B1700 - new 30A fuse blew immediately on start

[torch]

The upper terminal looks bent in your picture. I wonder if that has caused an internal short?

From the B1700 service manual:

"This plug is a two-material type QGS (Quick Glow System) for quick temperature rise, and has self controlling function as well as excellent durability. The heater (4) connected in series to the heater (3), which also functions as the resistor, is incorporated in the sheath tube (1) of the super glow piug. The resistance of this heater (3) cum resistor is small when the temperature is low, while the resistance becomes large when the temperature rises.

Therefore, because sufficient current is flown to the heater (4) during the initial period of energization, the temperature rises quickly and the resistance grows with the rise in the temperature of the resistor, the flowing current is reduced to prevent the heater (4) from being heated."

There's no other resistor shown in the circuit diagrams, so it appears the glow plugs get full battery voltage.

Ohm's law says V/R=I, so:
12 volts / 1 ohm = 12 amps. 12 amps x 3 glow plugs = 36 amps.

I assume the slow-blow 30 amp fuse can tolerate a small excess for a few moments while the resistance rises. However, that one 0.8 ohm reading may be enough to push things over the edge (12V / 0.8 ohms = 15.6A), or it may indicate that the internal "heater (3)" is shorted, so the resistance never rises in that plug.

An interesting experiment, but one which would require an ammeter capable of handling at least 20 amps, would be to disconnect the wiring from all 3 glow plugs and then supply each with battery voltage through the ammeter. If the plug is working properly, one would expect to see an initial current of 12 or 13 amps, that quickly drops off as the plug heats up.

Lacking that, I would replace the suspect glow plug.

 

[Maxtheutt]

Thanks torch. I'm going to do all of them And a factory slow burn fuse.

 

[tbronson]

Progress! I wasn't able to get back to this until today.

Last try, only the rectifier was disconnected and the fuse blew as described earlier.

Today, I disconnected the stop solenoid (second photo), and the engine turned over no problem.

What is the part with the "?", beside the rectifier? I also disconnected that today, at the same time as the solenoid, but didn't try starting with only that and the rectifier disconnected.

TEST 1: Rectifier disconnected - fuse blew.

TEST 2: Rectifier, "?" component, stop solenoid disconnected - engine turned over.

Hope that was clear. What next?


D

 

[whitetiger]

Progress! I wasn't able to get back to this until today.

Last try, only the rectifier was disconnected and the fuse blew as described earlier.

Today, I disconnected the stop solenoid (second photo), and the engine turned over no problem.

What is the part with the "?", beside the rectifier? I also disconnected that today, at the same time as the solenoid, but didn't try starting with only that and the rectifier disconnected.

TEST 1: Rectifier disconnected - fuse blew.

TEST 2: Rectifier, "?" component, stop solenoid disconnected - engine turned over.

Hope that was clear. What next?


D View attachment 49330 View attachment 49331

The module you have a "?" on is your flasher unit for the hazard lights.

 

[torch]

Whitetiger is correct. However, the flasher unit is fed through a 5 amp fuse, so I doubt that is the problem.

 

[GreensvilleJay]

I looked at the diagram again...the ONLY things that could blow the 30A fuse are
1) bad regulator
2) bad main switch
3) bad glowplugs
everything else is protected by lower amperage fuses.

re: 1 - you've disconnected it but fuse still blows, so not that
re: 2 - unlikely unless switch internally grounds( shorts) sometimes ( but that generall fries the switch..)
re: 3 - the most likely culprit.

As I said before, disconnect all the glowplugs and retest. If the motor spins and fuse doesn't blow, 1 or more of the glowplugs must be 'bad'.
Easy to test, when EACH is disconnected.
Run a +12V wire from battery to ammeter to ONE plug.
How much current does the meter show ?
Write down the numbers for all 3. Add them up, if over 30, the fuse WILL blow.

 

[Maxtheutt]

Glow plugs fixed mine.

Sorry I hijacked your thread OP.

Thanks for the help!

 

[tbronson]

Where it stands now:

With ONLY the stop solenoid disconnected, the engine turns over no problem.

This seems to go against most of the advice and schematic reading here, except for Dave_eng's original recommendation to disconnect the rectifier and the stop solenoid. So that's odd.

I'll reconnect the stop solenoid and see if the fuse blows.

I'll also test the three glowplugs with a multimeter.

 

[tbronson]

Tested the 3 glowplugs: 2 x 1.2 ohms, 1 x 0.6 ohms -- that means 2 are bad?

 

[Dave_eng]

Tested the 3 glowplugs: 2 x 1.2 ohms, 1 x 0.6 ohms -- that means 2 are bad?

View attachment 49463

The reference value is 0.9 ohms approx.

Clean yours up on a wire brush before deciding which one might be bad,

It is hard to get a good contact on dirty surfaces with a meter.

Note #3 about 0 ohms because your issue is a short and your readings do not indicate a short

Dave

 

[GreensvilleJay]

Actually I'd say 1 bad plug, the .6 ohm one.
'math'
say battery is 12 volts
#1 plug 12 V/ 1.2 ohms = 10 amps
#2 plug 12 V/ 1.2 ohms = 10 amps
#3 plug 12 V/ .6 ohms = 20 amps

Total current is 10+10+20 = 40 amps. That'll blow a 30A fuse real quick !!

ANY plug with LESS than the 'reference' is probably bad.

Odds are the battery will be closer to 10 volts when heating up the plugs, so each would draw 10 amps +-, dang close to 30, could pop a fuse.

When using any ohmmeter, you short the two probes and record the reading. It might be zero, odds are it's not, Take a real reading, subtract the 'shorted probe' value. The result is the true measured value.

 

[tbronson]

I'll clean the glowplugs and retest.

I watched several videos about testing diesel glowplugs, which I followed, as in the photo above. They all said that a reading of over 1 ohm indicated a faulty plug, 1 or less meant good?

So if these aren't shorted, that means the problem isn't with the glowplugs?

There's still the fact that with the the stop solenoid disconnected, the engine turns over.

 

[torch]

There's two failure modes for a glow plug. One is burnt out -- high resistance. The second is shorted -- low resistance.

Low resistance will draw too much current and blow the main fuse.

High resistance will not heat up the plugs sufficiently, and while the tractor will crank over, it will be hard or impossible to start.

 

[DrankTheOrangeKoolaid]

There's still the fact that with the the stop solenoid disconnected, the engine turns over.

That solenoid has a 5 amp fuse in front of it. That fact that the 5 amp fuse is not blowing means that the solenoid can not be the sole reason the 30 amp fuse is blowing. More like the sum of the draw of the glow plugs and solenoid is exceeding 30 amps. I would bet if you left the 0.6 Ohm glow plug disconnected, and connected the other two glow plugs and the solenoid, you would not blow the 30 amp fuse.

 

[Dave_eng]

That solenoid has a 5 amp fuse in front of it. That fact that the 5 amp fuse is not blowing means that the solenoid can not be the sole reason the 30 amp fuse is blowing. More like the sum of the draw of the glow plugs and solenoid is exceeding 30 amps. I would bet if you left the 0.6 Ohm glow plug disconnected, and connected the other two glow plugs and the solenoid, you would not blow the 30 amp fuse.

There are two coils inside the solenoid and only one is protected by the 5 amp fuse.

Dave

 

[torch]

There are two coils inside the solenoid and only one is protected by the 5 amp fuse.

Dave

Yes, there is clearly an error in the wiring diagram, as previously established. I believe the feed from the starter solenoid to the fuel cut-off solenoid should only receive power when the key is turned to the start position (IE: main switch terminal 50). That would be consistent with the photo showing a white wire connected to the starter side of the starter solenoid.

As I understand the description, the fuse only blows after the key is turned to Start. This would certainly be consistent with one shorted coil in the cut-off solenoid. The thing to do now is to check the resistance of the stop solenoid between the white wire and the black wire to see if it is near 0 ohms. I don't know what the value should be, but I would expect to see something in the order of 100 ohms or more if it is good. Alternatively, disconnect the 0.6 ohm glow plug, reconnect the cut-off solenoid and see if the fuse still blows or if the solenoid clicks.

It is equally possible that greensvillejay is correct: the glow plug current is right at the edge of blowing the fuse and adding the small additional cut-off solenoid current may just be "the straw that broke the camels back".

He was having starting problems for some time before the fuse started to blow. That could indicate that the coil insulation in the cut-off solenoid has been gradually breaking down. Shorts within the coil itself could initially reduce the power (so fuel did not flow) without necessarily blowing the fuse. Eventually of course, it would deteriorate to the point of blowing a fuse.

But.

He also has one glow plug with a resistance that is half of the other two -- and much of that resistance may be attributed to internal resistance of the multi-meter. A failing glow plug could also explain the history of starting issues. He may well have two separate problems.

 

[tbronson]

(Great discussion, especially for me over the last few posts. Following the detective work is cool. I'm learning a lot. Thanks!)

SUCCESS -- possibly limited. Yesterday, I got it started twice, no problem, immediate turnover, and used it for a couple of hours. But I didn't actually fix anything or find anything new.

Last test, the stop solenoid was disconnected and it turned over at key Start position, instead of blowing the 30A.

New tests:

1) Used the multimeter on the solenoid connector: just above 15 ohms. (The meter reads 0 when the probes are directly touched together.)

2) Reconnected the solenoid, disconnected all 3 glow plugs, and it turned over.

3) Replaced all 3 glow plugs, and it turned over and started no problem.

If I understand the electrical stuff correctly, could the temperature have something to do with it? The tractor is outdoors, and for the other test days, the temp was in the 50-55F range. Yesterday was unusually warm, hitting 75F. I tried the tractor in the early afternoon, after it had been sitting in off-and-on sun for a few hours. Does this mean that the engine started more easily, the glow plugs didn't have to heat up for as long?

So I'm thinking I should replace the glow plugs, at least the 0.6 ohm one. And that the fuse will probably blow if I try to start it in colder weather?

 

[torch]

If I understand the electrical stuff correctly, could the temperature have something to do with it? The tractor is outdoors, and for the other test days, the temp was in the 50-55F range. Yesterday was unusually warm, hitting 75F. I tried the tractor in the early afternoon, after it had been sitting in off-and-on sun for a few hours. Does this mean that the engine started more easily, the glow plugs didn't have to heat up for as long?

It is possible. As I understand it, your glow plugs' resistances increase as they warm up. It makes sense that they would warm up faster, and therefore draw high current for less time, if the tractor is warm to begin with.

 

[GreensvilleJay]

re: So I'm thinking I should replace the glow plugs, at least the 0.6 ohm one.

YES, as the spec says .9 ohms. Yours is 'bad', drawing 30+ % more amps than it should.

And yes, a warm day means less time to heatup the glowplugs, though by how much, I don't know.

I've always held the glowplugs on while the gauges on my BX23s 'bounce' until they're stable. Usually I look at the fuel gauge, when it's stable, I start the engine. Any time of the year, if the engine hasn't run for say 1/2hr or so.

 

[tbronson]

Is there any particular reason to replace all the glow plugs at the same time if only one is bad?