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  #1  
Old 06-29-2003, 11:54 AM
azhari
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Unhappy 1991 190e 1.8 - Bad mileage after switching back to Economy from Sport mode...

I normally get around 420km per tank before the low fuel light comes on.

Last week, I drove in Sport mode for a whole tank load and got to only 370km before the fuel indicator came on.

I switched back to Economy and filled up.But the next tank load only got me 360km.The next tank load was even worse - 250km and the fuel indicator came on.

Today, at half a tank, I have only driven 130km!

What is going on?

The only symptom I can see is that the car now seems to have more acceleration from stop.

It would seem that it is stuck in Sport mode, but counting the gear changes shows that it is still starting from 2nd gear.

Help!!!
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  #2  
Old 06-29-2003, 12:03 PM
azhari
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Oh yeah, to narrow the field :

1 Filled up with injector cleaner.

2 No fuel smell.

3 No puddles.

4 Smooth startup.

5 Idles smoothly.

Anyone?
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  #3  
Old 06-29-2003, 01:24 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Dragging brake?

Low tire?

Bad O2 sensor?

It sounds as if you have a rich running condition or transmission slip, dragging brake, etc. Could be a number of things, but I'd check the tailpipe first -- if it's black and sooty, your running rich and need to check the fuel system.

Rich running could be lots of things -- leaking cold start valve, leaking injectors, bad O2 sensor, bad ignition wires or plugs, etc.

Does it still run and idle properly, or is it rougher/slower than normal?

Just changing to Sport mode and back shouldn't increase the fuel consumption THAT much!

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #4  
Old 06-29-2003, 04:23 PM
Benz300
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azhari,
i know this is a trivial suggestion, but when you switch from economy to sport mode, other than the lever selection, does any light come on in the cluster panel, like it does in the japanese cars ? or is the switch the only thing to go by ? could it be the case that the switch has stopped working and even though you've put it back on the economy position, it is still in the sport mode ? I'm asking because you mentioned that now the car still has more acceleration from stop now. i'm assuming it wasnt like this when you were running in econo mode ?
just a suggestion...
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  #5  
Old 06-29-2003, 10:51 PM
azhari
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Thanks for the quick replies guys.

Peter - brakes do not drag and tires are inflated to spec (29psi Front/32psi Rear).

I know that the consumption in Sport mode should not be much different coz last month I drove the car one tank load in Sport mode and I got about 390km before the fuel warning light came on.

Plugs/wires changed 3 months ago which solved a misfiring issue.

I will check the exhaust now for black and sooty stuff...does a bad O2 sensor cause the car to run rich?

Benz300 - the E/S switch in my car is all there is to go by.There are no indications.

However, the car is still starting in 2nd gear coz I counted the gear changes.I have driven the car in Sport mode a couple of times before and I know the difference.1st gear on this car is short and it will accelerate quick and swiftly change to 2nd gear.Now it looks like there's more power coming from the 2nd gear start.

I wonder if a richer mixture causes this?

Keep it coming guys!
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  #6  
Old 06-29-2003, 11:41 PM
azhari
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Stuck my fingers up the tailpipe of my car and probed!

Took my fingers out and they are black and sooty.

Also, the is a rim (1/2 inch thick) of block soot on the exterior of the tailpipe end (wierd).

Is this an indication of running rich?

I read somewhere that to test the O2 sensor, one could disconnect it and see if there is any change to the engine running.

If there is no change with the O2 sensor disconnected, the sensor is fried.

Is this test valid?

Also, is there a convenient way to disconnect the O2 sensor from the engine bay or cabin?
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  #7  
Old 06-29-2003, 11:44 PM
azhari
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Stuck my fingers up the tailpipe of my car and probed!

Took my fingers out and they are black and sooty.

Also, the is a rim (1/2 inch thick) of block soot on the exterior of the tailpipe end (wierd).

Is this an indication of running rich?

I read somewhere that to test the O2 sensor, one could disconnect it and see if there is any change to the engine running.

If there is no change with the O2 sensor disconnected, the sensor is fried.

Is this test valid?

Also, is there a convenient way to disconnect the O2 sensor from the engine bay or cabin?

In any case, the switching from Sport mode to Economy is probably coincidental. I don't think that was the cause of the problem.If the car was stuck in S mode, it would start from 1st gear - but it doesn't; it starts from 2nd gear but now there is more power.So I believe the car is running rich.

Also, at idle, I can hear a mild fluctuation of the engine but I think it is very slight that I don't see the fluctuation on the tach.

Help!
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  #8  
Old 06-29-2003, 11:51 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
You are certainly running very rich -- you should smell sulfury smells, too.

The connection for the O2 sensor is just in front of the front seat, passenger side, under the carpet, I think (this is the location in the 300TE). Three wires, two together and one separate, unplug the two.

There are other tests, but I'm not sure on the 91 as it has LH Jetronic injection, I think.

I suspect the rich running problem has nothing to do with switching between sport and normal mode.

I would suspect the O2 sensor, though. You may not get a check engine light until it is completely non-functional.

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #9  
Old 06-30-2003, 11:46 PM
azhari
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Peter

Is it below the carpet (perpendicular to the floor) or at the 45 deg slanted area in the footwell?

I remember seeing a wired connector under the plastic cover at the slanted area when I was wiring up my new power amp.

I also remember seeing a plastic cover (just below the front of the passenger seat) with some cables running beneath it but this looks more like a cable tray.I'm not sure coz I did not remove the plastic cover.

Could you help confirm?

Last night, the low fuel indicator came on at 268km (yikes)

Thanks in advance, everyone.
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  #10  
Old 07-01-2003, 12:08 AM
MikeTangas's Avatar
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Join Date: Apr 2000
Location: So. Cal
Posts: 4,430
The connection should be under the false wall in the passenger side footwell (good info for a 126, not sure on the 201). The sensor leads will pass through the tranny hump about 10 inches or so back from the front of the footwell. The dramatic drop in mileage is an indicator the O2 sensor has taken a vacation somewhere to the south.

Not sure if your sensor is a 2 lead, 3 lead or 4 lead unit. Those with more than 2 are heated units.
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  #11  
Old 07-01-2003, 01:29 AM
azhari
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Thanks for the tip, Mike.

I'll be checking it in a while.
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