Pre-diagnostic-era M103 duty cycle - PeachParts Mercedes-Benz Forum

ps2cho · #1 01-17-2010, 02:14 AM

I found a lone vacuum hose unhooked below the fuel distributor and ever since I plugged it back in, the car is taking an extra 1-3 seconds to start up cold and I also think my mpg has dropped based on the fact I am at "empty" and only at 265mi when I usually get about 280-290mi before it hits empty. When I fill up tomorrow afternoon I will get an accurate reading, but nonetheless its still starting slower.

So maybe the fuel mixture/duty cycle needs a tweak towards leaner?

What is the CORRECT procedure to check the duty cycle on a car WITHOUT the diagnostic port near the battery? Do I simply probe the X11 when the car is warm or are there any preliminary steps to take? On my 88 california 300TE it requires preliminary steps, but she has the diagnostic port so I have always followed the

The readings before were a little finicky that is why I am asking the question to check I am not missing any steps at all.

Thanks,
Robert

JamesDean · #2 01-17-2010, 12:13 PM

To my knowledge, You should be able to pull duty cycle readings from the x11 port. Check voltage across pins 2 and 3.

I dont believe there is any prelim setup for a Federal car. Atleast the FSM doesn't indicate anything about doing anything special.

Use this formula to check duty cycle:

Duty Cycle = [1 - (V{pin 3}/V{max})] x 100%

where V{max} is battery voltage.

Once you've done that, if you are seeing a fixed voltage, rather than a relatively dynamic one you should consult this:

http://i98.photobucket.com/albums/l250/MafiaNicky/50006pdf2.png

It should assist you in tracking down the problem.

I used this method on my 93 190E. It should be the same for both of your vehicles.

ps2cho · #3 01-17-2010, 08:11 PM

Well the car is California, but does not have the diagnostic. Were all pre-88 cars "federal"?

I know how to pull the duty cycle reading...I just had some weird results before so I am checking that I am not missing anything here.

mak · #4 01-18-2010, 09:31 AM

On the overrun the fuel is cutoff and the EHA is in minus . check the operation of the switch for this .
mak

ps2cho · #5 01-19-2010, 01:07 AM

I have never probed voltage of the EHA, only fuel pressure. Is it redundant to check the voltage if the pressure has been confirmed correct?

tinypanzer · #6 01-20-2010, 08:04 PM

EHA controls upper and lower chamber pressures in the fuel distributor, not line pressure. So no, it's not redundant.

Quote:

Originally Posted by ps2cho

I have never probed voltage of the EHA, only fuel pressure. Is it redundant to check the voltage if the pressure has been confirmed correct?

JamesDean · #7 01-20-2010, 08:12 PM

You're probably aware of this, but there is a section in the FSM that covered diagnosis without on-off ratio. It a nice series of tests on different components in the system...