Are My Glow Plugs Bad???

[tyluk]

Alright I tested the bus bar and found I was getting about 17-22 resistance on the copper. Most of the time it was about 17 and would jump around to 22. I did this with the key on but the glow plug light was not illuminated. I had just gotten done driving it. So, does this mean the test gave me false readings? Do I need to do it with the engine cold and glow plug light on? Next, how do I tell if the glow plug is bad? Will I have to pull each one out to see it? Thanks again everyone, this forum rocks!

[Possum79]

You want to check to see if the buss bar gets voltage to it not resistance. Put the voltmeter on it and the other end to ground while having someone else turn the key to on but not start. If you get a voltage then work your way to each individual plug by removing the buss bar and using a test light to each plug and the other to positive on battery. In theory it should light when the plug is good.

[clbanman]

Resistance tests should be done with the key off.  Voltage test is to see if voltage is getting to the plugs.  Resistance test is to see if the plugs themselves are still good.


http://vwdiesel.net/phpBB/viewtopic.php?t=2242&highlight=glow+plug+resistence+resistance

[zukgod1]

Also it sounds like you need to get a Bentley ASAP..

[tyluk]

Yeah I agree on the bentley. Where can I pick one up? I'm going to try doing some tests on the plugs on Monday. I'll let you know what I find.

[tyluk]

Okay so I can't check my plugs til later today but I have another question. I left my car parked down in the valley last night which is about 2,000 feet lower than where I live and where it is started every morning. The temperature was nothing extreme (probably 50 degrees). I have started it like this up at my house before. At the house I have to crank it for about 45-60 seconds before it will begin firing on its own. So, in town this morning I thought the same thing (45-60 seconds). But, when I got in to start it the thing started after about 5 seconds. Now, smoke still came out for about 30 seconds but it was cut down by about 2/3 the amount. My question is: does altitude have any effect on starting the engine. Obviously the air is less up there. When it was in NJ I never had a problem starting it. The day it gets here it starts having problems. Like I said though, after that first start it starts no problem for the rest of the day. Just wondering if there is a mixture adjustment or anything? I will report back on GPs later. Thanks again!

[tyluk]

I want to say thank you in advance for everyones help so far. I hope I'm not asking stupid questions but I do still have problems. I"m wondering if the glow plugs always have power to them even when the light is not on? I drove the car 50 miles and then checked the glow plugs. With the key to the on position the light is obviously not on since I had just driven it. I checked the glow plugs voltage and was not getting anything. So, do I need to wait for the engine to cool, the light to come on, and then check them again? If not, where is the relay for the plugs? Could I have blown something down the line? Thanks again everyone. You have helped a ton!

[Vincent Waldon]

I hope I'm not asking stupid questions but I do still have problems.

No worries... there are no stupid questions. (except perhaps "how do I get the cool blowoff valve sound on my diesel so I can impress my friends"  :wink:   but that's another thread)

The glow plugs are controlled by the glowplug relay... a big black tall sucker on the relay panel that has really big copper lugs at its base. The glowplug relay makes decisions on how long to leave the glowplugs on based on coolant temperature.  If the engine is really really cold the glowplugs will stay on 15-20 seconds... if the engine is already warm the glowplugs won't come on at all, and there's a slight range in between.

What makes things a little more confusing is that the yellow light on the dash actually has little to do with the glow plugs getting power... the light is designed to tell the driver when the engine is ready to start.

So, for troubleshooting purposes you'll need to let the engine sit until it is stone cold.  Or, you can pull the wire to the coolant temperature sensor and trick the relay into thinking it's cold.  

If you don't get voltage at the glow plug bus the next thing to check is the glow plug fuse... it's in a small black box bolted to the firewall by the brake booster.  If that's OK the usual suspect is the glow plug relay.

[tyluk]

Finally had a chance to test the plugs and it appears that the bus bar is getting about 10.55 volts to it. I guess now I need to check each plug. Can I connect the positive lead to the battery and the negative to each glow plug to see if it gets voltage (with the buss bar off)? I thought that was what someone said to do but with a test light. Thanks again for your time and help.

[BlackTieTD]

there have been a ton of people with glow-plug troubleshooting questions.. there is a lot in the search here.

basically... there are many ways to check the plugs. the way that i think gives the most peace of mind is to actually observe the tip of the glow plug getting hot. so either with the glow plug out of the engine, or while the injectors are out anyway and you can see the GP tip through the injector hole.

when you put 12v to the GP it should begin to glow orange. sometimes its hard to tell in daylight so touch the GP to some paper or something to be sure if its hot if you can't tell.

you can check voltage and resistance with the plugs installed but like tyler said they sometimes fail closed.

if you have the right tools you can take the plugs all out in a few minutes. not saying this is a must, its just peace of mind.

[tyluk]

So under the hood it says the car has bosch fast glow plugs in it. Do you need to put bosch back in it or can I use an autolite? They are just so much cheaper. Thanks for any advice. I'm also wondering if 2 or 3 plugs are out should i just replace all of them. If i only replace the bad ones is there a good chance the others will go out shortly? Thanks