another '89 300e failed ca smog :( help! - PeachParts Mercedes-Benz Forum

think300E · #1 03-20-2009, 01:50 AM

Here is my info, car has 246k miles (hopefully i can hit 500k or a million why not?

)

With the economy the way it is, I opted to take the car to the test only smog check before a taking it to a shop.

I replaced the sparkplugs a week ago, and also added a can of bg44k around the same time, 133 miles since the bg44k was added.
I didn't do an oil change (it has an external oil leak).
I did warm up the car (drove on on the freeway for about 20mins, and there were two cars ahead of me but one was half way done.
Check engine light does not light up.
Car idles fine, was acting a little rough pre-sparkplug replacement.
Car is driven 120miles on one weekday, the rest of the days either it is not driven at all or short drives to store/post office.

I have limited tools but would appreciate some indication of what might be wrong here, just so I have a better understanding about it when I take it to a shop (and/or in case I may be able to replace some item myself and save some money).

@15mph RPM:1695

HC:181 -FAIL (max is 110)
CO:0.44 - PASS (max is 0.71)
NO:904 - FAIL (max 772)

@25mph RPM:1701

HC:152 - FAIL (max is 85)
CO:0.41 - PASS (max is 0.59)
NO:816 - FAIL (max is 711)

Thank you

ps2cho · #2 03-20-2009, 01:59 AM

I am running through the same deal right now.

First I'd follow these steps:

Quote:

It is suggested that before the active (engine-running) tests are attempted, some static tests should be performed to check a few of the basic components of the Bosch fuel injection controller.

With the ignition on but the engine not running, the duty cycle tells which version of controller is installed. A 70% duty cycle indicates the standard controller with the ability to read some faults by monitoring the duty cycle. 85% indicates the California controller, which ordinarily displays the faults as a blinking LED on connector X92, although it can be programmed to display the faults as an X11-pin3 duty cycle. 100% indicates the controller does not display fault codes in this manner, or is faulty.

For California cars, starting in 1988: Press the push button switch on test connector X92 (passenger side, between the two firewalls) for two to four seconds. The LED will flash once, indicating no fault code is stored in the system. Now press the switch again for two to four seconds. The LED will be on continuously, and the injection control is switched over to an on/off ratio output.

Assuming the "standard" 49-state controller (70% duty cycle with ignition on but engine not running, or about 4 volts average), the following tests should be performed before attempting to adjust the idle mixture.
1) Idle Contact: Deflect the air flow sensor plate. The duty cycle should decrease to 10%. If it remains at 70% test the throttle valve switch (Job 07.3-121).

2) Full Load Contact: Open the throttle completely. The duty cycle should decrease to 20%. If it only decreases to 40% test the air flow sensor potentiometer (Job 07.3-121).

^Start with those then do the following:

First check fuel pressures using a CIS fuel pressure gauge.
Then check that the airflow sensor plate is level and centered (job 07.3-1665)

Should be basic things to check first. You didn't fail by too much...

Oracle12345 · #3 03-20-2009, 10:06 AM

NOx forms when cylinder temps reach above 2500F and above. The fuel system is air starved, and not enough fuel. Check O2 sensor, lamda ratio AFTER checking x11/4 for pulse read outs

think300E · #4 03-07-2011, 06:17 AM

btw, just to add more info to this post. The cat converter was diagnosed to be bad and it was replaced back on 08/09

These were the measurements post cat converter replacement:

@15mph RPM:1671
HC:88 - PASS (max is 110)
CO:0.02 - PASS (max is 0.71)
NO:37 - PASS (max 772)

@25mph RPM:1753

HC:25 - PASS (max is 85)
CO:0.01 - PASS (max is 0.59)
NO:16 - PASS (max is 711)

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