High Gas Consumption

[ako]

Hi All,

Since Nov. 2002, I've had this problem:

1. Higher gas consumption---from previous 21--23mpg to 18 mpg

2. Engine a little rough ONLY on cold startup--a little rough for about 1 second, then it becomes smooth. On some cold startups, it isn't rough.

Other than that, my 300 TE runs fine. Lots of power on acceleration. No engine hesitation. But sometimes can sense an occasional SLIGHT engine miss at idle.

--Spark plugs are new--Bosch copper H9DC (.032 gap)
--Air filter is new
--Changed one of the vacuum lines w/c I broke from the top of the engine which is connected to the breather hose
--Cleaned and filed distributor cap and rotor with sandpaper
--This week, I put two bottles of techron injector cleaner but to no avail.
--Have always used branded premium fuel, either Chevron or 76

Tire pressure is right. And I drive sensibly.

I've had the car since 75K miles and to my knowledge, it still has the original fuel injectors. I'm thinking the injectors are the culprit.
I also haven't changed the fuel filter since I got the car but I don't think the fuel filter is the problem since the car has smooth acceleration and the car is Starmarked.

Hope the pros can help. Thanks, RV
---------------------------------------------
92 300 TE (103 engine) 115K miles

[timreid]

ako, It probably or may be the O2 sensors, do a search on 02 sensors.

"Cleaned and filed distributor cap and rotor with sandpaper"
If the parts were heavily corroded or worn, I would haved replaced them.

enjoy your drive, timreid

[ako]

Hi Tim,

I've read from this forum that if the 02 sensor is the problem, then
I will have one of the dashboard lights like check engine (CE) light light up. But I've never had that problem. And I know the lightbulbs are working since when I turn the ignition key to start the engine, all of the dashboard lights up. I also read that the 02 sensor only kicks in once the engine has warmed up.

As I mentioned in my post, my car has a little rough coldstart for one second, then the engine becomes smooth.

But I've also never changed the 02 sensor since I got the car at 75K miles. It now has 115K miles. Could it be defective and but the CE light doesn't light up.

RV

Ako,

Did the drop in milage coincide with the plug change?

You mention the spark plugs are new.
This required removing the plug wire connectors. Perhaps this is a plug wire resistor problem.

There are posts here on the forum which indicate the resistors by themselves can be changed.
I have not tried this yet, as until recently I thought the plug wires were ready for social security at around 130k mi.

You might also do a search on plugs, I seem to recall a suggestion that the plugs be gapped a little wider than spec, say to .035.


Good luck!

[timreid]

Ako, from what I've learned (manny), the O2 sensors slowly goes bad, and the light may not come on until it does not function, I just had a bad O2, with no light. Sounds like your handy, there are several good post that informs you how to check the O2 sensor, but with 115,000 miles it may be time to change. Good Luck, timreid

[95E320cab]

There was a good post in the last couple of months about 02 sensors going bad gradually, not like a lightbulb that works or doesn't.

I'm big on resistor ends, but the idle at warm temp would be rough. Cold startup and idle would appear fine. Look for that thread about the 02 sensor. I recall, Larrybible, Stevebfl, Suginami and other reputable posters.

[ako]

Thanks for all your suggestions.

1. How do you test whether the resistor ends or the 02 sensor is malfunctioning? I do have the Sears multimeter that's famous in this forum but don't know where to set it.

2. And if the resistor ends are the problem, how do I change them? Do they screw on or are they plugged in?

3. Can one just change one resistor tip (in case only one is not working) or do all six have to be changed?

Thanks again.

RV

For the O2 question, the quick n dirty method is connect your meter on 'duty cycle' setting and see if it reads 50% steadily. This indicates a faulty O2 sensor. For more in-depth testing which might assist you in identifying a marginal O2 sensor or other problems, see this post:

My LAST ovp/eha question, I promise!!!!

For testing plug wire resistors, see this post:

Ignition wires 300E

Resistance for all will be either 1k 2k or 5k ohm If you can get the resistor out of the connector. If not, you may need a new set.

Next test, wait till after dark. Start the engine, raise the hood and look into the spart plug holes. Do you see any blue sparks?
This will indicate flawed insulation on the plug wires.

[ako]

ZHANDAX,

the high gas consumption DIDN'T start after I changed the spark plugs. The only reason why I changed the plugs was bec. they are over 35K miles....Tried to unscrew the resistor tips as you suggested, but unsuccessful. So what I did was to remove each plug wire with the resistor tip one at a time, started the engine and see if the engine ran rough. At all six cylinders, the engine ran a little rougher when the wire for that cylinder was removed. But the engine ran better when the wires were in the s. plugs. This suggests that the wire and resistor tips are ok, right? Also, there are no spark leaks when I tested them by starting when it was dark. The cap and rotor (with slight pitting) still looked good. I did change the rotor but was unsuccessful in changing the cap bec. it was stuck to the black plastic cover.

While the engine was running, I also removed the top part of the air filter and lightly depressed the airflow plate. The engine immediately stalled. Does this suggest a rich mixture?

TIMREID,

Anyways, I'm starting to believe that TIMREID is right about the 02 sensor going bad. But I also think that my problem is partly ignition related or I have a vacuum leak since I can hear the engine sound change while idling on Park. There is also this strange noise coming from the area of the power steering fluid reservoir but not the p.s. reservoir.

Will you tell me where the 02 sensor is located? I've been looking at the 02 threads but to no avail.

Thanks,
RV
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92 300 TE 115K miles

Ako,

The connector for the O2 sensor is under the carpet in front of the passenger seat.
The cable goes thru the floor, and the sensor screws into the exhaust. You can test at the connector, to change the sensor requires access from underneath the car.

The last post on this thread
O2 sensor failure and lambda testing
gives some good directions for testing the O2 sensor with an ordinary Walmart $10 multimeter.

Unless you alredy have a multimeter, I suggest the $35 Sears version with the duty-cycle function, so you can perform further testing if your O2 sensor tests ok. For example, you will need this type meter to check for rich/lean. Just depressing the airflow plate will not move the throttle plate so you are telling the ECU there is a lot more air entering the engine, but no air can get in.

The BMW distributor caps I have bought come with a new black plastic cover. I guess you have to ask to get them for a Benz.

Ako,

Please accept my apologies. I was trying to get you some info you could work with while the sun was still up.
After re-reading the entire thread, I see you already have the Sears meter.
To set it up, look for the X11 diagnostic connector pictured below (red arrow).
It is located on your driver's fender well.
Unscrew the cap. The pins are numbered from left to right. Put the (-) test lead into pin 2, and the (+) test lead into pin 3.
Remove the air cleaner. Set the meter to 'duty cycle' and turn it on.
Switch on the ignition, but do not start the engine. (key on engine off)
If you see 85% on the meter, you have the California controller. If you see 70%, you have the federal version.

If you have the Calif controller, you really need help from someone who has worked on California systems.
However, my understanding is there is yet another connector called X11/4 located on the passenger side, between the firewalls, around the battery. (diagram below) There should be a button (#2 in diagram) and LED (#4 in diagram) on this connector. Have a paper and pencil in hand. Press the button once for 2-4 seconds. If the LED flashes once, this indicates there are no codes stored.
If it flashes more than once, write down the sequence of flashes you see.
When you get a solid green LED, press the button again for 2-4 seconds. If there is another code, write it down, and then press the button for another 2-3 seconds.
At the point where the LED stays green after pressing the button for 2-4 seconds, control is passed to duty-cycle output.

I am not certain these last two tests work on California cars.
Depress the airflow sensor plate. The duty cycle shown on the meter should decline to 10%. Release.
Next move the throttle linkage to wide-open throttle. Meter should read 20%.

Let us know how things progress to this point. Particularly whether the car is Calif or federal.

[ako]

Zhandax,

No need for apologies. I really appreciate your help. My 300 TE is definitely a California car since it's been in California all its life.

Question for everyone:

Can someone confirm if the tests for o2 sensor that Zhandax was telling me will work for California 300 TE???

I have the famous Sears multimeter w/duty cycle but don't know where to set it or use it.

RV
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1992 300 TE (103 engine) 116K miles