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1995 E320 Sedan
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450 Posts
Discussion Starter #1
My E320 1995 has went through a recent tune up and I have fixed a couple of CELs. I have changed the bio-junk upper wiring harness and throttle body. New air filter, spark plugs, spark wires and coils. New 02 sensor. Cleaned MAF sensor. Transmission fluid and filter change and that's about it. My car is getting ~220 miles on a full tank (city and highway).

It is definitely slower than it is supposed to be, but feels a lot better than before the tune up. It was getting 160 miles on a tank (city and highway) before the tune up.
I also don't drive that rough.

Anyone have any ideas that could improve mpg and performance like specific things that could be worn out at 98,000 miles.
Thank You.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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16,860 Posts
Most likely bad MAF meter. "Cleaning" MAFs is a myth, it does nothing.

Amazon has the best prices on brand new Bosch MAFs.

And are you running all Bosch ignition components, i.e. the F8DC4 plugs? That is the only proper plug for that engine.
 

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1995 E320 Sedan
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450 Posts
Discussion Starter #4
and iv'e done the unplug test and the engine goes crazy when I unplug the Maf while its running so is their anyway to diagnose the MAF, because it's like 200$
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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16,860 Posts
Have you checked the emissions values recently? High HCs are a good indicator of a MAF that has gone past its sell by date.
 

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1993 300CE Cabriolet (mine) ; 1994 E320 Wagon (wife's) ; 1990 Benz 300E 2.6 (son's)
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6,755 Posts
have you tested the O2 sensor? the connectors are under the passenger floor board... unplug the round connecter, wrap a thin strand of bare copper wire around the pin, and reconnect it with that wire hanging out. set a digital volt meter for a single digit DC Volt range (0-5V or whatever), and start the car, let it warm up a couple minutes til the idle drops ... measure the voltage from that strand of wire and a handy chassis ground... the voltage should swing from something like 0.1-.3V and something like 0.7-0.9V and back every couple seconds. the actual voltages aren't important, its that its swinging from the lower value to the higher value and back. it won't start doing this til the engine is warmed up and the fast idle warmup cycle has ended. if someone gently revs the motor, the cycle of low-high-low-high should speed up a bit.

if the cycle is slow, like 5-10 seconds per low-high, then your O2 sensor is mostly shot. if it stays low or stays high, then your engine isn't running in lambda balance and something is wrong, which *could* be lots of things, like the o2 sensor, the HFM MAF, air leaks in the intake air path, etc.
 

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1995 E320 Sedan
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450 Posts
Discussion Starter #7
Ok I just got a code 2: o2 sensor inoperative AS A CHECK ENGINE LIGHT so I'm pretty sure it's my oxygen sensor.
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,144 Posts
A lot easier on your diagnostic port to hook up #2 and #3 to an analog voltmeter and watch the needle swing. You can also check your duty cycle that way with the appropriate formula.

Kevin
 

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1995 E320 Sedan
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450 Posts
Discussion Starter #10
Ok now I replaced the 02 sensor and got an oil change and my car is like sputtering, hesitating, and shaking softly at idle. It is going below like 500 rpm and stalling when I'm at a stop. I also don't think the 02 sensor fixed the mileage.
 

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1993 300CE Cabriolet (mine) ; 1994 E320 Wagon (wife's) ; 1990 Benz 300E 2.6 (son's)
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6,755 Posts
The idle air control function on a HFM-SFI car is built into the throttle body. too slow of an idle suggests your ISC/CC (or EA/ISC/CC if yoru car has ASR) throttle body has the bad wiring disease and you need one made 1998+
 

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1995 E320 Sedan
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450 Posts
Discussion Starter #12
The idle air control function on a HFM-SFI car is built into the throttle body. too slow of an idle suggests your ISC/CC (or EA/ISC/CC if yoru car has ASR) throttle body has the bad wiring disease and you need one made 1998+


Your not wrong, I changed my throttle body with a rebuilt one a couple months ago. Turns out my engine coils gave out and they eventually were causing misfiring. I replaced them and now the car runs smooth like butter.


Sent from my iPhone using Tapatalk
 

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1995 E320 Sedan
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450 Posts
Discussion Starter #13
Back to this topic, my car's gas mileage is S*** I drive in city like 80% of the time and I'm getting like 150 miles on a FULL tank, I have replaced spark plugs, wires, MAF, throttle body, wiring harness, 02 sensor, and they are all genuine Bosch parts. I use 91 octane chevron gas. I don't accelerate hard anymore, I follow the speed limit everywhere. My car has just hit 100,000 miles and the idle is good. Sometimes when I roll my window down and accelerate at around 2,000-3,000 rpm there is a weird hissing noise, When I go slower than 2,000 ish rpm there isn't and when I go faster that 3,500ish there isn't. Idk if that's normal, but that could be an issue.
 

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1993 300CE Cabriolet (mine) ; 1994 E320 Wagon (wife's) ; 1990 Benz 300E 2.6 (son's)
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6,755 Posts
we get 15-18 around town in either of our E320's, maybe as bad as 13 if its lots of stop-n-go leadfooting. 24+ on the highway if you go exactly 65 steady on cruise control and don't hit any traffic for a whole tank.

do you have any HFM fault codes on the blinky-box ?

I've found our wagon, its very hard to fill the gas tank all the way, because the filler cap is lower than it is on a sedan.
 

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Premium Member
1993 300CE Cabriolet (mine) ; 1994 E320 Wagon (wife's) ; 1990 Benz 300E 2.6 (son's)
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6,755 Posts
when you replaced thee throttle body, did you use a new gasket? reusing that paper gasket is notorious for causing air leaks, messing up the mixture.
 

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1995 E320 Sedan
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450 Posts
Discussion Starter #20
A brand new gasket in a sealed package, screwed evenly. Cleaned both surfaces well, definitely not from there!
 
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