What in the ignition system could cause a large enough voltage drop to not let anything function I took off the battery to test them and the starting and hooked up the grid heater to a manual push button cause it wasn’t working and it’s been very cold lately and when I put the starter and battery’s back on every time I turn on the ignition there’s a huge voltage drop at the ignition battery terminal on the ignition switch and nothing works however if I turn it to acc position no drop and the grid heater is unhooked so it’s not that
brokedown-SKO
Senior Member
Voltage drop is normal under a heavy load like a starter... Is your starter not spinning?
cadillackid
Senior Member
are you saying that while the starter is spinning nothing works? if so, thats normal, the ignition switch turns off the power to the accessories solenoid while the starter is spinning..
I’m not explaining it right :
lights go off as soon as you turn it to the run position a the relays try to hum as if not getting enough voltage to click on the ignition switch there’s full power on the battery side when turned to the acc. Position however when turned to the ignition position voltage drops dramatically at the battery terminal of the ignition switch
Before turning the ignition switch to the start position the ignition position works as it should ie. dash lights buzzers and power goes to the starter signal wire however when hooked up to the starter and turned to the start position every thing stops working,voltage drop ect. As mentioned above until it sits about a half hour the returns to normal until attempting to crank it
It’s as if there’s a large load in ignition circuit
lights go off as soon as you turn it to the run position a the relays try to hum as if not getting enough voltage to click on the ignition switch there’s full power on the battery side when turned to the acc. Position however when turned to the ignition position voltage drops dramatically at the battery terminal of the ignition switch
Before turning the ignition switch to the start position the ignition position works as it should ie. dash lights buzzers and power goes to the starter signal wire however when hooked up to the starter and turned to the start position every thing stops working,voltage drop ect. As mentioned above until it sits about a half hour the returns to normal until attempting to crank it
It’s as if there’s a large load in ignition circuit
BlackJohn
Senior Member
How good are battery connections as far being not corroded?
And the ends of the cables to ground and to the starter itself.
Would explain a huge voltage drop so would check those first of all.
John
And the ends of the cables to ground and to the starter itself.
Would explain a huge voltage drop so would check those first of all.
John
Tell us more about your bus- cummins is a company, not an engine model.
Is your bus rusty/corroded or clean?
If it's that big of a draw, it'll get hot somewhere- hot enough to really burn your finger. Get some more eyes on it while you try?
Battery terminals are all tight. Batteries are bridged properly w/ bus bar/cable? photos help us see something you miss.
Charge the batteries between attempts. don't keep cranking or you will be changing a starter, too.
BlackJohn
Senior Member
Just looking doesn't tell the story. Remove and clean the posts as well as the cable ends at the battery. When disconnected do the starter too as well as the other wires attached there. Gotta do it sometime or you get these problems of no starts. Make everything shine with a wire wheel, starter posts included, solenoid etc and try. Then coat with dielectric grease after you get it all running again.
Interior of the cables could be corroded or burnt up too so you will need to megger them for resistance or replace to be safe. Not sure of the age but likely the best idea.
Are the batteries up to snuff or is one dying which will kill the other ck and pull down the needed voltage/amperage to start?
John
5.9 Isb motor
Vin:4uz6cfaaxycg63516
Model:fs65 school bus
Esn:56681364
Year:2000
Condition: been driven on dirt roads most of its career dusty frame/undercarriage
It’s too late for photos tomorrow i’ll voltage drop test isolating the starter by jumper wire and post results that should cover any questions on cable resistance and battery hookup batteries are known good and charged while working on it to assure full charge however it doesn’t crank so there’s no in between crank charging to be done
Jolly Roger bus 223
Senior Member
You can also use a screw driver or wrench to jump across the starter solenoid with the key in the on position and see if the starter kicks in or while trying to crank use a small ish hammer or heavy ish wrench to tap on the solenoid to see if the starter kicks in.
If either works then you need a new solenoid.
The other stuff mentioned is a good starting point and should almost be yearly preventative maintenance.
With the info we have been given it could be quite a few things as mentioned but if you know your batteries are charged all the connections at the battery,solenoid,starter,ground at a minimum are clean and tight then I would bank on the solenoid hanging up and a good wrap with a hammer while trying to start should free it up. And could buy you a few more starts but is gonna quit period soon.
Good luck
If either works then you need a new solenoid.
The other stuff mentioned is a good starting point and should almost be yearly preventative maintenance.
With the info we have been given it could be quite a few things as mentioned but if you know your batteries are charged all the connections at the battery,solenoid,starter,ground at a minimum are clean and tight then I would bank on the solenoid hanging up and a good wrap with a hammer while trying to start should free it up. And could buy you a few more starts but is gonna quit period soon.
Good luck
Ok, same motor as me- 24V Cummins w/ the VP44 Injection pump.
Where are you? what are outside temps? Block heater?
My bus would not want to start right now without block heater. Too cold.
The grid heaters pull a lot of current when the "Wait to Start" light is on, but you disconnected. Those dash gauges can get wonky- VDO?
Where are you? what are outside temps? Block heater?
My bus would not want to start right now without block heater. Too cold.
The grid heaters pull a lot of current when the "Wait to Start" light is on, but you disconnected. Those dash gauges can get wonky- VDO?
Last edited:
I’m in Arkansas it’s in the 20’s-30’s my block heater works, my grid heater was not working no signal to the relays even plugged in overnight had hard time starting it since it’s been cold did a compression test since I recently bought it and it had some blue smoke on acceleration changed the injection o rings and adjusted the valves put it back together started it using the gas rag trick ran it long enough to make sure it was all bled out kept it plugged in overnight next morning hooked up the heater grid to a push button on the dash via signal wire to the selinoid no made no difference starting so checked the staring rpms 130-150 seems a bit low so tested the battery’s and starter at the auto parts store starter passed battery’s we’re bad got had room in there for 3 battery’s so grabbed some known good ones a little lower than the cca recommended for the 5.9 but I figured 3in parallel are better than two in parallel so went with that
Twigg-SKO
Senior Member
Every symptom you have described points to either dying batteries or a poor electrical connection either hot or ground. A stalled starter could do it too, if the engine isn't cranking.
Jolly Roger bus 223
Senior Member
You don't always get charged batteries from an parts store.
That's why they have a battery charger on hand if you have them replace the battery.
They don't say that if you just exchange and walk out with one/three.
Next time you tell them you want the ones in the back not the ones on the front shelf and you want to see the standing charge in them before you buy them.
Should be at least 13 at a minimum or it barely has a chance. Especially if it's not the same replacement. I have two 8d's and one in mild temps does it just fine but in colder temps I do believe both have to play the game.
That's why they have a battery charger on hand if you have them replace the battery.
They don't say that if you just exchange and walk out with one/three.
Next time you tell them you want the ones in the back not the ones on the front shelf and you want to see the standing charge in them before you buy them.
Should be at least 13 at a minimum or it barely has a chance. Especially if it's not the same replacement. I have two 8d's and one in mild temps does it just fine but in colder temps I do believe both have to play the game.
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