Why do my glow plugs only stay on for a split second?

[Hellajoe]

it just started happening a couple days ago. i went to start my truck (1990 HDJ81) and the glow plug light only stayed on for a split second the truck was already warmed up so it started easily. yesterday -13 deg c in the morning and the light only stayed on for the split second again and it was hard to start and idled rough. again the same thing this morning. i looked mud here without much luck. the glow plugs are a super glow system, as it has the coolant temp sensor. cold starting seemed to get progressivly worse over the last winter compared to last. i tried to measure voltage at the glow plugs, my volt meter (fluke) only flashed some numbers for a split second but not long enough for me to make them out which leads me to believe the relay is working. it seems that the power isnt staying there long enough for it to do anything. so is it a shorted glow plug which fried the fuseable link that goes back to the timer? or is it the timer itself? or just burnt out glow plugs, or am i totally out to lunch? any inslight would be appreciated. thanks.

 

[Hellajoe]

I should add that the glow plugs used to stay on for about 3-4 seconds before.
Thanks

 

[IanB]

You need to check the resistance of each glow plug seperate from the rest of the system to see if they are still good, I'm not sure the effect a bad plug would have on the entire glow system, if this could cause your symptoms or if you should be looking elsewhere. Do you have the factory service manual? Should have a troubleshooting section for the glow system.

 

[GTSSportCoupe]

Could be the coolant temp sensor?

 

[IanB]

Could be the coolant temp sensor?

That would make sense.

 

[Hellajoe]

No I don't have a FSM but I do have the factory wiring diagrams. Looking at them a faulty coolant temp sensor would make sense. Is there a way to check it?

 

[Bandit_guy]

Yup, here's how you can check the sensor. Check the wires to is as well because a broken wire to the sensor will give the same information to the timer as a hot engine. If the truck hasn't run in a while then the outside air temperature will be close enough to the water temp to tell you if the sensor is faulty or not.

hope this helps

 

[bj40green]

View attachment 881540
Check the wires to is as well because a broken wire to the sensor will give the same information to the timer as a hot engine.

Hmmmm, A hot engine gives a low resistance (± 0.6KΩ), a cold engine gives a high resistance (± 10KΩ), a broken wire gives no resistance.

Better to take the sensor out and put it in hot water and check the resistance as per the diagram.

Rudi

 

[Hellajoe]

Checked the resistance this afternoon befor leaving for home from work (not started for 8 hours) it was about 6 deg c outside so I imagine my coolant was about the same temp which was about 4 ohms iirc then when I got home the temp was about 1/3 the way up the gauge (don't know the exact temp) and the resistance was 0.9 ohms. So I recon the sensor is working correctly. No visible wire damage. I didn't have time tonight to test the glow plugs tonight but will get around to it this weekend.

 

[Hellajoe]

Anybody know where the fuseable link is that goes from the glow plugs to the timer is? Is this it?
Part number 90049-42060. It's located just below the oil filter coming from one of the wire bundles. Thanks

 

[Hellajoe]

Here another pic of it

 

[bj40green]

Checked the resistance this afternoon befor leaving for home from work (not started for 8 hours) it was about 6 deg c outside so I imagine my coolant was about the same temp which was about 4 ohms iirc then when I got home the temp was about 1/3 the way up the gauge (don't know the exact temp) and the resistance was 0.9 ohms. So I recon the sensor is working correctly. No visible wire damage. I didn't have time tonight to test the glow plugs tonight but will get around to it this weekend.

The numbers in the diagram are in KΩ = Kilo ohm.
Are you sure that it was 4 ohms????? At 6 deg C the resistance should be (more or less) 6 Kilo ohms = 6000 ohms.
If it really is 4 ohms..... your sensor is defective and that explains that there is no glow time.

Part #90049-42060 is unknown in my Toyota database, but it can be the manufacturers (Nippon Denso) part#

Rudi

 

[bj40green]

Your fusible link should look like the top one in this picture marked "MAIN/GLOW/HEAD AM1".

Note: If your FL is blown, you have no voltage at all.
If it's blown, the part# is 90982-08266

Rudi

BTW, it helps if you put year, model and market in your signature line.
Something like: 1990 HDJ81 JDM RHD
I had to check 4 databases before I found your 1990 HDJ81 to be a JDM model.

 

[Hellajoe]

Bj40 green good catch!! I didn't see that "K" there and yes it was reading Ohms I checked again this morning. Looks like I'm in need of a new sensor! Thanks for pointing that out!! I'll post again after chaging it.