1995 E300D Glow plug issue.. Yes I've searched.. - PeachParts Mercedes-Benz Forum

stcbenz83 · #1 11-10-2011, 06:41 PM

For the past week, after getting off work until I go to bed, I've been searching online for the Glow plug issue I've been having and it seems that no one else has this issue.. One post on here was close to my problem but, the thread was never finished and no end result post.. So I'm posting and hope to get this issue resolved...

car: 1995 E300D OM606 N/A

Here is my issue. It has progressively become more sporadic but, usually on the first start in the morning I get no pre glow light on the dash.. This has happened a few times (different times of the day and usually never on the same day). However, if I turn the car off after its just started (roughly) and turn the key back to the pre-glow, I then will get the light and the car start smoothly and without hesitation.

I know from the 240 that usually a no glow light coming on ever indicates, from my experience, a bad relay but, in this case with my 95 it does come back on and work as normally the rest of the day.

In some of the post's I've read, there is mention of the water temp sending sensor being correlated with the GP/ relay unit. When I bought my car 3 weeks ago, this sensor (located across from the stop knob on the filter housing) was leaking anti-freeze. Turns out there was no washer on it... Put a crush washer on it, stopped the leak.

Also, from what i've read and experience, if I were to have a dead plug, the light would come on after I had started it, correct? wouldn't I also still get the pre-glow light even with one dead plug, just rougher starting? with This issue the light never comes on before/after start up. Only after i go to restart it do i get the NORMAL pre-glow light, light goes out, I start it and it fires up without hesitation, clatter or smoke. when I dont get the light, its rougher starting, lots of nailing and smoke out the exhaust.

with that said, I'm here scratching my head.. As of now, i'm thinking the relay is whacked out. But, having read that the temp sensor (which i've already had a problem with) is related to the GP unit, I don't want to drop $150-$200 for a GP relay and have it turn out to be the sensor which costs $35

So, anyone have Idea's?!

TMAllison · #2 11-10-2011, 08:40 PM

What shape is your wiring harness in?

How old is the OVP relay?

stcbenz83 · #3 11-10-2011, 09:24 PM

Quote:

Originally Posted by TMAllison

What shape is your wiring harness in?

How old is the OVP relay?

Wiring harness looks to be in decent shape.. as far as i can tell, the relay has to be original but, not 100% sure as I just bought the car 3 weeks ago and service history was limited

stcbenz83 · #4 11-10-2011, 09:27 PM

If the water temp sensor was causing the circuit to 'shut off the GPR' for over load protection or what have you then, tomorrow morning if I have the same issue with the GP's not coming on, do you think temporarily disconnecting that sensor would show if that where to blame?

compress ignite · #5 11-11-2011, 02:24 AM

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chazola · #6 11-11-2011, 03:44 AM

Sounds like the same symptoms I had when my relay was on it's way out. But like you say, it could be the sensor too. You need to troubleshoot each component and rule out which is good/bad- get your multimeter on the relay output pins and test you're getting 12v when ignition is on, test the glow plug connector sockets for resistance to see if you've got any bad plugs. Like you say, if you have a bad plug the light should come on after starting for around a minute, you're not getting this so I suspect the relay.

You can easily take the relay out and open it up (4 screws on top and the cover slides off) to look for anything obvious too, and run it with the cover off to see if it's physically working or not.

good troubleshooting guide here: Mercedes Diesel Glow Plug Repair

Scorch · #7 11-11-2011, 05:45 AM

I have a '98 E300TD and this week I got a similar code. In my case, the glow plug light came on while driving and I got a engine electronic light. I had a diagnostic run and got a code for the glow plug relay. I also had a code for a lamp and checked that first. Bulb was good so checked the wiring harness and found several cracks in the insulation around the wiring. Cleared the codes and checked again and no codes and the light started working. Rechecked several of the wiring harnesses and though they looked fine externally, opening them up, I found literally dozens of cracks in the insulation around the wiring. I'm sure that I'm getting a short or three that's causing the problem. At this point, I'm trying to figure out what the best course of action would be. I'd check the wiring harnesses first, even if they "look" good.

stcbenz83 · #8 11-11-2011, 08:23 AM

Thanks guys for the reply.. right now I'm looking directly at the system Vs. The wiring harness as the harness looks to be in fairly good shape though, if it comes to it I will take a closer investigation if nothing else works/ is causing the problem

Chazola, your post back in 09 was the closest issue to what I'm experiancing now. I will get my multi meter out and check the connections this weekend. I'm thinking along the same lines I.e. relays taking out.

On a side note, this morning same problem, went to start and no gp light.. this time I just bumped the starter without starting it, turned the key off and back on and I then had The GP light, light up. ???

This morning I was thinking, say it was the water temp sensor. It's been getting cold here in the suburbs of Chicago (27F last night) so say when I go to start it since its so cold that the temp sensor is telling the gp system that 'its to hot, no gp needed' and closing the circuit. By bumping the starter, having the water pump pass some coolant past the sensor and then it realizing ' oh, it really cold out, need GPs' hence the light coming back on. Just a theory.

Ill get my meter out this weekend and see what I come up wit and report back

chazola · #9 11-11-2011, 10:12 AM

Your theory about the sensor could be true, might have any issue from it having been leaking before. Another thing if it's the relay- you could also have something like a dry solder joint or a marginal component that's cold and doesn't work on the first start of the day then heats up once it gets some current through it and works ok. I'd test the relay cold since you say it seems to work after a rough first start... with the cover off so you can see if it physically clicks into place.
The fact that you said it starts roughly makes me think relay or 1 or more plugs out, according to MB's diagnostics no light can be plugs or relay, so just a case of ruling out bits one-by-one I think...

Zulfiqar · #10 11-11-2011, 11:24 AM

The temperature sensor for the GP relay is the 2 pin one closest to the firewall and requires removal of the intake manifold to access. The one across from the shutoff is for the climate control unit.

Your problem seems like your relay is giving up the ghost, the starter trigger is connected to the GP relay and is somehow kicking into life.

stcbenz83 · #11 11-11-2011, 04:53 PM

I only get rough starting when I have No gp light

When the light comes on, the car starts smoothly

Also, as of this morning, I found that I do not need to even start it, I can simply bump the starter, turn the key to off, back to pre-glow and then the light and system come on

Ok, that's what sensor it is... that climate sensor wouldn't by chance effect the gp function would it?

compress ignite · #12 11-11-2011, 11:34 PM

As soon as you find the "BAD" WIRING (Grounding) [Or HARNESS] problem
,you won't have to avail yourself of it's protection!

It's forcing you to RESET the Protection!!! (That's the Clue)

LOOK at the Two tool options suggested in reply #5.

(You're NOT gonna find the Problem,Interfacing with us.)

(EDIT: 'Quickest Diagnosis for you is the FSM Diagnostic tool. AND the
DMM. I've already shown you the part pertaining to the Relay.)

"Open circuit in wiring or short"

"Open circuit in wiring or Short in GPs"

benedict · #13 11-12-2011, 03:35 AM

STCbenz83

I just removed my crossover pipe--> disconnected one glow plug--> turned key to ACC and result is NO glow plug light either. There is some kind of circuit continuity monitoring in that GP relay.

With this GP disconnected, I then proceeded to start the car and with a little bit of difficulty it fired up (blowing some heavy white smoke) and carried on like an old chook for about 30 seconds or so. But the interesting thing is my Glow plug light is illuminated and stays illuminated whilst the car is on and running, stating that there is a fault somewhere.

Does your GP light stay on when started?

You might have a GP plug not quite seated or your harness could be toast as someone suggested.

The easiest way I've found to check the condition of the harness is at a sensor soewhere. There is a blue sensor at the top of the engine closest to the front, which pulls the high speed aux fans in: the wires will look hard and brittle and if you gently move them you will see they are no longer flexible.

chazola · #14 11-12-2011, 05:00 AM

As Compress/Ignite said I think you're definitely going to need a multi meter to troubleshoot this one, unless it's the relay confirmed from a visual inspection. As Benedict says there is a on-board diagnostic in the GP relay that detects open circuit when a glow plug dies. I recently had a glow plug die and go open circuit, and I had no pre-glow light then light coming on for 1 minute after start.

As the others have said it could quite possibly be the harness too, the wires are usually ok but the insulation becomes very brittle and cracks, which could cause the short.

If you can't see anything obvious visually, and your relay and the wires around it check out ok, you'll need to measure resistance in the glow plug wires- prise the big 6-way connector off and set your DMM to ohms... it'll be obvious if you've got a bad wire/plug as good ones are low resistance normally (under 1.2) - if you get a bad resistance reading at the glow plug connector you'll know it's either that plug or that plug's wire... they're numbered on the connector and the plugs run 1-6 from the front of the engine. If you get this you'll need to do the no-so-fun job of removing the crossover pipe so you have access to the plugs/harness, disconnect the wire at the plug and test between there and the connector and if it checks out ok you know it's that plug...

stcbenz83 · #15 11-23-2011, 10:35 PM

OK, so I finally have had the chance to tear into the GP system... Still experiencing the same problems..

First, after reading another similar post to my issue and also, the attachment that compress ignite posted (http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/605_606/15-4000.pdf), the most obvious was that the water temp sensor needed to be replaced...

Ordered the proper parts and, tore the IM apart and replaced the sensor....
brought the DMM out and decided I might as well test the sensor....

put one lead on one of the metal connector prongs and the other on the other prong of the sensor. Anyone know what the reading(s) should be for this sensor.. it appears to be working as the ohm's fluctuate with temp difference (put it in the freezer and also used a lighter while taking readings.

While I had my meter, I tested the rest of the components as you guys suggested. The method I used to test where from dieselgiants page.
From the connector, all 6 of my GP's read 0.6ohms (thankfully wont have to dive into that yet)

Testing the relay, I verified it's getting around 12.4X volts.

so w/ the GP's testing fine (thankfully) and having replaced the water temp sensor (though I'm still suspect if the original one is ok) and verified the GP relay is getting juice... what would the next suggestion be?

Was the original W.T.S. possibly bad even though it is reading as though it's functioning?

Glowplugs are reading perfect so, no issue there right?

GP relay is getting juice.. is there any way to test the functionality of it? Also, if the problem isn't fixed from the sensor replacement, would that be my next suspect in terms of parts replacement?