testing glow plugs???

My 81 rabbit is having a hard time starting when cold.

I tried some basic glow plug trouble shooting but got conflicting results... :confused:

I leave the door open and watch the dome light when turning the key on and energizing the glow plugs. The light stays bright and does not dim. I would expect it to get dim if the glow plugs are heating. I would assume no power to the glow plugs. :uhoh:

I then attached a test meter to the glow plug ends. 0.0 volts with teh key off. 12 volts with the key turned on. Stays at 12 volts for about 15-20 seconds, then drops back to zero volts. Looks like the relay and timer are working fine. :smile:

It's like one test tells me glow plugs not working. But another test says glow plugs fine. :screwy:

I am confused. My first rabbit, but not my first diesel.

just because you get voltage on the glow plug bus does not mean that the plugs are good. an ammeter will tell if the plugs are good or not, and based on that reading it is possible to tell, with a high degree of accuracy how many are good.

and if i may correct you (no offense intended): one test says the glow plug circuit is good, and the other says the glow plugs are bad.

take a test light. put the clip on the battery pos. post take the harness off the glow plugs. touch the other end of the test light to the tip of the glow plug. It should light up bright. if its dim, replace the glow plug. remember that when replacing glow plugs only use the same brand (ex- beru or bosch. I seem to have better luck with the beru ones)

Hmmm, I'll give it a try...

I pulled the cover off the glow plug relay/fuse link thing on the fire wall...the fuse link looks fine...but then again I did get voltage to teh glow plug ends.

I'm guessing maybe the glow plugs are burnt out or whatever. The VW manual says to clean the plugs every 60K. I guess they probably have never been done. Could be all covered and thus insulated too much to pre-heat the chamber. Or maybe shorted out after the flat glow plug bar?

Any suggestions for getting the plugs out easy? A couple are tight behind the IP. Not looking too fun.

Hire someone with small hands. It's a royal pain, but I've used grabber tools, pieces of rubber hose and lot's of band-aids to get them in and out. Long 1/4 inch drive extensions with flex joints on the ends will work on some. Try doing them on one with A/C!