glow plugs stuck on - quick fix?

[Sickleweed]

86 1008 glow plugs are always getting power. Truck has been converted to 12 volt (resisters removed). I have 2 questions...

I've been pulling the #17 fuse to kill the power to the plugs after start up...could this affect the charging system?

Can I put a momentary switch on the blue wire at the coil to interrupt the ground?

Truck number one is in the shop - this is my back up truck. I intend to trace the problem per TM, until then, I just need to limp along for a couple weeks.

 

[tbearatkin]

Just take the blue wire off the relay after starting. Until you figure it out.
Bet your relay is bad.

 

[doghead]

Have you tested the relay to determine if it functions properly(no point trying to use it if it's bad).

Is the relay the correct relay(isolated ground). If it is the wrong relay, it would be on all the time(your current problem).

Of course you can rewire to manually control your relay, but you need to understand what relay you have to wire it to function correctly.

The stock system simply switches the grounds(light blue wire) to activate the relay.


Have you tried removing the light blue wire from the GP relay? With it removed, does the relay activate still(with the key on)? If so, you probably have the incorrect relay.

You can use an ohm meter and test your relay to determine if it is an isolated relay coil, or chassis grounded. The later will not work with a stock cucv controller card.

 

[doghead]

Just take the blue wire off the relay after starting. Until you figure it out.
Bet your relay is bad.

If it was known to be all stock, that should work.

But, if someone has replaced the relay with a "Ford" type stater relay, it will still power the glow plugs.

 

[Sickleweed]

Not sure about the style of relay, here's a pic..

What about # 17 fuse??? Will pulling it cause a cascading effect of @#$!???

 

[doghead]

Truck has been converted to 12 volt (resisters removed)

Where does the big red wire(on top of the relay) come from?

What is the voltage at that terminal?

Not sure without looking at the TM, what fuse # 17 is for. I'll look in a bit

As for a "cascading effect of @#$", not unless someone booby-trapped your truck.

Have you tried disconnecting the light blue wire yet?

Any good reason not to follow the -20 TM troubleshooting section, for the glow plugs? It covers it all.

 

[Nick Danger]

When I bought my m1009 the glow plug light would stay light
ended up being a bad glow plug control card.

 

[Sickleweed]

Have you tested the relay to determine if it functions properly(no point trying to use it if it's bad).

Is the relay the correct relay(isolated ground). If it is the wrong relay, it would be on all the time(your current problem).

Of course you can rewire to manually control your relay, but you need to understand what relay you have to wire it to function correctly.

The stock system simply switches the grounds(light blue wire) to activate the relay.


Have you tried removing the light blue wire from the GP relay? With it removed, does the relay activate still(with the key on)? If so, you probably have the incorrect relay.

You can use an ohm meter and test your relay to determine if it is an isolated relay coil, or chassis grounded. The later will not work with a stock cucv controller card.

I have tested the relay between lt blue and pnk/blk terminals = 5.6 ohm
What other tests can I do on the relay itself?
Remove the lt blue wire and the GPs are off. Does this meen the control card isnt working properly? Or could it still be the relay??
I dont hear the relay clunking at all.

I think a Control card bypass is in order either way.
Being said How do I test the relay to verify it isnt bad, or that it is the isolated ground version?

Where does the big red wire(on top of the relay) come from?

What is the voltage at that terminal?

Not sure without looking at the TM, what fuse # 17 is for. I'll look in a bit

As for a "cascading effect of @#$", not unless someone booby-trapped your truck.

Have you tried disconnecting the light blue wire yet?

Any good reason not to follow the -20 TM troubleshooting section, for the glow plugs? It covers it all.

Big red wire comes from Pos side of bus bar. 13.5 volts at that terminal - always hot.

Fuse 17 is for "20 amp engine control" I can't see it affecting any other circut...??? I prefer this method over removing the wire because, my girl needs to drive it as well, and pulling the fuse is much easier to explain then going under the hood .

I have done some tests per manual (not for the controller because plan on bypassing it any way) but didnt see a specific match to "glow plugs always on" test.

My electrical deductive reasoning is not so good and I need all the help I can get.

 

[tbearatkin]

Hard to say what the issue is could be anyone of several. Bad temp sensor (back side of driver side of engine on top), bad card (thought they usually did not turn on GP when failed
but could be wrong), in my case it was just a bad relay. If your card is still good why replace it? Could see a back up switch in case it failed or an EMP fried it. I prefer to keep as stock as possible. Makes it easier to use the TM's to troubleshoot when things are kept stock.

 

[cpf240]

As suggested previously, the trouble shooting guide in the TMs is a great place to start, and *should* find the problem part for you. Another source would be the Glow Plug Theory of Operation that has been posted, and I think CUCV Electric also has some great guides to the GP system.

Also as mentioned before, the GP relay *must* be an isolated ground relay. There must be NO conductivity between any of the terminals and the relay case / mounting tabs.