Glow Relay Question - PeachParts Mercedes-Benz Forum

VA-Merc · #1 12-09-2013, 01:55 PM

Hey guys, quick question on my OM 603 glow plug relay. The temp has been dropping a bit lately, and the wife noticed the car has been starting rough. I checked it this morning, and after sitting all night with an outside temp of about 30 degrees the relay only stayed on for about 10 seconds before it clicked off. That seems way too quick, as last winter I remember I could let it cycle for something like 30 seconds on cold mornings before it would click off. I feel like there is a temp sensor that controls how long it cycles for. Which one is it (there are like 3 on this car)? Also, what would be the best way to test it? Just to clarify, I am not talking about the glow plug light, but how long the plugs actually stay energized. Thanks for any help!

sixto · #2 12-09-2013, 02:22 PM

The original glow relay for an '87 300D has an internal ambient temp sensor and no coolant temp sensor. Sounds like it's time for a new glow relay. If so, consider an afterglow relay from a 90-95 SD. If you've disabled EGR and ARV because you only drive off-road, you can swap the EDS temp sensor for an afterglow temp sensor. Or swap the gauge sender for the later type with built-in afterglow sensor, but it's a chore to get to behind the IP. So you were wrong, there are 4 coolant temp sensors on your car before afterglow

Sixto
87 300D

zorecati · #3 12-09-2013, 02:45 PM

If I'm not mistaken, do the gp's not stay on for some time until you start the car? Just leave the ignition on for some additional time before starting.

VA-Merc · #4 12-09-2013, 04:16 PM

Thanks for the help sixto, I didn't realize there was an internal ambient temp sensor in the relay. If I have to spend the money I will, but I wanted to check...do you think this modification will still work with my relay acting the way it does: W124/OM603 Afterglow DIY ? If so, I may give that a shot. The relay is still kicking on properly, it just cuts out much earlier than it should during colder weather.

In reply to zorecati, this is with the ignition switch in the on position but without starting the engine. I believe the relay (if it was working properly) would allow a cold engine on a cold morning to energize the plugs for about 30 seconds or so. Mine only does it for 10 seconds or less (you can hear the relay click off).

If I have to replace the relay, I will just get an afterglow one and replace one of the temp senders as you mentioned.

sixto · #5 12-09-2013, 04:32 PM

There's a simple way to try the mod. Open the small connector at the relay and remove the pin at the end of the purple wire. Note its position then pull it out. Cap and install the connector then see if the glow relay runs the plugs for longer. If it glows longer, you might have a flaky key switch.

Sixto
87 300D

Diesel911 · #6 12-09-2013, 07:48 PM

Is there some Member in the Monroe, VA that is willing to loan a good working Relay to the Guy to see what happens.

While I think it is nice to take all the readings the OP did for Myself with out a Manual that has what the specs for where the readings are being taken or being able to compare readings to aother set of readings from a GP System that is working I don't find the OPs readings to be of much help.

Nor do I see an issue of creating a new ground for the Glow Plug Relay Wire. They sell those Plastic camp on Wire Taps at any Auto Parts Store. You simply need room enough on the Wire for the Plastic clamp.
When you squeeze a sliding metal Part it cuts through the insulation of the Original Wire and what in this case sould be the New Ground wire and connects them together. After that all that is needed is to add an Eye Connector to the opposite end and make a Hole for a Screw to Screw the Eye into a place on the Fender Well.

ah-kay · #7 12-09-2013, 10:14 PM

Quote:

Originally Posted by VA-Merc

Thanks for the help sixto, I didn't realize there was an internal ambient temp sensor in the relay. If I have to spend the money I will, but I wanted to check...do you think this modification will still work with my relay acting the way it does: W124/OM603 Afterglow DIY ? If so, I may give that a shot. The relay is still kicking on properly, it just cuts out much earlier than it should during colder weather.

In reply to zorecati, this is with the ignition switch in the on position but without starting the engine. I believe the relay (if it was working properly) would allow a cold engine on a cold morning to energize the plugs for about 30 seconds or so. Mine only does it for 10 seconds or less (you can hear the relay click off).

If I have to replace the relay, I will just get an afterglow one and replace one of the temp senders as you mentioned.

I think the glow light goes off does not mean the GP are off. If you leave the ignition sw in the on position then the GP light will go off in a few seconds to indicate the engine can be spinned by turning the key. The GP are still on if I am not mistaken. The GP will only go off if (1) engine starts, (2) Relay times out in about 30 sec with no key turned, (3) key back to 0 position.

You can simulate after glow by disconnecting the purple wire as suggested by Sixto. This will leave GP on, until timeout happens, after engine starts. You can see whether it helps. I suspect it will not. I did the After Glow mod in the SDLs and it helps the engine run much smoother during cold start but nothing else. After Glow will not help cold start IMHO.

VA-Merc · #8 12-09-2013, 11:41 PM

Thanks for the replies. I will try pulling the purple wire And see what happens in the morning. If no difference, then it was worth a shot. I found a few relays for a decent price online. I would type more but I am on my phone right now. Thanks again!

VA-Merc · #9 12-10-2013, 09:55 AM

So I tried pulling the purple wire out of the plug on the relay this morning, but same symptoms. About 33 degrees ambient temp out this morning, car had been sitting all night. Turn ignition key to on but didn't start, glow light on dash goes off after about 2 seconds, relay clicks off after about 8-10 seconds (cutting power to the plugs). I am assuming whatever internal circuitry the relay uses for timing is malfunctioning.

Is there anything else I should try before buying a new glow relay? All of the plugs pass the resistance check, the strip fuse was replaced, and the appropriate 12 volts is going out to each plug...just the timer cuts off way too early.

In response to a couple of member's replies...I am not concerned about the glow light as I don't pay attention to it in cold weather anyways (the light goes off after about 2 seconds). I am leaving the key in the on position without starting the car, and the timer cuts off power to the plugs after about 8-10 seconds on a cold start...which is way too early to have a decent start in this colder weather. I hope that helps to clarify!

Also, as Diesel911 mentioned...if there are any members in the greater Lynchburg VA area that would be willing to let me test with their relay, that would be a huge help!

I am taking a trip up to New Hampshire in a couple weeks, so I am hoping to sort this before then or it could get really interesting haha. Thanks!

ichris93 · #10 12-10-2013, 10:06 AM

A) Pre-glow time
B) Is safety shut off

VA-Merc · #11 12-10-2013, 11:04 AM

Thanks IChris...so in looking at the chart, I am guessing the times I am reporting corresponds to A on the graph in the 8 second or so range. I am a little confused by your interpretation of b as "Is safety shut off." Do you mind explaining a tiny bit more?

Last winter my pre-glow times corresponded more along the lines of the top (b) part of the graph.

ichris93 · #12 12-10-2013, 12:39 PM

Quote:

Originally Posted by VA-Merc

Thanks IChris...so in looking at the chart, I am guessing the times I am reporting corresponds to A on the graph in the 8 second or so range. I am a little confused by your interpretation of b as "Is safety shut off." Do you mind explaining a tiny bit more?

Last winter my pre-glow times corresponded more along the lines of the top (b) part of the graph.

Basically A is when light goes off. B is when relay goes off.

VA-Merc · #13 12-10-2013, 01:25 PM

Makes sense...I am a bit tired today so forgive me...that should have been obvious. In looking at the testing procedure in the FSM (http://www.w124performance.com/service/w124CD1/Program/Engine/602_603/15-4000.pdf), it does make mention in the table on the last page of testing a coolant temp sensor when the pre-glow light goes out too early.

Both my pre-glow light, and the glow relay turn off way too early. From what Sixto said, however, this doesn't apply to mine correct? Just want to make sure I am understanding correctly before I go out and buy another relay.

sixto · #14 12-10-2013, 02:36 PM

Yup. The last page is part of section B which is the with afterglow variety.

FWIW, a Hueco brand afterglow relay for a 140 SD is $100 from Pelican. That's what I've used since the original glow relay had an internal meltdown. Unlike OE afterglow relays, the Hueco has a strip fuse. In the grand scheme of things, I'd rather be able to replace a fuse than wonder why a self resetting breaker isn't

Sixto
87 300D

TnBob · #15 12-10-2013, 03:08 PM

If you feel comfortable with electronics, you may want to replace the capacitors in the GP circuit. Radio Shack, Mouser ect can provide what you need. Just make sure the replacement caps have the same or higher voltage rating.