753 starting issue

[corporal32]

Hi all, Purchased a used bobcat 753(508620114).starts hard when its cold and i don't want to burn out the starter,replaced the glow plugs but not getting power to the power bar that runs across them,after looking around at the wiring there seems to be a lot of splicing here and there,i found 2 fuses and 2 relays by the motor,manual seems pretty fuzzy about them and the wiring diagram doesn't seem to have my serial number,fuses test fine,the 2 relays are a omron(G8JN-1C6T-F-R-DC12) and a bosch(20065116),looks like it using only the 4 outside pins so NO?I'M pretty sure these aren't original but will they work if i replace them with a similiar type,so far i've replaced the lcd display for the boss system and now trying to fix what errors i'm getting,runs fine other then being hard to start so i figured to start here,any words of wisdom on the wiring is appreciated,first of many posts trying to get this thing looking and working good again.

 

[mmsllc]

I would start by testing the switch in the cab for power, first. (It could be that the wiring only looks sketchy, but is actually good.) After confirming everything there checks out, then move to the relays & testing of each glow plug. Use a test light to test that switch because I have seen quite a few of the corrode all to hell, due lots of moisture. Switches are cheap & easy. I hope that helps you out.

 

[Bobcatdan]

I would start by testing the switch in the cab for power, first. (It could be that the wiring only looks sketchy, but is actually good.) After confirming everything there checks out, then move to the relays & testing of each glow plug. Use a test light to test that switch because I have seen quite a few of the corrode all to hell, due lots of moisture. Switches are cheap & easy. I hope that helps you out.

Checking the switch is a good place to start. The dash connections on a F series are not sealed at all. I bet if you look at all the rocker switches, the terminals are about corroided off.

 

[corporal32]

I would start by testing the switch in the cab for power, first. (It could be that the wiring only looks sketchy, but is actually good.) After confirming everything there checks out, then move to the relays & testing of each glow plug. Use a test light to test that switch because I have seen quite a few of the corrode all to hell, due lots of moisture. Switches are cheap & easy. I hope that helps you out.

i found some corrosion on the relay sockets,went ahead and bought 2 new relays,omron type,and cleaning off the corrosion,relays are cheap so i figured it wouldn't hurt to have them around,while i'm waiting for them to be delivered i will check the key switch,has to be getting power to the switch otherwise the motor wouldnt turn over,(turn to left for glow plugs and right to engage starter)will check the terminals for corrosion and continuity back to the relay,trying to use a wiring schematic that's close to the right serial number,if the switch is bad in one direction i will just install a toggle or buy new key switch. thanks for pointing me in the right direction

 

[Tazza]

i found some corrosion on the relay sockets,went ahead and bought 2 new relays,omron type,and cleaning off the corrosion,relays are cheap so i figured it wouldn't hurt to have them around,while i'm waiting for them to be delivered i will check the key switch,has to be getting power to the switch otherwise the motor wouldnt turn over,(turn to left for glow plugs and right to engage starter)will check the terminals for corrosion and continuity back to the relay,trying to use a wiring schematic that's close to the right serial number,if the switch is bad in one direction i will just install a toggle or buy new key switch. thanks for pointing me in the right direction

You are turing the key to the left first to power the glow plugs? The newer ones have the glow time controlled by the computer.

 

[Bobcatdan]

You are turing the key to the left first to power the glow plugs? The newer ones have the glow time controlled by the computer.

Maybe I forgetting something for on s/n break, but glow plugs were normally a separate rocker switch and not part of the ignition switch. It sounds like somebody did a lot of messing around with the wiring and put a different key switch in. Pretty sure 743 had that style switch so maybe with out checking your s/n, maybe yours is an early C series.

 

[7LBSSMALLIE]

Maybe I forgetting something for on s/n break, but glow plugs were normally a separate rocker switch and not part of the ignition switch. It sounds like somebody did a lot of messing around with the wiring and put a different key switch in. Pretty sure 743 had that style switch so maybe with out checking your s/n, maybe yours is an early C series.

this easy enough to test. test light on glow plugs. does it light. ? if it does. ohm check. plugs. or old school it. pull apply twelve volts. light a cigar. until you see a glow plug lit up. you cant apperacite how hot they get. older engs with low compression will still start and run for example a 743 with a 2203. yea supposed to 400 psi. yet with 125 psi it will run (and run good) A. check for power to glow plugs. B check glow plugs. can do ohm check in unit pull the bridge ohm check it

 

[corporal32]

this easy enough to test. test light on glow plugs. does it light. ? if it does. ohm check. plugs. or old school it. pull apply twelve volts. light a cigar. until you see a glow plug lit up. you cant apperacite how hot they get. older engs with low compression will still start and run for example a 743 with a 2203. yea supposed to 400 psi. yet with 125 psi it will run (and run good) A. check for power to glow plugs. B check glow plugs. can do ohm check in unit pull the bridge ohm check it

thanks for all the info guys,i went ahead and put in new glow plugs,figured it was a easy change,the relays are cheap so i ordered 2 of them which should be here tomorrow.once i install them i will check again for voltage to the voltage bar(or whatever the correct terminology ).if no luck i will tear apart the key switch panel and go from there,my neighbors have a 763 around the same year and operate there glow plugs the same as mine(turning key to the left)i think bobcat told me it was a 93 with a kuboto v2203 motor..some of the other faults relate back to wire or sensor not plugged in.Thinking a lot of wiring issues.it also has the boss system

 

[Tazza]

thanks for all the info guys,i went ahead and put in new glow plugs,figured it was a easy change,the relays are cheap so i ordered 2 of them which should be here tomorrow.once i install them i will check again for voltage to the voltage bar(or whatever the correct terminology ).if no luck i will tear apart the key switch panel and go from there,my neighbors have a 763 around the same year and operate there glow plugs the same as mine(turning key to the left)i think bobcat told me it was a 93 with a kuboto v2203 motor..some of the other faults relate back to wire or sensor not plugged in.Thinking a lot of wiring issues.it also has the boss system

My 751 had a seperate blow switch, but i was pretty sure my 763 just uses the key to the left, i know my 743 does too.
Hopefully the relays and plugs do the trick.

 

[mmsllc]

My 751 had a seperate blow switch, but i was pretty sure my 763 just uses the key to the left, i know my 743 does too.
Hopefully the relays and plugs do the trick.

Most older machines have separate momentary rocker switch that mounts on the left side over head panel. I've yet to see (or recall) when they started using the key or other controls for glow plugs. Either way, if he looked behind both overhead panels, he would most likely find corrosion & be able to repair its effect on the wiring. I like to start with either the control switch or at the plugs (for power) to try to decipher where the issue most likely is. A routine method is key for a solid diagnostic result. (I am just too new to bobcats to know all of their terminology yet.)

 

[corporal32]

Most older machines have separate momentary rocker switch that mounts on the left side over head panel. I've yet to see (or recall) when they started using the key or other controls for glow plugs. Either way, if he looked behind both overhead panels, he would most likely find corrosion & be able to repair its effect on the wiring. I like to start with either the control switch or at the plugs (for power) to try to decipher where the issue most likely is. A routine method is key for a solid diagnostic result. (I am just too new to bobcats to know all of their terminology yet.)

absolutely right on the routine method,im a maintenance worker by trade and normally have a wiring schematic,I/O book and my laptop to troubleshoot,I know i'm kinda doing a no no playing change a tronics(its slang term from work) but as old as it is i figured it wouldn't hurt.without the correct wiring schematic i'm not sure where its pulling its power from to check the whole circuit,new to bobcats and this is a great place to hear from people who have some experience on them...thanks again for all the posts and i will respond when i get it figured out

 

[corporal32]

absolutely right on the routine method,im a maintenance worker by trade and normally have a wiring schematic,I/O book and my laptop to troubleshoot,I know i'm kinda doing a no no playing change a tronics(its slang term from work) but as old as it is i figured it wouldn't hurt.without the correct wiring schematic i'm not sure where its pulling its power from to check the whole circuit,new to bobcats and this is a great place to hear from people who have some experience on them...thanks again for all the posts and i will respond when i get it figured out

finally have the glow plugs working,turning the key to the left wasn't how to engage them,one click to the right starts the boss display and the glow plug wiring,with other alarms you cant see the timer but its there,after spending hours going over a schematic and wiring that didnt make sense to how i thought it worked,chalk this one up to no operators manual,.without boss turn key to left,,,with boss turn key to right first position ..new glow plugs,new relays,scratching my head,only good lesson i learned was BUY THE MANUALS,,thanks everyone for the input..next alarm is ECL-1

 

[Oil Pig]

I have the same issue with my 753, trying to figure out why I'm not getting power to the BUSBAR, glow plugs are good, I checked the fuses and relays and they were good as well. I get no countdown on my BOSS when I turn the key to the first position to the right.

 

[DaleM 753]

Oil Pig, I did not read through all the above, but the coolant temp is what tells the computer whether to energize the glow plugs and for how long. If coolant temp sensor is bad, the computer may never know temp is cold enough to energize the plugs. Might be worth a check Dale M

 

[Oil Pig]

Oil Pig, I did not read through all the above, but the coolant temp is what tells the computer whether to energize the glow plugs and for how long. If coolant temp sensor is bad, the computer may never know temp is cold enough to energize the plugs. Might be worth a check Dale M

I wondered if that would also be a factor. I'll probably pick up another sensor and put in it to see if that helps. Operating temp never gets over 1 bar on the BOSS temp gauge.