PeachParts Mercedes-Benz Forum - '94 E320 124.032 high fuel consumption question

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Quote:

Originally Posted by birkhoff (Post 3970206)

I got it by a search on this forum! Admittedly a wide range of reports ranging from low teens like mine (obviously something wrong) to nearly 30 if I recall (that one probably user error). The official EPA numbers are around 22 combined. But I take your point. Kicking around 3500 lbs of iron, rubber and glass has got to cost something . . .

22 combined means it's gonna do 17-18 city, 24-26 highway. The diesels don't even do 25mpg in town.

As an example, my '94 BMW 530i Touring claims 16-18mpg city, 23-25mpg highway, 20mpg combined. I've been lucky that I've been averaging around 20mpg city (where I drive most) in it. Keep in mind this car has a 5 speed transmission (yours is 4) with overdrive (yours has 1:1 final ratio) with an electronically controlled lockup torque converter (yours has no lockup). If you do 20mpg in town, you're doing well. 17-18mpg is more in the expected area. If you run E10 gasoline (most gas these days is E10) you can deduct 5-10% off your expected economy due to the lower power density of the fuel.

Quote:

Originally Posted by Diseasel300 (Post 3970225)

I hear you. There may not be much more efficiency to eek out of this beast. FWIW, we are running 94 octane pump gas here with no ethanol whatsoever. Looking at CAN $6.84 per US gallon or about US $5.20 per US gallon so every little bit helps (hurts?)

Quote:

Originally Posted by birkhoff (Post 3959724)

Good point. I just realized that there are two senders on this car, one for the dash gauge (which appears to be working) and another one for the ECU. Perhaps that one is not working! That would give the 'open loop' diagnosis some merit.

Probably it is easier to just replace it rather than try to diagnose.

If I had access to socket 3 codes it might show up. Nothing showing yet on Socket 8 (where code 2 is temp sensor).

Thanks for the suggestion.

How many coolant sensors are on this car? I assumed the Pelican walkthrough correctly identified the 2-prong sensor as the ECU feed. But then, the more I think about it, since it tests as a switch, not a variable resistor, I'm increasingly doubtful. Maybe this is the radiator fan control? If so, where is the engine management sensor?? There's a lot of information on the web, but all over the place given the different versions of M104 over the years. This is a 93 E320, california version (with the DM under dash) and HFI ignition.

Is there a third sensor?

birkhoff, check that the front wheel bearings are greased and adjusted properly. Also, inflate tires to 32-34 psi.

Jan 2020 update.

Got access to the car again over holidays. It had popped a CEL a couple of weeks earlier that was still on when I started the following:

1. found a loose vacuum connection on intake m'fold. corrected.
2. Swapped in new diagnostic module under driver-side dash. On-board blink button now works, as does query through socket 3. So the old module must have been internally shorted.
3. Swapped in new MAF sensor.
4. Checked for tight brake caliber/ wheel bearings. All normal.

If I'd had time I'd have done this sequentially to get more information but I only had a couple of hours with the car. I still don't know where the second coolant sensor is, or if there is one, feeding ECU.

Result: CEL is gone and not returned. Socket 3 shows no codes recorded. Recent mileage check is 18 miles per US gallon or 13.07 litres per 100km. I'm happy with this.