everywhere from just after battery all the way forward. Hence why bypassed the PPD.

Tag Polarity Protection

What do you mean by "just after the battery"? - when you discover the first voltage drop from the battery positive post, you need to stop and address it.