Mercedes-Benz Forum banner

1 - 15 of 15 Posts

·
Registered
87 190d 2.5TD, 98 ML320, 09 CLS550
Joined
·
119 Posts
Discussion Starter · #1 ·
Unable to find anything certain on this, but let me first give some back story..

This morning, I decided to start my 190d (2.5 Turbo, factory). The car has sat a while since I have been doing the restore and I figured with the cold weather to let the thing run for a bit.

She started just fine.

Now before I go any further, let me preface the following with this: I have the gauge cluster removed. Each lamp that plugs into the cluster (including the GP light) is labeled (I added labels with a label printer myself couple years back to make re-installing cluster easier).

Now for the strange part... the GP light never goes off. At first, I sat and sat waiting to start the motor - waiting for the light to go off. Nothing - the light remained ON for over 1 minute.

Finally, I broke out the tester and did some investigating.

From what I can tell, the GP relay is working fine. When you turn the ignition over to run, the GP's are getting juice for 10-15 seconds and power is then removed. You crank, and the engine starts.

But this light staying on puzzles me.

Thinking something in the relay (some of the solid state control crap) may have been messed up and just holding the light on - I removed the relay to test the relay by itself.

But here is where things are really strange: even with the relay completely unplugged and removed from the vehicle, the light is STILL on!

Could this have something to do with the fact I have the cluster out? It has never affected it before.

Perhaps the single digit temp outside is the culprit?

So looking at how everything is wired, I first turned to MItchell OnDemand. This was about useless. It seems every wire in this car is accounted for except the GP system - MB really did not want anyone seeing how it was wired into the car. In fact, Mitchell shows schematics for both 4 and 5 wire control plugs for the 190.. on the same schematic!

My module has 5 small "control wires". What does each wire to? I hear some mention that older relays had 5 pins, and after early 80's, went to a 4 pin setup (after glow?). Mine is an '87 and has 5 pins. What gives? I can also say that watching power on the GP's: they come on for the pre-determined period and shut off - period. They do NOT stay on when cranking, they do NOT stay on once the engine runs for any length of time. They ONLY come on for initial pre-start time period.

And why would the wire from the relay not run directly to the dash indicator?

I would like to get this straitened out once and for all. There is so much mi-information floating around the net about these things it drives me crazy!

Any help much appreciated!

P.S.

Again, my vehicle is a stock 1987 190D 2.5 Turbo.
The relay part number is 006-545-22-32
The pins are as follows:

(T )
(31) (LA)
(50) (15)

This version does NOT have a built-in metal fuse link held down w/ screws. The fuse is external.



- Dean
 

·
Registered
81 500SEL, 84 300TDT, 86 + 87 190E 2.3, 91 + 92 300D 2.5T, 95 E320 Wagon, 09 C300 4MATIC
Joined
·
1,758 Posts
Hi Dean,

I'm taking a look through some of my resources. The Mercedes-Benz electrical troubleshooting manual doesn't have any useful diagram pertinent to your issue. I found an image of the GP system that may be helpful.

It appears that the glow-plug light runs through a harness to the fuse-box, then into the 15 pole harness that connects to the back of the instrument cluster. So maybe this will help you narrow down your search.

 

·
Registered
87 190d 2.5TD, 98 ML320, 09 CLS550
Joined
·
119 Posts
Discussion Starter · #3 ·
This helps a lot

Now I just have to map out the pins on my relay to that on the diagram.

Also, what is the "F1 Electrical Center" that is referenced?

My particular vehicle does not route the glow plug light through any harness on the gauge cluster: that light (as well as srs, abs and few others) are all hard wired into a jumble of wires that goes under the dash. You have to push each light into the correct spot on the back of the cluster before installment of the cluster itself.

Many thanks!
 

·
Registered
81 500SEL, 84 300TDT, 86 + 87 190E 2.3, 91 + 92 300D 2.5T, 95 E320 Wagon, 09 C300 4MATIC
Joined
·
1,758 Posts
Hi Dean,

My best understanding is that the Electrical Center is the fuse-box. There are a number of harnesses that plug in underneath the fuse-box that are accessible from the foot well.

On my gasser, the lights on the left side (looking front to back) are taken off the instrument cluster, and those on the right side do come from... some mess in the dash. Maybe there's a 15 pole connector that the lights plug in to.

Looking at the ETM, there's a 16 pin connector on the bottom of the fuse-box that is labeled "D". I'm guessing this is xD which is labeled in the diagram I posted above coming from the fuse-box. xS is a 14 pin connector that comes in to the underside of the fuse-box from outside of the car.

From what I'm getting off of that diagram, the glow plug light originates at pin 3 of a 4 pole harness off of the pre-glow relay, then it is pin 6 at 14 pole connector xS which enters the fuse-box, then it leaves the fuse-box as pin 3 of 16 pole connector xD, then it branches off as pin 10 of a 15 pole connector, to the light, then to ground at pin 1 of a 15 pole connector which ends up at ground W1,

I can't guarantee that I'm right, but this is my best interpretation. Here's a picture of other stuff that grounds off of W1. If you've pulled the relay and the light still comes on, maybe a ground is faulty and another circuit is feeding back up W1 and up the pre-glow indicator light.

 

·
Registered
87 190d 2.5TD, 98 ML320, 09 CLS550
Joined
·
119 Posts
Discussion Starter · #5 ·
Closer

Thanks guys so far for all the help.

So I think I may have traced things down.

To start, I think I had the wires mis-labeled. The SRS and GP lights may have been backwards. You know how the SRS light comes on shortly when you turn the ignition on then goes out (presumably once the electronics inside the SRS module build up the required charge)? Well, I have been mistaking that for the GP light ever since I had the car it *seems*.

I tore the damn dash apart to trace this down.

The light I thought was the GP light was a pink and black/red wire. I traced it down to the passenger side footwell where it runs into the SRS and Seatbelt voltage transformer and condensor modules. Tracking down those part numbers and realizing they should have noting to do with the circuit in question, I quickly referenced Nfsjunkie91's schematic (thanks again!).

First, I want to point out that the actual GP indicator grounds itself through the cluster frame.

Next, I can a continuity test from the (newly discovered) GP light (black wire) to the black wire pin on the relay harness... bingo!

Next, I tested the bulb by grounding one side and jumping the black wire pin on the relay harness to 12v (relay unplugged, of coarse).. bingo!

This means the relay has NEVER been lighting the bulb ever since I owned this car!

Time to test the relay...

Before I begin, for anyone who comes across this thread, let me give the complete pinout (as of at least MY 1887)...

-------------------------------------------------
MB Part# 006 545 22 32

Control harness pinout:

(T )
(31) (LA)
(50) (15)

What goes where:
T == White wire, Temperature sensor, ties in to the engine temp wire in the cluster
31 == Brown wire, ground
50 == Purple wire, Starter wire - is energized when the starter is cranking
LA == Black wire, Lamp indicator to the dash (hence the LA!)
15 == Black w/ red stripe wire, start/run wire - energized as long as your ignition is in the "run" position.

Testing:

Apply 12V to large nut (where large red wire hooks to)
Apply ground to pin 31
Apply 12v to pin 15
-->> Relay should energize
-->> Terminal LA should provide +12v for your indicator lamp
Eventually, LA should become de-energized as the timeout is up and it is time to crank...

...this is where I am not sure of things...

I **think** the relay should stay energized until you crank the engine (apply 12v to pin 50) and release. At least that is how it worked for one person I watched bench-test one that LOOKED like mine on YouTube. Once he released the starter wire, THEN the relay kicks off. Mine, however kicks off after the timeout - period.

I think that, based on reading from coolant temp sensor, the relay should additionally stay on when the engine is cold for a pre-determined time period - not sure here.

-------------------------------------------------

So perhaps this is why it is so much more difficult to start in colder weather than others I have seen? My GP's were only coming on for a short time and kicking off... staying off while I cranked?

I suppose it is off to the scrap yard to find a couple.

Will post an update once I test a couple more relays.

- Dean
 

·
Registered
1987 190D Turbo
Joined
·
1,281 Posts
You may want to start by checking the resistance of your plugs. If one of them is open, the light doesn't come on. There's an odd sequence to this...I think if more than one is bad, the light comes back on after a few minutes of driving, and doesn't go out. This is determined by the circuitry in the "relay". Whenever I've had erratic behavior of the preglow light, I change the plugs and all is well.

The coolant temp sensor affects the amount of glow time you get. On warm days, my light goes out in a few seconds. Today, it was on for a good ten or 15 seconds.
 

·
Registered
87 190d 2.5TD, 98 ML320, 09 CLS550
Joined
·
119 Posts
Discussion Starter · #7 ·
Already did that

Already did that.

I replaced all 5 GP's just 6 months ago w/ OEM Bosch.

Nonetheless, I tested all 5 when I removed the module. I tested for continuity as well as applied 12vdc to each FROM THE relay plug, measuring the current draw on each. Each is drawing around 20 amps (as expected).

I did find an older GP relay (a 4-pin version) laying around from an older (early-80's) 300-class. The 4 pins are identical - only missing the 5th (temp) pin. Looks like I could plug the older GP relay into my vehicle in fact!

Anyways, I put it on the bench and hooked it up the same way I had the previous one hooked up to compare behavior.

Here is what happens:
-> I apply 12v to the large input post
-> I apply ground to pin 31
-> I hook a test light between ground and pin LA
-> I apply 12v to pin 15
....relay clicks ON
....LA pin turns HOT (to light the indicator)
....few seconds later, pin LA goes dead, light goes off (ready to start)
-> Apply voltage to pin 50 (simulate start), and release
....relay goes off
....LA turns HOT (to light the indicator)

This is to be expected as no real GP's are hooked up and the light comes on to signal this (as mentioned, light stays on when driving to indicate GP problem).

What does not make any sense is the fact that - with my original relay - the light should at least come on when you initially apply power to pin 31 (pre-heat) and then go out to signal "ready to crank". It is also my understanding that the *proper* operation is as the older version relay I have functions: light goes on for pre-heat regardless, goes out, crank, once running, light goes back on to signal GP problem.

I cannot imagine the engineers deciding to NOT have the light come on if one or more GP's have failed until pre-heat is complete... how else would you know - at the very least - when to start cranking? The way the older relay functions makes sense and is in-line with other reports of how the system works.

I tried replacing the 3 electrolytic capacitors w/ new ones on the relay for good measure.. no change in how it functions.

I will hook the older module up in her tomorrow sometime if I get a free moment and will report back.

- Dean
 

·
Registered
Blue/Blue 1985 190D 2.2 Auto, Red/Palomino 1984 190D 2.2 5MT
Joined
·
561 Posts
I believe the glow indicator light will not come on at all if (possibly) 1 and (definitely) 2 glow plugs are burned out.

That was the way it was on my sister's 1985 190D 2.2 when we first got the car. The key was turned on, no GP light at all, and after a 10 count the engine would start up with a little rough idle. I ohmed out all 4 plugs and found #1 open. I replaced just #1 and the indicator has behaved normally ever since (a year and a half). Normally of course, means when you turn the key on, he GP indicator comes on and goes off after the suggested glow time is reached.

HOWEVER she once again has one other burned out or weak glow plug, because when the car starts cold it "isn't right" and blows a small amount of white smoke. The indicator functions normally, even though it is obvious that one glow plug is weak or open.

The indicator, in my opinion, is good for two things only. It is good for showing the suggested glow time given the engine temp, and it's good for telling you that for sure something is WRONG with the glowplugs (1 or 2 completely open).

If you can't get the automatic glow relay to function correctly, you can always construct a manual glow system using a Ford starter solenoid and a push button under the dash or next to the key. Replacement GP relays are pretty expensive.
 

·
Registered
87 190d 2.5TD, 98 ML320, 09 CLS550
Joined
·
119 Posts
Discussion Starter · #9 ·
Varied by year?

Perhaps the functionality of these things varied a bit over the years?

I am seriously considering overriding the *original* relay so that a push button under the dash will manually control the original MB relay.

Manual control just like the "starter relay mod", but will all original MB parts and nothing to really look out-of-place under the hood.

I am wrapping up a complete restore on this car and trying to keep it as original as possible given the rareness of it.

- Dean
 

·
Registered
1987 190D Turbo
Joined
·
1,281 Posts
No, the functionality was always the same, but it's another rube goldberg design.

The no 1 glow plug is fed through a choke coil inside the control unit. The nos 2-5 plugs are fed through another choke coil, which is counterwound with fewer windings. So you have four plugs on one circuit and one plug on another. Between the chokes is a magnetic reed switch, which reacts to the fields created by the chokes. In this way, the current draw of the four combined plugs is compared to the no 1 plug, which is the reference. If the magnetic fields balance, the reed switch remains opened, and the control unit will light the light during the preglow cycle. If not, the magnetic switch closes, signaling the control unit to turn off the light. That's why no light usually means bad plugs. The glow plugs are fed a small current while the motor is running, which keeps the detection mechanism going. If the fields are imbalanced, then the light will eventually come on while you drive. The function can vary quite a bit depending on ambient temperature and the condition of the plugs.

A few things could cause your problem, some of which you've already eliminated: bad wiring, bad bulb, bad ground. Things to check: is the relay receiving voltage? Is there a short on the output side of the wiring? If all of these are eliminated, about the only thing left is a bad control unit.

If you're serious about restoring the car in any sense, then a properly functioning preglow system is a must. I wouldn't suggest mucking it up.
 

·
Registered
87 190d 2.5TD, 98 ML320, 09 CLS550
Joined
·
119 Posts
Discussion Starter · #11 ·
If you're serious about restoring the car in any sense, then a properly functioning preglow system is a must. I wouldn't suggest mucking it up.
Agreed 100%. Although insanely tempting from a preference and functionality standpoint (I have re-wired my '85 K20 6.2 diesel the same way) - I am going to figure out what the issue is.

Will report back in a bit.
 

·
Registered
87 190d 2.5TD, 98 ML320, 09 CLS550
Joined
·
119 Posts
Discussion Starter · #12 ·
Older style relay installed

So I installed the older style relay today - an older 4-pin style control relay that has the temp sensor built-in.

Works perfectly.

Light comes on, GP's are heating, light goes out (GP's still have power), crank, engine starts, release starter, GP's are de-energized.

Absolutely as it should work.

let the engine idle for a few minutes to ensure the light was not going to come back on - all is good. Light stays off.

Just to triple-check everything, I measured each GP from the harness: .6-.8 ohms and drawing around 20 amps. Again, perfect.

With this older relay, only thing I have lost is the external temp sensor... I think the newer relays also featured an after glow timer too? Are they not supposed to keep the GP's heated for a few seconds AFTER the engine starts depending on the temp?

Other than that, the older style relay's DO fit exactly in the newer style harnesses. Wire bolted right up, 5-pin GP harness plugs up exact and the 6-pin harness (with 5 wires) plugs down perfectly over the 4 available pins on the older style relay (pins are the same - I checked). So just in case anyone ever wonders about this.

I will hunt down a good 5-pin style relay sometime soon. Meanwhile, I will tag this as another issue resolved as I now know I have all the dash lights working correctly.

- Dean
 

·
Registered
1987 190D Turbo
Joined
·
1,281 Posts
I checked the FSM. The external temp sensor (connects to the 5th pin) is what makes the afterglow work. It holds the plugs on until the engine warms up. Sounds like a good thing.
 

·
Registered
Blue/Blue 1985 190D 2.2 Auto, Red/Palomino 1984 190D 2.2 5MT
Joined
·
561 Posts
Research the "purple wire mod" and read about it.

By disconnecting the starter signal wire and feeding it through a temp sensing switch, the glowplugs will run for the full time-out time (1 minute) and then the relay will kick off. Once the engine reaches the temp that the switch closes, the starter signal will be allowed to pass, and the glowplugs will turn off as soon as the key is released from the start position.

It is "the poor man's afterglow" for older engines that don't have an afterglow relay.

You can remove the signal wire from the plug and leave it open, causing a full time-out glow EVERY time the relay is activated.

You can run the signal wire into the dash and put a switch in line so that you can disconnect the wire whenever you want. Cold start, flip it off, hot start at op temp, flip it on so the plugs shut off right away.

The best way is to hook up to a temp switch so the on/off is automatically controlled for you. You can use an empty temp sender socket if you have one, or you can replace one of the senders with a two in one sender from a later model.

Just a thought. :cool:

Sent from AutoGuide.com Free App
 
1 - 15 of 15 Posts
Top