1983 380SEL Abrupt Stalling - Auto-Trend Repairs and Service Information Forums

oneklassy1 · Senior Guest

1983 380SEL Abrupt Stalling

Administrator · $y$Op

Welcome to the forum, its good to see other folks whom share the W126 love.

At first when reading your post I thought maybe something as simple as an adjustment however after reading that the vehicle stalled while driving at speeds of 45 MPH I have ruled that out.

I know you dont want to hear this, however without being able to make test it will be very hard to nail this problem. I do have some suggestions that should help you to find out what is going on.

One of two things is happening here, (1) You are loosing spark, or (2) You are loosing fuel pressure. In an effort to narrow down the list of possibilites that I am about to give you, I suggest testing for spark and fuel when this condition happens again. From the sounds of it, the problem is getting worse, and it would make it easier to test if it were not intermitant.

Here are a few things that MAY be at fault from what you have indicated

(1) Fuel Pump Relay (FPR) - This relay is known to cause a problem like you discribe. If the FPR relay is at fault you will not have power to the fuel pumps located in the rear underside of the car. If bad you will have no fuel pressure.

(2) Ignition Control Moduel (ICM) - This module on your vehicle is a aluminum box about 3 inches by 2 inches. This unit controls the spark or ignition.

(3) Over Voltage Protection Relay (OVPR) - This item controls power to most all of the fuel and ignition circuts and usually has a red top with a fuse that will be visable from the top.

(4) Clogged fuel filter - When is the last time it was done?

These 4 suggestions are just that.... Suggestions. You will need to test the vehicle while it is acting up to find out if it lacks fuel or spark. Once you do that you can narrow this list down. You can then check back with us and we can advise you from there as going thru it all now would be rather confusing.

Do you know how to check for spark and fuel? This is the first step in trying to narrow down where the fault lies.

oneklassy1 · Senior Guest

Thanks so much for the reply and your suggestions. The W126 is a wonderful car and worth the time and effort.

You are absolutely right that you have to be able to test it to be able to narrow the suspects. Since the car will not start ( I haven't tried today) I will look at the items you suggested.

During the service this week, the fuel, air filters, lube, and all of the fluids were replaced. Sadly, while MB had the car all that day, it never exhibited any problems.

I will first check to make sure that it is getting fuel and spark. Then, I will try to find the FPR. Is this item also known as the WAG? I will look at the contacts, clean them and see if there is any corrosion.

I will start today and will keep you posted on my progress.

Administrator · $y$Op

Yes it does appear that your vehicle is an earlier model (85 and lower) so I am not as familar with the terms. I will have to dust off the books to get you the proper names and locations for these electronics I speak of. Regardless of the terms/names of the electronics there is still the question of what we are dealing with, (a) lack of spark/ignition or (b) lack of fuel.

It would be easiest to check for spark providing that you can make the vehicle act up again. Do you know how to check for spark? If not I can give you some pointers.

Good luck and try not to get poked by the spark, it really does get your attention in a hurry when that happens. biggrin

You may want to practice checking for spark while the vehicle runs, that way when it quits, you know what it was looking like, and everything is for the most part in place to test.

-- Edited by Administrator at 15:14, 2007-12-23

oneklassy1 · Senior Guest

I do have an spark plug attachment for my multimeter that I have used on domestics and motorcyles. If you have another method to check spark for MBs, I will gladly try it. I have the car ready to start testing.

I have checked for loose connections, checked all the fuses and now ready to go further. Oh yes! Getting zapped will wake you up instantly!

Will update in a few minutes. smile

Administrator · $y$Op

Might you have a photo of this attachment you are using? Some are better than others, the best are the magnetic scoping kind that clamp over the wire so you dont have to pull the wire from the plug. There are other kinds also, like ones that plug into the spark plug boot and have a light bulb, and my personal fav. is the one that plugs into the boot and arc's the spark accross a gap so you can see how orange or blue it may be.

With the exception of a scope style which it sounds like you have, all of the other kind must be grounded in order for them to work.

oneklassy1 · Senior Guest

Here's my multimeter. It is the gun style clamp-over. The blue attachment is the temp sensor for the multimeter and on the right is a Raytech laser automotive temperature reader. Works great to check for cylinders and plugs not firing properly.

Administrator · $y$Op

That's some serious hardware you got there "Just Johnny"... (Quote from- Johnny Neumotic movie)

If you do not work in the Automotive Industry I am most impressed with your arsenal and think you have a very good chance for success on this mission.

Let me know what you find on the spark. One thing is for sure, most of the times here at the shop cars will never act up. If this problem arises I have my customers sign a waiver stating I can drive their vehicle for extended periods of time. Then I put it in use as my daily driver. Works every time and it sure is nice to drive a different car every once in awhile.

oneklassy1 · Senior Guest

Thanks! Yes, I always believed in getting quality tools and doing as much work myself as possible. So much gratification when you do it yourself. biggrin

About the 380, it didn't start but it is getting a very healthy spark to all eight. confused

I am getting it ready to start testing the relays, fuel supply, and anything else to check. I don't have a repair book on the 380 so I'm a bit blind. I will take more pictures of the engine and systems to post and maybe you can point out what to check.

In the military, for a time I was a depot-level mechanic on tactical vehicles. I have owned several notable domestic cars and performed a majority of work and mods myself. I work in the federal government in administration.

You are right that cars usually don't act up when in you have them brought in on a "mystery symptom" like what I have. By not smelling any fuel, I wonder if it is getting fuel. Does the 380 have two pumps? Are they by the fuel tank?

More pics coming. smile

Administrator · $y$Op

Well it seems like you are doing alright, now if we can figure out what's going on with your 380 we will be getting somewhere.

Since your test show we have spark to all eight plugs then its time to consider fuel supply problems.

The first test you will need to make will be in the back passengers side undercarriage. There you will find the fuel pumps. I have attached a photo of what they should look like. Some older models only had one pump however your model sounds like it will have two. You may have to remove the plastic shields that protect the pump if they have never been serviced. Sometime we get lucky and they are missing, but its best to have them on as it keeps the pump connections nice and clean.

You will need to test for power at the terminals on both the fuel pumps. Do this with a test light or your digital millimeter. You will see two wires going to each pump. You should be seeing 12V at both the pumps, however you will need someone to turn the key on while you are testing. Until the system recognizes that the vehicle is running the fuel pump relay will only kick the pumps on for some 2-4 seconds. Be sure to have your leads connected and then have your helper turn on the key while you monitor the readings. It is not nessisary to have them crank the engine however remember that you will only see power for 2-4 seconds after the key is turned to the on possition. You may have to cycle the ignition several times to get a good reading on both pumps.

Good luck and I let me know your findings. Really you should be able to hear the pumps prime up when the key is turned on, however testing for power is nessisary in eleminating the pumps from the list of possibilites. No power means we will be looking at the Fuel Pump Relay next. Should there be 12 volts for 2-4 seconds after the key is turned on, we will have have many other test to run.

Please let me know your findings and from there we may move to artificially injecting fuel into the intake track.

-- Edited by Administrator at 13:00, 2007-12-24

oneklassy1 · Senior Guest

I attached the pics of the pumps and the engine compartment for reference points. I am doing the test with the multimeter as when I turned the key, I could hear some actuation but I will check to see if there's 12V. Coming up is the results. In the meantime, Merry Christmas!!

On Christmas, I will be working on the 380 and I truly feel that we will find this.

I am documenting the steps with pics to help others. Stay tuned biggrin

Administrator · $y$Op

You did a super job with your photos! I am very impressed!

Looks like you have the single fuel pump, I am supprised but I guess its just one less to test. Usually when you hear a hum it means that its working however it would be good to establish we have 12 volts at the pump just to be safe. Also inspect the connections as sometimes they are real bad. It looks like the little rubber boots on yours are in-tact so yours should look pretty good. Be carefull when you lift them up to check for voltage. Sometimes they like to crack and thats no good.

Just remember if we got spark, something must be out in the fuel department.
I re-read thru and I am under the understanding the problem is no-longer intermitant?

Merry Christmas to you!

oneklassy1 · Senior Guest

Thanks so much!
I was able to access the leads by softening the boot with a light grease, then piercing the boot with the probes. This minimizes the chance of cracking or tearing the boot. When finished, I always use a fingertip of silicon or RTV to seal the minute hole.

Here's the results of the tests at the pump. My readings were 12-14 volts when the ignition was turned to ON just as you said.

The first picture shows the reading just before the ignition is turned. The second shows a reading of 14V. I did this many times and it fluctuated between 12 to 14V, mostly 12.

I also decided to "listen" to the pump by putting a long solid metal rod to it. I couldn't hear any noises or actuation of the pump. I also felt it to see if I could feel it vibrate and felt nothing. Unless MB uses ultra quiet pumps, is this typical?

Also, the car will crank but not start. I didn't want to strain the starter. When it died the last time, it has not restarted.

I hope you had a great Christmas day. Oh, I ate too much!

Ready to keep looking.

Brian

Administrator · $y$Op

Looking at your readings leave me feeling like there is next to no power. The reading looks like 0.014v rather than 14.0 or 12.0 volts. When you say it goes to 12 and 14 volts does the meter read it as 14.0 thru 12.0? I am just asking because the photos do not indicate so much as even ONE volt let alone 12 or 14.

Thanks, and I ate wayyyyyy too much also. It was a good holiday here and hopefully the new year will be the same.

Talk soon

oneklassy1 · Senior Guest

Yes, you are right. I should have said it is 0.012 to 0.014V. No sounds at all. Is it a relay possibly?

Administrator · $y$Op

Yes asside from assuring you have a clean contact area on the terminals you are probing, I would say the Fuel Pump Relay is the next thing to check.
On 86 and up models its located between the two firewalls next to the AC relay. I cant quite make out the area in the photos you have taken, but it almost appears like you have a replacement style relay (KYB) installed at this time but a better photo of that area would help me.

Do you know where the fuel pump relay is located on your vehicle?

Here is a photo of both the fuel pump and AC relay on 86-91 US models. I would imagine yours has a similar set up.

-- Edited by Administrator at 18:02, 2007-12-27

oneklassy1 · Senior Guest

Greetings to you. On the contacts, I tested it multiple times to see any voltage with none showing. I took more pics of the engine compartment and I hope one of those will show this relay. I don't know where it is, sadly I don't have a repair manual. confused

Anyway, the pics are from the left side. Let me know and I will take more pics. I'll be here all evening. biggrin

-- Edited by oneklassy1 at 22:05, 2007-12-27

P.S. I added four more pictures

-- Edited by oneklassy1 at 22:07, 2007-12-27

Administrator · $y$Op

I looks to me that most all of the relays are located in your fuse box. The one all the way in the back right looks like a fuel pump relay however it would be nice if the sheet on the lid of the fuse box said so for sure. Have a look at it and see.

Let me know the part number on that unit it may help me to find out for sure.

-- Edited by Administrator at 22:36, 2007-12-27

oneklassy1 · Senior Guest

I listed the part numbers. The sheet is a legend for the fuses. Also, is there a trick to removing these relays?

Correction: The relay with the arrow on the left has the number 001 5425819

-- Edited by oneklassy1 at 23:37, 2007-12-27

-- Edited by oneklassy1 at 00:06, 2007-12-28

Administrator · $y$Op

I have no form of manual on the 380 so I am going out on a limb stating that the relay that says "Kickdown" is the fuel pump relay.

Here is a link that shows one for sale on e-bay-
http://cgi.ebay.com/ebaymotors/Mercedes-Rebuilt-Euro-107-126-Fuel-Pump-Relay-380-500_W0QQitemZ170181372769QQihZ007QQcategoryZ33553QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

I have one in my hand that is part number 001 545 94 05 that come out of a 1984 190E with a single pump. I also looked at some of my later model stock and it and one of them has "KICKD" printed on it.

Removing it is just a matter of carfully pulling it upward. You may have to rock it ever so slightly from side to side in order to work it free. They are in there pretty tight but there are no clips that hold it down that I am aware of. Then once it is out test for power in all of the female sockets. You should see 12V on at least one of them with the ground terminal of the tester grounded. If you find 12V to the relay its safe to say yours is burnt out.

You can jumper them however its risky considering I dont have anything that pin's out the 1983 Fuel pump relay. Most of the time its the pin right next to the one that has power. I have seen people strip a small wire and wrap it around the male terminals of the relay to jumper it. If you try this, you are doing so at your own risk. Driving a vehicle with a jumpered relay is dangerous and doing so could cause your fuel pump to overheat/burn up! Worse case is a fire and thats no good. People talk about jumpering them but many of them forget to mention that jumpering a relay is not a fix and can be dangerous as the pumps will never shut off and stay running whenever the key is on.

May the force be with you. Excellent photos it was a pleasure. Please let me know what you come up with.

Edit-
After looking at the bottoms of the relays it seems there is pin numbers on the bottom. I think pin number 87 or 30 is the one that should have power. The other one is the wire that sends power back to the pump. Pull yours out and have a look at the bottom of the relay and let me know what you find.

-- Edited by Administrator at 01:12, 2007-12-28

-- Edited by Administrator at 01:48, 2007-12-28

oneklassy1 · Senior Guest

Yes, you are right. That is the relay and it came out with just a wiggle. I will test it as you instruct. I'm sure it is bad and I will replace it. I have seen what happens to those who try to cut corners...auto cremation! I will post more on my progress. It has indeed been a pleasure and I'm here to stay. Check back in the morning, I'm heading down to check the relay now. biggrin

Administrator · $y$Op

Yes be sure to read my response above as I have edited it. You will want to test for power in female pins 87 and 30. One of the two should have 12V. If yours is out of the vehicle check the bottom. There should be numbers by all the pins. I am thinking pin 87 or 30 is the one that should have the 12V power (With the key on).

Thanks and be sure to let us know how it went.

oneklassy1 · Senior Guest

Got it! Thanks for the update. Results in seconds and I most definitely will give my results of everything, including the progress with this car. Be back!

oneklassy1 · Senior Guest

You were right! There was 12V in 87. I made sure it was 12V, not 0.012 biggrin

I will start looking for a new one in the morning. Will keep you posted. Thanks so much!!

Administrator · $y$Op

Well I guess after 145,000 miles the relay could use a replacement. After all it works hard to provide the proper juice to the fuel pump. After awhile them contacts and armatures get a little tired and burnt up. I say she has earned a new one, go on and give it to her!

With any luck you will find one local and be back on the road in no time. I know this information should help many and it is also a good comparison between the early and late model fuel systems. Just a super thread.

oneklassy1 · Senior Guest

A very happy ending!! Replaced the Fuel Pump Relay with a brand new one in kind that arrived today. The 380 fired instantly. Took it for a drive today and it is back to rest.

Yes, this car deserves the best. Kudos to you!

Thank you so much for your help, it was invaluable

and I am with you on hoping this thread helps others. Truly a great thread!

Have a Happy New Year!!

Administrator · $y$Op

This is real good news! I knew from the quality of tools and photos you were going to nail this problem from the start. Super job and I am sure this information will help even myself the next time someone brings in an early model W126.

Happy New Year to you! Sounds like the year is already off to a good start!

oneklassy1 · Senior Guest

Greetings! Been a long time.

It has been almost three years since I've installed the new fuel pump relay on my 380 and it has worked just fine. Your advice was great and I hope it helped another 380SEL owner. About 6-7 months later, it quit again and after doing the checks you advised above, the new relay turned out to be faulty and was exchanged under warranty.

Now, I have the problem again and I want to make sure that the fuel injection system (or something related) is not causing a problem. Last week, I drove the car about 5 miles for a short visit and when ready to leave, the car wouldn't crank and I had to have it towed home.

I am getting 12v at 87. Is there another check I should perform at the fuel pumps under the car? Also, the unit just under the air filter clip, (see pic) it has a small relay. Any checks with that?

Thanks in advance again for your help.

Brian

Edit: Just removed the breather housing to look at the fuel injection system. From just looking at it, nothing amiss. I also checked all of the fuses. All are fine.

-- Edited by oneklassy1 on Monday 27th of September 2010 06:57:51 PM

-- Edited by oneklassy1 on Monday 27th of September 2010 07:56:25 PM

SELLC · CERTIFIED POST WHORE

Welcome back Klassy!

I have heard reports that aftermarket Fuel Pump Relays have been known to fail in short order. Going with an original Mercedes branded unit can be costly no doubt, and having a spare is always a good idea but as you know they can be jumpered to get you home in a pinch. A fuel pump drawing too much juice (load) could cause a FPR to go bad also.

I don't think your most recent problem has much to do with the Fuel Pump Relay because you stated the vehicle will not crank. If the vehicle will not crank it's possibly a bad battery, starter, netural safety switch or even a bad connection.

Have you inspected the vehicle at all yet? What have you come up with?

-- Edited by SELLC on Wednesday 29th of September 2010 03:34:33 PM

oneklassy1 · Senior Guest

Yes,

Glad to be back. I did make a mistake, the car will crank but not start. I have looked over the fuel system and will perform the tests today. I forgot that I could've jumpered it and made it home.....

I did buy the K.A.E. (Kaehler Automotive Equipment) aftermarket fpr part # 0015455305. They are made in Germany for about $129.00. I will buy the MB unit next time.

With the relay out, I did check for voltage in female 8 & 7 and got 12v with the ignition on. If I were to jumper the unit, to test whether the inj system works or not is there another way to check the pump unit itself?

I will check the fuel pump under the car next. Let me know what you think. Thanks again! biggrin

oneklassy1 · Senior Guest

RE: 1983 380SEL Abrupt Stalling REVISITED

SELLC · CERTIFIED POST WHORE

RE: 1983 380SEL Abrupt Stalling

oneklassy1 · Senior Guest

Good evening,

Had a good but wet day here. Finally, I was able to get to the car and I did the test for spark at the coil wire at the distributor. There was none. So, I pulled a spark plug wire and did the same thing.......nothing. The coil is probably the culprit. confuse

SELLC · CERTIFIED POST WHORE

Well it could be the coil, however there are some other things that could be causing the problem.

(1) As you mentioned, the coil could be bad
(2) Ignition Spark Control Module could be bad
(3) Timing chain may have broken

Usually #3 will leave a nice crack in your valve cover, however I am unsure if your model has the single row or dual row timing chain. Good way to inspect this would be to take off the oil filler cap, have somene crank it and see if the cam is spinning.

I also am unsure if the 83 380 SEL has a crank possition sensor. I don't think it does, so I wasnt willing to add that to the list. You can check the coil by attaching the positive and then touching a ground to the other terminal, however you will want to have a plug wire on it, with it grounding away from you or you could get a serious shock.

I am also not too sure what the ignition modules look like on that car, if memory serves me right it should be a smaller aluminum box with a round plug on it. They too are known to go bad.

Give her some more checking and let us know how it goes.

oneklassy1 · Senior Guest

Hey there,

Thanks! This one has the double row. Oh boy, I hope that the cam hasn't gave up!

I will check and shoot a pic. Doing it now. biggrin

oneklassy1 · Senior Guest

The cam spins (whew!) I removed the cover from the coil and the aluminum box below the coil is in the picture. Is that the ignition module? On checking the coil, I'm not sure how to do it. Do I attach a wire to the positive and another to negative? Or do I use a multimeter?

SELLC · CERTIFIED POST WHORE

Glad the cams are still spinning! Most of the times when the guides break they get stuck in the gears, throw off the timing and bend valves. Real nasty. Most all the time they will still have spark, but it's a quick test and worth it.

Now it seems were in Ignition land with this problem. Some other things to check real quick would be to pop off the distributor cap, inspect the ignition rotor to be sure its not broken or damaged. Also inspect the top of the distributor cap to ensure the center pin is not worn away or missing. Finally have someone once again crank the car over without the cap installed to ensure the distributor rotor is turning. If everything checks out there we can test the coil.

Bare with me it's been awhile since I have had to work with the older coils, however to check you will need to attach a positive lead to the + side of the coil. Once again be sure the wire is on the coil and the metal part protruding from the wire is close enough to a ground to arc. Next you just tap a ground on the - side of the coil and it should fire. Tap it in an ON/OFF sort of way, just like the distributor does. It should fire every time you touch it.

With regards to the ignition module which I am 90% sure that silver aluminum box is, I know of no way to test these outside changing them out for a known good unit. I am sure there is some area to probe, I am just not aware of it and have never had to test the older ones.

Hope that helps, let me know what you find.

oneklassy1 · Senior Guest

Great! I will check the distributor cap, rotor, and test the coil. I just installed a new cap and rotor about a month ago. I changed the plugs, wires, cap and had MB service the trans, do an oil change, and service the suspension. They gave it an A+ as it has never missed its scheduled maintenance.

You are certainly right, the little things are the ones most commonly overlooked. I will hang in there. On the module, there are some leads coming out of it. I will see if there is any voltage in-out of it. Getting to it now. aww

SELLC · CERTIFIED POST WHORE

Back in the old days with points and condensors they had balast resistors. Yours should not have one of these as it has the ignition control module, however you will want to follow the wires back that goto the coil in an effort to see where they go.

If the coil checks out and everything in the distributor appears to be in good order then its safe to say by process of elemination that the module is the culprit. Wish I had more info for you on that module but I mostly deal with the 86-up which uses a diffrent ignition control module with provisions for barometric pressure and manifold vacuume influences. I don't even have any wire diagrams for the older modules, however you can probe them with the tester to see if it's getting power at least.

How many pins are on the module? Looks like maybe 4?

I was going to mention how clean the engine bay looks on your vehicle and how nice everything looked, but I assumed you knew that because you are the one that keeps it looking that way. smile

Hope you get her sorted. Let us know when you pin down the fault.

-- Edited by SELLC on Thursday 30th of September 2010 10:00:25 PM

oneklassy1 · Senior Guest

Just tested the coil and there was no spark.

In fact, that coil is very old, same with the module. Looking in the records ( I have all records) I think it was changed at 100K during major servicing. The module looks original. It is at 151K now. It's only driven on good days and never in the cold or rain.

What should I check next?

SELLC · CERTIFIED POST WHORE

Well you could check for KEY ON POWER at the positive of the coil. Using a test light or volt meter to see that there is 12 Volts when the key is on.

While I have never tried this on an 83 380 MB, you could check the ground connector at the coil to see if its opening and closing. I guess you could do this by putting a test light lead on the positive side of the battery and then probing the negative while someone cranks it. The light should go on and off as the engine turns (Again this is not something I have personally tried on your model). If however the light does turn on and off its safe to say the ignition control module and distributor are doing their job.

One thing is for sure, the ignition control module is way more expensive than the coil. If you are not sure you could try sourcing a used one for testing purposes and then if thats the problem you can roll with it, or replace it with a new one, keeping the used one as a spare. Personally I would go the used route, and then stick with it until it failed, then buy another used one again (LOL).

You would also want to check your connections to ensure they are not melted or damaged anywhere. There is a pickup in the distributor, but this should be okay as it opperates with magnets rather than the old style points and condencer.

Let me know how the tests go.

oneklassy1 · Senior Guest

Great advice! I will do this right away and let you know how it turns out in the morning.

When I was doing the preliminary checks, I checked almost all of the connections to see if anything was burnt, loose, or disconnected. I didn't see anything amiss nor any leaks. When the car went down, there were no warning symptoms.

I will follow your advice and shop around for both. Thanks so much and have a good evening. We'll continue tomorrow. biggrin

oneklassy1 · Senior Guest

I hope you had a pleasant day. For me a late busy day. biggrin

I didn't find a used module just yet but I did get a new coil. I carefully transferred the wires and cranked the car. Still no spark.

So, it may be the ICM? I found prices ranging from as low as $54.00 to $180 for a new coil. I should locate a ICM tomorrow. What should I check next? confuse

SELLC · CERTIFIED POST WHORE

Usually when a vehicle just cuts out when driving due to lack of spark it's the ignition control module, but that's not to say it will always be the problem.

I find it odd that you were not able to get the old coil to fire manually. I would also find it odd to have an ICU and a coil go out at the same time.

There are of course some other things that should be checked before buying any more parts. Things like the fuses in the OVP relay, fuses in the fuse box, testing the coil wire itself, and also the secondary connections at the battery just to name a few. I am also assuming that you are checking for spark properly, as sometimes I have seen it done improperly and as such we could be barking up the wrong tree. When helping people online I try to lead them to the most likely causes based on what I am being told.

I have been leaning twards the ignition control module/unit but the ones I have seen for sale have been much more money than $180. The one for $50 is pretty cheap and I am most certian that the total cost of both the $50 ICU and the cost of the coil will total up to be less than the min. charge at your local Mercedes-Benz dealership.

How much did you have to give for the coil?

oneklassy1 · Senior Guest

What a beautiful Saturday!

I am starting to retest the coil and have a friend help me to make sure we are following your advice.

I agree that it is very odd for a car that drove perfectly to just all of a sudden just fail to restart. So I am going to inspect all of the connections again, just to make sure. You are probably right that I may have incorrectly tested something. When I got the car home, I checked all of the fuses and wires but all seemed okay.

It is 530PM and I haven't yet tracked down a ICM. The coil was $118 inc tax with 2 yr warranty. So, I will be on the car checking those systems again and will report back what we find. I attached pics of the previous coil (and area) and what I think is the ICM.

Thanks much and enjoy! biggrin

SELLC · CERTIFIED POST WHORE

It's been mostly rainy all day here, then again this is typical fall weather here in Michigan. Soon everyone will be hibernating indoors when the snow and ice comes in December.

Sounds like you are on your way to fixing the problem. $118 sounds a little steep for a coil was it a Mercedes Benz part? The aluminum box located at the bottom center of the third photo is indeed the ICU. The OVP is the red topped relay in your fuse box, and I am sure you already know where the FPRelay is. The little silver relays are for your windows and seats if I am not mistaken.

From what I see in your fuse box it appears most all of your relays are located in there, as the newer 560's have so many fuses that they had to mount the FPRelay, AC Relay and OVP relay outside of the fuse box! Guess Mercedes did not antisipate the need for a bigger fuse box back in 1983. Seem's they added so much more crap thru the years that they ran out of room in there.

Here is a photo of a later model fuse box, notice how the OVP, FP and AC Relays are no longer located in the fuse box.

oneklassy1 · Senior Guest

It has been hot but starting the fall cooldown. Soon, it will be a beautiful sight in the mountains.

I have checked so far all the fuses, distributor, plugwires, and just got prices for the ICM....YIKES!! A low of $229 used on eBay to $693 at Partsgeek.com. No wonder I am not finding one cheap. It is the original unit. No way to test is it?

Doing the coils.

-- Edited by oneklassy1 on Saturday 2nd of October 2010 09:06:03 PM

oneklassy1 · Senior Guest

Good evening,

We just got finished testing and there was no key on power, no power at all from the coil from testing the coil itself. The coils are both Bosch units. With those high prices for the ICM, and no way to check, I will try to find a good used one.

What else do you suggest I check? Are those ICMs known to just quit abruptly like this? Is it an item that can be repair/reconditioned? I see that it has a removable cover with the tamper mark on one screw.

Sunday, I will start my search. I will let you know how it goes. biggrin

SELLC · CERTIFIED POST WHORE

Yes the ignition modules are known to give out all of a sudden and usually when driving. I don't have any diagrams of the early W126 380 SEL, so I really can't offer much help with the wire diagram. The coil and module are both diffrent on the years I work with. For example on my coil both leads have 12V, but with your coil I think it has a positive and a negative.

Seems like the Ignition box would be the problem after hearing everything you have done/checked thus far.

How did you end up making out?

PowerStroker · UNSTOPPABLE!

SELLC wrote:

For example on my coil both leads have 12V, but with your coil I think it has a positive and a negative.

You silly, dumb bastard.

I see you backprobed both terminals with the key on but engine off. If you do that, of course you will read battery voltage on both terminals if the coil isn't faulted open.

The coil is fired by switching it's ground on and off to collapse it's field and induce the high voltage to the secondary windings. B+ is always present at the coil any time the key is on, but if the engine isn't running, the ground isn't switching, thus you will read 12V on the ground side too. It is just a coil of wire after all. If you know anything about Ohms Law, you would know that open circuit voltage is ALWAYS system voltage.

If you would have checked power at the 2 coil primary terminals when the engine is running, you would find the input side has steady system voltage, and the post load side has a rapidly switching ground that can be seen with a tri color led logic probe, or a fancy meter with a duty cycle function. Though even a regular Voltmeter will show some DC voltage as it sees an average of coil on vs off time on the ground side of the coil.