Low Voltage at bus bar to glow plugs bj60 3B (1 Viewer)

[Macktastic]

I've been hunting trying to find other examples of this issue but haven't seen any, and I looked through the FSM and troubleshooting manual and can't find enough info, and I've read a ton of glow plug threads on here with nothing.

At startup, my 3B turns over fine, but it takes several hits of the superglow system to get it to start (pretty sure I have superglow, July 83 build, but would love a simple pointer on how to check). When it does start, it often dies right away unless I feather the throttle. Batteries are both good (12.5V). When it does get going, it runs pretty rough as if one or two glow plugs are bad. But when I check the voltage anywhere on the bus bar, it's showing 1.5V at the start, climbing to 3.5 by the time the timer shuts off. I think this low voltage condition is what's causing the rough start because the plugs aren't getting hot enough, but wondering if anybody can help me figure out why this might be happening. Took the pre heater circuit apart and nothing obviously wrong, followed the startup troubleshooting in the engine manual and the leads are behaving totally normal, so I know the switch is fine. I'm at a loss and am sure it's something simple that is escaping me.

 

[duncanrm]

If you scroll down at my Toyota Diesel site you'll find a section on Superglow.

Toyota Diesel Documentation

2H Specific Reference Information

sites.google.com

Also

• Be aware that measuring voltage of a system under load can be very misleading.
• Superglow becomes very problematic as it ages.. considering just moving to a simplified glow system
• My best indication my glow system is working well is the voltage drop I see on my battery (using a dash mounted digital voltmeter) when I activate the glow system.

 

[Squash]

You might consider a Wilson Switch. Do a search.
A great test is to put positive power to the busbar to light up the glowplugs.
Also if you have dodgey plugs replace them as a set. One bad glowplug will make the engine cough and smoke until that cylinder warms up.

 

[kouglof]

Hi,
A few things to help you diagnose your system:

- When you say the engine starts fine, in what kind of temperatures is that happening? Is it starting rougher on cold mornings ?
- You mention 1.5 to 3.5v at the busbar, is it between busbar (any glow plug) and ground ? If so this is absolutely not normal, you should be expecting at least 18V.

From what you tell us I see three options:
A: Your plugs are burned.
It is hot enough outside to allow the engine to start but there is no post-glow so idle is hard to maintain. You should see some amount of smoke at the exhaust too.
From my personal experience there is little chance you have only 1 plug burned. It is most likely all of them or none.

B: Your superglow timer is KO.
It can fail in several ways so you may get the pre-glow phase but not the post-glow or even the opposite but in any case the post-glow will be ineffective due to plugs not at correct temperature.
Same consequences as for A.

C: Short circuit somewhere between busBar and ground.
In that case the plugs do not get the correct voltage leading to the same consequences.
Mostly unlikely because any short circuit at 24V with this kind of battery capacity would result.in a fire or at least some damage...

Diagnosing the superglow timer if it is not completely KO requires an oscilloscope, a simple meter won't be enough to get the timings and most importantly the shape of the pre-glow phase.

TLDR:
What to do:
- remove the plugs and post some pictures here. Add the model too.
- remove the busbar and try to start (from cold engine status) to see if symptoms are identical.
- check wiring between glow relays and busbar

If the cause of your problems is the superglow timer, I may be able to further help you. I built some superglow knowledge retro engineering my system on my BJ42 (24V too).

Superglow electronic replacement

After enduring too much trouble with my original superglow timer which frequently did not operate correctly I decided to use my electrical engineering knowledge to make a timer replacement. This board is based on an ATMEGA328P for the logic part. Current features support: - Water temperature...

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