unique glow plug problem? - PeachParts Mercedes-Benz Forum

bill.schweig · #1 12-16-2006, 01:10 AM

as much as i have scoured the threads here, i still can't seem to locate someone with the same GP situation. ok, to start out...

background:
1980 300CD 281k
replaced glow plugs and battery Jan '06
anti-gel formula in diesel tank
have not run veggie oil in 2 weeks

problem:
about a week ago, i began to start the car. temp was cold but not bad (40). the glow plug light came on like normal. i heated the GP 2 or 3 times as i usually do in colder weather. cranked. turned over, fuel being delivered, etc, yet car wouldn't run. when i released the ignition, the GP light flashed on and off indicating some kind of problem with the GP (i don't think it indicates anything in particular, just that there is a GP problem?).
heated, cranked, hooked up to battery multiple times. checked visible wires. no luck!
my car was about to get towed so i used starter fluid on it and it finally started.
back at my house, i tested the GP resistance, all except one were running 30,000 ohms (registered 'infinity' on the 200 range). rechecked connections w/ multimeter, no problems. i wasn't present, but my friend checked the relay to the best of his (and my) ability and couldn't find any problems indicated by voltage/resistyance, fuse is intact.

replaced all 5 GP, even replaced some wiring and filed down leads on battery to make sure connections were good.

car still won't start, GP light still turns on for 'heating' and flashes on and off after cranking to indicate problem.

questions:
1. why did the GP go bad after only 11 months (14k mi)?
2. what is wrong with it and are the GP themselves even responsible for the starting.

any answers that would spare me from slicing up my knuckles again taking out or installing GPs would be excellent. if not, so be it.

thanks!

phil2810 · #2 12-16-2006, 01:58 AM

If your reading that high of resistance on your GP's, it wouldn't matter if the relay was good, you wouldn't heat at all. It does seem odd they all read approx the same...... could you detail how exactly you measured them (ie, disconnect relay connector and checked the GP itself to ground or the connector to ground). What wiring was replaced?

#3 12-16-2006, 02:08 AM

There must have been an error in your measurement. The glowplugs should read in the 0.5-1.0 ohm range.

bill.schweig · #4 12-16-2006, 02:21 AM

Quote:

Originally Posted by ForcedInduction

There must have been an error in your measurement. The glowplugs should read in the 0.5-1.0 ohm range.

the one good one did read 0.6, one read something like 10k and the rest read up to 30-35k. the last 4 read infinity on the 200 ohm range, i just checked it at higher range b/c i was curious. hayes manual says if the meter reads infinity they are bad.

i tested them by disconnecting the relay and testing plugs themselves. also checked them after taking them out and got same readings. i just re-did the wire terminals where they attach to the GP b/c the insulation was frayed...i doubt it had much to do with the problem but i don't know a whole lot.

t walgamuth · #5 12-16-2006, 06:34 AM

what brand of glows did you use?

if not bosch then i suggest just getting bosch and replacing all of them. this is one place where the brand matters.

bosch is best, imho

tom w

running-snail · #6 12-16-2006, 07:16 AM

Did you ream the glow plug cavity before inserting new plugs?

I've never glowed more than once when starting, certainly not at 40 degrees. - is this typical when running WVO?

Palangi · #7 12-16-2006, 12:31 PM

Quote:

Originally Posted by t walgamuth

what brand of glows did you use?

if not bosch then i suggest just getting bosch and replacing all of them. this is one place where the brand matters.

bosch is best, imho

tom w

I agree with Tom. This sounds like Autolite or some other mystery brand of glow plugs. Get a set of the proper Bosch plugs and this problem will be gone.

bill.schweig · #8 12-16-2006, 01:52 PM

Quote:

Originally Posted by Palangi

I agree with Tom. This sounds like Autolite or some other mystery brand of glow plugs. Get a set of the proper Bosch plugs and this problem will be gone.

i used bosch. replaced all 5. i usually glow twice when it feels chilly out, just to make it easier on the starter. i haven't been running WVO for a couple weeks b/c i have been out.

i did not ream the GP chamber before replacing them. please elaborate.

would not doing this cause the GP light to flash on and off. it has done this flashing beofre but replacing the GPs made it function normally.

Brian Carlton · #9 12-16-2006, 03:30 PM

Quote:

Originally Posted by bill.schweig

i wasn't present, but my friend checked the relay to the best of his (and my) ability and couldn't find any problems indicated by voltage/resistyance, fuse is intact.

Please provide the exact details of how your friend checked the relay to be sure the plugs are getting 12V when the key is in the #2 position.

whunter · #10 12-16-2006, 04:06 PM

Quote:

Originally Posted by bill.schweig

I did not ream the GP chamber before replacing them. please elaborate.

Here are some links to help you.

Glow plugs link thread
http://www.peachparts.com/shopforum/diesel-discussion/137732-glow-plugs-link-thread.html#post1019018

Have a great day.

leathermang · #11 12-16-2006, 04:11 PM

Don't glow twice. Turn your glow plugs on and time it for one minute.. the FSM says it continues to get hot if you just leave it on even after the light goes out...

bill.schweig · #12 12-16-2006, 04:48 PM

Quote:

Originally Posted by Brian Carlton

Please provide the exact details of how your friend checked the relay to be sure the plugs are getting 12V when the key is in the #2 position.

ok, because my friend didn't do so hot a job explaining it over the phone, i retested the relay myself to the best of my ability and i have a couple questions.

first i tested resistance thru each socket in the GP relay connector. There are 8 sockets. What does each number next to the socket stand for? shouldn't there only be 5?

my meter reads .3 in its own wires so i subtracted that from the reading...

AFTER replacing with new bosch glow plugs, #2, 3, 5, 7 all tested .5 or .6 - good right?
# 8, 6, 1 all tested infinity - bad, right?
# 4 didn't have any conducting material in the socket. what is the deal with that?

tested large guage wire and each side of 80a fuse for voltage, all tested same as battery 12.6-12.7

then, with ignition on, GP light on, tested each pin in relay for voltage.

each pin tested battery voltage 12.6-12.7 except for #6 and #8. (#6=7.1v and #8=5.6v). again, i don't know if this is even significant since, i'm assuming, only 5 of these pins are supplying power to the GPs, what are the rest for?

this is all i knwo how to do, and i'm not even so sure what all these values are indicating...

OMEGAMAN · #13 12-16-2006, 07:09 PM

Since you have replaced all 5 glow plugs you can rule those out.
Get a decent test light. Not one that uses LED's Just a simple one that uses a nice bright bulb.
Turn on the key and see if you get power to all five glow plugs and report back.
It sounds like you have a broke wire to one or more of your glow plugs and this will tell us if so and which ones

Jadavis · #14 12-16-2006, 07:21 PM

Quote:

Originally Posted by leathermang

Don't glow twice. Turn your glow plugs on and time it for one minute.. the FSM says it continues to get hot if you just leave it on even after the light goes out...

Depends on the model/year.

My 87 300D will go for about 36 seconds. If it is really quiet you can hear the relay click off. Another way to check is to watch your dome light. It will brighten up when the relay kicks off.

-Jim

whunter · #15 12-16-2006, 07:33 PM

Here are some links to help you.