Are glow plugs supposed to work like this?

[Gubbtratt1]

I'm testing electrical shenanigans on my 1987 LJ70 and found that the glow plugs does some weird things, I'm just wondering if this is normal or if something is broken.

When I first turn on the key the glow plugs run on 12v for a millisecond and then switches to be connected in series with the big glow plug in the intake and the current sensing resistor, as toyota calls it. The first 12v mode works as expected, but when it switches to 6v the voltage across the glow plugs are just 3.5v, with 3.5v over the current sensing resistor and 5.5v over the big glow plug. The indicator light also isn't lit, it's only on with the very short 12v cycle. It takes several minutes for the plugs to turn off, at first I thought they would never turn off but I left them on while I wrote a post asking about that problem, and just as I was about to post it I heard the relay turn off.

 

[Rigster]

Yes, this is normal. It is a quickglow system, and the half voltage keeps the plugs glowing enough to allow the cylinders to build enough heat to run on their own.

 

[Gubbtratt1]

So I'm not supposed to wait until the second relay turns off before I start it up?

This is what a (not very) cold start sounds like.

 

[Rigster]

So I'm not supposed to wait until the second relay turns off before I start it up?

This is what a (not very) cold start sounds like.

No. When the initial glow plug light in the dash goes out, then start it up. The "afterglow" period is to help it stay running.

 

[Gubbtratt1]

No. When the initial glow plug light in the dash goes out, then start it up. The "afterglow" period is to help it stay running.

I just noticed it doesn't show in the video, but the light and 12v cycle only being on for a fraction of a second is also normal? I feel like it should be much longer if I'm supposed to start cranking as soon as it switches to the reduced voltage.

Edit: I looked at some other LJ70 cold start videos and they had the light on for about five seconds and then started smoothly. So, next question, what could cause the 12v cycle to be too short?

At a later start attempt it stalled after running for a little while, and as I cranked it again the glow plug light came on for about a second.

 

[Rigster]

I just noticed it doesn't show in the video, but the light and 12v cycle only being on for a fraction of a second is also normal? I feel like it should be much longer if I'm supposed to start cranking as soon as it switches to the reduced voltage.

Edit: I looked at some other LJ70 cold start videos and they had the light on for about five seconds and then started smoothly. So, next question, what could cause the 12v cycle to be too short?

At a later start attempt it stalled after running for a little while, and as I cranked it again the glow plug light came on for about a second.

Check resistance on the glow plugs, make sure they are good. Check contact points and make sure everything is tight, check grounds to make sure they are good.

Do you have the engine manuals (can download them from the resource section). I have not checked, but there is likely a section on testing the glow plug timer module.

 

[Gubbtratt1]

Check resistance on the glow plugs, make sure they are good. Check contact points and make sure everything is tight, check grounds to make sure they are good.

Do you have the engine manuals (can download them from the resource section). I have not checked, but there is likely a section on testing the glow plug timer module.

I haven't checked the exact resistances, but I have checked all plugs individually for continuity. I have also cleaned most contacts with brake cleaner and steel wool and sprayed all of them with wd40. I have an engine manual for 2LTII, I believe it mentions how to test the non-emissions glow timer. I remember not understanding exactly how I'm supposed to do the testing, but I'll read the manual and take a look at the glow timer tomorrow and ask for help if it's still unclear.

 

[Eurasiaoverland]

I believe both initial and afterglow periods are controlled in part at least by coolant t temperature. There is a separate temperature sender in the back of the block. I would check this for a good connection and correct operation.

 

[bj70bc]

^^this

 

[Gubbtratt1]

Today I took apart the timer. The board was a bit darker underneath three resistors, and checking the resistances of them one is fine, but the two others are way off.

The three suspects are the blinding one and the two directly underneath. The blinding one says 100 ohm and measures 100 ohm, the middle one has very unclear colours, but no matter which one of the closest options you choose it should be just over 60k ohm, and it measures 360 ohm. The bottom one is similar, says 2200 ohm and measures 770 ohm.

I still have to remove them and measure them independently to make sure there isn't some other part of the circuit that throws the value off, but based on the miscoloration of the board underneath and the fact that the alternator regulator broke a few years ago and made it charge 20 volts (don't know if I mentioned that actually) makes me believe this is where the problem is.

 

[Eurasiaoverland]

Today I took apart the timer. The board was a bit darker underneath three resistors, and checking the resistances of them one is fine, but the two others are way off. View attachment 3857552
The three suspects are the blinding one and the two directly underneath. The blinding one says 100 ohm and measures 100 ohm, the middle one has very unclear colours, but no matter which one of the closest options you choose it should be just over 60k ohm, and it measures 360 ohm. The bottom one is similar, says 2200 ohm and measures 770 ohm.

I still have to remove them and measure them independently to make sure there isn't some other part of the circuit that throws the value off, but based on the miscoloration of the board underneath and the fact that the alternator regulator broke a few years ago and made it charge 20 volts (don't know if I mentioned that actually) makes me believe this is where the problem is.

Nice work! One thing that often annoys me on this forum is that pretty much any question on troubleshooting the Superglow system ends up with the bodger community recommending to 'fit a Wilson switch'. Great that someone has the intelligence to properly troubleshoot and hopefully fix the problem.

I can relate to the soldering comment. I would say I'm a fairly capable welder (in the scope of car repairs), but for some reason I can barely solder two wires together and I hate the prospect of a soldering job! Nice chassis welds btw!

 

[AirheadNut]

I can relate to the soldering comment. I would say I'm a fairly capable welder (in the scope of car repairs), but for some reason I can barely solder two wires together and I hate the prospect of a soldering job! Nice chassis welds btw!

That's me too. I've been welding for a job for a couple of years now but am terrified of trying to solder electronics.

 

[bj70bc]

has anyone mentioned a wilson switch yet

 

[Gubbtratt1]

has anyone mentioned a wilson switch yet

To be fair nothing but the water temperature sensor and checking continuity have been mentioned since it was concluded something is indeed wrong.

can relate to the soldering comment. I would say I'm a fairly capable welder (in the scope of car repairs), but for some reason I can barely solder two wires together and I hate the prospect of a soldering job! Nice chassis welds btw!

I was looking for my soldering comment for quite a while before I realised you've been reading my other thread.

 

[Gubbtratt1]

I haven't replaced the resistors yet and I still believe they're the problem, but the problem changed a bit once I got the charging working.
Video
Edit: accidentally clicked the post button. The square relay is on for at least 30 seconds, I haven't had the ignition on for longer than that. The round relay cycles between on and off, can be heard in the video.

 

[bj70bc]

Nice work! One thing that often annoys me on this forum is that pretty much any question on troubleshooting the Superglow system ends up with the bodger community recommending to 'fit a Wilson switch'. Great that someone has the intelligence to properly troubleshoot and hopefully fix the problem.

I can relate to the soldering comment. I would say I'm a fairly capable welder (in the scope of car repairs), but for some reason I can barely solder two wires together and I hate the prospect of a soldering job! Nice chassis welds btw!

btw... whats a bodger and should i be offended....
google says its a chippy (carpenter) and I am.... should i still be offended?
so confused

 

[Eurasiaoverland]

I haven't replaced the resistors yet and I still believe they're the problem, but the problem changed a bit once I got the charging working.
Video
Edit: accidentally clicked the post button. The square relay is on for at least 30 seconds, I haven't had the ignition on for longer than that. The round relay cycles between on and off, can be heard in the video.

The controller is basically a timer that switches over from one circuit to another, so I'd have to agree that dead resistors are causing it to cycle incorrectly.

btw... whats a bodger and should i be offended....
google says its a chippy (carpenter) and I am.... should i still be offended?
so confused

In informal English, to bodge something is to make a poor or temporary fix to something rather than repair it properly. So like wrapping gaffer tape around a split intake hose. It's distinct from botching something, which implies a failed attempt to do something.

According to the OED:

bodger Google Search - https://g.co/kgs/RTLQDEE

I think in American English, a 'hack job' is an equivalent of a bodge, but I don't think there is an equivalent 'hacker' to a 'bodger'; certainly not in contemporary usage.

 

[Gubbtratt1]

Almost two months later I've continued on the glow system. I removed the resistors and one was at the exact right resistance, 2200 ohm, but the other was a bit off. The colours were as I mentioned a bit unclear, but me and the electronics store clerc concluded that it's most likely 680 ohm. I got it replaced, and the exact same behaviour remains:

The square relay is on for at least 30 seconds, I haven't had the ignition on for longer than that. The round relay cycles between on and off, can be heard in the video.

I have a theory that it's supposed to do this though. As I don't start it when the light goes out like I'm supposed to, what if it cycles 12v through the glow plugs to keep them hot(ter than with 3.5v)? Is this a reasonable theory? Could someone with a working system test it?

 

[Gubbtratt1]

It behaves like it should if I start it, but I'd be very happy if someone could verify that this is correct operation.

 

[nuclearbeef]

Sounds like it is working kinda like it should, only the high volt glow cycle should probably remain on a little longer.

But, even at -12c, mine only stayed on for 4 seconds before changing to low volt glow.