Glow Plugs...

[LouNY]

I only removed one glow plug. The easiest to access. (It was a bit too cold and a storm was pending to risk running into difficulties removing the end ones.)

All four GP's were tested after the buss bar was removed. This could be done without removing anything.

The GP located closest to operator looks questionable if it can be removed due to the fuel tank. The one closest to the radiator also looks questionable due to the AC compressor and supporting bracket for windshield washer fluid.

In other words the middle ones are easy to remove and the ends questionable. I think it's possible for the end ones to be removed and might give it another go when I find time.

The other day it was approximately 15F and it took several GP cycles and a long crank time to start. I'm a bit surprised that after the 10-13 seconds of GP activation there isn't enough to GP heat to start withing 4 seconds of crank time. (Battery is fully charged and I verified state of charge based on specific gravity and ambient temperature. Crank speed seems fast). These glow plugs look white hot in 4-5 seconds.

Your glow plugs are not igniting your fuel, they are warming up the combustion chamber and head,
I have had good luck in extremely good times cycling the glow plugs 3-4 times giving them 30 seconds or so between cycles.
On diesels with intake manifold heaters I have done similar heat for 45-50 seconds, roll the engine over a turn or two, heat again,
my old Oliver would take about 3 cycles like that then she'd fire up nice, might have to carry the engine with the starter for a few seconds in -10F or colder.

 

[moship]

UPDATE...

Situation: Temp 12F, battery fully charged.
First attempt was to try 3 glow plug cycles (on-off = 1 cycle) and then engage the starter. The purpose of the multiple cycles was to ensure there was some heat in the combustion chamber. Tractor would turn over at a good rate but not initiate combustion. Did this at least six plus times varying the glow plug cycling scenarios during these attempts (put a charger on battery and waited to make certain voltage didn't drop in battery). Think of this as a mini experiment to see if some magic sequence would work. Motor turns over quickly but it simply would not ignite. Diesel can be smelled from the exhaust.

Made a jumper (12 awg) wire to connect the battery to the glow plug white connector (see pictures). With only 5-7 seconds of supply voltage to GP it started within 1 revolution of the motor. (My wife was inside the tractor while I momentarily touched the wire to the wire connector). In this scenario the tractor GP control and circuit was bypassed. It has never started this quickly since I've owned it with air temperatures 30 F.

So while I have 12 volts to the glow plug buss bar through the tractor/CPU/relay circuit it doesn't have the amps (my guess as I don't have the appropriate DC current probe) to energize the glow plugs appropriately.

In previous tests I know the relay tested good, but guessing it might be faulty or one of the wire connections is not good.

Not certain when I'll be able to test further to find the root cause(s), but the bypass jumper wire helps narrow this down. GP and buss bar to connector OK... So now to test the rest of the circuit.

I'll keep you posted.

 

[moship]

Did some trouble shooting today and found the root cause!!!

Started from ground zero to double check everything I've done so far.

Cleaned battery positive and ground side terminals, ground to frame, positive terminal to slow burn connectors, removed wire terminals from plastic connector at slow burn fuse, removed terminals from power supply white connector in engine bay, cleaned buss bar and buss bar wire. In other words disconnected every connector cleaned and inspected.

All four Glow Plugs can be removed without removing anything besides the buss bar. Verified GP ohm values and even powered them to make certain they all glow bright red in just a few seconds of power. They stay red hot for at least 8 seconds when energized for 10 seconds. They do become hotter with multiple on cycles.

Verified relays function as they should. Used another battery, lights and jumper wires to make certain they work under light load. Even bought a new 40 amp relay just to make certain. Each relayed was tested using meter and physical test mentioned previously. Stock Relays are 40 amp sealed 4 pin units from Panasonic.

Verified battery voltage at the buss bar when GP activated. What? Why doesn't it want to start? Run a 12 wire from battery to buss bar wire white wire connector and it starts amazingly fast.

So where is the problem?...

There's only one place left to investigate with vengeance. In the relay socket itself. Visually it looks OK and there are no clues it is defective though.

Used a spare male terminal and inserted it into the four connectors on the relay connector. Two were tight and two were very loose. The tight ones were on the control (cpu side circuit, small diameter wire) and the two loose ones were on the power side of relay with the two large diameter wires. This has potential to be the root cause. But now to remove the relay connector from the metal support structure. But how to do so? Used mirrors camera, but nothing clearly visible on how to remove. Elected to slide a 0.010" feeler gauge down between the plastic and metal hoping it would depress the holding tab. Wiggling side to side while pushing downward finally set the housing free. Now to take the housing apart and remove the wires to see what is going on.

The white structure needed to be removed from the black housing by gently prying on locking tabs while trying to remove. It took a bit of effort but it came off. Now to get the wires removed from the housing.

Need to use two small screwdrivers to release the plastic tabs holding the wire terminal in the housing. The terminal/connector is not a common design one would find locally. There is little to no interference when a male connector is inserted to simulate the relay terminal. Tried bending the metal detail that provided the spring force, but after the first insertion it would relax. Ended up using pieces of a paper clip to provide the necessary shim to provide additional clamp force. Not the greatest solution, but it works. Fixed both power side terminals using this method. Reassembled housing, inserted relay with significantly more insertion/extraction force. Now I'm certain there is good electrical continuity between the relay wires and relay itself. If I had more time, more area to work behind the dash and it wasn't so cold out, I'd make up my own relay connector.

The design of these wire terminals is not something that inspires confidence. I'd be hesitant to use them even if I could find a source for them.

Additional comments:

1. The two power side female terminals found inside the relay housing are much wider than the 0.25" wide terminals found on 40 amp relays. They can definitely accommodate the wider terminals typically found on 60 amp relays. I don't think these wider terminals would matter because they are the same thickness and this is the dimension that is critical to generate clamp force to yield good electrical continuity.

2. The relays initially seemed to assemble into the housing with some force, but this was due to the two control side terminals. ie: It masked the poor fit of the power side terminals.

3. I'm guess there was just enough metal to metal contact for the meter to read battery voltage at the buss bar, but not enough to drive the high current demand of the GPs.

4. Purchased a 40 amp relay from Advance Auto for about $9. Currently using have this installed. The housing is slightly larger but it still fits as the pin spacing is identical. Auto Craft 40 Amp HD Relay Part # ACA715A Advance Auto Parts - Down for Maintenance

5. The stock Panasonic relay is nothing special although it is sealed. No diodes, resistors, etc... to suppress voltage spikes when the field is collapsed. (Went through the effort to decode the part number on Panasonic's web site and relay technical info.)

Although the temperature wasn't that low when I finished (28 F). It is amazing how fast it starts after just one GP cycle. It seems to start within one revolution of the motor.

If it's much colder tonight I'll try in the morning and see what happens. At this point in time I'm very confident the root cause has been found.

Hope someone finds this info beneficial.

 

[bferris01]

Thank you for the pics, I am having the same issue.

 

[LouNY]

Good troubleshooting and a viable repair for a poor connector.
Some wheres I have seen some relays with heavier tabs on the power leads,
I don't recall where or what the amp ratings were would a 60 amp relay physically fit?
They may have the heavier contacts.

 

[moship]

Good troubleshooting and a viable repair for a poor connector.
Some wheres I have seen some relays with heavier tabs on the power leads,
I don't recall where or what the amp ratings were would a 60 amp relay physically fit?
They may have the heavier contacts.

60 amp relays have 3/8 wide tabs on the power side and 1/4 on the control side. It will definitely fit without issue.

The I致e found mixed information on the 3/8 tab thickness. One source showed them being the same thickness (0.031? as the 1/4 tabs, while another had them slightly thicker. If they are thicker it would help with the compressive force on the tab, but I didn稚 like how the internal detail of the female connector fatigued or lost clamp load on the male connector.

Considering the work involved in taking the connector apart I would recommend buying the larger tab 60 amp relay to see if it works. Especially if the tab is a bit thicker.

I was more into finding the root cause than looking for an easy fix.

Personally I think Kubota blew it on this socket design. It is obviously designed for the large tab 60 amp relay and they decided to use a 40 amp relay with the smaller more popular sized relays. With poor contact the connector is likely to heat up causing fatigue issues reducing clamp load even further. Electrically the 40 amp is adequate but the fit is wrong.

Started the tractor this morning with temps in the 20痴. With one glow plug cycle it started within one revolution of the motor. It starts so quickly now that I just want to keep starting it.

I do have a picture of the smaller tab in the larger connector to demonstrate how much width is available. I値l have to post it later.

 

[FatTire]

Thanks for the update, good job tracking this down, and nice fix with the paper clip. I wonder if your clearances for the GP are different than on the 5740, i just can't quite see how I would get my glow plugs out without dismantling stuff.

 

[moship]

Not familiar with this he L5740 layout, but I'm thinking it might have a turbo.

The hardest one is the rear most one under the fuel tank. Having an assortment of wobbly extensions and small flex had ratchet helped. The other three can be accessed with relative ease from the exhaust side leaning in.

 

[moship]

would a 60 amp relay physically fit?
They may have the heavier contacts.

Yes, the wider tabs on (power side only) will fit. While I didn't have the relay at hand, I did have a 3/8" wide terminal for an old headlight project that fit into the female connector without issue. Sorry, but I didn't take a picture of the 3/8 male terminal inserted as proof, but perhaps the photo below will give confidence in my statement.

The picture also shows the white piece that helps support the wires/connectors in the 2-piece relay socket

 

[BertZegers]

Thanks for the nice write up. I check amperage rather that voltage, since each glow plug draws about 20 amps cold then a 3 cylinder will draw 60 amps and as the plugs warm they draw less. It's an easy check around that wire you showed with a cheap amp clamp.

The other thing you can check for slow starting is the starter revolutions while cranking, faster is better. My 3940 doesn't seem to have much cranking speed but always starts. Mine cranks around 225 RPM (checked with a labscope on the crank sensor by the fuel pump) and that's not very fast.

Regards, Fred

What meter do you use with the amp clamp to measure DC? I have never seen a cheap meter with amp clamp that can measure DC, only AC.
I would love to have one.