Glow plugs question

coke · Post by **coke** » Wed Dec 30, 2009 5:33 pm

I feel like such a frigging noob, but my 91 has treated me well and I haven't had to do jack to it except brake hoses and brake shoes/pads. BUT my glow plugs are fried and she will not start below 30 degrees. It has at least 2 bad ones. I need to know the resistance values for a good plug and what is considered bad so I don't have to tear them all out and check them one by one. If I find the post with the information I shall promptly lock this one. Thanks.

caveman · Post by **caveman** » Wed Dec 30, 2009 5:42 pm

The easiest way to check them without removing anything is with a clamp-on ammeter. Disconnect temp sensor, turn on glow plugs, let the gauge settle down [about 10- seconds] then read- with them cold they will draw about 7-12 amps each [depends how cold everything is] so 10 A for one, 20 A for two etc. If you don't have a clamp ammeter then the next easy way to check is to remove the buss bar, and use a good 12v test light. Clamp one end of the light to the positive post of your battery. Then touch the end of each glow plug. If it lights, it's good, no light [i.e. no continunity] no good.

caveman · Post by **caveman** » Wed Dec 30, 2009 5:43 pm

Oh and don't forget to check the glow plug fuse !

coke · Post by **coke** » Wed Dec 30, 2009 5:49 pm

Yeah first thing I checked. (Fuse) I can tell at least one of them is working, and I listened as I cranked and cranked as it picked up 1 and 2 cylinders then started on all four.

I'll have to remove the bus and use the test light trick. Thanks, that is indeed what I was looking for. I appreciate your help guys.

VWCaddy · Post by **VWCaddy** » Wed Dec 30, 2009 7:02 pm

coke wrote:I feel like such a frigging noob, but my 91 has treated me well and I haven't had to do jack to it except brake hoses and brake shoes/pads. BUT my glow plugs are fried and she will not start below 30 degrees. It has at least 2 bad ones. I need to know the resistance values for a good plug and what is considered bad so I don't have to tear them all out and check them one by one. If I find the post with the information I shall promptly lock this one. Thanks.

Something in the 1 ohm range is good (12 volts / 1 ohm = 12 amps). A dead plug will likely read infinite resistance (open circuit):
- http://www.4crawler.com/Diesel/CheapTri ... lugTesting

wmasscaddy · Post by **wmasscaddy** » Wed Dec 30, 2009 7:16 pm

My $20 Craftsman multimeter came with a temperature probe. One glow cycle raises the temp aruund the plug enough to notice.

coke · Post by **coke** » Wed Dec 30, 2009 9:35 pm

Yea. I finally found VWCaddy's website and read his writeup on them. Luckily, I was able to dig 2 "unknowns" off the floor in the garage and they both work. Going after two more tomorrow, and going to replace every one of them that is questionable. Then in february when the government gives me a little of my money back I'm gonna slam some new duraterms and possibly injectors in.

82vdub · Post by **82vdub** » Wed Dec 30, 2009 11:54 pm

This is one of the easiest ways of testing if they're good..........

Post by **Fatmobile** » Thu Dec 31, 2009 1:24 am

Great pic

rabbit_man · Post by **rabbit_man** » Thu Dec 31, 2009 4:02 pm

The continuity test isn't really very good, I had one test good that method that failed when hooked straight to a battery. I've heard of it happening to other people too.

The best fix is to run a separate wire to each GP, it really helps with troubleshooting.

coke · Post by **coke** » Thu Dec 31, 2009 4:53 pm

Okay folks. So, 3 tested good. 1 tested bad.

Only two were actually good, and I replaced both of them with ones I had my hands on and tested.

One behind the pump tested good on the test light, but when I measured resistance, it was 10 instead of hte normal 1ohm. So, out it came and sure as hell, it was bad. Since it was the one directly behind the IP and closest to the cam, I decided to play it safe and when I hooked her to the battery, it was dead.

I now have 4 working plugs and the thing seems to be starting like normal again. Hopefully it'll last me till February, then I'll put 4 new bosch duraterms in.

surfcam · Post by **surfcam** » Thu Dec 31, 2009 6:39 pm

I only run new GP's behind the pump and old one's on the two right positions. I just can't throw anything out that's still usable. Sometimes I get other people to throw stuff out for me. I'm going to pimp my GP system this spring with connection box I got at Princess Auto. Then it will be a breeze to check each GP with separate connections to each GP. I have a ammeter hooked into a jumper cable. If it doesn't read 45 amps you have dead soldier.

wolf_walker · Post by **wolf_walker** » Fri Jan 01, 2010 1:50 pm

It's always the one behind the IP. I've won money on it before.
Funny how mechanical life works that way.

coke · Post by **coke** » Fri Jan 01, 2010 11:27 pm

Yup. I won't be had again. New ones go in it soon, but all is well now. Starting great again.

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Glow plugs question

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