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Lost HP and Bad Mileage.

12K views 285 replies 15 participants last post by  Real1shepherd 
#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.
 
#2 ·
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.
 
#6 ·
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.
 
#12 ·
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.


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#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.
 
#14 ·
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.
 
#22 ·
"Cleaning" MAFs is a myth, it does nothing.
I have to disagree with this, Ive brought MAF's back several times via cleaning.
 
#23 ·
I've *never* heard of the hot film module on a 3.2 HFM-SFI needing cleaning.

I *have* heard of several hot wire (LH) MAF's dying (commonly used on Volvos, but I gather M119 were also LH) *after* they were 'cleaned', due to the spray contaminating the electronics module.
 
#24 ·
Back to this crap again: I got a check engine light, the weather is a lot hotter.
My code reader is giving me codes DTC 13 on Pin#8 which means O2S system operating at rich limit, mixture too lean. Possible cause: Intake air leak, fuel injectors, diaphragm pressure regulator.
or O2S system operating at lean limit, mixture too rich. Possible Cause: Intake air leak, fuel injectors, diaphragm pressure regulator
and also the classic 14-7
Message from CC/ISC control module (N4/3) faulty N4/3
Reception from engine control module (N3/4) faulty

I JUST CHANGED my 02 sensor so if it's the problem idk
My car is running terribly in the heat making this loud fan noise when I accelerate
The temps are a little higher than usual, but not bad.
The car just feels like it needs help honestly.
 
#30 ·
I used this green hose no vacuum suction at all, I don't even know what it is. I don't understand this at all. Isn't there just one line that will tell me if I have an intake leak. Can someone just tell me EXACTLY what to do? I searched for this topic and I'm more confused than before. I want to see if I have an intake leak or whatever is causing the hissing noise, I think it's affecting my cars performance.
 
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