Glow plug relay failure caused by new glow plugs! - PeachParts Mercedes-Benz Forum

Fattyman · #1 02-21-2013, 09:49 PM

I swapped out my wife's GP's on her wagon and noticed it didn't start the way you would expect it to.
The glow plug light would only stay on for a second and the relay would pop after 5 seconds! Everything worked normally before.
I change out the GP's every year and have never had this happen before so I just thought I'd throw the info out there just in case someone runs across the same problem.
Now I know why I always grab a GP relay at the junkyard. $15 beats $250 any day.

compress ignite · #2 02-22-2013, 03:24 AM

I.E. Your attempt at connecting unrelated actions!

If you're replacing GP relays on a regular basis...
ZomeZing (Other than "New" Glow Plugs) is the culprit!

Your model GP Relay doesn't Know (or Care) what's "Down-Wire"
from it.

qwerty · #3 02-22-2013, 08:51 AM

Quote:

Originally Posted by compress ignite

Your model GP Relay doesn't Know (or Care) what's "Down-Wire"
from it.

Agreed. (Except for the fuse.)

If the relay is remaining closed for only five seconds, it is not because the glow plugs are new.

Zacharias · #4 02-22-2013, 11:23 AM

If you are saying that you need to replace the plugs every year, something is indeed wrong. Even in eastern Canada, with our extreme cold periods in the winters, no one replaces their glowplugs annually. I have got up to four years from mine, though that was probably pushing it.

What brand of glowplugs are you installing?

And what is the part number stamped on your glow relay (if you clean off the front you should be able to read it with the relay in place)?

Fattyman · #5 02-22-2013, 12:04 PM

We run WVO in all of are cars and the GP's get hammered.
That why I change them every year.
Especially in my WIFE'S car if you know what I mean!

Mine can wait longer.
I change the GP's every year, not the relay.
This is the first time the relay went belly up as a result of changing the GP's.
That's why I posted the subject, who would have thunk that new GP's would cause that kind of failure? Strange huh!
I guess the sudden lack of resistance was too much for it. RIP
As an aside, we have never had any sort of WVO related failure in over 10 years and over 100K miles so changing GP's once a year is a price I'm more than willing to pay. That and extra fuel and filter changes and we're still on top of the curve.

Diesel911 · #6 02-22-2013, 12:13 PM

Take apart the Relay and see if you can find where it failed.

compress ignite · #7 02-23-2013, 03:57 AM

One more time (In Chorus)
"Good or Bad glow plugs CANNOT Kill a GP Relay!"

Your trying to blame the Demise of the GP Relay,on installing New GPs is the
classic definition of Mechanical Insanity.

X2
(Look inside the Relay and "SEE" what's BAD...
It'll give you something to do,other than slandering the GPs)

Brian Carlton · #8 02-23-2013, 08:46 AM

Quote:

Originally Posted by Fattyman

who would have thunk that new GP's would cause that kind of failure?

Nobody.

Quote:

Originally Posted by Fattyman

Strange huh!

Impossible would be a better word.

The relay doesn't know anything about the glow plugs unless it suffers a direct short from them............in which case the fuse would immediately burn through.

You mention the relay "popped". Is this an improper word for "melted" or "burned" or "failed"?

vstech · #9 02-23-2013, 09:17 AM

Quote:

Originally Posted by Fattyman

We run WVO in all of are cars and the GP's get hammered.
That why I change them every year.
Especially in my WIFE'S car if you know what I mean!

Mine can wait longer.
I change the GP's every year, not the relay.
This is the first time the relay went belly up as a result of changing the GP's.
That's why I posted the subject, who would have thunk that new GP's would cause that kind of failure? Strange huh!
I guess the sudden lack of resistance was too much for it. RIP
As an aside, we have never had any sort of WVO related failure in over 10 years and over 100K miles so changing GP's once a year is a price I'm more than willing to pay. That and extra fuel and filter changes and we're still on top of the curve.

in all likelyhood, what killed your relay was TIME
it's an electronically controlled SWITCH...
it does have a circuit in it that compares one GP to the rest, to control the light circuit... but that's it. total coinkidink that it picked that time to begin it's quick click... most likely, the timing circuit resistor/capacitor in the relay failed, possibly even a simple cold solder joint in there on the timer.

as for your annual GP schedule... that's up to you, but if you are not reaming the GP bores, you are not doing the job fully.

Fattyman · #10 02-23-2013, 07:14 PM

Quote:

Originally Posted by vstech

but if you are not reaming the GP bores, you are not doing the job fully.

That's the fun part! I'm going to pull the old one apart for a look see. Both Diesel 911 and I are curious. Film @ 11

Fattyman · #11 02-25-2013, 12:29 AM

I took the cover off the relay to see what makes it tick. Or what used to make it tick. Couldn't any signs of damage but I got some pics anyway just for fun. The contacts are on the right side and the 5 pin harness is underneath the left side on the pics. I wonder if these were hand made at the time?

TnBob · #12 02-28-2013, 05:04 AM

Wouldn't a schematic be nice ?

GregMN · #13 02-28-2013, 09:21 AM

Reaming the glow plug holes annually makes sense if you run on VO.

So, every fall, adjust valves, ream holes. And on some level, if you have them out anyway it makes sense to put new ones back in. I could definitely see doing that for the wife's car, but I'd save the old "good" one's for use in my car because I am cheap (that's why I run VO).

The only GP relay I have had fail was a 603 one with separate contacts for each GP. When replacing the manifold I ended up with a bracket dead shorting against a GP. For a short while I used a relay from a 617.

GP cannot ruin relay.
Dead short can.