glow plug light staying on

[stueveone]

Hey guys,
So I've noticed a few times where my glow plug light on my 81 Rabbit will stay on and not shut off. After waiting for about 25 seconds or so, the engine fires right up, no problem, eventhough the glow light didn't go out. What's the problem then? A plug that's not turning on? GP relay or something not working to spec?

Thanks,
stueve

[coke]

The glow plug indicator light on the dash actually has nothing to do with the plugs functioning at all. The light is triggered by a timer that is hooked up to the temperature sender to tell the glow plug relay how long the plugs should stay on. The light goes out after the engine is started, right? Try another glow plug relay and see if that takes care of the problem. No worries though, the light is mostly for looks.

[VWCaddy]

Yes, likely the relay is suspect. But also check all the inputs to the relay, especially the temp sender input, if that is bad, some relays do strange things:

http://www.4crawler.com/Diesel/CheapTri ... lugs.shtml

[Up North]

On my '90 jetta my glow plug light flickers on and off all day long. Last month when I pulled my injectors I checked to see if my glow plugs were cycling normally and they were. The dash light keeps flickering. I just ignore it.

Doug

[Vincent Waldon]

If your car has a water separator it's connected to the glow plug light and can cause it to stay on, flick, blink, and other weird signals.

Drain it or delete it and the incessant flickering will stop forever.

[stueveone]

Water separator? Not sure what that is?!

[Vincent Waldon]

Dunno which years had them (someone else know for sure ??) but on some early models there's a square plastic box bolted under the car on the passenger side by the fuel tank. It has a drainage knob on one side and traps water in the fuel... the glow plug light comes on when it has water in it that needs to be drained... or when it misbehaves !


Vince

[VWCaddy]

Water separator? Not sure what that is?!

I think that is an A2 part, near the fuel tank and traps water before the fuel goes up front the the fuel filter and the IP. Has a sensor in it that turns on the GP light when it is full of water and needs to be drained. The A1s have the water separator in the fuel filter and you drain it with the valve at the bottom.

[wewantutopia]

The light is triggered by a timer that is hooked up to the temperature sender to tell the glow plug relay how long the plugs should stay on.

Is there any way to make the glow plugs come on no matter what the temp of the engine is? Like the mercedes glow plug relay mod? Can you unplug the connection from the temp sender to the relay and still have the glow plugs work? If the glow plugs were to cycle everytime the vehicle was started what if any are some possible draw backs aside from extra ware and tare on the plugs themselves?

[coke]

Thats the way my 90 jetta is set up. No input from the temperature sender so they stay on until the car is started then they go out.

I see nothing wrong with it. My car has been running this way since I bought it at 185k miles, and I've only replaced the glow plugs once, and that was 3k miles ago when I had the head off.

Preventative maintenance.

[VWCaddy]

Is there any way to make the glow plugs come on no matter what the temp of the engine is? Like the mercedes glow plug relay mod? Can you unplug the connection from the temp sender to the relay and still have the glow plugs work? If the glow plugs were to cycle everytime the vehicle was started what if any are some possible draw backs aside from extra ware and tare on the plugs themselves?

Yes, that would do it, assuming you have a "robust" GP relay. I have a whole drawer full of assorted GP relays. I once built a tester for them where I could vary the assorted inputs and watch what the relay did. I found the Bosch relays worked just fine given an sort of input, including open and short circuits at the temp sender input. Other off-brand relays (many of which I had pulled as "bad") worked fine given "normal" inputs but went crazy given out of range inputs (like open circuits). Those relays would kick either the plugs or LED on at random times, likely their design is susceptible to noise.

[wewantutopia]

thanks for the response. Which blade on the realy is for the temp sender?

[wewantutopia]

never mind...I found it

http://www.4crawler.com/Diesel/GlowPlug.shtml

if I took the wire off of the L blade and ran it to the 1st glow plug, is that how I would enable the led to let me when the glow plugs are actually cycling?

[VWCaddy]

I suppose that would work, the dash LED output has a different time delay to the actual glow plugs.

What I did to observe the plug operation was to connect some LED windshield washer nozzles to the glow plug bus (one to each side the the fusible link works as a good diagnostic tool to detect a blown fuse). This way, the nozzles light up with the plugs (I needed to replaced the old nozzles anyway, one was broken and the other badly clogged).

[KAC]

Thats the way my 90 jetta is set up. No input from the temperature sender so they stay on until the car is started then they go out.

I see nothing wrong with it. My car has been running this way since I bought it at 185k miles, and I've only replaced the glow plugs once, and that was 3k miles ago when I had the head off.

Preventative maintenance.

Cool that's what I'm gonna do...my diesel buggy chuggs when a first start it...sounds like time for new glow plugs