hi everyone, I have an 88 240dl that upon cold start runs rough and you can smell the fuel in the exhaust. Even after it has warmed up you can still smell fuel. I've owned it for about a month now and the previous owner said he put new plugs wires cap button and maf sensor on it. Even at 77 deg. air temp outside still runs rough until it warms up. Any thoughts

 

Could be a multitude of things. Since the car is new (to you), you don't have any history of what the previous owner did to it. I have seen cars for sale that have the oxygen sensor wires cut. The car runs but it doesn't run well.

I would start with inspecting the wiring. Make sure the wires to the oxygen sensor are intact. Also check the wires to the air mass meter. Also, check the entire air intake system from the airbox all the way to the intake manifold. Make sure there are no holes or missing hoses. If there are missing hoses, replace them. Holes will need to be patched (difficult to do) or the intake hose replaced.

If that all checks out, are there any exhaust leaks upstream of the oxygen sensor? If so, those will let in oxygen causing the sensor to falsely detect a lean condition. The ECU will try to compensate by enriching the mixture.

The engine coolant sensor could also be a source of a too-rich mixture. If it reads cold all the time, the ECU will enrich the mixture. Search the forum here as there have been multiple writups on how to check/replace this sensor.


Good luck