b7500 Glow Plugs removal and testing

[drewzee87t]

FIXED!

Ignition switch is extremely dirty but still works. A lot of resistance there and basically throughout the circuit. It's fine for low AMP work. I put a relay on it, triggered by the original GP wire that hooks onto the GP buss bar. Went from getting 9-10V at GP's to full battery volts. It fires up from stone cold with 10 seconds on the GP and with about 3 seconds crank time.

I will do the compression tests whenever I get the adaptor, but my problem is fixed. It starts up like it is supposed to now. I am really thankful for you guys helping me walk through it.

I attached pics of my fix, it's probably better to spend the time and money on a new ignition switch, but the whole circuit has a lot of resistance and really probably not very well designed. This works WAY BETTER. I would almost want to recommend this to anyone that has an old Kubota with this type of GP circuit.

Cost - Nothing. I had all the stuff lying around in my shop.

 

[mendonsy]

Definitely a better fix than the factory setup!
One question though .... is that relay protected by a fuse?? It needs something to protect the wiring from a short circuit.

 

[drewzee87t]

The trigger side of the relay is protected by the original circuit 30A slow blow. The hot side is protected by the relay itself. At least that's what I think....hmm. I did think of putting a fuse in there, probably a good idea, but I think if the hot side shorts out between battery and relay - the relay takes the hit. I need to look at that again, but I am pretty sure that automotive circuits just rely on the relay to die if something goes wrong on the hot end.

 

[mendonsy]

Yeah, you should be fine! The 30a main fuse will protect the wiring and relays are expendable.
One thing you could do is to wire each glow plug separately back to a fuse block and fuse each one individually. That is the fix I mentioned in an earlier post for the 5 cylinder M-B engines that have a glow plug issue, but it's a lot of work and probably not worth it on a Kubota.

 

[OLD GAR]

I have not had any luck sourcing a compression tester. I did finally end up with finding one and it does not have the correct adaptor for the glow plugs. Any idea what the right size adaptor is and where one might be sourced? I am just going to put it back together for now. I can get to the GP's pretty easily now that I cleared out some room.

Harbor Freight sells a complete diesel compression test kit for under $30. I just ordered mine. 3 tractors and two are hard start in 60 or below.

 

[200mph]

Do a voltage drop test and you’ll uncover where the approximate 2 volt loss in the circuit is taking place.

I believe there are different style glow plugs that require different on time. Many older ones take a minute or so while the newer ones are quick heating. The ones in my grand L 30’s and 40’s are nearly white hot within 5 seconds. (Confirmed in bench test) There’s no way these style should be heated for more than 10 seconds. The risk is in expanding the tip making it difficult to remove.

If I owned the slow heat up style GP I’d consider looking for the equivalent size rapid rise GP style to reduce GP cycle time.

Bosch has a decent catalog with all the specs and dimensions if interested.

 

[Mark_BX25D]

This is a 4 year old thread, folks.

 

[200mph]

Do a voltage drop test on the glow plug circuit. This is different than just measuring voltage and will pinpoint where the voltage loss is taking place.

there are plenty of videos showing how to perform.