Lean at idle, rich at 3000rpm
 

My 300ce (1990, 104 engine) was blowing black smoke and guzzling gas.

The indy shop replaced the fuel pressure guage. This reduced the smoke but fuel consumption is still poor.

I took it back and they found that although it is now running nice and lean at idle, it's running rich at 3000rpm! The shop can't figure it out yet. Compression is good. Fuel divider looks fine. Engine pulls well through the range.

Any ideas?:confused:

When was the last time you put in a new O2 sensor? That's usually a good place to start when you are dealing w/ the infinitly complicated (and damnable) MB fuel injection (Lamda is a curse-word in my shop)!
I would also make sure my EGR wasn't plugged or stuck open.
Start w/ the cheap and simple first!
Then get out your wallet!
-Matt-

Thanks for your reply Matt

I asked the shop to check the EGR valve ( i read some posts about that) last time, but the mechanic said the engine is too smooth and powerful for that to be an issue (so he didn't check!). Unfortunately, I don't have the skills, space or tools to do it myself. The O2 sensor was changed a year ago. The mechanic wants to wait a few tanks before he tries that (so the exhaust can clear of soot). He thinks it might be the control unit, but is ruling out cheaper options first.