Poor Gas Mileage on '93 400E
 

I have a '93 400E with about 60k mi. on the clock. It seems to run very well and is smooth and powerfull but I only am getting about 9 mpg in the city. I do tend to push the pedal to the floor quite often and I expect that my mileage definately should suffer but I'm consistantly getting the 9 mpg even when I try to take it easy for a tank. I've replaced the spark plugs and removed and cleaned the distributors and rotors when I first bought the car. That had a noticable effect on the power but didn't affect the mileage. I'm thinking of replacing the dist and rotors now.

Can anyone suggest what the problem could be?

Are there any other owners of 400E's who drive them aggressively in the city who are getting higher mpgs?

Thanks for any help.

Jerry

A bad O2 sensor would cause your mileage to tank like that.

Not sure what the problem is but you should certainly get a log better mileage. I have never gotten below 19 or 20 mpg in town. I don't floor it after every stop light but I'm not gentle on the accelerator either.

Have you pulled the codes?

I drive my 400E pretty aggressively, I often shift the transmission by myself and heat 80kmph in first gear.

We use winter gas in Canada, my gas mileage is now 12.5L/100km (18.8 mpg) for combined highway/city stop and go traffic. If I take it for a long highway ride, and keep the speed at 120-140 kmph, I normally get below 10L/100km (23.5 mpg). It does better than this in summer.

9 mpg is definitely unacceptable unless you drive on a race track and keep your engine rpm above 4000 all the time. Like other has suggested, O2 Sensor should be checked, I would guess somebody can see black smoke from your tail pipe with that gas mileage.

I have not checked the codes yet. I will have to research how to do this so I can avoid the dealer. I do remember seeing some slight black smoke on the accelerator ramp and night. Will the codes tell me if the O2 sensor is bad?

Jerry

Yes.

I know dirty fuel injectors can severely affect mpgs.

They may need cleaning, but MB says DO NOT use injector cleaners of any kind! :confused:

The only thing that can catastrophically cause your gas mileage to drop from about 20 mpg to about 8 mpg is your O2 sensor.

This is the characteristic symptom of a bad O2 sensor.

Just got back from my mechanic who hooked up his computer to my car. There were no fault codes and he assures me that everything was running within specs. I watched the O2 sensor millivolts vary from about 80mv to 800mv. He said that was normal and that meant it was doing its job.

His explaination for my 9mpg was that I may have had the A/C on or that I was just driving it hard. The truth is that I do like to speed away from a standstill and I do accelerate quite often. I guess I'll have to take it easy for a while and see how that affects the mileage. I'm a little dissappointed since I was expecting to get at least 16 mpg with my driving style in city driving.

Anyway, thanks to all for the help.

Jerry

I don't know if it aplies to your vehicle but I have a '91 300E that black smoke would come out of the exhaust when accelerating hard and was getting really poor mpg. Fuel distributor was bad replaced it and now the car runs great.