I have been working on my 1989 mercedes 300se and have run into a problem. My duty cycle reading reads 99.9% all the time. It reads that with the key on accessory with the engine not running, when it should read 70%. It reads that with the engine running and cold, and with the engine running and warmed up. I am reading it at the X11 port pins 2 and 3.
I have replaced spark plugs, wires, cap and rotor, injectors and related seals, OVP, and had to replace the EHA due to it leaking. I have replaced the ICV hoses, CIS system rubber boot and the throttle gasket due to vacuum leaks. I have done a smoke test with no visible smoke anywhere.
Also, the car takes a few cranks to start after sitting for a few hours and over night. It idles at about 800/900 rpm in Park and Neutral, and 650 rpm in drive and reverse.
One more thing I have noticed is that in Park and Neutral, the economy gauge sits on the far left. In Drive and reverse it is sitting about 1/4 away from the left.
Does anyone have any ideas?
Based on trouble diagnostics by means of on off ratio and the work you've said that you did, it could be one of the following:
- Mixture set too lean (beyond EHA enrichment limit)
- Bad connection to X-11 unit or your meter sucks
- ECU not receiving power or not grounded
- O2 sensor signal implausible (shorted)
First verify your meter and the integrity of the X-11 by testing the meter with an assortment of batteries (AAA, 9V, the car battery, standard cells, whatever you got), then take voltage readout (or duty cycle, whichever you prefer for your DMM) between pin 3 of the X-11 and a chassis ground (the battery ground strap is a good place to go when in doubt).
The second thing I would check is oxygen sensor output. You should get fluctuating values from the O2 sensor ranging from 100 mV to 800 mV (should be 450 mV +-350mV with a 0.5 Hz 'refresh' rate), if your reading is continuously low then go and check EHA current as well to see if you're beyond the leaning limit. Hopefully someone can chime in on what the max EHA current will be if it's fully compensating for a lean condition because I'm blanking on the max value the ECU sends. If you're EHA current is maxed out and you have a lean condition you'll likely have to adjust the mixture and the EHA to obtain a duty cycle of 50% and a differential pressure of 0.4 bar between the upper and lower fuel distributor chambers. DO NOT GO AND FIDDLE WITH THE SCREW WITHOUT CONSULTATION, PREPARATION, AND MULTIPLE VERIFICATIONS THAT THE MIXTURE IS IN FACT PAST THE EHA ENRICHMENT LIMIT, I CANNOT STRESS THIS ENOUGH.
Car must be in closed loop, e.g. with O2 sensor providing feedback. If it doesn't or the O2 sensor does not have any voltage (no power) and you can't get voltage by grounding its wires then you'll have to check power supply to the ECU but we'll cross that bridge when it is determined that it is needed.