Glow Plug Issue---No Start, No Dash Light---'81 W123 (Relay?) - PeachParts Mercedes-Benz Forum

iladelf · #1 04-04-2017, 02:51 AM

Hey all,

My old 81 w/84 powertrain 300D has been performing pretty well as a daily driver, until this past eve. Went to start it, noticed the glow plug light not working, and...no start. I live in the MO/IA/IL Tri-State region, so the weather was conducive enough to not be a cold start issue today.

From reading on the forums, I suspect a Glow Plug Relay issue, but...how would you suggest me going about tracking down this issue? The glow plugs have been working like a champion for about a year and a half, until now. Of note, the car was driven in the rain for a couple of hours today at highway speed, so I'm wondering if water somehow got forced into it.

Let me know what your thoughts are on diagnosing. I know already that the unit is on the driver's fender; that's about it. I also know that I have (potentially) access to 3 300D's at a local junkyard (a '78 and 2 '83s); my guess is IF there are any relays in any of those, they would work for a quick swap out. I also kind of like the easy-to-find-American-parts-solenoid swapout idea as well, but first...I need to get the thing back on the road!

Thanks for your input.

Rogviler · #2 04-04-2017, 03:23 AM

Check the easy stuff, like the big strip fuse in the relay box. Also, I had a ground failure completely at random. Ran a new ground to the body about 6" away and it's been fine ever since. It's probably going to be something simple if you just poke around with a multimeter.

-Rog

Maxbumpo · #3 04-04-2017, 11:32 AM

x2 on the strip fuse, 80 amps, which lives under the cover on the pre-glow relay. It is held down by two phillips head screws. Remove it and try to flex it a little, it may be brittle and will break as soon as you touch it. If that fuse has simply aged out, you should be fine with replacing it. If a glow plug is shorted to ground and that caused the fuse to blow (blown fuse should be obvious with a melted chunk missing from it), then you need to fix that first.

When you buy a new fuse, order three so you've got a couple spares.

iladelf · #4 04-04-2017, 11:46 AM

Danke schoen, folks. Haven't had a chance to poke my head under the "bonnet" to look at it yet today, but I will check that fuse. And ground wiring...sure could be. I ran a ground from my passenger headlight connector this past summer to the body and...have had no further issues with a flickering passenger side headlight. Bonus!

Junkman · #5 04-04-2017, 12:08 PM

No glow is most frequently a bad glow plug. Measuring resistance between the plug terminal and body will identify the bad one but not always. Dieselgiant has basic trouble shooting with pics. Don't jump out and tackle the relay unless that is the problem. Diagnosis of this system is pretty easy.

iladelf · #6 04-04-2017, 12:35 PM

Well, looked at the relay, now that I've had some time to do so, and...believe it may very well be the fuse. If you look at the picture, the fuse shows a pretty good hairline crack in the center, plus it's caved in quite a bit (the cave-in is hard to see from the photo).

My question, since that's an oddball-looking fuse, I'm guessing I can't just go to any big-box auto parts store for a replacement. Is that correct? I got to thinking that perhaps a better fix would be placing a fuse kit between the fuse posts, and just use an 80A bladed fuse. I've seen the fuses online and am guessing auto parts stores have those. However, I'm not sure if they have a kit beefy enough for an 80A fuse.

Thanks also for the tips on the Dieselgiant page, Junkman. That should help immensely!

Maxbumpo · #7 04-04-2017, 01:08 PM

Definitely the fuse, cracked and aged out. Replace that and you'll be fine. Some Mercedes dealers may stock them, I doubt any FLAPS will but you can ask. I order them online and try to always have at least two spares.

Diseasel300 · #8 04-04-2017, 01:24 PM

x2 on the fuse. That's an age/stress/vibration fracture, not an electrical failure. Time for a new fuse. Keep an extra on board, nothing sucks worse than being stranded because a fuse failed and you can't get a spare locally.

Don't bypass it either. Another member tried that recently out of desperation and cooked his wiring glow plug harness due to a short circuit that the fuse properly protected against.

iladelf · #9 04-04-2017, 02:03 PM

Thanks on the confirm of the fuse. Good news is, I'm just down the street from a marine shop (boat repair), and I see online that some boats use these very same 80a strip fuses. Perhaps I can find a winner; will let ya know!

Btw, when I swap this, do I need to disconnect the car battery or am I ok to simply unscrew and replace the fuse as is?

Diseasel300 · #10 04-04-2017, 02:06 PM

For safety's sake, I'd unhook the negative of the battery. The fuse is on the unswitched side of B+ (before the relay contacts). If you accidentally short your screwdriver to anything in the engine bay, you could discover what welding is all about.

Maxbumpo · #11 04-04-2017, 03:22 PM

Quote:

Originally Posted by iladelf

Good news is, I'm just down the street from a marine shop (boat repair), and I see online that some boats use these very same 80a strip fuses. Perhaps I can find a winner; will let ya know!

Do tell! It would be nice to find out that these fuses are available a boat parts place.

iladelf · #12 04-04-2017, 04:15 PM

So far, no dice on finding said fuse locally (a no-go with my local marine parts places). But, upon further review, I am wondering if a Mini ANL 80A fuse would work (see link below). I measured the original, and indeed it does seem that the 42x12mm Mini ANL fuse would be a direct drop in. And if I am reading right, believe I may be able to find those at OTR truck parts stores. Let me know your thoughts everyone.

https://www.elliottelectronicsupply.com/fuses-holders/mini-anl-fuses/mini-anl-80a-anl80-fuse.html

Maxbumpo · #13 04-04-2017, 04:32 PM

That looks like it will work. That one is more expensive than a strip fuse, but if locally available, I say go for it.

ah-kay · #14 04-04-2017, 04:41 PM

It is pricey. Normal 80A fuse is < $1. You can solder back the old one in a pinch, been there and done that, until you source a new one. There is no risk as the good remaining fuse will blow should anything bad happen. Fuse blows at the point of least resistance.

iladelf · #15 04-04-2017, 04:55 PM

Well...A-HA! Looks like I've found a winner at my local...Best Buy store, of all places. AFS apparently is the same (or quite close to) Mini ANL, fuse-wise. Only issue; they have 60A and 100A in this kit only. I'm guessing to be safe I should use the 60A? This basically is to tide me over until I can order some of the "original style" online.

Metra 60- and 100-amp AFS Fuse - (4-Pack) Gray TCAFS-60100 - Best Buy

Appreciate the solder idea as well. I do have a soldering kit, so hey, I can always go that route if the AFS fuse doesn't work for some reason.