755 John Deer Will turn over but no power to glow plugs

[schmitt2585]

Been having a hard time with this one. I have a 1991 755 John Deere that will crank over but not start. I believe it is a power issue. My dash lights that normally will light up are not working and i can not hear my glow plugs warming up. I check the glow plugs with the light stick test. They each lite up but i ground the light tester to the negitive batter cable. I have check my fueses all check out good and batter is charged up. I replaced the glow plug module and still have the same issues. I know it is not fuel issue. I think it has to do something with the dash not giving power to the glow plugs or I am missing a fues somewhere that i did not see. maybe even a ground issue. My test stick has the batteries that does not need the key turn on the tractor for it to work. With that in mind, the tester being connected to the negitive cable and everything that lite up should of told me my ground wires are good??.. This one is a litte tricky

 

[jimmysisson]

Your grounds might be good enough for a little test light but not have enough for the glow plugs. Though then the starter might not spin either. I'd remove, inspect, clean, reinstall both battery cables and see what you get anyway.
Did you test the battery? Might be gettin old, like the rest of us.
Do you get power at the glow plugs? What's missing here? Does the timer run the glow plugs on that tractor, or just the light?
Jim

 

[dusty3030]

If the tractor is somewhat warm will it should start without them. Even cold it should try.
Anyway you can put it in a heated garage or shed overnight then try it?
Does it have a block heater you plug in?

 

[schmitt2585]

Thanks Jim
im not going to lie, Im not a diesel mechanic.. I thought about what I did today. Im going off the basic elertricity rules positive into the glow plug and negitive out to complete a circuit. Im going to try to upload a video on wednesday Jan 14th to show a better idea what I have going on. What stumping me is that engine does turn over strong. I have no dash light indicators that would normally light up. I will take your advice and let you know how it goes..

Thanks,
Steve

 

[skyhook]

It does sound like an electrical problem, (if the dash lights were working before, as you stated).
You said "it's not a fuel problem"....remember, the fuel solenoid needs power to send fuel,
have you checked for power there with the key "on".
Check your ignition switch connections also, your dash should get it's power from there via a fuse.
Problems like this are pretty hard to tell without a wiring diagram of the machine.

 

[yankeerider]

I may be misunderstanding, but it sounds like you have verified that you have power to the glow plugs, but not that the glow plugs are good, because you said you connected the negative side of your test light to the negative battery cable. You need to check each glow plug for continuity. If resistance is very high, it indicates an open (bad) glow plug. You will need to disconeect the wire that connects all three glow plugs together to perform this test. My similar vintage 755 did not want to start in cold weather with only one bad glow plug. Replacing it corrected the problem.

Sent from my iPad using TractorByNet

 

[schmitt2585]

FIXED IT!

Has anyone ever heard of a fuse that is bad but not fully blown?? some how this fuse allowed enought amps to show power to the glow plugs and glow plug modual and everything I tested. I my fault not useing a amp metter which I think investing money into will help trouble shoot these problems. I used a test light.. which what Jim told me would only prove there is an amp but not enought.





Some how the glow plug fuse powers something in the dash that allows the glow plugs to light up. Hopfuly pictures loaded. The top 10 amp fuse is allowing enough power to go through reaching th glow plugs telling my i have power. I replaced all three glow plugs and a modual and still had the same problem. After testing again with a metter fuse was bad. It looked good to the human eye and pass a test with a test light but it would not provide the amps that it should of.

Thanks for everyone input and help

Steve

 

[schmitt2585]

Top picture is upside down... my bad.

Also, something I tried today. I spryed ether into the air intake and with the glow plugs disconnected I was able to start the tractor right up

 

[skyhook]

Where you have your test light on the GP will not tell you if the GP is good or not.
It will only tell you if you have power to the plug, the plug may still be bad ( in this setup).
You need to remove the wire from the plug, then test for "resistance between the top of the plug (where the wire goes) and the ground on the plug.
Glad you got her going in any case.:thumbsup:
A fuse is either open (dead) or not (good), never heard of the situation you refereed to.
Sometimes the contacts that the fuse plugs into are dirty, causing a bad connection.