Pics: Inside a glow plug relay - Page 3 - PeachParts Mercedes-Benz Forum

vstech · #31 03-04-2011, 11:38 AM

that's what the relay will look like if it sticks on. the ampdraw is low enough to prevent fuse failure, but constant enough to build heat inside the relay and melt plastic, etc...

funola · #32 03-04-2011, 11:43 AM

Looks like poor contact of the fuse strip which results in local heating at the contact area which melted the plastic. If you have continuity in the coil and no shorts, cleaning the fuse contact and making sure the 2 fuse screws are tight it may work just fine

micalk · #33 03-05-2011, 11:19 AM

Quote:

Originally Posted by Codifex Maximus

Back when I used to run a Video Game arcade, we'd use a dollar bill to clean contacts for joysticks and buttons. Very low abrasion and high utility as far as cleaning electrical contacts. Might be useful for the final buff.

Quote:

Originally Posted by Craig

Also useful for cleaning valves on musical instruments, rolling papers are good too.

Rolling papers are useful for so many things!

micalk · #34 03-05-2011, 11:23 AM

Quote:

Originally Posted by funola

Looks like poor contact of the fuse strip which results in local heating at the contact area which melted the plastic. If you have continuity in the coil and no shorts, cleaning the fuse contact and making sure the 2 fuse screws are tight it may work just fine

I'd agree. Just a little resistance could cause quite a lot of heat with the amount of current being drawn. Make sure the relay contacts are clean too. Use rolling papers to their best effect, then clean the relay contacts.

hjoab · #35 10-20-2014, 09:10 PM

I cannot get my preheating to work, no light at the dash, no heat either.

I remember that just before the preheating light stops working, a strange sound like of short circuit was heard sometimes from the inside the dash at the left close to the door.
It is possible the some other fuse or relay could be damaged than the glow plug relay instead and it is the one to blame instead of the glow plugs relay??

I any case, does anybody here know how to test a glow plug relay and cables to it with a multimeter?

That is ...

1) voltages in the female pins in cable coming from ignition when it is set on and when is set off?
2) voltages in the corresponding male pins in the relay when the cable is removed but the relay is connect to battery?
3) voltages at the relay male pins out for the glow plugs when the ignition is set on and when is set off?

BTW, when I test the continuity of current in the female pins cable from the glow plugs (negative attached to the negative battery) I get a lecture in my multimeter in all the pins between 1.5 and 1.8 (set at 200 ohms position on tester).
I read here
http://www.dieselgiant.com/glowplugrepair.htm
that these values must be below 1.
So from it, I conclude my glow plugs are bad but working yet, so these cannot be the issue with my problem.
That was why it always start with some difficulty at mornings, but not like now.

Ideas???

TNX

PackerEdgerton · #36 10-21-2014, 12:43 AM

Quote:

Originally Posted by JamesDean

0015459832 (300TD)
0015459732 (240D)

They're about $100 for each of them...

When my glow plug relay went out a few months ago, the dealer wanted $270 for one! I ended up buying a used working unit from the PickNPull for $12.

If that didn't work, I'd probably get a new one either from Pelican or possibly Walt (He carries the newer Hella type ones that glow a lot longer).

Packman

Maxbumpo · #37 10-21-2014, 10:52 AM

Quote:

Originally Posted by hjoab

I cannot get my preheating to work, no light at the dash, no heat either.

Does the dash pre-glow light come on with the "light check" function when you first turn the key? This is when all the lights in the instrument panel are supposed to light up as a bulb check. If not, then your bulb is dead.

If there are 12 volts at both ends of the strip fuse at the pre-glow relay, then your relay is _probably_ getting power.

Remove the fuse. Hold it in your hands, flex it a little. If it crumble or breaks, or if a crack becomes evident, the fuse must be replaced. It is an 80 amp strip fuse, not easy to find locally except maybe an MB dealership. Check with FLAPS, some do carry them, they certainly can order them.

If your multimeter is not a good, accurate meter, it will have a hard time measuring a resistance of less than 1 ohm. I wouldn't be to worried about those values if you have a cheapo-meter that cost less than $50 or was made in china. The resistance test is best used to find dead shorts (zero ohms) or blown plugs (infinite resistance). Very unusual for all the glow plugs to fail at once, so if the readings are consistent, they are probably good.

Beyond that, you'll need a wiring diagram to chase down all the wires and what each should measure.

SD Blue · #38 10-21-2014, 12:20 PM

Really, the "best" way to see if your glow relay is working is watching for the slight dim of warning lights when the relay engages upon turning the key. If the car sits a while between starts, the FSM recommends cycling the key several times to the #3 position to charge an internal capacitor of the glow relay.

As mentioned, it is difficult to really determine the quality of a glow plug with an multimeter. The best way is to remove the glow plug and attach it to the harness, while suspended in free air. (CAUTION! Absolutely do not touch, even accidentally, the plug while there is even a possibility of it being hot. Major burns are possible!)

Most likely, from your description, you have a glow plug or two that are on the decline. Some folks onesy and twosy the replacement of the glow plugs but I'm of the mindset to change them all at once and be done with it. I figure that if one or two fails then the others will not be far behind. Murphy's law states that they will fail at the worst time and situation.