albertsoo

Guys, I just bought a second hand S350 2003.
all interior and chassis looks clean.

But after driving for a tank, it yield 20lt/100km.
I thought this can't be right, then drove another tank, and its around this mark.

I had change the MAF thinking this might be the cause, but no improvement.

I don't have another S350 to compare to regarding torque and power. I had a S320 before, and I do feel this is probably a little under performing. but that S320 was driving a few year ago.

Anyone know what I should be doing? my mechanic is saying this is normal for this car at this age. Which doesn't sound right. seeing people with 11-
13lt/100km.

I am drinking up a full tank in 400 km.

albertsoo

for the Gallon's and miles terms that is
14.7 MPG

cybertronicify

Wow that is pretty bad. My 4.3L v8 gets 29-34 mpg highway 15-22 mpg local. Very impressive for a V8 of that size. (The S350 gets about the same because of the weight of the s class)

For bad fuel consumption I usually start with the fuel you are putting in. These cars require that you put in 91 octane, or the performance will suffer and in turn you get a lower mpg. 14.7 mpg is acceptable if you are driving in bumper to bumper traffic all day and semi lead footed. Is there any lights? Check engine? Can you find any codes on the computer?

albertsoo

Thanks Jason for replying.
No engine light, No codes from STAR.

I am light footed, its semi highway traffic at around (60 mph), semi urban (25mph). But its Hong Kong. so I am averaging around say 30mph on the overall. Still don't think it is a reason for 14.7 mpg.

I am sure something is wrong. but the mechanic says all things checkes out to be normal on STAR. its pissing me off.

cybertronicify

When checking STAR you can request to have the STAR report printed out. The important items should check out as normal. What type of gas does Hong Kong offer? Are you putting in 91 octane USA equivalent?

One test you can try to see if your getting the power you are supposed to get is to take it out to a open road and floor the car, please mind the speed limits, see if the car struggles to speed up, or if you experience unusual power output from the engine. It should pull you to the back of your seat. Your car is 4000 LBs, so a 240 HP v6 might feel a bit slow. If the engine hesitates, then gives gas you may have a bad Throttle Pedal or the new MAF was defective. Both those items should throw a code, but I have seen cars that doesn't.

If they are all normal, then you might have a part or parts that are performing not to spec but in tolerance. Start with the easy stuff and check like the engine air filters, see if they are completely covered with dust and debris. You stated earlier that you changed out the MAF of you had to have taken out the airbox, did you disassemble it?

Next would be to check the spark plugs, if they are worn down or coated in carbon, it can make your car ignite the air/fuel mixture inefficiently. The car is a v6 in a v8 engine compartment, so taking those spark plugs out should be a easy job. You have a aluminum head so be careful of the tightening torque when screwing the plugs back in.

See if any of those are the problem.

91 AKI USA OCTANE should be 95 RON

albertsoo

I had a mechanic look at it, he suggested changing out the MAF. He has a presumption that this is the mileage I should be getting, which is not what I am seeing on websites and Not what I am seeing in my s500 w221. Which does around 13lt/100km (31 mpg)

Going to floor it like u suggest. And see what happens. It's getting to me that it arnt performing.

Going to give it to him to double check again.

albertsoo

Yep it's 95 octane.

And I don't want to touch the hood, as I have zero ezperience in that department, don't want to get it into limp mode

cybertronicify

BTW 13 Liters/100km is actually 18.09 US MPG or 21.72 British MPG. Very confusing. But Merica.

Your mechanic is wrong that you are getting the correct MPG, 11.7 US MPG is far from the advertised mpg. I would suggest you go to a different mechanic, preferably a certified Mercedes one. If you have a s500 w221, you can compare the power between the two cars. It would be a very rough estimate but you should be getting half the power on the v6 as opposed to the v8.

Just curious, how did you measure the mpg? Did you do it at the pump? The correct way to measure it, is to drive until the reserve light comes on, then pump exactly "X" amount of gallons of fuel. Reset the total odometer. Drive until the reserve light comes on and calculate the miles you driven per "X" amounts of gallons you put in.

Oh and the MAF you use is very important, your mechanic might have put a chinese clone, which will even cause more trouble. Make sure you are using the genuine BOSCH MAF.

albertsoo

Jason,

Yep floored it as you suggested.
it did much better than I expected.
above 2000-2500 rpm, I did feel some G force.

I have taken it back to the mechanic, he gave me the palms up, saying there is nothing else to change. But he will give a ECU reset, a try, and see if this might improve the situation.

I am thinking of pumping in some seafoam to see if its carbon build up inside the engine, giving a good clean, see if that helps.

then will move on to putting in premium petrol from now on.

you are right 13lt/100km is around 22 MPG. hell! how do people get 30+ MPG. I can buy a new car with that kind of saving every year.

cybertronicify

Great to hear that the engine is running strong. On my S430 when you pass 3000 rpm, it feels like the turbos kicked in haha. (even though I don't have any) You can try a ECU reset and an Adaptive Transmission Reset:

- Turn the ignition key to the "on" position.
- Press the gas pedal to the Wide Open Throttle position (do not click the button at the end of the throttle) and hold it for 5 seconds.
- Now turn the key to the off position but don't remove the key.
- Release the throttle.
- Wait 2 minutes (must be 2 minutes)
- Start Car / Drive

As for seafoam, I wouldn't put seafoam in these cars filled with electronics.

https://mbworld.org/forums/s-class-w...p0410-cel.html

Premium gasoline is required when running these luxury cars, except when you can't get ahold of them, thats what the knock sensor is for. I think the reason why your getting a lower MPG is because the engine is struggling to bring the 4000 LBs luxobarge up to speed. With a V8, it has the torque to move the car struggling less. So thats why on the S500 and S600 models they have a cylinder deactivation option, which turns half the cylinders off when going at highway speeds. So pretty much, V6 good for more highway, V8 good for more stop and go.

albertsoo

=) They found the problem, its a dragging brake.
and some vacuum leaks, will be getting back the car tomorrow, will let you know on how it is.

did the Techron give you extra MPG? or it just gave you more HP?

Think I might use some of this to clear up any carbonization if there were any.

I hope I am getting those 27+ MPG that other people are getting.
will update you after driving it for the weekend.

btw, when you use the Techron, do you need to give it some Italian tuning?

tusabes

Yes drive it hard , high rpm

cybertronicify

Wow a dragging brake? Never thought of that.

The way I used the Techron was too concentrated, it actually generated less power and less MPG, but I only used it for cleaning purposes. I poured 3 20 oz bottles of it inside my 23.3 gallon tank. Then drove it HARD for 15 minutes on the highway. You want to get everything hot so you can use the pressure and heat to take the carbon off. Make sure the engine is warmed up correctly, drive it for 20 minutes before attempting the Italian Tune Up.

I did a small test and applied some marine grease right at the exhaust pipe to catch some carbon to prove that it was actually working. Which worked perfectly. You can see the white spot where the carbon "sanded" the exhaust pipe. (See Pictures)

After the full tank of gas was used I put in fresh premium gas, and it felt like more power. (Proven by a couple of friends)

As for 27+ MPG, you probably won't see it on the local streets. My S430 gets at best 26 MPG local.


How to do Italian Tune Up:

0) Put in Techron (Optional, but its Mercedes approved.)
1) Warm car by driving calmly for 20 minutes, that will ensure everything is warmed up, not just the temperature gauge.
2) Get on the highway and never let the revs drop below 4k. Keep oscillating between 4k-6k. Gas pedal should be on the floor 60% of the time. What I do is, speed up to speed limit as fast as I can, let the car slow to a reasonable speed then repeat. Do that for 15 minutes. Mind the speed limit.
3) Drive calmly and let the car cool down, 10 minutes is fine.
4) Oil change, although some people don't change their oil after. If your oil is at the end of its life, just change it.

albertsoo

Okay back again after doing a full tank with techron.
The car is definitely more snappy after the techron.

However the Milage problem was NOT SOLVED. a full fillup gets me 410km which is (250 miles). that is with 72 liters of gas. works out to be 17.56 lt/100km. Mpg still SUX.

What else can be wrong? I checked O2 sensors on OBD2, flucturates between .2-.8v. looks to be nornal.

MAF was changed

Vac leak is supposed to be fixed.

Brake drag was fixed.

Btw, I notice the long term fuel trim LTFT is constantly 20+. STFT is normal. +/- 3 approx.

Frustrating.

Albert

cybertronicify

Wow. Very frustrating indeed. What is the fuel flow at idle? It should be 0.30-0.45 US gallons per hour. And have you taken a look at the fuel injectors?

wallyp

The STFT should eventually become the LTFT (or vice-versa - they should be close to the same). Perhaps you need to check the STFT under all driving conditions, to see if there are situations where the STFT goes way out of spec.

cybertronicify

Just to clearify what Wallyp said. STFT means Short Term Fuel Trim. And LTFT means Long Term Fuel Trim.

wallyp

And perhaps additional clarification might be helpful for the readers who aren't as familiar with the way the control system works.

The ECU (Engine Control Unit) contains "fuel maps", which are very complex multi-dimensional tables that relate some of the operational factors to arrive at the times the injectors are held open for each cylinder firing. Some of these operational factors include engine speed, engine temp, air temp, throttle position, etc. As the engine runs (in closed-loop mode), the ECU reads the sensors giving each of these factors, and arrives at the calculated injection time, which of course would determine the amount of fuel injected, with a stoichiometric ratio being the goal. A stoichiometric ratio is one where the amount of fuel and air are balanced so as to exactly burn all of the fuel, and is about 14.7 to one for gasoline.

But - the key to the control system is that the ECU also constantly monitors (instantaneous readings at a high rate) the output of all of the oxygen sensors. It uses the O2 sensor outputs to trim (slightly adjust) the calculated injection time so as to bring the air/fuel ratio closer to 14.7/1, and thus keeps the burning in the area where the catalytic converters can finish cleaning up the exhaust. The trim for the last brief period is the Short Term Fuel Trim, and the loaded average over the long term is the Long Term Fuel Trim.

These numbers can tell you when something is causing the ECU to have to adjust the amount of fuel injected to be different from that calculated by the engineers. This might be a vacuum leak, a failed plug wire, etc., etc.

The system works well enough in our cars that the 2003 S430 was rated as an ultra-low emitter of exhaust pollution. Other model and years will differ - some better, some worse.

albertsoo

Guys,

went to a different mechanic, He said all is normal. and that the 3.7 drink petrol like this. that is 400 km/ a fill of 72 liters. I SO disagree with this.

but I had 2 guys telling me the same ****.

Question:
1) Was wondering if the tires matters that much? I have 235's on them. instead of the factory speced 225's?

2) Another question is, I had a new MAF installed, but I was remembering that with the old MAF, when I first bought the 2nd hand car, it was doing slightly better on the fuel efficiency, maybe 10% or so.

How do I check if I have a NEW, but bad MAF?

Would the mechanic fail to install it properly? I searched online, and some say the O ring on the MAF might be bad, would the guys here miss that?

I have no engine trouble codes, on the OBD2. I am guessing the mechanics here thinks I am nuts, as they don't see no codes, so assumes all is well.

This really craps out my day knowing that something is wrong, can't fix it myself, and the mechanics thinks they can do nothing about it.

cybertronicify

Tires would matter a lot with the mpg displayed, since it changes your moving speed. Which in turn will throw your mileage off. Your tires could well be the problem.

albertsoo

Ok guys,

Changed new spark plugs, and also the Charcoal Canister.
Immediately after the change, the first trip looks to be better on the numbers.

I will update after I have gone through a whole tank.

As to why the charcoal canister will make any difference, I do not know, but the mechanic swears that he has fixed many cars low MPG by replacing the Charcoal canister. So we will see.

KenMiyake

Hi Albert, what is the status after the new change? Has it been improved? How much did you pay for the Charcoal Canister?

Albysoo

Ken,

Unfortunately no. I think the immediate better MPG came because he pump up the tires. The charcoal canister was like 1200 Hk with labor. So around 180 used.

Meanwhile I tried adding in techron to see if it's something I can fix with an OTC product. No change on LTFT.

Last time I check my LTFT went from 18.8+ to 24.1+. I am going to have my Fue injectors ultrasonics clean. If this doesn't fix it.

Might need to de carb my engine. If these don't work, the last thing to change is the O2 sensor. After that I think I will give up. Actually I might give up after the ultrasonic clean. that will set me back 200 bucks.

Albert

mcguirja

I'm surprised this isn't setting off a CEL, it is an odd scenario. I know it isn't really comparable, but I have a GLK350 that is awful on gas. I had expected it to be better than my S Class, but not even close. It is more in line with what I get in my SL63!

KenMiyake

Thanks Albert for getting back to me. Please let me know the status as I am in the same situation and is drinking like hell.