Poor mpg and possible auto gearbox problems

[LvR]

[FONT=&quot]I don’t profess to know all the different scanners on the market but ...............

O2 B1S1 and [/FONT][FONT=&quot]EQ RAT B1S1 1.999 imo refers to the Bank1 fuel trim values derived from the upstream O2 sensor.

There should be similar values for bank 2 IOW O2 B2S1 and [/FONT][FONT=&quot]EQ RAT B2S2

To me it looks like possibly percentages are getting reported for those? ..............
............ if so that motor's mixture control for bank 1 seems fine imo (based on the small and close to 0 values reported).

Lets hope you can get to the same values for bank 2 ........................ and if bank 2 is similar then the motor as a whole is under fairly good mixture control and the ECU seems to be doing its thing.

If you can get close to the same values (of those parameters) for both banks under a range of different driving conditions the engine mixture management imo is fine

You will have to study the particular scanner's documentation to make sense of the rest of these parameters .

My guess:
DTC 0 - no faults logged.
IAT is inlet air temperature - 38C seems high unless the vehicle is standing idling.
MAP is manifold absolute pressure - 100kpa seems reasonable
ETC 88 is engine coolant temp ....... seems normal depending on what you have been doing and thermostat seems to be ok
[/FONT]

 

[E280Tim]

Thanks LvR

There don't seem to be any values relating to bank 2 which seems strange maybe as you the instructions for the reader will shed some light on this (if I can find them).. maybe Google will help..

Would you expect the EQ RAT to fluctuate when the engine is revved? It doesn't.

IAT was at standing idle so probably ok.

Thanks for taking the time to discuss.

Cheers

Tim

 

[fabes]

Tim, where are you in the UK?

It might help if one of the 'recommended' indies on here could plug it into STAR instead of using a generic code reader.....

 

[E280Tim]

Hi Fabes,

I live in Hertfordshire, my local Merc indie is AA Merctec in Hoddeston I'll try to get it booked in with them.

Cheers

 

[Philip1972]

I have the same car as you and get the same MPG. To be fair, I think 35-36 is pretty good for the size of car.

I have done 20k in mine and its not changed, and its done regular 200 miles trip to France and back at 85 ish, again 35-36.

 

[LvR]

Tim, where are you in the UK?

It might help if one of the 'recommended' indies on here could plug it into STAR instead of using a generic code reader.....

I agree with that - Star is the only thing that knows exactly what the expected fuel trim values and waveforms off the air/fuel sensors are supposed to look like.

While a generic scanner may indeed be able to come close or even match a Star ito only reporting values, you don’t have the exact built-in knowledge of the ECU mixture compensation design to guide you during fault-finding.

A lot can be said and typed up about the theory of O2s and air/fuel sensors - way too much for here.

If you cannot get a Star on the motor , I only can suggest spending an hour with these videos to understand why we say get the Star - see parts 1 and 2 for very nice explanations on general interpretation of reported mixture parameters and the influences of various conditions on them. Also realise you don’t have a mechanical throttle on the diesel so some of the tests and conclusion suggested there will not be applicable to your motor

https://www.youtube.com/watch?v=XQYDwIWS6Ho

If other people are reporting the same economy figures for the same vehicles I am not sure how far down this air fuel interpretation road one need/has to go except for possible interest sake

 

[paul73mt]

Hi Fabes,

I live in Hertfordshire, my local Merc indie is AA Merctec in Hoddeston I'll try to get it booked in with them.

Cheers

Have used them before and there very good!!!

 

[KeithJG]

Had an error code for O2 sensor and had it replaced with the MB one and it made quite a bit of difference to performance.

My C320cdi is similar engine to the op`s E280cdi.

These models only have ONE O2 sensor.

 

[E280Tim]

Hi Keith,

The O2 code hasn't come back. So I'm unsure if there is a problem with the O2 sensor.

Out of interest what sort of mpg do you get at 70-75 on the motorway 35-36 seems really low to me although others seem happy.. I used to get 40+ from my old E39 530d estate and that was a 2002 I would have thought an 09 Merc should at least be able to match that.

 

[E280Tim]

Hi Paul

Thanks for the thumbs up for AA Merctec.

I have used them in the past and have always been happy with their work and prices.

 

[E280Tim]

Hi Philip,

When you say 35-36 on a trip back from France, was that the average for the trip? I reset mine every 100 miles or so out of a 450 mile trip while cruising at 75 on the motorway.

 

[E280Tim]

What does seem strange is, if I give the car a good spirited drive/thrashing then hit cruise at 75 and reset I get 43-44mpg (once it went to 47) this seems to last for 10-15 miles then it starts to drop steadily back down to 35-36...

 

[Philip1972]

Hi Philip,

When you say 35-36 on a trip back from France, was that the average for the trip? I reset mine every 100 miles or so out of a 450 mile trip while cruising at 75 on the motorway.

I usually reset when i leave home. The post should have said 2000 miles not 200. I dont hang around (at least 85 and if travelling at night, more like 95) and always race out of the tolls booths

There is also a 50 miles road up the mountains at the far end (pretty tough on MPG) and then the usual driving between resorts while I am in the Alps.

The very best I have seen was 43, but that was at 60 mph on the 30 miles trip down the M40 to work one morning, again, after a reset at home that morning.

 

[LvR]

What does seem strange is, if I give the car a good spirited drive/thrashing then hit cruise at 75 and reset I get 43-44mpg (once it went to 47) this seems to last for 10-15 miles then it starts to drop steadily back down to 35-36...

The more data-points like this you can list the easier it will be to figure what’s wrong if anything is indeed wrong - there is a range of parameter values that is deemed acceptable for use to control mixture/fuelling/timing under different driving conditions by the ECU.

IMO I would again refer to STAR while monitoring/logging real time data to see if you can pic up anything that shows a funky behaviour - if you thrash it and it rewards you, I would for a start be interested in investigating engine temperature, manifold pressure(turbo) and the O2 output/voltage graph in particular and then compare those with the "bad" consumption situation

 

[E280Tim]

Hi Philip,

Like the sound of the Alps drive.. Did it for the last couple of years in my old 530d last time this season just before I got rid of it. It managed 42mpg between Moutier and Calais and as you say quit a heavy right foot leaving the toll gates..

 

[E280Tim]

Hi LvR,

I'll get it booked in to get it checked out on STAR in a few weeks, just about to hit my busiest time of year so no chance of getting anything done till early June. I'll just have to live with it until then.

I'll update as soon as I have any more. I'm off round the M25 tomorrow so I'll leave the reader plugged in and get my wife to take some readings and see if anything interesting show up.

Once again thanks to everyone who has commented

 

[Guy.Pap]

I have a 2008 E280 estate and when on the motorway it will now average about 40mpg although that will quickly head south if I am playing about with my right foot. around town its about 32 which I am more than happy with.
I am almost positive that the E280 came with a different set of rear axle gears to that fitted to the 320 and 350 so that alone would account for the difference in fuel economy, but I could be wrong.
My car has been remapped and is an awful lot quicker than a std E280,320 and 350, but before it was mapped I too, suffered with very sooty tail pipes as the car was overfueling but now they stay fairly clean.

One thing I did do before the mapping was to carefully remove the two MAF sensors and cleaned them. This also helped the MPG slightly. I take it the air filters are clean and the ECU was reset afterwards..

 

[SL300-24]

Tim my 320 CDI has always done the same MPG that you are quoting

 

[Borris1954]

Personally I am not too convinced about how accurate the displayed mpg really is. I had an early W211 270 CDi (52 plate) in which I drove 106k miles. I always keep records of fuel I put in and the mileage at the time. After a few tankfulls and several thousand miles you can then calculate an accurate average mpg as discrepancies on exactly how full the tank is become insignificant. So this W211 averaged 44mpg over the time I had it. OK this was probably about 80% motorway to 20% around town. My feeling in this 3 years was that the computer was a bit over optimistic on long motorway drives and pessimistic around town.

My current 2006 S211 320CDi has done just over 8k in my ownership with about a 50:50 motorway to around town split and my average mpg is 34mpg if that helps. The computer figure also still looks pessimistic around town.

If you keep records and do some sums you may be surprised.

Sent from my Nexus 7 using Tapatalk

 

[KeithJG]

Hi Keith,

The O2 code hasn't come back. So I'm unsure if there is a problem with the O2 sensor.

Out of interest what sort of mpg do you get at 70-75 on the motorway 35-36 seems really low to me although others seem happy.. I used to get 40+ from my old E39 530d estate and that was a 2002 I would have thought an 09 Merc should at least be able to match that.

At the end of the day all engines are different just like the drivers are.

Mine is the C320cdi and i bought this model to use as i don`t dawdle anywhere but stick to lower limits.

But on Mways at 80+ constant i get 38mpg minimum but slowing to some 50mph roadworks puts me up to mixed Mway at around 45mpg.

I only put Shell Nitro diesel in plus two stroke oil every fill up.
It gets red lined at least three times per average journey.