My car is getting about 14 mpg. Cruising on the interstate at 62mph it gets a little less I think.

Here is what I have done:

Rebuilt the head
New valves, and refinished seats
New guides/ seals
Head was perfectly flat
Intake and exhaust gaskets
Chain guides for timing chain, front seal
Custom cam grind, very mild- probably less than a "euro" cam
Plugs, wires, cap and rotor

Had the EHA and fuel mix reset

About 6 months ago I was getting 22mpg average, no matter how I drove.
The economy dropped off, and oil consumption increased, so I decided to rebuild the head. Pulled it myself, and had a pro do the machine work.

Now, after close to $1000 of parts and several weeks of my free time I cannot figure out why it uses more fuel than an overloaded Freightliner.

There are two things that possibly could help. Injectors and a new O2 sensor. Will these two things, in combination, or alone, cause such a drop in fuel economy?

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The Wolf: That's thirty minutes away. I'll be there in ten.

Think of more obvious things...what about a fuel leak? Is it possible you're leaving a trail of fuel as you drive? Any signs of leak (smell or puddles)?

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

What can cause high fuel consumption? bad inj. would show more like pore power,if they are leaking you would get more of a start up when warm problem.Now the o2 sensor dose tell the system it might need more fuel,if it is bad it could send a signal for more fuel when it dose not need it, try that first,look through the posts to find one on a mustang o2 unit its cheaper.

Sounds like you mixture is rich and you need to adjust your on/off ratio. Lots of posts on how to do this with a dwell meter or DMM with a duty cycle. Maybe do this after you've replaces the O2 sensor as JNT suggests.

Other causes, less likely, are a sticking plunger in the fuel distributor, or a bad temp sensor, telling the computer to enrich because it thinks the engine is still warming up.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

What is your water temp like? Is it staying on the cold side of 80 degrees and has your heater output diminished? If so, the problem could possibly be your thermostat. If the thermostat is either opening early or not closing properly the water temp will remain low which tricks the engine to stay enriched causing poorer gas mileage. I was getting 17 miles before Christmas. In January I noticed that my water heat was barely making 60 degrees and my mileage was about 12-13 miles/gal. Switched in a new thermostat and I'm back up to 17 miles again. Another avenue to explore.

Thermostat is new, heat is hot.

Engine power is very lacking. I park on a painted concrete garage, I now if anything leaks... no gas leak to be found.

My tech friend says it could be my collant temp sensor, and definetly old injectors.

Saturday or Sunday I am reinstalling the r-16 resisitor, installing new injectors, and re-reseting the mix. Will update from there.

Too bad... I have been relying on my BMW to get me there now, it gets 28 mpg!

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The Wolf: That's thirty minutes away. I'll be there in ten.

where r u at? my car was getting 19.4MPG mostly city but last 2 months it dropped to 15MPG b/c of the bitter cold temp & also the winter mix gas. i can already tell the mileage is going up agian now

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Current cars:
2001 MB E55 AMG
2003 Honda S2000
2000 Honda CRV

Gone but not forgotten:
2004 BMW 325i 5sp sport
1999 BMW 540i sport
1997 MB E420
1995 BMW M3 coupe

Winter blend fuel will slightly reduce gas mileage but not by a whole lot.

My 260e had a problem with poor mileage and poor performance that I spent almost a year trying to diagnose. Finally, I noticed a gas smell under the hood and traced it to the EHC that was leaking slightly. Fear of an engine fire led to shell out the $$$ for a new EHC and it cured the poor mileage and hesitation problem.

I would have a properly equiped shop check the fuel pressure and chamber differential. Also check for a black tailpipe!

Other things that cause trouble are vaccum leaks, bad spark plugs (I assume you got new ones), bad plug wires (you may have the originals, after all), bad distributor, defective vacuum line to the computer on the left fender, leaking idle control valve hoses (you did get new ones, right?), leaking boot between throttle body and fuel distributor horn, plugged fuel filter (usually give rotten acceleration).

You can check the mixture with a duty cycle meter (remembering that US made ones usually measure "upsidedown" on a Benz). If you have trouble setting the mixture to get 50% duty cycle, look for vacuum leaks and a leaking electro-hydraulic actuator on the back side of the fuel distributor.

Also, you can leak lots of fuel on that car without leaving drips, it evaporates off the bottom panel instead of hitting the ground. I had the pressure line fail, you can replace it with high pressure (75 psi minimum pressure capable hose) and hose clamps, the actual line is expensive and has to be ordered from Germany because no one every uses it, they use fuel line,

If that's a sedan, you should be getting 25-27 mpg, not 14 -- my old 280 SE 4.5 gets 14, but it would spank that 300e!

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!

I was told to make sure the EHA was not leaking... I looked and everything is dry, really clean...

Terry, my tech friend, said the O2 was good... not to worry about that.

The next thing is the coolant temp sensor, as the car starts and idles rough every now and then when it is cold.

I am starting a "real" job so I will actually be able to afford to have my baby worked on, instead of trial and error.

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The Wolf: That's thirty minutes away. I'll be there in ten.

I started with the least expensive component...

The coolant temp sensor.

after driving to school last night and got 21 mpg average over 40 highway miles and 10 city. I would say that fixed it.

She did not start right up this morning, so I will have the mix readjusted... keeping my fingers crossed until I can afford new injectors, because I am sure they need replaced as well.

I would recomemend the four pin sensor as a maintenance item, as it is $25 or so. I had a BMW that did the same thing once as well...

Peace

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The Wolf: That's thirty minutes away. I'll be there in ten.

Pardon my ignorance, but where would Ilocate this on a 300E .. and is this something easily replaced.

Thanks

Hi AldeNYC,

it is the #3 on the picture

89 300CE Please help identify engine component

It is easy to replace.

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1996 E320 since 1/16/08, 171K miles as of Feb 2011

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1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE

No, the one for the fuel injection is further back than #3. It has four pins.

I just found out that my fuel pressure regulator is leaking - I am getting horrible mpg. Might want to check yours out....see if it is leaking fuel into your intake after shut-down. (give it a min.)

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D