Afterglow and the Violet Wire
 

I posted this on the mbz.org diesel list earlier today:

As many of you are probably aware, if you snip the violet wire at the GP relay, you can get your GP's to glow for an extended period after the engine is running. This should theoretically reduce smoke, emissions, and coking issues. The problem is that snipping the wire also forces the GP's to run 'afterglow' even when the engine is warm, which will diminish the life expectancy of the plugs. Many folks have wired in a manual switch to turn off this feature, but I wanted a more 'hands-free' operation.

I installed a thermally switched relay into the GP relay's violet wire circuit. I used an NC (normally closed) relay from a Volvo 700 series fusebox. These are a 5 terminal relay, similar in look to the familiar 4 terminal NO (normally open) versions used in Euro headlite conversions and countless other little projects. These NC relays have an additional 87a terminal to which one side of the violet wire is connected, opposite the 30 common for the other side. http://www.the12volt.com/relays/relays.asp Be careful of other similar 5 terminal relays with an 87b terminal--these are just NO relays with two bridged terminals--these won't work.

I piggy-backed onto the 50 C thermal switch above the thermostat housing on my '87 300 td OM 603, which is apparently designated to assist and smooth cold shifting in the transmission.

When the relay is energized, the violet wire is snipped--afterglow enabled. In this phase, the 50 C thermo-switch has continuity with ground.

When the relay is not energized, the violet wire is bridged--afterglow is disabled. In this phase the thermo-switch has no continuity with ground.

I'll let you know how well this works in real world situations.

That's ingenious! I will investigate this further and will wire up a switch to mine. That is if my relay HAS a purple wire.

I believe all MB GP relays for the OM 616/617 and OM 601/602/603 series engines have a purple wire. All of the later OM 606 engines, and possibly some '90's era OM 603's had an afterglow relay installed at the factory. Try the switch first, then if you like the results, go for the relay option.

Good luck.

I'll just stick with the switch. That way I can keep her glowin when I want. I have no problem with a switch.

This is a great way to add "afterglow" cheaply, although plug life will be less than normal (duh). At next plug replacement time you could get the special afterglow-rated plugs which would help. A full factory conversion (for the 603) is expensive- you need the late relay, plugs, temp switch for the cylinder head, and some custom wiring... $200+ last time I checked. The relay+50C switch trick costs about ten bucks, tops, for a new relay. I've been meaning to do this on my car and haven't gotten around to it yet. Hmmm... maybe this weekend....

:D

Bump! I finally did the install last month, after discovering two dead plugs (only 20kmi old - don't buy Monark brand, stick with Bosch or Beru.) Anyway the mod works GREAT. It's 100x better than simply yanking the purple wire, as it only afterglows when cold. Wish I had done this a long time ago...

:) :)

Cool, need to look at my car and see about it. Would help cold weather starts a lot.

I suggest more folks give this mod a try, as it really does smooth out those cool early morning startups.

Thanks - my 603 engine is particularly cold natured. Starts up instantly and runs smoothly, then within about three seconds when the glow plugs cool down it smokes and rough idles. Less of an effect when I am patient enough to run an extended glow cycle. :) But what it really needs is the afterglow system that MB went with in the 1990s.

I want more direct control so I'll probably go with a toggle switch and indicator light. This is a low current-carrying wire, right?

Ken300D

Correct. You can make it look factory by using a rocker switch in the center console or above the ACC unit, if you can give up one of the stock switches... the fader is often bypassed when installing aftermarket stereos, that's the first candidate, second would probably be the antenna level switch (can be hardwired for 'full up' whenever the radio is on). Or you can get new (or used) wood with extra holes, but that's pricey (and hard to find used). If you add an aftermarket switch setup, try mounting them next to the headlight switch - they'll blend in pretty well over there.

:)

Nice idea. Bosch has incorporated this feature in the new glow plug relays. I think this is the kit that Phil is selling this month for 10% off. About $100 with 4 or 5 new glowplugs.

Yes, but if you have a 116 you are out of luck........the relay is different on those........ :mad: :mad: :mad:

That's for the OM617 engines only. There is no retrofit kit for any OM603's. You have to either do this mod, or build your own kit using factory afterglow parts from 1990-95 model OM603's. That's the preferable method but the cost is ~$250 for the relay, coolant temp sensor, and six afterglow-rated plugs. The 'poor mans' 603 mod with the 50C switch and relay gives almost the same effect for under ten bucks. Hard to beat that...!

:D :D

Potomac had a bunch of used OM603.97 GP relays on ebay last week. Was tempted to go for it as they were going cheap...

another variation of this idea.using a 555 timer ic and solid state relay to give you a fixed duration after glow.this could be packaged in a 35mm film canister.advantage here would be longer life on your glow plugs.details to be worked out

tried disconnecting the violet wire from the plug on the gp relay this morning.it was a cold start(0 deg c).definately smoothed out the start and reduced the smoke.i could tell when the relay timed out by a brief period of roughness lasting maybe 2 seconds.so far so good ill leave it like this for awhile see what happens

Usually the signal that the relay has timed out is the headlights (or other lights) suddenly get brighter. I wouldn't expect any roughness unless you have a weak plug or two, or it's REALLY cold out... ;) Glad to hear it helped, though!

:cool:

Can someone clarify the snipping of the violet wire? if I cut it, then the GPs are just always on? Wiring a switch into the wire should be real easy but I am just curious about whether they are permanently on otherwise. Thanks, Andy

And while we're at it..
We are talking about the violet wire that goes from the fuse box to the glow plug relay located (in my '81 SD) above the left front wheel. Is this all correct? I'm headed to the wrecking yard today to get a switch for where my fader wheel is now located, and make this modification.
What exactly does disconnecting this wire do? Remove the timer from the glow plugs entirely? How then does the gp relay ever shut off? I just want to be very clear on what is happening. Simply saying that it causes the relay to power the plugs for an extended amount of time is a little vague for me. Why does it? Thanks!

The relay has a timer built in that runs it for a specific length of time. That time is generally longer than the time it keeps the preglow lamp on. If I remember correctly it cuts off at 1 minute. The violet wire tells the relay that you are starting the engine, so the relay cuts power to the glow plugs. Interrupting the signal on the violet wire by whatever means just makes the relay run for its full time before turning off. No, it doesn't leave the plugs on all the time.

Rick is correct. I thought this was explained earlier in the thread but I guess not - ooops. Note that we are specifically discussing the OM60x engines from 1984-1989, for which there are no aftermarket afterglow retrofit kits. 1990-up has factory afterglow. And you can get a nifty Bosch retrofit kit for the older the OM61x engines complete with correct plugs, afterglow relay, etc.

The OM60x engines (well, the 603 anyway) has a temp switch which makes this mod even better. If you simply disconnect (not cut!) the violet wire, you'll get a full 60 second burn on every hot start too, drastically reducing plug life. A manual switch might work better if you don't want to mess with adding a thermal coolant switch (assuming your engine doesn't have a handy switch to borrow, like the 603 conveniently does. ;) )

To reiterate, the relays usually turn off at 60 seconds if they don't receive an "engine started" signal. Therefore with this mod, if you glow for 12 seconds, then start the car, the plugs will remain on for another 48 seconds since the relays doesn't get the message that the engine is running.

Too bad I missed out on the eBay relay deal from PGA, I would have picked up a couple if they were cheap enough. :o

Great explanation. I checked the schematic out, and it was very clear. Thanks for another great mod guys...

OK, I missed the 603 refference earlier too, there is no afterglow kit availible for my 116 that I have heard of, would it apply to my car too or not?

116 afterglow
 

Good question. Do you have the old "loop style" series plugs, or the newer "pencil style" parallel plugs? I would have sworn there was a conversion kit, maybe not, if the 116 has a weird glow relay. Regardless, I believe the mod will still work, since they should all have a wire that provides a 'start signal' to the relay. Interrupt this signal and you should get afterglow. Then it just depends if you want it all the time, or want to control the afterglow with a manual switch, or an automatic setup like on the 603's...

:thinking2

I believe the '79 300SD uses pencil style glow plugs ( I think anyway)....they are NOT series wired in any case. Part numbers for the 123 , 126 and 116 glow plug relays are not the same, but being as this is the only one I ever had, or even looked at under the hood I couldn't tell you the differences, and why they would be different.

just started having serious cold start problems but to be fair I have other issues right now that may be the cause. I plan on pulling them this weekend to check them.

Definitely check the plugs if you're having starting problems. If they're all good, the next biggest factor to poor cold starting is valve adjustment. I assume you're waiting a good 10-15 seconds after the glow light turns off before you crank the engine, right?

:wacko:

Oh yes....several times....valves were just done about a thousand miles ago.

Hard start could be related to this.....

http://www.peachparts.com/shopforum/diesel-discussion/105386-loss-power-briefly.html

Problem started just as temps dropped. Related? maybe but not certain.

2nd day of testing modification.what ive noticed so far.morning starts have been cold starts both days were below zero the night before.definately much smoother startup alot less smoke.but engine rpm at idle was very low almost like electronic idle was not in effect.this is different than situ before mod but i dont know if its related.does anyone know if the start circuit is somehow tied in to the electronic idle regulation

Last year I was trying to start my 300D (with old loop style plugs) in the cold. Of course it had a weak battery, but the glow circuit really pulled the current. I would think one reason the plugs shut off while cranking is to get all the battery power directed into the starter motor.

One consequence of severing this start signal could be less cranking ability, especially on the loop style plugs, as they are extremely inefficient, putting half their heat outside the engine.

Just a thought I had reading this thread. I'm now driving a 240D with the pencil type plugs and a standard plug relay. Yesterday after work, the temperature had dropped to the high 20s (F), and it fired right up after leaving the plugs on right up to the point where the relay times out. A new battery helps out a lot though.

My battery is less than 2 months old. forget exactly when I got it. But I had to scream at 5 different Exide dealers before any would replace a failed 10 month old battery.

No, there's no connection to the ELR (idle control). However, the alternator is now dealing with a big load at idle that it can't keep up with - the stock unit can only cough out about 40A at idle, and the glow plugs are probably pulling close to that when warm (cold inrush current is higher then it drops off). That might be part of the issue - I'm not sure. I have a 150A alternator upgrade on my car, so the electrical load isn't a problem (the big unit can pump out 100A at idle!).

:beerchug:

the low idle may also related to a fuel injection issue.for some time now ive suspected that im losing prime due to a leak or siphon.tough to track down though

Just a little something to keep in mind. My 606 only gets about 40,000 miles out of a set of glow plugs. So the afterglow definitely does shorten their life. But I guess if you live in a cold climate the tradeoff is worth it.

What is the sensor that comes from the block to the GP relay on a OM617 turbo?
I've seen some huge sensor on there and a wire that runs over to the GP and could that be used to run the purple wire relay?
Does it even have anything to do with that?
Just curious...I have no electrical diagram.
THanks!

I believe that you are looking at the coolant temp sensor for the dash gauge. The wire runs over near the GP relay but doesn't actually connect to it. AFAIK, that's the only switch on most 617 turbos, although I'm not *that* familiar with the 617...

The good news is, if you really want to add a temp switch, it should be possible using factory parts. Wiring it up is the easy part.

:rolleyes4

Isn't that sensor up near the water inlet and the ERG vacuum temp deal?
This this is huge and I may go take a pciture of it here shortly...if I can do this violet wire setup using that sensor (somehow) I will for sure do so...
I am savvy enough to do the 555 timer deal but I am rather lazy and a fan of the descrete components on a old timer like this ;)

The 555 timer's fundamental flaw is that it will still gived a fixed time when the engine is warm. You need an engine coolant temp switch for the most efficient setup (no afterglow when warm will extend plug life significantly.) The manually-operated switch inside the car theory works great but requires, well, manual intervention!

:vbac47679

Pictures
 

OKay so here it is...
I took some pictures...yay heh.
(my engine compartment is still dirty from the oil line explosion....so excuse the mess please :)
This is the Temp Sensor for the dash gauge (tested by unplugging, reading, etc)
http://brandon.importtransmissionexc...p/Picture1.jpg
http://brandon.importtransmissionexc...p/Picture2.jpg
This is a Temp Sensor/Switch for?
http://brandon.importtransmissionexc...p/Picture4.jpg
http://brandon.importtransmissionexc...p/Picture5.jpg

None of these go to the glow plug relay it seems, must be internal like was suggested...this sort of rules out the ease of just doing some wiring. Damn.

New or old GP relay? Old from how it acts....
http://brandon.importtransmissionexc...p/Picture3.jpg
(I do have the cover for this...it is just off for the picture/ID'ing

I just snipped my wire last night.

WOW, what a difference the next mourning. Usually it's fine for 5 seconds after start but now it's much better.

I will be sure to do this mod to Honeycomb when the time comes.

I was thinking you could incorperate a variable temp sensor (possibly use the prexisiting water one or the dash one?) into the mix and thus have a variable in the 555 Timing cycle dependent on the temperature of the auto. Yes/no?

For those who were wondering, the other temperature switch by the thermostat housing is the switch for the auxilliary fan.

Perhaps, but only on certain models. For the late W123's, the electric aux fan is *only* triggered by a referigerant temperature switch, not by coolant at all. I need to go look at my W123 and see if it has that switch on the t-stat housing or not, and if so, what it does!

:o

How sure are you about that?
I did a ohm test and as soon as the car gets to a mid range temp (not even "that" hot the sensor closes (pulls to ground)
My fan doesn't come on in this situation so thats what makes me wonder. Figure it would be worth being sure about it before I go attacking my fan for inoperation hehe
Anyone?

BTW this is dealing with a w126 (the pictures are too)

My 1986 300SDL (OM 603) recently developed a glow plug that isn't glowing. Previously, #4 checked open circuit, then fixed itself. Now the glow indicator doesn't come on and it's a bit lumpy after starting. I mean, even lumpier than the ususal 603's cold-blooded lumpy idle when first started.

I let it glow until 5-10 seconds after the annoying seat belt buzzer stops, which is about 5 seconds after the glow indicator used to go off. I turn to Position III (Start) and away it goes. The cylinders with functioning glow plugs fire right off, the one(s) with issues don't. I leave the starter motor engaged for about 10-20 seconds until I fel the non-glow cylinder begin to fire.

The Owner's Manual says leave the starter engaged until the engine is running smoothly. The cylinders that do fire help the starter spin the engine around those that don't.

I also understand that the glow plugs are on as long as the key is in Pos III. So, without cutting a single wire or modifying a single circuit, you can just keep the key turned and afterglow as long as you need.

Best Regards,
Jim

P.S. I plan to check/replace the glow plug sometime, just don't have time or garage space right now, and 603 plugs are much more PITA than 617. I don't look forward to this, and might have Dealer do it if I can't find time.

Hi Jim,

1) You probably have one or more GP's out. My GP light was working fine while I had at least one dead plug - when the light finally did quit lighting during normal glow, I tested and found TWO bad plugs. Replacing them helped starting immensely - no more shaking for the first 5-10 seconds.

2) Yes, the GP's stay lit while the starter is cranking - that's normal. But they go out when you stop cranking. The afterglow mod is much preferred over keeping the starter engaged for 5-10 seconds, IMO...! :eek:

3) You can kill that irritating seat belt buzzer by disconencting the 2-pole electrical connector under the driver's seat. On the W124, it's near the front, in a metal clip - remove it from the clip and unplug the two halves. No more buzzer!

4) Replacing the GP's in a 603 means one of two things. First, if your metal injection lines have never had the plastic clips & foam buffers replaced, and/or you have oil seepage at the #2 head port, remove the intake manifold. This gives easy access to the GP's and allows simple installation of the clips/buffers (which MUST ALL be in place). It also allows easy access to the dash temp sender, which is good to replace after 15+ years (they're ~$10 and tend to read low as they age.) Total job time about 3-5 hours depending on your skill level. If the clips/buffers are fine and you're not leaking at the gaskets, the intake can stay in place. You can access all 6 plugs using various 1/4" drive extensions, wobble/universal joints, a 12mm deep socket, and (most important) a telescopic magnetic pickup. Figure about 2-3 hours with this method, if you have the tools. DO NOT overtighten the plugs. Just past snug is plenty. Don't use a torque wrench.

:cool: :cool:

OK, I stand corrected. On my 1981SD the temperature switch located on the thermostat housing near the EGR is the lockout for the heater blower. In EC mode it prevents the blower from starting if coolant temperature is below 33C or in normal mode below 37C. (I guess they don't want to blow cold air in the cabin, or delay the engine reaching operating temperature, who knows) I apologize for any misleading information. The aux fan is operated by a relay, which is in turn operated by the thermal switch on the receiver/drier reaching 52C (126F) Anyone need the schematic? :cool:

ok here is the million dollar question
(and yes please the schematic would be nice for records and my possible mod)

COULD one use the temp lockout sensor to also run our violet wire setup? This sensor grounds once it gets hot (I believe from tests) and thus you hook that to the neg side of a relay, the postive to power, and switch the violet wire with the NO contacts (power=contacts closed).

This way, if the engine was cold, the relay would get no juice, the violet wire in turn snipped, and the GP relay on a long time.
When the engine is warm (by previous post statistics) it would turn on the relay (probably have to run it to key on/start = +12v so that it would not be draining the battery when the car was warm and not running)
and thus the relay contacts would close and make the purple wire complete.

Sound good?
I can forge up a schematic if someone is interested...
:)

It sounds like it operates the opposite of the 50C switch on the 603 engine - it grounds when hot, where the 603 switch is grounded when cold. You are correct, just have that trigger a relay and use the NO (normally open) contacts. Should work great!

:idea:

The Schematic
 

http://brandon.importtransmissionexc.../Schematic.JPG

Only important factor here is that they key power must be on also when the starter is running otherwise the starter signal will never get to the relay (violet wire) when the engine is hot and the GP need not run.

Nice diagram, that is exactly what I'm going to do tomorrow. My only addition will be another line off the relay to an additional light in the instrument warning panel, to indicate when the afterglow is in operation....