What Urban Gas Mileage For ML320
11-03-2004, 07:26 PM
#7
Super Member
Wouldn't a faulty MAF cause the mileage to go down, not up?
That's what my MB dealer told me, when I complained about my mileage having dropped to 12 mpg in city, and he detected a voltage on my Mass Air Flow Sensor on my ML320.
He told, me there was nothing that could be done to the MAF, except for replacing it....I removed the MAF from the, truck, did a quick DIY clean up on the sensor wire...and my mileage went up back to 15-16 mpg. Its been almost 10K miles, since I cleaned the MAF, and have had no problems yet.
Haven't heard of the mileage going up because of a faulty MAF...how could that happen?
He told, me there was nothing that could be done to the MAF, except for replacing it....I removed the MAF from the, truck, did a quick DIY clean up on the sensor wire...and my mileage went up back to 15-16 mpg. Its been almost 10K miles, since I cleaned the MAF, and have had no problems yet.
Haven't heard of the mileage going up because of a faulty MAF...how could that happen?
Last edited by mihir_d; 11-03-2004 at 07:29 PM.
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11-03-2004, 07:48 PM
#8
Typically the sensor fails and does not read enough airflow. It causes the engine to run lean, which would actually improve the mileage under certain circumstances. Its bad for the engine to run lean though....
11-03-2004, 09:00 PM
#9
Super Member
I was told, mine was running overly rich....
That caused the drop in mileage..
The in-spec voltage on the MAF is said to be 0.79 V...mine was showing close to 1 V.
I was given the explanation, that as carbon/dirt builds up over the MAF sensor wire, it causes the sensor to read less oxygen, than what actually is in the air being taken in.
The ECU compensates for this apparent lack of oxygen by pumping more fuel in to ensure a proper ignition..that causes the extra use of fuel, and thus, the drop in mileage...
I cleaned my MAF sensor wire by heavily spraying it (to the point of soaking) with some electrical terminal cleaner...left it soaked until all the cleaner evoparated (about an hour)
Plugged the MAF back in, and the mileage gradually climed up to the normal 15-17 mpg.
The in-spec voltage on the MAF is said to be 0.79 V...mine was showing close to 1 V.
I was given the explanation, that as carbon/dirt builds up over the MAF sensor wire, it causes the sensor to read less oxygen, than what actually is in the air being taken in.
The ECU compensates for this apparent lack of oxygen by pumping more fuel in to ensure a proper ignition..that causes the extra use of fuel, and thus, the drop in mileage...
I cleaned my MAF sensor wire by heavily spraying it (to the point of soaking) with some electrical terminal cleaner...left it soaked until all the cleaner evoparated (about an hour)
Plugged the MAF back in, and the mileage gradually climed up to the normal 15-17 mpg.
11-03-2004, 09:23 PM
#10
The mass air flow sensor doesn't read oxygen content... It computes the amount of air entering the engine, and the computer adds a proportional amount of fuel.
14.7 parts air to 1 part fuel. Less air quantity = less fuel quantity. More air quantity = more fuel quantity. Usually when a mass air flow sensor quits working properly, the sensor reads less air entering the engine than is actually entering the engine. This causes a lack of power due to the fuel quantity being provided is less than sufficient. Above 4000 RPM we often encounter misfires due to the lean condition present. Hesitation, rough idling and late shifting are also symptoms.
14.7 parts air to 1 part fuel. Less air quantity = less fuel quantity. More air quantity = more fuel quantity. Usually when a mass air flow sensor quits working properly, the sensor reads less air entering the engine than is actually entering the engine. This causes a lack of power due to the fuel quantity being provided is less than sufficient. Above 4000 RPM we often encounter misfires due to the lean condition present. Hesitation, rough idling and late shifting are also symptoms.
11-04-2004, 03:10 AM
#11
Super Member
I'll take your word on that...
although, I could do a more indepth research on MAFs and how they function, but since you are a pro, I'll take your word...
Wonder then, if what explanation I got from my dealer was just a make up story....the diagnosis really sounded a bit fishy to me..
Here's what happened...at about 65K miles on my truck, I started to hear the exhaust getting a bit coarse...it just worsened by each passing day, until one fine day, the ML almost sounded like a steam engine...I immediately took it in to the dealership...
Diagnosis - Cracked Catalytic Converter.
Covered under the emissions warranty, both CATS were replaced No Charge...as soon as new CATS were installed, in the first 10 miles of my driving,, the mileage dropped to 12 mpg...I took it back to the dealership...
They looked at it again, and said, that the leaky CAT was compensating for a bad MAF...now that the leakage is gone from the exhaust...the bad MAF effect is showing up on the mileage..wonder how much of that is true...
Wonder then, if what explanation I got from my dealer was just a make up story....the diagnosis really sounded a bit fishy to me..
Here's what happened...at about 65K miles on my truck, I started to hear the exhaust getting a bit coarse...it just worsened by each passing day, until one fine day, the ML almost sounded like a steam engine...I immediately took it in to the dealership...
Diagnosis - Cracked Catalytic Converter.
Covered under the emissions warranty, both CATS were replaced No Charge...as soon as new CATS were installed, in the first 10 miles of my driving,, the mileage dropped to 12 mpg...I took it back to the dealership...
They looked at it again, and said, that the leaky CAT was compensating for a bad MAF...now that the leakage is gone from the exhaust...the bad MAF effect is showing up on the mileage..wonder how much of that is true...
03-05-2008, 10:15 AM
#12
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ML320 1999 MY2000
How To Improve Mileage / Fuel consumption ML320
i just bought a 1999/MY2000 ML320 two months ago and was disappointed with the mileage in city/suburban driving.
i was getting 17 l/per 100 km or 13.5 mpg (400km/250 miles, a 70 liter tank)
now i get 14.3 l/per 100 km or 16.5 mpg (500km/310 miles a tank)
the 20% improvement has made a big difference and it is now closer to the original ML320 ideal specification of 13 l/per 100km or 18mpg.
after reading this forum, this is what i did:
1. clean the MAF
2. change oil
3. inflate tyres to max 44psi
4. use 98 premium fuel
i was getting 17 l/per 100 km or 13.5 mpg (400km/250 miles, a 70 liter tank)
now i get 14.3 l/per 100 km or 16.5 mpg (500km/310 miles a tank)
the 20% improvement has made a big difference and it is now closer to the original ML320 ideal specification of 13 l/per 100km or 18mpg.
after reading this forum, this is what i did:
1. clean the MAF
2. change oil
3. inflate tyres to max 44psi
4. use 98 premium fuel
03-05-2008, 10:43 AM
#13
MBWorld Fanatic!
Cleaning the MAF - ok
Changing the oil - good
Inflating the tires to 44 psi - This will result in rough/harsh ride.
98 Octane rating Fuel - Is it available normally at regular gasoline (petrol) stations?
Changing the oil - good
Inflating the tires to 44 psi - This will result in rough/harsh ride.
98 Octane rating Fuel - Is it available normally at regular gasoline (petrol) stations?
Last edited by pcy; 03-05-2008 at 10:49 AM.
