95 E320 Running Rich-Why?
 

The car is pre-OBDII, so no MIL lit, and no easy diagnosis. The obvious culprit is the H02S. The car has 105k on it, the last sensor was done by me at 59k miles. The car has been running rich for a couple of thousand miles now, anyway. In town gas mileage is poor, highway isn't great. I just can't see the o2 sensor needing replacement until 120k.

So, what could cause this? Car has been running a K&N filter since 40k miles. What about the air temp sensor on the air intake?

Also, what would happen if the air pump ran all the time? When the car shredded a serpentine belt last summer, it cut the wires to the pump. I spliced together as best as I can, not sure if the pump runs all the time or none at all, or correctly.

What about the MAF? How do you test?

In very hot temps, the car needs to cool down before it restarts.

Any ideas?

Thanks.

Pull the vacuum line off of the fuel pressure regulator and look for any sign of raw fuel. Quite common, and if left alone can kill your catalytic converter.

...and dump the K&N filter ...then clean the MAF with CRC cleaner..those oil filters rairse hell with the HFM MAFS...

Give the regulator a minute before you put the hose back on. Mine took its time when it came to leaking/dribbling.
Installs with an internal spring clip.