HELP! EDS system '87 300D - PeachParts Mercedes-Benz Forum

toknow · #1 10-21-2003, 12:54 PM

Hi,
I appreciate some help about my '87 300D,

There is an electronic diesel control (EDS) in this car that regulates the idle speed and other things, it also provide the signal for the tachometer. I am not sure if it works OK in my car, also this is a possible cause for intermitent AC compressor cut off.
There is a test connestion in front of the battery to the left, it has 4 poles. You need to open the plastic door or so and pull the connection from the buttom. terminal # 2 has 2 gr/yl wires in it.
Terminal #2 is the engine speed signal comming from the EDS, the test in the CD says that:
AC~ voltage measured between terminal 2 (as +) and a negative source (car body) should be "" > 4 V AC with rising speed, rising voltage ( < 3 V AC with ELR)""

I measured mine and it was about 11.7 V AC, if I measure using DC voltage it is about 5.5 V DC..
There could be mistakes in the CD and a confusion between gas and diesel, also I heared there is different versions of this system... and I am not sure that I understand what they said in the CD as in the previous qoute. ELR is the idle solonoid or so, does this mean it should be about 3 V AC at idle without EDS!!...

I am confused and I appreciate if one owener of similar car could check this for me at his car, without AC on. And if somebody knows more technical explanation.

Thanks,

ALso, there are 3 other wires on this test terminal, does anybody know what they are for and how to check them...

jfikentscher · #2 10-21-2003, 02:28 PM

Tach goes out, AC out at the same time.

Possibly the Over Voltage Protection relay behind the battery. Mine goes on and off intermittantly. When it is off I lose the Tach, AC, and the idle gets rough. About a $50.00 part. Some on this board have taken theirs apart and resoldered the connections. I have not done this as this is my daily driver and if i screwed it up I would have to wait for a new part to arrive.

Regards,

Joe

toknow · #3 10-21-2003, 03:14 PM

I checked the OVP, it is Ok, and its fuse is OK. The OVP relay provides power to the EDS system. If I run the car without the OVP, idle will drop substantially and ABS light comes on (it gets power also from OVP). I do not believe that the OVP could provide unstable or diffrent moods, otherwise I will be seeing the ABS light comming on sometime.

That is why the next step is to verify the EDS before other things. I am sure some generous 300 D owners will check this for me.
thanks

psfred · #4 10-21-2003, 08:02 PM

The OVP can certainly give you intermittant power on only one circuit, and is in fact famous for doing just this. The ABS circuit is powered by a separate set of contacts in the relay than the ignition computer (or EDS on the diesel), and if it is giving you variable voltage or current, you will get variable operation of the EDS. If you have intermittant idle problems, a "hopping" tach, and so forth, I'd expect the OVP first.

Peter

toknow · #5 10-21-2003, 09:44 PM

thank psfred
the car has some tach hesitation, but idles Ok. this could be because the ELR (the physical idle solonoid) is powered from and separately from the EDS, when EDS does not provide correct voltage, it matters only for the tach and the car idles in a safe mood. this is my interpretation!

The test connection (4 poles) is a good place to check the EDS signal and provide clear result- but I cannot interprete the CD test (as I mentioned in the start). The CD provides MINIMUM text about the data only, with possible mistakes and without explaining any logic

I appreciate further explanations, tests etc
thanks

I am trying to attach the wiring diagram in the next post

toknow · #6 10-21-2003, 10:04 PM

here is the diagram

toknow · #7 10-22-2003, 01:25 PM

here is the second diagram with test connection

gsxr · #8 10-22-2003, 03:22 PM

I forget exactly what pins to measure at, but the tach signal will be AC voltage, rising smoothly with increased RPM. Taking a DC reading will be zero or near zero. If the tach quits or is flaky, it will kill the AC compressor via the KLIMA relay. Sounds to me like your tach sender (below starter, left side at front of tranny) may be on the way out. It's a nuisance to replace but not that expensive. Mine would stop & go, and was cured after I replaced the sender. If you can't find the right pins, locate the 2-pole connector in the wire from the sender. It's approximately near the OVP relay area, behind the battery, possibly towards the center of the car. Disconnect it and plug the voltmeter directly into the two wires from the sender - should get AC voltage. My problem was that it worked most of the time, then just would quit - no voltage, no tach reading at all. Then it might magically start working again if I wound it up near redline - or not. New sender fixed it.

The EDS is mostly useless except to regulate idle speed. You don't need the L7 connector at the injection pump either. All that jazz is simply to control the emissions garbage (EGR and ARV), and you should have disabled both of those by now anyway - all they do is sap power and reduce MPG!

toknow · #9 10-22-2003, 04:02 PM

Thanks gsxr
I agree with you on the sending sensor, and in fact that is where I started, I blindly assumed that the sender is faulty due to the age of the car (wear etc.)..So, i replaced the sending sensor and unfortunatly nothing changed!!!
So, I am assuming (up till now) that it is just the tach itself not accurate (it has a capacitor inside and it might not be consistent when idle, but it never failed while driving and the RPM is about 2100 at 60 mph - approx.)
Because of the AC problem, I started to suspect everything agian. I know for sure that the AC speed sensor does not give higher AC voltage as supposed to be, but sometimes the AC and the klima just keep working without cutting the compressor. I know that the klima monitors the idle and compares it with AC compressor speed, so if the EDS (which generates the idle signal to tach and klima as in the second diagram) if it is not generating the correct signal alway, this could be a good reason for the klima to cut whenever the signal telling that something may be wrong in the idle speed due to the compressor trying to lock up and slowing the idle (which is not the real situation). The fault could be the AC rpm sensor or the EDS signal itself or a short in its wiring. I am planning to replace the AC comp. sensor if I know for sure that the EDS signal is OK. My last option, after the AC sensor, is to replace the klima with simple relay, but I am not sure about the concequence if the compressor locked at some point, I think the clutch will fail before the belt breaking, I do not know!!??

I think the EDS doing much more than just regulating the idle, there are many inputs going into it. I just want to verify that the EDS generated the correct voltage as in my first post - it is from the test connection terminal # 2 - do you think calling the dealer can help!!??

regading the EGR and ARV, I do not have much time to take them out or plug them, I just plugged the vacuum line towards the EGR, I am not sure if this completely disabled the EGR, I will do the same for the ARV

gsxr · #10 10-22-2003, 04:22 PM

Yes - plug the vacuum lines to both the EGR and ARV - that will suffice.

About your problem, I'd be tempted to swap out the EDS computer and/or the KLIMA. There are quite a few parts cars available these days, you could probably snag them cheap. Might even find a nice forum member (or MBZ.org diesel list member) to let you try them before buying. There's a guy in the classifieds parting out an 87 300D right now. Sorry I'm not more help - I'm kinda stumped mysefl!

toknow · #11 10-22-2003, 04:33 PM

thanks,
what I need is a simple test on a running car (no AC problems), as I said there is a test connection with 4 poles (designed for test and easy access in front of the battery to the left), if someone, using voltemeter, could test AC voltage between terminal 2 (+ side) and any ground (terminal 2 has 2 green/yellow wires), then tell me what is the number (mine is 11.7 V AC (and if to use, not important, DC it is 5.5)). Based on this I will know if my EDS works OK or not..that is all!!
waiting for help,
thanks

toknow · #12 10-24-2003, 11:50 AM

Hi,
I am still need help in this matter, may be I will have to offer a cash rewards for whoever provides this info, but I do not want to make such a precedent!
thanks