How to troubleshoot B7800 fuel delivery issues?

ADDfarmer · Oct 11, 2013

My saga continues, though it's morphed! NOTE: I'd installed the alternator upgrade kit while simultaneously adding a couple new relay-controlled light circuits; in the process I got the leads to the relays' switch connections reversed (learned all about diodes for use in relays!), resulting in blown fuses, which I wasn't aware of existed (which led me to incorrectly diagnose as key/ign switch problem- new switch out of the deal).

All seems as it was before I'd embarked on all of this, except, the engine won't fire. I'm also thinking I no longer hear the fuel shutoff solenoid clicking. Suspect that I couldn't get it to work if I'm out of the seat: can't reach it to feel it while sitting in the seat! (yeah, need to employ an assistant)

- Plenty of cranking power.
- All fuses (NOW I believe I am aware of ALL of them!) test good.
- Fuel exists up to the injector pump.
- Had been working very reliably up until I did all this work/damage!
- Fuel is fairly fresh, so too the fuel filter (in three years running this tractor I've never had a fuel issue)

I've waded through a ton of postings from here and there talking about troubleshooting fuel shutoff solenoids, but I just cannot find anything definitive for this tractor: many present generalities, which I understand, but I need specifics to ensure I don't go off on another wild goose chase like with the ign switch.

It's a two-wire connector to the solenoid. I'd like to test for proper voltages/continuity. What ign switch positions and wires do I check for what? Do I test between the wires, for continuity? Do I test each for voltage (between, or separately)? In which key setting?

Also, can anyone state with certainty whether there is or isn't a fuel control relay? I've looked at the electrical parts diagrams from Messicks and I don't see anything called such; there is, however, one relay that is just referenced "relay"- totally nondescript.

I'd pulled 12v power from a switched wire off of the OPC wire harness (red with white dashes wire). I'm doing that now and my light circuits are working exactly as they're supposed to. I don't know, however, whether that module/relay(?) was harmed when I'd had the new light relays wired incorrectly: my understanding is that this is all about OPC stuff, and seeing as the tractor will crank over I figure that all the OPC stuff has to be working well enough; also believe that I might not have had the harness plugged in when I'd blown fuses, though I can't say for certain. And, at some point I recall hearing a buzzing noise from one of the relays in the dash: it seemed like it came from the far left side, which is where the nodescript relay lives.

So far I've managed to keep myself busy without the aid of my tractor, but it's looking like I'm starting to run out of such tasks and will be needing a functional tractor pretty soon. Panic is starting to set in.

ADDfarmer · Oct 11, 2013

Just another note... I went to take out the solenoid but, like someone else on this board noted, it's just not very easy. Can't seem to get anything on the inner (toward engine block) bolt. Thin-walled socket in a 9mm? (or whatever size) Frustrating when one gets stopped in one's tracks with something that should be so simple! What's the trick?

lsmurphy · Oct 12, 2013

Remove the plug to the solenoid and see if there is voltage to it with the key on.

Crack the fuel line at the injector and crank to see if the injector is getting fuel........as you would to bleed the line.

ADDfarmer · Oct 12, 2013

OK, I tested for voltage on each wire (with a test light, ground to frame) and I get nothing.

Cracked loose an injector line and nothing.

So... clearly it's in this circuitry.

Can I test the solenoid IN the tractor by applying 12v directly to it? If so, how (what terminals of the two)?

And now that I think about it there clearly has been no clicking of the solenoid.

lsmurphy · Oct 12, 2013

I would first figure out why there is no power to the solenoid.

Get power to the wire and your problem will be solved without removing the solenoid.

Apogee · Oct 12, 2013

You need to check all OPC's. The engine will crank but not run if a safety is tripped.

Check to be sure the clutch is in, you (or an assistant) is in the seat, the gear shift (neutral) and the PTO lever.

Second would be to check the non-descript relay to see if that is the problem.

Might be a good time to refresh with the owner's manual on the various OPC's if you have one.

Apogee · Oct 12, 2013

ADD,

Was just searching for more info on this issue and found the following on info on the SSBtractor site. Figured I'd repost the info here as well. Hope it helps! Steve

http://www.ssbtractor.com/wwwboard/view_all.cgi?bd=kubota&msg=23595

B7800 Forward Reverse Safety Switch

Bill Magee - I have a 7800 and am trying to understand how the seat safety switch works with the forward and reverse pedals. I always have to hit the reverse pedal to start the tractor as the pedal does not seem to be coming up enough to trigger the seat safety switch. Is there a way to adjust that pressure? Spring tension? What else could cause this? thanks

Ralph - I have a B7510 and I believe it is wired the same way as your B7800. I do not even have to be in the seat to start mine. Frequently when I just want to start the engine to raise the implement I will mash the clutch lever with my left hand and reach over to the key switch and turn it to start the engine. I would imagine that your problem is the forward reverse safety switch position. Before you try to adjust anything grease the fitting on the transmission pedal pivot. If you have never done this it is shown in the manual(at least it's in mine). There is a nipple on the large part of the pivot attachment point. If this point is dry it will cause the pedal not to return to the correct position and result in the switch not making contact. The fact that you have to wiggle the reverse lever is a good indication that this is your problem.

Zac - Had same problem with my B7800. I would get off the tractor and it would quit. Would have to hold the key on start and wiggle the peddle around till it would start. Dealer came out, lubed the hell out of some rod close to the grease fitting, sprayed safety switch and worked pedal back and forth countless times. Been a year now and haven't had any problems with it.

Don - b7800 hydromatic want start before I could wiggle the forward reverse pettle and it would start but not now
cliff thank you, I read about what the dealer did to your forward reverse switch and tried it. worked great! thanks again

ADDfarmer · Oct 12, 2013

Folks, thanks for the input.

I do not believe the OPC (and thus any safety switches) comes into play because the engine cranks.

I will troubleshoot the solenoid wiring as lsmurphy suggests: I was really trying to do anything I could to not have to rip the instrument cluster back off

Looking at a few pictures here and there (some are that I have*, though none are fully conclusive on this) it appears that the nondescript relay is in fact in the circuitry as it seems to have two heavier guage WHITE wires going to it (and one large red one)- the connector to the solenoid also has two heavier guage WHITE wires.

* This pic shows the relay to the far left (and the two white wires); it also shows the new relays for my work lights (straddling the OPC):

http://farm4.staticflickr.com/3754/10197802425_b7ffc560e2_b.jpg

So...

Tomorrow I will (whine and) pull apart the console and check continuity of those white wires. I cross my fingers that it'll end up being just the cheap "nondescript" relay ($11?).

Apogee · Oct 12, 2013

ADDfarmer said:
Folks, thanks for the input.

I do not believe the OPC (and thus any safety switches) comes into play because the engine cranks.

I politely beg to differ. If the OPC controls aren't in the picture, how else would the engine shutoff if the operator leaves the seat with certain levers engaged?

The reason Kubota put the fuel solenoid on the engines was to automate shutdown in case of the operator leaving the seat, loss of oil pressure, etc... The same system is also tied into the key switch and is how the engine shuts down when you turn off the key. If this weren't the case, they would have stayed with the mechanical shutdown that was directly hooked to the pump that all of their early models had.

You really need a wiring diagram so you can figure out which switches need to be closed to trip the fuel relay and subsequently activate the fuel solenoid. It's hard to know which ones prevent cranking and which prevent running as they're two different circuits.

From the owner's manual:

Page 28 - "Note: [B7800] - When you stand up from the seat with the speed control pedal stepped on or the speed set lever engaged {ON}, the engine will stop regardless of whether the machine is moving or not. This is because the tractor is equipped with Operator Presence Control system {OPC}."

Page 33 - "Note - Tractor engine will not start if Mid-PTO gear shift lever is in the engaged ("ON") position."

Page 34 - "Note - Suppose the PTO system is engaged but you stand from the seat or the seat is not tilted forward. In such case, the engine stops itself."

Also you might run through the 50 hour adjustments on pages 51 & 52 (specifically test 5) & also double check that the fuses are all good and match what's on page 65 for the B7800...

Again, my point in posting the above is because there are two distinct circuits in play here. If the switches on the fuel run circuit are not closed, the engine will crank but not run. What I'm thinking is you may have bumped one of them while you were wiring the lights and not realized it.

http://www.kubotabooks.com/AutoInde...df&AutoIndex=ae32228e89ff1959833916d16319b3f9

Good luck!

Steve

ADDfarmer · Oct 12, 2013

"Won't start" is a pretty generic category, one which I do agree OPC plays a BIG part in. In my case, however, my "won't start" is qualified as "not firing"- the engine turns over, which, if I'm understanding its purpose correctly, means that the OPC has cleared all the safety checks and gives the green light to starting (which begins with allowing the starter solenoid to be engaged). If I am wong on these assumptions/understandings then I apologize and would like to see some condition in which the OPC would allow the engine to be cranked but not fired.

Again, here is what is happening:

- Turn key to start, all the normal lights on the dash appear and the engine's starter engages

- There is no fuel coming out of the injectors (I cracked one a bit and nothing)

- Fuel is getting to the injector pump

- I hear no fuel solenoid click

- I have NO voltage on either of the two wires going to the fuel shutoff solenoid

Believe me, I'm pretty aware of the various safety switches. I've probably managed to stop this tractor by agitating every one of them at some point: heck, I've even managed to stop the tractor via having the main fuse pop out! As much as they can be a pain I have never considered bypassing any of them.

I've put nearly 350 hrs on this thing, in less than 3 years. Other than breaking a few things here and there this tractor has been bulletproof (I make it work REAL HARD, because I WORK REAL HARD), though not against my latest wiring snafu (and for me this current thread, hopefully, is the last thing to get all the skeletons pushed back into the closet).

North Idaho Wolfman · Oct 13, 2013

I do believe that is the type of solenoid that can be removed and it will start, you will need to re-insert it to shut it off.
This will tell you if it's the solenoid or wiring that's failed or if it has other issues.

lsmurphy · Oct 13, 2013

ADDfarmer said:
"Won't start" is a pretty generic category, one which I do agree OPC plays a BIG part in. In my case, however, my "won't start" is qualified as "not firing"- the engine turns over, which, if I'm understanding its purpose correctly, means that the OPC has cleared all the safety checks and gives the green light to starting (which begins with allowing the starter solenoid to be engaged). If I am wong on these assumptions/understandings then I apologize and would like to see some condition in which the OPC would allow the engine to be cranked but not fired.

Again, here is what is happening:

- Turn key to start, all the normal lights on the dash appear and the engine's starter engages

- There is no fuel coming out of the injectors (I cracked one a bit and nothing)

- Fuel is getting to the injector pump

- I hear no fuel solenoid click

- I have NO voltage on either of the two wires going to the fuel shutoff solenoid

Believe me, I'm pretty aware of the various safety switches. I've probably managed to stop this tractor by agitating every one of them at some point: heck, I've even managed to stop the tractor via having the main fuse pop out! As much as they can be a pain I have never considered bypassing any of them.

I've put nearly 350 hrs on this thing, in less than 3 years. Other than breaking a few things here and there this tractor has been bulletproof (I make it work REAL HARD, because I WORK REAL HARD), though not against my latest wiring snafu (and for me this current thread, hopefully, is the last thing to get all the skeletons pushed back into the closet).

Again, not knowing your machine but knowing how things work........

Here is what I suspect. There is a safety switch circuit, a ground wire that makes the rounds of all the switches, normally open switches. When all the switches are closed a circuit is complete which allows for the starter to engage and the fuel solenoid to be released and fuel to flow.
There must be a fuel solenoid relay, when the safety circuit is complete the relay is activated allowing the current to flow to the solenoid allowing it to release.

Either the safety circuit is open or the relay is bad..........there can really be no other explanation.

The relay can be triggered by a ground wire.

I would trace back the safety circuit to the relay, if it is a ground.......ground it...........if it is a hot wire......put current to it.

Bypass the safety circuit to test.........also may have to replace the relay.

ADDfarmer · Oct 13, 2013

Opened up the console and did continuity and voltage checks. But, before jumping into the results of these I figured I'd try to provide some more detail/clarify on the wiring itself, so here is what I have/see:

Wiring harness has two wires going to the fuel shutoff solenoid, one is a heavier (14ga?) all white wire and one is a lesser (16 ga?) white with blue stripe wire. At what I believe to be the other end of this harness (relay end) I see two similar wires, along with a heavy gauge red wire and a light gauge (18 ga?) black wire: these four wires are in the plug that goes to the "nondescript" relay.

Here is what continuity testing shows (reference from relay plug end) through the wire harness going to the solenoid; YES = continuity, NO = no continuity:

White to white: YES
White to white/blue: YES
White/blue to white/blue: NO
White/blue to white/blue: NO

Here's what voltages show up (relay unplugged):

Red: 12v+ non-switched, 10v-ish when cranking
White: 0v non-switched and 0v when cranking
White/blue: .8v non-switched, .5 in Run, 3.8v cranking

There is no voltage on either wire at the solenoid end when I crank the engine over (starter engaged and spinning).

The relay itself shows 80 ohms of resistance across the two lighter colored terminals (brass?), which, I think, correspond to the Red and White wires. No other continuity across any of the other combinations of terminals.

North Idaho Wolfman · Oct 13, 2013

The numbers that you posted mean to me that the relay and / or the solenoid could both be bad or burnt.
Some of what people think are relays are actually relay timers and work differently than a normal relay, I would need the part # to be able to tell you what you have.
You can keep trying to crank it and possibly burn out more parts or you can disconnect the solenoid, un bolt it, find out if the tractor starts.
If that lets it start then you are assured that it is the solenoid or something beyond that and is an electrical problem.
If it doesn't start, stick it on a trailer and haul it to the shop as it got bigger problems than just the electrical!
Next step, put power directly to the solenoid with jumper to the battery white to ground and colored to hot the solenoid should move, if it doesn't then solenoid is toast, get a new solenoid.
If the new solenoid installed still won't let it start then replace the relay, and double check the fuses to make sure it didn't cook one of them too.

Apogee · Oct 13, 2013

You need to pop the cover of the relay off and figure out which two terminals supply the coil. Usually, there is a diode across the coil terminals on the inside. Check using VOM to see if it's good. If you don't see a change checking between the coil terminals while reversing polarity, then either replace the diode or the whole relay assembly.

Assuming the diode is good (if it has one) you can test the relay by supplying 12v to the coil terminals. It should click. Try not to hook it up backwards because you will blow the diode.

Look at the socket and figure out which of the coil wires supplies +12v to the coil. If the 12v wire connects to one of the coil terminals, then you should be able to make the tractor run by grounding the other coil terminal. If you find you have no power to the coil, then check the 5 amp fuel fuse to see if it's blown.

If the diode in the relay is blown, it could be blowing the fuse as soon as power is applied.

Apogee · Oct 13, 2013

Wolfman is definitely right in that it could be a timer relay. Hopefully, you can get the cover off to check. If it's potted in epoxy, then it's a timer relay like he mentioned.

ADDfarmer · Oct 13, 2013

Hi, Folks, I think that I've tracked down specs for this part (part number is ACA12115, CA1a-12V-A-5):

http://doc.chipfind.ru/pdf/nais/ca1a12va5.pdf

I'm not an electronics expert, but it appears that this relay doesn't have a timer function. The resistance as they state for this part number is 80 ohms, which is what it tests at, so I'm good there. I "think" that it has a diode ("1 Form C"), however, I'm unsure whether I could still have 80 ohms of resistance with a trashed diode.

I was itching to take out the solenoid from the get-go but I don't have the right tools on hand to do it: someone else also struggled with this: http://www.ssbtractor.com/wwwboard/view_all.cgi?bd=kubota&msg=28951 I can loosen the outer bolt, though I'm not sure if it's 10mm (seems like it might be 9mm?), but I cannot get a small 10mm socket on it because of the tolerance between the bolt head and the solenoid casing (no way a wrench would work).

Because I have no voltage coming to the solenoid I'm figuring that I still have either a relay or a wiring issue. Not sure how I can properly rule in or out the wiring. The relay is cheap, so maybe I just go that route.

Apogee · Oct 13, 2013

If the relay has an internal diode the test is easy. Measure resistance across the coil terminals one way, then reverse polarity and measure again.

If the diode is good, you should get 80 ohms one direction and a short (0 ohms (or close)) the other way.

The relay only conducts juice one direction, so that is why 80 ohms one way and a short (if it's working right) the other.

eserv · Oct 13, 2013

You should have battery voltage at the white/blue wire if all the safety switches are satisfied. if you jumper between the red and white wires the solonoid should activate and the tractor would start if cranked. doing that will prove whether the solonoid is working and the fuel system is ok.
It is a simple relay without a diode, 80 ohms resistance should be between the white/ blue and black terminals

ADDfarmer · Oct 13, 2013

I just did a simple ohm test across the "switch" terminals and I get 80 ohms in both the forward and reverse direction/bias.

Using the diode test (Fluke 23) I get 0.055 in both directions: initial probe sets the meter pulsing to .2+ and then drops off around 0.055.

How to troubleshoot B7800 fuel delivery issues?

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