528E runs rich

I have an "86 528E that runs very rich. I had it into a shop for a tune up and it was better for a bit. It starts hard and runs rough. It will push some blue smoke consistant with running rich. Any suggestion on what to check and in what order I should look?

TNX

RR

If it starts OK, and that is a big deal.

Then I would suspect the o2 sensor output.

As the sensor gets weaker it will provide less voltage.

o2 sensor readings.

You can check it on your volt ohm meter.

Use a VOM on pin 24 on the ECU or the black lead on the O2 sensor.

.6 volts is dang rich .3 volts is dang lean.

http://www.kemparts.com/TechTalk/tt07.asp



Later,

A few other possibilities might be:
1] Poor or broken connection @ the coolant temp. switch [NTC] located on the thermostat housing. If your car received the "Summer Campaign of 1987 it had a 480 ohm resistor added at the connector and they can break causing an open circuit.
2] The M20's also had a "35 degree switch" added to the throttle heater hose coming off the t-stat housing, these also fail, can safely be removed ALONG with the harness to the NTC that was installed during the "Campaign". Both these will cause a rich condition.
3] As "KC Ron Carter" mentioned, the BEST way to diagnose your problem as electrical is a complete pin test at the DME Control Unit, no guess work needed then.
4] Also check for a sticking fuel pressure regulator though it's a little late in the fuel blend season for this to happen, they still fail.