Glow plugs are strange in the 617 - PeachParts Mercedes-Benz Forum

yuke · #1 01-14-2017, 07:23 PM

Wow always did have a lot of problems in keeping the glow system working in these motors. About a week ago on naturally the coldest day of the year about 3 degrees my glow light in dash stopped working. In checking out the plugs found 3 bad ones seems 3 went bad at same time well since no one around me just stocks glow plugs on the shelf I took 3 used ones out of a motor I have sitting around and presto glow light in dash working again all seemed well. Then light would not go on turned key off on couple of times then it would go on day or 2 later would not go on at all no matter how many times turning key off and on. So started checking plugs again all seemed well then checked bulb in dash (simple way to check bulb is take small connector off and jump red+white wire to blue+white wire bulb and ground is good now Im really scratching my head tested plugs again now one test bad replace that one with another known good used one and now got a light in dash again but is kind of iffy sometimes takes a second on off on the key to get it to go on.
Am wondering if sometimes the key switch connection can go bad and cause light to not go on? Also wondering if you would just take the red+black wire out of the 4 prong connector and route it right to battery and thru a toggle switch if that would be the easiest way to get a manul glow system then you would still be retaining mostly all stock set up including light in dash as I like that to warn me if I have a plug failure and just cut the ignition switch out and glow only when you have to which I think would lengthen the life of rhe glow plugs because they are not that easy to change unless you really remove injector lines. I have 5 new Bosh 80006 on order just getting tired of changing them and the light on the dash working so intermittently. Glow plugs are kind of like the funace in your house seems they never fail in the summertime.

Diesel911 · #2 01-14-2017, 09:14 PM

Yes it is possible for the the ignintion switch issues.

My own experience with toggle switches is that I eventualy forget to turn them off. I started off with a rocker switch that works like a toggle switch for the glow plugs. Even with a lighted switch I would forget to turn the glow plugs off.

Forunately I was able to take the switch apart and shove part of a ball point pen spring inside so when I released the switch it turned the switch off.

t walgamuth · #3 01-14-2017, 10:34 PM

I would suggest testing the plugs with a jumper cable. Attach the cable to the positive on the battery and on the body of the glow plug and touch the stud on the top of the glow to the negative terminal on the battery. It should glow bright orange/white in a few seconds. It it does not glow up nice and bright and pretty quickly I'd throw it away and get five that do.

mach4 · #4 01-14-2017, 11:29 PM

Stories like yours are why I eliminated the glow plug relay in favor of a manual system....and why I've never regretted the decision.

yuke · #5 01-16-2017, 03:52 PM

Quote:

Originally Posted by mach4

Stories like yours are why I eliminated the glow plug relay in favor of a manual system....and why I've never regretted the decision.

Yes I read your write up on the manual glow system Mach what I was wondering is could you just take the ignition switch out of the stock system and keep all else stock then you would have a manual system on a timed glow but only use it when you want to? I do like the feature of the light in the dash giving you a warning if you have bad glow plugs and with your way of totally going manual I think you lose that benefit. Right now I am pretty surr all my glow plugs are working but if I turn the key on might take about 3 seconds for the light to come on in dash where as before it would come on immediately. I guess what I am saying is could you just take the hot wire that feeds the relay and instead of it being on ign. switch put it on a toggle or button switch?

mach4 · #6 01-16-2017, 04:23 PM

Quote:

Originally Posted by yuke

....could you just take the ignition switch out of the stock system and keep all else stock then you would have a manual system on a timed glow but only use it when you want to?

I don't consider myself a glow relay expert, but if this video is accurate, it would appear to work - https://m.youtube.com/watch?v=6BAgO0ZR54U

SD Blue · #7 01-17-2017, 08:20 PM

Sounds like the glow plug relay is very intermittent. may be bad capacitors.

Pics: Inside a glow plug relay

Diseasel300 · #8 01-17-2017, 09:19 PM

I'll second the bad caps issue, I just went through it in my SDL. Basically the light would blink (or not) on the dash quickly and the glow plug relay would cycle in less than a second. You can see my thread here: Glow Plug Relay Troubleshooting...

In my case, I installed new capacitors and the GP relay has been working like a champ since then.

Maxbumpo · #9 01-18-2017, 08:46 AM

Ok, I think a little perspective is in order. The car is 32 years old (or more) and probably has a couple hundred thousand miles, likely more. Its an _OLD_ car, and so things will break and need to be diagnosed and repaired. I fail to see how any of this justifies converting to a manual pre-glow system. All the parts to repair this are available if you have time to wait for them to be shipped. You even have a choice of MB original parts, or aftermarket.

One of the systems that has three components (relay, fuse, glow plugs) is acting up. As designed, the light in the dash is telling you that there is something wrong. There is a diagnostic circuit inside that compares the current draw of the first glow plug to the other four, and if that comparison indicates a problem with any of the glow plugs, the circuit will tell you (the driver) that there is a problem by either not lighting the dash indicator, or lighting the dash indicator after the engine is started, or maybe both. You had three bad glow plugs, replaced them with used plugs, and the light was happy for awhile. Another plug failed, light told you, so you've replaced that. Now the light sometimes thinks there's a problem, and sometimes doesn't. In other words, the system is telling you that it is not really happy about the used plugs.

Why wouldn't you simply install the new glow plugs and be done with it, or then also replace the pre-glow relay with a new relay? Generally the relay fails in one of two ways: Doesn't work at all, or randomly turns on and drains the battery.

Last note: The indicator light in the dash doesn't mean plugs are energized or not energized. If the key is turned but the light doesn't come on, power is STILL going to all the glow plugs unless the fuse is blown. The car MAY still start, with a failed plug or two, because the other good plugs are heating up.

t walgamuth · #10 01-18-2017, 09:32 AM

I concur with Max. I'd as minimum test the glow plugs. Replacing with used is a last ditch measure. If you want reliable starting, put in all new bosch plugs. Switching to manual glow is fine but won't help if you have bad glows.

Diseasel300 · #11 01-18-2017, 10:12 AM

Quote:

Originally Posted by Maxbumpo

Last note: The indicator light in the dash doesn't mean plugs are energized or not energized. If the key is turned but the light doesn't come on, power is STILL going to all the glow plugs unless the fuse is blown. The car MAY still start, with a failed plug or two, because the other good plugs are heating up.

Yes and no. If the relay is operating correctly, the light should be on for at least a few seconds. In my case with bad capacitors in the relay board, I would get nothing but a quick blink of the light and a greatly condensed glow cycle ~10 secs total cycle when I got the car, down to less than 1 second when I finally redid the capacitors. If you're following, that meant when the key was cycled, I had less than 1 second of glow time, regardless if the light lit or not. The car started - just.

Electronics wear out, if all other avenues are exhausted, switch the key to pre-glow and run a timer or stop watch until you hear the "clunk" of the relay dropping out. It should be ~30 seconds. If it is much less than that, time for a new relay or rebuild the one you have if the contacts aren't toast.

Maxbumpo · #12 01-18-2017, 10:58 AM

Quote:

Originally Posted by Diseasel300

Yes and no. If the relay is operating correctly,

Good point, I was assuming the relay is still good. A failed relay would probably not light up the light and would not power the plugs, similar to a blown fuse.

funola · #13 01-18-2017, 11:31 AM

The glow relay in my 85 was intermittent for about 2 years where it would not glow approx 1 out of 10 times, only in the winter (figures!). I had it apart many times attempting to fix it unsuccessfully, which included resoldering all connections, replacing all electrolytic caps. My final fix was to convert it to manual operation. That was the best thing I did. No more trouble after that.
My conversion has one wire coming out of the glow relay which is wired to a momentary push switch to +12. The glow light is rewired internally/ connected to the glow plugs thus indicating actual power to the plugs. I offer this conversion service - PM me if interested.

If you are having problems with your glow relay and re-capping/ resoldering does not help, my recommendation is buy a new relay instead of used, or convert to manual glow.

yuke · #14 01-18-2017, 04:55 PM

Many good points made currently my glow cycle is good at 30 sec. I really do not think you need the full 30 sec. as 10 seems fine currently when I turn the key on it will take about 2 sec. before light on dash comes on then goes off in 2 seconds I wait a couple more and then hit the starter and it starts very easily and quickly in these a little above freezing temps. Yes I do believe that the first thing I should do is replace all g.p. with new bosch then go from there yes maybe there are bad caps in the relay. It is good to know that just because the light might not be on dash does not mean the glows are not getting juice it just means that all the glows might not be working or the light sensor does not like the amount of juice they are pulling in that it might be unequal. I will look much closer at it when I get a chance and the new glow plugs should arrive shortly.