After Vehicle Inspection-No Glow Plug Light - PeachParts Mercedes-Benz Forum

gmaltz · #1 10-02-2007, 01:55 PM

After required annual vehicle inspection in NY, (only $10) the glow plug light is out during start!

I told the grumpy mechanic as I was leaving "Oh, don't know anything about it" was his response. I think he left the the key on too long and burnt out the plugs or the relay!

Engine does start the same. Its been a little rough running after start up lately though, so I just ordered new Bosch glow plugs at $14 ea from the PartsBin (good deal).

I also jumped pin 1 and 3 on the fourpin connector of the pre glow time relay and the lamp tested O in the dash.

Not sure about the next step to test the relay itself. Any ideas?

jkoebel · #2 10-02-2007, 02:13 PM

Quick and Dirty Glow Plug Electrical Testing. Adapted from Diesel Giant's electrical glow plug testing, to take advantage of not having to run wires across the entire engine bay.

(1) Make sure you've got voltage going to the glow plug relay.

Find a good metal screw that goes into the chassis, use that as your ground. (Battery Ground and Chassis Ground are the same, so pick the closest one that works.) Open the relay cover...test with multimeter between where the line comes in and that screw. Then test at each side of the strip fuse. It should be battery voltage at all 3. (Battery voltage should be above 12.5V with car off, above like 13.3V car on. If not, alternator problem.)

(2) Check wires going to each plug.

Remove the relay cap that goes to the individual glow plugs. Set the multimeter to check ohms, and test between Cylinder 1 on the connector and Cylinder 1 glow plug wire on the engine. Repeat for all cylinders. The number should be very, very small -- below 1 ohm optimally. Very high numbers mean the wire is broken.

(3) Check eack plug itself.

With multimeter in ohms, connect the positive end to the incoming power wire to each glow plug, and the negative end to the metal valve cover. This works because the valve cover is a grounded metal structure, so valve cover ground is the same as chassis ground and battery ground. You want a little bit of resistance, like between 0.2 and 1 ohm. 0 ohms means internal short (dead plug), very high/infinite means internal break (dead plug.)

(4) Test the voltage coming out of each relay while the glow timer is on.

This one can be done with 2 people, a lot of running, or two alligator clip extensions. Measure, on the relay itself with the plugs unplugged, voltage between pin 1 and chassis, pin 2 and chassis, etc. during the time the glow plugs would normally be on but aren't. It should be battery voltage. If any of the pins corresponding to a cylinder are, in fact, not -- then bad relay.

Cheers.

gmaltz · #3 10-02-2007, 02:37 PM

Thanks - jkoebel - for the quick reply. I will try your suggestions. This is for a 1987 300 D Turbo. It might be similar though. Pencilglow plugs, not loop type.

My maintenance CD says in step two- after verifying the dash indicator lamp was good states;

" If the glow lamp is in order, test the black cable from connector contact 3 of the preglow time relay to the preglow indicator lamp for interruption. Rectify interruption. If the preglow indicator lamp lights up, the preglow time relay is faulty. Renew preglow time relay."

I do not understand this test. An help would be great.

I have a test lamp and a cheap digital multi meter.

gmaltz · #4 10-02-2007, 03:44 PM

Can you in fact burn out a glow plug or relay by leaving the ignition switch on?

barry123400 · #5 10-02-2007, 04:46 PM

The word interupt is a description of an open ciruit condition I believe. In a way it's a poor choice of words by north american definition at least. Better than chinese english though.
As I see it they are saying check for continuity from the third relay prong up through the wire and indicator bulb to ground. If not there fix the bulb or wire or even the ground for the bulb. If continuity there they say to call it a bad relay.
I think the relay times out if the key is left on. If so leaving the key on would have no negative effect. I also think the bulb goes to ground or they would have asked you to check for twelve volts on the line from the bulb rather than continuity.
The preffered relay check I would do. Make sure the relay is getting it's twelve volts. With the engine cold see if there is any voltage output to the plugs. With the key turned to the glow position of course by a helper. First make positive the heavy strip fuse is really good. No voltage output by the relay does not totally condem it as it could be a switch failure or perhaps a defective temperature sensor on the block. With no output from the relay at all and not even a flicker of the glow light I would substitute the relay with a known good one for a test. Too many times people rush out and buy electrical parts without doing enough checking. Electrical parts are usually non returnable if not required. A test substitute can usually be gathered up at a junkyard.

jkoebel · #6 10-02-2007, 05:07 PM

Quote:

Originally Posted by gmaltz

" If the glow lamp is in order, test the black cable from connector contact 3 of the preglow time relay to the preglow indicator lamp for interruption. Rectify interruption. If the preglow indicator lamp lights up, the preglow time relay is faulty. Renew preglow time relay."

Check that the wire feeding the glow plug light on the dash, which goes between the glow plug relay and the glow plug light, isn't broken. If it is, fix the break and re-test.

If that wire is good, then proceed with the rest of the tests. That paragraph above suggests that the glow plug relay itself is bad if the wire between the relay and the light is in working order, but that's not necessarily true.

gmaltz · #7 10-02-2007, 05:58 PM

Quote:

Originally Posted by jkoebel

Check that the wire feeding the glow plug light on the dash, which goes between the glow plug relay and the glow plug light, isn't broken. If it is, fix the break and re-test.

If that wire is good, then proceed with the rest of the tests. That paragraph above suggests that the glow plug relay itself is bad if the wire between the relay and the light is in working order, but that's not necessarily true.

The glow plug light in the dash works OK when pin 1 and 3 are jumped. This is the first step on the CD so the contiuity is good, right? I don't understand why in step two it says to check for interruption if in fact I just did, in step one! I must be missing something here.

jkoebel · #8 10-02-2007, 07:31 PM

Quote:

Originally Posted by gmaltz

The glow plug light in the dash works OK when pin 1 and 3 are jumped. This is the first step on the CD so the contiuity is good, right? I don't understand why in step two it says to check for interruption if in fact I just did, in step one! I must be missing something here.

I think you tested it a different way than they had in mind, which necessitated checking continuity.

All the same, do the rest and report back.

gmaltz · #9 10-02-2007, 08:46 PM

Step 2 shows checking the wire between the indicator bulb and pin 3 with an ohm meter but does not indicate any values.

What am I looking for on my meter?

I should get the 6 new glow plugs that I just ordered tomorrow and with luck they might go in if I remove the inake manifold again. Just had it off last month when removing the ALDA.

Darnit! Wish I had the gow plugs then.

babymog · #10 10-02-2007, 08:51 PM

In the '87, a burned out glow-plug will cause the lamp to not come on, that is the indicator that the glow-plug is out. I believe that either #1 or two of the other plugs will cause the fault, check glow-plug resistance.

As far as burning them out, there is a timer, it turns them off after something like a 20second max. heating time or engine start or coolant temp.

jkoebel · #11 10-02-2007, 09:35 PM

Quote:

Originally Posted by gmaltz

Step 2 shows checking the wire between the indicator bulb and pin 3 with an ohm meter but does not indicate any values.

What am I looking for on my meter?

I should get the 6 new glow plugs that I just ordered tomorrow and with luck they might go in if I remove the inake manifold again. Just had it off last month when removing the ALDA.

Darnit! Wish I had the gow plugs then.

Anything below about 2, I'd imagine.

gmaltz · #12 10-03-2007, 09:58 AM

I think I'm on the right track!

OK, I got the ol meter out and did a simple test. Removed the six prong connector to the GP relay and started checking the GP's through the wires using the ohm meter.

VIOLA

All checked out with no resistance except #3. It measured .9 ohms.

This must be the bad glow plug or wire.

Now the problem with the 603 engine is getting to the plug. Can't get my hands in there.

Anybody out there done this before without removing the intake manifold?

siral3x · #13 10-03-2007, 10:42 AM

yes, this guy does . chk it out:
http://www.dieselgiant.com/glowplugrepair.htm

jkoebel · #14 10-03-2007, 12:01 PM

Quote:

Originally Posted by gmaltz

I think I'm on the right track!

OK, I got the ol meter out and did a simple test. Removed the six prong connector to the GP relay and started checking the GP's through the wires using the ohm meter.

VIOLA

All checked out with no resistance except #3. It measured .9 ohms.

This must be the bad glow plug or wire.

Now the problem with the 603 engine is getting to the plug. Can't get my hands in there.

Anybody out there done this before without removing the intake manifold?

On my 240D w/ an OM 616, my 3 good plugs measured 0.3 each between the spot the wire comes into the plug, and the metal valve cover. The bad plug measured like 53.5.

If you're measuring from the wire on the relay plug to the valve cover, I could see it being 0.9 and being good. When you say there's "no resistance" between the other three, do you mean "0", or do you mean the meter couldn't give a value (infinite)? Either one isn't correct, since a glow plug is a resistive heater it should have at least a little bit of resistance. 0 ohms = internal short, it'll never glow...infinite ohms = internal break, it won't pass current.

Quote:

Originally Posted by siral3x

yes, this guy does . chk it out:
http://www.dieselgiant.com/glowplugrepair.htm

That's where I came up with the original technique for testing, actually.

gmaltz · #15 10-03-2007, 11:11 PM

Success!!!

I fixed it! Thanks to you guys on this great forum. Many thanks to all who responded and the write up in dieselgiant.com was what made it all crystal clear to me.

I was measuring wrong with the ohm meter. After correcting my mistakes I found plugs 1 to be 3.6 bad and plug 3 infinite. The rest were all good at .9 ohms.

Now I used the idea of very long small extension sockets and replaced 1 and 3 plugs without taking of the intake manifold. What a relief!

Going on a 500 mile trip tomorrow so I am sure glad that it worked out.

Still idles like crap after start though until warmed up, but that's another story. Maybe a bad lifter or two.

20,000 miles now on Frybrid veggy system too!

Thanks again guys!