I've got the sears multimeter with duty cycle and would like to read the codes on my '90 300D. I need to know what to do next- I assume the probes go to the diagnostic connector, but which pins? Do I need to read duty cycle in Percent or Hertz?

I have the MB manual to lookup codes, if I can read them.

Anyone done this or know how to read these codes with the meter?

Thanks friends!

John

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1994 E420 43k (pickup, solid)
1990 300D 2.5 127k (sold) (now driven by friend)
1991 300D 2.5 73k (sold) (incredible car)

El Presidente,

You need either an OBD I or an OBD II (I can't remember which) dianostic
scanner[handheld] to plug into the diagnostic port by the battery compartment.

BUT, somewher in the recesses of synaptic storage , I remember NOT buying
either ...because the only function controlled by the EDC (Electronic Diesel
Control) on the 1990 is engine idle.

There may be a way to tap code info with a multimeter ...BUT you would
have to find out which of the entry points in the port to "Spike"
AND what if you have to "Spike" multiple points with only two leads???

Better yet, what symptoms are you experiencing?

I am getting power loss - no turbo kick in. The MB repair manual says that the computer kills boost if it senses one of a gazillion things (vacuum transducers, sensors etc.) are not providing the correct signal.

So, rather than test these items I would like to read the code thrown by the ECU, which I have a table of codes and their meanings.

Problem is I don't have a reader- and I am told that a multimeter with duty cycle will read the codes perfectly, but I don't know which pins!!

Thanks

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1994 E420 43k (pickup, solid)
1990 300D 2.5 127k (sold) (now driven by friend)
1991 300D 2.5 73k (sold) (incredible car)

The EDS diagnostic ouputs are accessed via the X11/4 connector. This connection is located right next to the battery. The pins you are interested in for EDS testing are 1) Pin 1 - ground and 2) Pin 4 - EDS diagnostic.

Ground pin 4 for about a second and the ECU will respond by flashing any error codes. I've not read these codes with a multimeter using a duty cycle setting but I don't see a reason that would not work. Diagnostic codes (for this engine) should be read with the engine running.

Great, so I can just plug into 1 and 4 with the two leads, read frequency % after touching 4 to ground WHILE the meter is still connected?

Sounds very easy.

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1994 E420 43k (pickup, solid)
1990 300D 2.5 127k (sold) (now driven by friend)
1991 300D 2.5 73k (sold) (incredible car)

No you don't read frequency or duty cycle. The codes at that connector are simply pulses. They are best read using an led. It is pretty simple to make a box with an led and a pushbutton switch, with a resistor in series with the led. When you push the button it grounds the pin, then the LED will blink out any codes that might be stored.

If you will do a search, you can find an old thread with a schematic of this tester box.

Using a digital voltmeter would be tough to read the pulses. You could get by with an analog meter and count the sweeps.

Good luck,

The Pulses could be viewed as a percentage of time on vs time off - this could be interpreted by your meter as a "duty cyle" but the problem is the time scale - I'm not sure how your meter would deal with the pauses between sets of codes or matter the passage of time before and after the actual deliver of coded data. I have read these codes with an old analog meter but its kind of a pain in the neck.

Here is a link from fellow MB-shop member JIMF website that details how to make in impulse counter for less than $10 using Radio Shack parts (he even supplies the Radio Shack part numbers). Jim's site is an amazing collection of MB diagnostic info. The info is at the bottom of the following page.

http://pages.prodigy.net/jforgione/MB_X11.html

Yes, JIMF! That was the info I was asking him to search for. I made one of these boxes and it works great.

Good luck,

But I have been told by several people whom I trust that the duty cycle reading as % will read out the codes. Search on this forum for "duty cycle."

I'm confused. I don't mind making the LED counter, but I think I'm doing something incorrectly in my procedure and that is why the duty counter is not doing its duty.

I tried with car running, put positive in hole 1 and negative in hole 4. Then I grounded 4 to the car negative bat terminal. This causes the meter to go from 5 to zero for a moment while grounded then back up to 5 again. Touching to ground again at this point doesn't change the reading or erase it.

__________________
1994 E420 43k (pickup, solid)
1990 300D 2.5 127k (sold) (now driven by friend)
1991 300D 2.5 73k (sold) (incredible car)

I used an analog (needle) dc voltmeter this time. When I grounded #4 it went to zero. 2 seconds later, the needle dipped to zero then back up quickly ONCE. I ground again and it again does ONE jump.

Could it be that I don't have any codes?

So what could be causing this loss of power and nailing at idle? Time to clean the injectors?

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1994 E420 43k (pickup, solid)
1990 300D 2.5 127k (sold) (now driven by friend)
1991 300D 2.5 73k (sold) (incredible car)

Sure it's possible - Do an experiment to see if your analog meter is reading correctly. Re-run your code reading procedure with key in position "2" (ignition on) but this time don't have the engine running. Using your meter you should be able to read the code for "faulty engine speed sensor" - I think it's code 7 if my memory is correct. The ECU throws this code because it can't detect an engine RPM reading since the engine is not running.

It did its dance 7 times with the position at II

Great help, thank you. So the thing is reading, and there are no codes.

So where to begin on a nailing idle and loss of power on hills?

I pulled the rubber line from the steel line that runs to the tank (under the hood) and diesel dripped out at a pretty good stream. I had suspected the fuel screen.

Could the nailing, vibration-filled idle and lack of power be related to an injector? Any other suggestions to help diagnose this one? Thanks friends.

__________________
1994 E420 43k (pickup, solid)
1990 300D 2.5 127k (sold) (now driven by friend)
1991 300D 2.5 73k (sold) (incredible car)

The correct procedure to verify fuel delivery is to observe the amount of fuel delivered by the lift pump in a specified time.

Sounds like you have multiple symptoms here......

Having the injectors tested for opening pressure and pattern is never a bad idea but I'd start by trying to document just how bad the lack of power is - have you timed any 0-60 timing runs? A good running 2.5 turbo will run about 11-12 seconds. A 2.5 turbo without boost will take 18-20 seconds to get to 60 MPH. If your acceleration times indicate lack of boost I'd suspect a plugged ALDA line, a lack of vaccum to the boost control system or a bad vacuum control servo (in that order of likelyhood).

I've got to admit I'm not actually sure what "nailing" sounds like - the term is thrown around here quite a bit but I've never had any of my MB Diesels emit noises that sound like the descriptions I've heard here described as "nailing"

Nailing is a sort of clatter- metalic sound that sounds like a loose piston.

I have a '90 and '91. My other 300D is silent and smooth sounding. Really quite quiet. The '90, with the power loss, has much more clatter, and shakes a ton.

I checked the lines from intake to overload switch to alda. Lines are clear but I don't have a mity vac to test pull.

0-60 is about 19 or 20 seconds. I have trouble climbing hills at more than 5mph

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1994 E420 43k (pickup, solid)
1990 300D 2.5 127k (sold) (now driven by friend)
1991 300D 2.5 73k (sold) (incredible car)

Wouldn't one of them, if spoiled, throw a code?

__________________
1994 E420 43k (pickup, solid)
1990 300D 2.5 127k (sold) (now driven by friend)
1991 300D 2.5 73k (sold) (incredible car)