B7800 starting issue, electrical

[erniev]

B7800, 350 hrs. I have a starting issue; a couple of wires chewed on; motor cranks fine, won't run; whitish smoke when it cranks; 12 v at solenoid, 5.9 at relay ; can jump relay sometimes it starts; put in new relay from dealer, didn't help. Does anyone think its a bad relay or can they go bad if contacts get jumped and burn it out?? Do I have to remove entire cover assembly to trace all the wires?
Thanks for any advice. (all new fuel , etc.)

 

[GreensvilleJay]

Without a wiring diagram.......my guess...
'motor cranks fine' means starter spins, so NOT a starter solenoid problem.
I suspect one of the 'chewed' wires controls the 'engine shut off' gizmo, and that's why engine doesn't start.
You really need the wiring diagram as other functions my not work due to the 'chewed wires'. Be sure to inspect ALL the wiring...might be 'chewed' elsewhere....

 

[Fedup]

My guess - if you're getting smoke, you're getting fuel, so it's probably not the gizmo. I'm betting you're not getting power to the glow plugs.

 

[GreensvilleJay]

hmm, sounds goods, maybe as simple as a blown 'glow plug ' fuse ??
I know glowplugs take a lot of power,easy to pop a fuse....or maybe 2 of 3 opened...

 

[erniev]

It definitely is not getting fuel; when I jump the relay and the fuel solenoid clicks, it starts right up (sometimes); the wires were not chewed through, but some were bare for a half inch or so. I also have a completely smashed blinker light with bare wire open(to be replaced), if that could do anything?

Do I have to remove the entire cover to trace all wires, or just remove the gauge assembly

 

[Henro]

It definitely is not getting fuel; when I jump the relay and the fuel solenoid clicks, it starts right up (sometimes); the wires were not chewed through, but some were bare for a half inch or so. I also have a completely smashed blinker light with bare wire open(to be replaced), if that could do anything?

Do I have to remove the entire cover to trace all wires, or just remove the gauge assembly

Did you check all the fuses? A blown fuse would give you an area of the wiring to suspect...

Also, you can download the B2410 through B2910 Workshop manual at kubotabooks.com, which has a section on the B7800 in the back of it...

 

[erniev]

Did you check all the fuses? A blown fuse would give you an area of the wiring to suspect...

Also, you can download the B2410 through B2910 Workshop manual at kubotabooks.com, which has a section on the B7800 in the back of it...

Fuses are all good; Thanks for suggesting the workshop manual; I think it must be a wire shorting somewhere or I got a bad relay?

 

[Dave_eng]

It definitely is not getting fuel; when I jump the relay and the fuel solenoid clicks, it starts right up (sometimes); the wires were not chewed through, but some were bare for a half inch or so. I also have a completely smashed blinker light with bare wire open(to be replaced), if that could do anything?

Do I have to remove the entire cover to trace all wires, or just remove the gauge assembly

I think there are two versions of B700 wiring. With with OPC (Operator presence Controller) and one without.

I have attached the WSM supplement for the one with OPC

With OPC, the engine stop solenoid is powered for a second to cut off the fuel and stop the engine.

Engine can be shut-off under the following two conditions since these conditions cause delay timer in the control
circuit of the controller to operate and it controls the fuel cut solenoid and fuel injection, and stops the engine. The
delay timer holds the fuel cut signal for about 1 second.

You should invest in a 12 volt test light.

With the test light you can easily see if the glow plugs are getting power and also if and when the engine stop solenoid is receiving power.

From memory, the B7800 without OPC has to power the stop solenoid for the engine to run whereas with OPC the stop solenoid is only powered to stop the engine.

If you don't know which system you have it is very hard to troubleshoot.

EDIT: I have found and attached the non OPC section from the WSM. As I thought with the non OPC the solenoid has to be powered for the engine to start and run.

Dave

 

[Russell King]

Do I have to remove the entire cover to trace all wires, or just remove the gauge assembly

Not really that familiar with your model but Kubota does similar things at similar times. From my L185, there will be several parts to the wiring harness, but basically there is one part under the dash and one on the engine. The other parts extend to headlights or rear lights. They should be covered in electrical tape for the most part.

I assume you will have to remove the side covers and raise hood or remove it to get visual access to the wiring harness. On my L185 there are not side covers and the hood raises towards the front so access to the engine is easy. I have to remove the steering wheel and then remove the cowling and dash panel to get any good access to the harness under the dash. You may be able to use some camera to look but honestly it is about a 10 minute effort total to get it off. If you have not removed the steering wheel recently that time can be extended to days trying to get it loose with penetrating oil. Just see how the dash and cowlings comes off to make sure that the steering wheel has to be removed.

 

[Henro]

I think there are two versions of B700 wiring. With with OPC (Operator presence Controller) and one without.

I have attached the WSM supplement for the one with OPC

With OPC, the engine stop solenoid is powered for a second to cut off the fuel and stop the engine.

Engine can be shut-off under the following two conditions since these conditions cause delay timer in the control
circuit of the controller to operate and it controls the fuel cut solenoid and fuel injection, and stops the engine. The
delay timer holds the fuel cut signal for about 1 second.

You should invest in a 12 volt test light.

View attachment 56284

With the test light you can easily see if the glow plugs are getting power and also if and when the engine stop solenoid is receiving power.

From memory, the B7800 without OPC has to power the stop solenoid for the engine to run whereas with OPC the stop solenoid is only powered to stop the engine.

If you don't know which system you have it is very hard to troubleshoot.

EDIT: I have found and attached the non OPC section from the WSM. As I thought with the non OPC the solenoid has to be powered for the engine to start and run.

View attachment 56285

Dave

Dave, is the RED text in the image something you added?

The reason I ask is because my recollection is that the B2910 ( I have one) earlier versions did not have an OPC, but later versions did.

My recollection (and I could be wrong in what I remember) is that the B7800 was offered as a no frills substitute for the B2910, and since it came later in time, incorporated the OPC which was also added to the B2910.

The PDF supplement to the WSM that you posted does not show a B7800 version without an OPC.

I absolutely am not sure, but I would have guessed that the B7800 all had the OPC, unlike the B2910, where some do not (my version) and some do (later versions).

 

[Dave_eng]

Dave, is the RED text in the image something you added?

The reason I ask is because my recollection is that the B2910 ( I have one) earlier versions did not have an OPC, but later versions did.

My recollection (and I could be wrong in what I remember) is that the B7800 was offered as a no frills substitute for the B2910, and since it came later in time, incorporated the OPC which was also added to the B2910.

The PDF supplement to the WSM that you posted does not show a B7800 version without an OPC.

I absolutely am not sure, but I would have guessed that the B7800 all had the OPC, unlike the B2910, where some do not (my version) and some do (later versions).

Henro

The red text is my writing.

Tractordata.com show the B7800 built from 2003 to 2008
It also shows "Variants:" with the B2910 shown as Delux and B7800 as Economy.

I have never owned one of these machines and accept your thoughts that the guy with the problem has an OPC system.

His starting problems did not fit an OPC system but he needs to verify GP operation as a start.

Unplugging the stop solenoid connector (if he has an OPC system) would let the engine start.

Dave

 

[erniev]

Henro

The red text is my writing.

Tractordata.com show the B7800 built from 2003 to 2008
It also shows "Variants:" with the B2910 shown as Delux and B7800 as Economy.

I have never owned one of these machines and accept your thoughts that the guy with the problem has an OPC system.

His starting problems did not fit an OPC system but he needs to verify GP operation as a start.

Unplugging the stop solenoid connector (if he has an OPC system) would let the engine start.

Dave

Thanks so much for that advice; I do have a test light, but was just using an ohm meter before. When I did get it to run, I had to keep the 12 v power at the relay jumped; as soon as I took that off, it stopped instantly. Will do everything you guys suggested. Really appreciate it.

Ernie

 

[GeoHorn]

...
I absolutely am not sure,....).

 

[erniev]

Thanks so much for all the help. Dave, the wiring diagram helped the most. I was finally able to find 2 issues-- one was the solenoid connector plug was shorting intermittently, and I just squeezed the female connectors inside the plug to make a little better contact. The other main cause was the OPC unit; all of the pins in it had 12v except for 1 set; I jumped those and it started right up. Ordered a new one and that solved the problem. Again, thanks to you all! Truly appreciated--feel lost without my tractor.

Ernie