Very Bad Fuel Consumption

10802 Views 42 Replies 15 Participants Last post by jbanks15, Dec 27, 2017

Blueprintone

Discussion Starter · Dec 23, 2015

Hi everyone,
I am new here :smile:
I hope you can help. I bought a SLK 320 V6 - 2001 Face-lift 3 months ago, and I have recently noticed that I am getting REALLY BAD MPG, as bad as 8 mpg the last time I checked, and 12 mpg the tank before that.
I went about buying a DIY icarsoft Diagnostic tool because my OBD11 reader didn't show any faults, I figured a model specific Mercedes scanner would show a fault code, but No code came up. Though it does give me various live readings which would be useful, but as a novice, I haven't a clue what the readings are for, or what they should be!
So, with no fault codes I am asking for help here probably in relation to what certain readings should be at in order to find the problem causing such severe fuel consumption when it ought to be around 25 mpg around town, not 8 mpg.
As for the drive, and engine performance, It seems fine. There is a slight missing noticeable only on ide, but nothing to write home about. I drive very sensibly and haven't raced the car around. I just can't see what on earth could effect fuel economy so badly! especially without any dash lights on, or fault codes showing, with an engine that seems to perform well. I've resorted to looking for a big hole in the fuel tank! :grin: It is getting that ridiculous....lol.

Any live readings that would effect fuel consumption you can suggest I take a look at, and what the correct reading ought to be?

Or any other thoughts on what could effect fuel economy so severely?

Thanks in Advance! :smile:

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1 - 20 of 43 Posts

jbanks15

· #2 · Dec 23, 2015

http://www.slkworld.com/general-dis...ock-sluggishness-hesitation-top-tier-gas.html

Reactions: 1

Mark999

· #3 · Dec 23, 2015

Look at the obvious first. Leaks, binding brakes, clogged filters, correct/faulty spark plugs. If all else fails find a local independent specialist for diagnostics.
Mark

Reactions: 1

Blueprintone

Discussion Starter · #4 · Dec 24, 2015

Thanks Mark.

I have bought a good additive fuel system cleaner and am about to use it on my long distance travels over Christmas to family.

I've tested breaks n none are binding.

Will be lookimg for leaks both on idle and under load. I believe the fuel filter abd lines are at the rear axle centre on the slk320, yes?

Plugs and coils have been recently changed, and air filters. I don't know about the fuel filter though. But will change that too soon.

will let you know how I get on

Reactions: 1

raymond.harper

· #5 · Dec 24, 2015

Clean the MAF and sensor
MAF DIY PICTORIAL: replacing/cleaning - Mercedes-Benz Forum
click on PDF. Also reboot the ECU

Reactions: 1

Mn car guy

· #6 · Dec 24, 2015

How does it run? Does it make good power? How many miles on the car?

Pictor

· #7 · Dec 24, 2015

I am surprised Jeff hasn't already offered the following....,,
Go inside, look in the bathroom mirror, catch a glance of the person in the mirror. Do they have a big grin? If so, problem found.
Look out the window, are there mountains visible? .....
Are the signs you see in German, ( possible Autobahnitis).
If no to all these you've rule out driver and environment, must be the car........

Another quick one to check not mentioned by others is a fractured cat matrix that can cause restriction.

With fuel consuption as bad as you have, there must be clear cause.

By the way,
I did a 200km freeway run, top up at 110 kph, in my 230k R170 for 8 L/100km consumption, ( about 35.3 mpg uk) ,
and came back the same 200km top down , side windows down too, for 8.5. L/100 km, 33mpg uk,
Both ways were light traffic, on cruise control, light winds.

So the high drag configuration only costs about 6% extra at highway speeds.
I am pretty happy with that.

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Reactions: 2

slkDennis

· #8 · Dec 27, 2015

So how did your drive for Christmas work out????????

Blueprintone

Discussion Starter · #9 · Dec 29, 2015

Addtives made no change

jbanks15 said:
http://www.slkworld.com/general-dis...ock-sluggishness-hesitation-top-tier-gas.html

Thanks jBanks, I followed that link you gave. And I have just given the car a 500 mile run, the first 250 with additive, and the second with Super Quality unleaded. The fuel I use is always over 95.... but this was 97 Oc.....

Unfortunately, No change in symptoms. But worth a go, at least I know the rest of the fuel symptoms have been cleaned. But just to be sure, I will re-run the additive, after a fuel filter change, and when this problem is resolved.

If, I can somehow get a recording of my engine and the noise I discovered at 4000 rpm in neutral, will it accept the upload on here?

jbanks15

· #10 · Dec 29, 2015

No
Only if you upload to YouTube
And link it

Reactions: 1

Blueprintone

Discussion Starter · #11 · Dec 29, 2015

Replies....

raymond.harper said:
Clean the MAF and sensor
MAF DIY PICTORIAL: replacing/cleaning - Mercedes-Benz Forum
click on PDF. Also reboot the ECU

Mn car guy said:
How does it run? Does it make good power? How many miles on the car?

Pictor said:
I am surprised Jeff hasn't already offered the following....,,
Go inside, look in the bathroom mirror, catch a glance of the person in the mirror. Do they have a big grin? If so, problem found.
Look out the window, are there mountains visible? .....
Are the signs you see in German, ( possible Autobahnitis).
If no to all these you've rule out driver and environment, must be the car........

Another quick one to check not mentioned by others is a fractured cat matrix that can cause restriction.

With fuel consuption as bad as you have, there must be clear cause.

By the way,
I did a 200km freeway run, top up at 110 kph, in my 230k R170 for 8 L/100km consumption, ( about 35.3 mpg uk) ,
and came back the same 200km top down , side windows down too, for 8.5. L/100 km, 33mpg uk,
Both ways were light traffic, on cruise control, light winds.

So the high drag configuration only costs about 6% extra at highway speeds.
I am pretty happy with that.

slkDennis said:
So how did your drive for Christmas work out????????

Sorry for the delay in replying to you guys! Unfortunately, I have M.E. which I have been dealing with for over four years now. Severe Fatigue, Leg pain, nerve pain and many other symptoms can make it hard for me to reply, or do the vehicle mechanics/suggestions quickly.

However, after recovering from a 500 mile round trip over Christmas to see family. Happy Christmas!!! to you all

I gave the Additive fuel cleaner a real chance to work and filled up with super unleaded fuel. But no joy with that. Yet, I did a thorough check of looking for fuel leaks under the car, and found none. What I did find! was at 4000rpm there starts a Bang Bang Bang noise from the engine, and a unusual rocking of the actual engine itself, plus the odd pop out of the exhaust, and a subtle ping ping noise out of the engine on idle. The Banging noise was achieved in revving from Neutral only.

The performance is still great on a run (apart from the MPG which was better Long Distance at 25 MPG, but not what it ought to be) the engine is still strong when power is required. You would never know that there was an issue when driving other than the very poor MPG.

I have run a diagnostic on the car with a SLK specific diagnostic tool (Icarsoft) prior to the long distance drive when I discovered a cylinder issue on 2 saying that there was a lead/coil issue, but nothing to trip a Misfire Fault Code.

I will next run the Diagnostics again to see if after the long run it comes back with the same cylinder 2 fault.

From there, as I suspect the MAF to be OK due to great vehicle performance including plenty of power left under labor. I will start the engine under the cover of darkness to see if there are any sparks from any of the cylinders to lead us to plugs or and coils.
If, all is well there....... I am thinking that I is possible cylinder 2 could have a stuck injector needing either tapping to loosen and then another Additive treatment or sending off to get properly restored.

What do you think about this plan of action Guys?

Thank you all for your help and suggestions, I hope I have covered them all for now.

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Blueprintone

Discussion Starter · #12 · Dec 29, 2015

Re Boot the ECU

raymond.harper said:
Clean the MAF and sensor
MAF DIY PICTORIAL: replacing/cleaning - Mercedes-Benz Forum
click on PDF. Also reboot the ECU

Hi Raymond, is reooting the ECU safe? Will the car need retuning?

How is that done?

raymond.harper

· #13 · Dec 29, 2015

You reboot the ECU by removing a battery terminal ( negative ) for about 15 mins. You do this every time you change a battery.It is quite safe. The ECU will reboot and adapt to your driving habits so drive carefully. Only think to watch is the radio code may need to be re entered

Reactions: 1

Mn car guy

· #14 · Dec 30, 2015

I'd pull the #2 plug. You've got a misfire. That's what the noise at 4 k is. The odd popping of the exhaust is the ignition kicking back in and causing an explosion. Could be a coil issue but start with the simplistic first.

Reactions: 2

jbanks15

· #15 · Dec 30, 2015

raymond.harper said:
You reboot the ECU by removing a battery terminal ( negative ) for about 15 mins. You do this every time you change a battery.It is quite safe. The ECU will reboot and adapt to your driving habits so drive carefully. Only think to watch is the radio code may need to be re entered

http://www.slkworld.com/general-discussion/70666-reset-transmission-adaptive-learning.html

Reactions: 1

ABTguy

· #16 · Dec 31, 2015

I was thinking about :

1. Plugs & coil packs
2. Fuel filter
3. O2 sensors, both upstream (more critical) and downstream

No fault appear on dash doesn't mean there isn't a problem, CEL can be turned off via STAR diagnostic tools.

Better get the car hooked on a STAR machine.

Reactions: 1

Blueprintone

Discussion Starter · #17 · Jan 4, 2016

Hi Guy's!

Thank you for your comments and advice so far. I haven't got to the bottom of it yet. However, I have as a Green Horn discovered that the spluttering and rocking of the engine when revving to 4000 rpm in N or P, is in fact the transmission limiter kicking in. Well, that is what I am led to understand from a UTube clip and the comments below the clip.....

After my Christmas 500 mile run, the motorway mileage returned 25mpg, still short of the expected 37mpg, I ran high octane fuel through as well as fuel cleaner additive.

I have checked for arching/earthing from or around the plugs and coil boots last night, but no signs are there to see.

I re ran the diagnostics with the icarsoft software tool after the 500 mile trip, and found that fault code P1201 -001 and found from this useful Mercedes SLK R170 fault code site listing ALL fault codes! List of OBD codes for Mercedes-Benz SLK R170 that P1202 represents Injector Circuit Open / Shorted - Cylinder #2, remembering I have no clue about cars, can anyone tell me what this means. I have located cylinder 2, but I am not sure, if, this is referring to a faulty coil, plug, or HT lead. OR as it says an injector problem?

The reason I haven't yet taken the coil off, and plug out of cylinder 2 is because a special tool is required to remove the HT leads from the V6 R170 engine only sold in USA, but I will get there in the end.

There were not other fault codes re appearing other than P1202 Injector Circuit Open / Shorted - Cylinder #2, could it possibly be that this problem could cause one third fuel economy loss, what do you think guys??

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john hannon

· #18 · Jan 4, 2016

Not sure why you'd expect to get 37mpg from a 320
Here are my stats, I'm no boy racer!!

Text Font Line Screenshot Number

Regards all

John

Sent from my iPhone using Tapatalk

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Blueprintone

Discussion Starter · #19 · Jan 4, 2016

ABTguy said:
I was thinking about :

1. Plugs & coil packs
2. Fuel filter
3. O2 sensors, both upstream (more critical) and downstream

No fault appear on dash doesn't mean there isn't a problem, CEL can be turned off via STAR diagnostic tools.

Better get the car hooked on a STAR machine.

ABTguy, Your right and that is my next move now. I am interested to know if you can or anyone else here can tell me what the O2 sensors should read on R170 SLK 2000 reg?
I can get them on my icarsoft tool I believe. Thanks.

Blueprintone

Discussion Starter · #20 · Jan 4, 2016

john hannon said:
Not sure why you'd expect to get 37mpg from a 320
Here are my stats, I'm no boy racer!! View attachment 256202

Regards all

John

Sent from my iPhone using Tapatalk

Hi John,

Thanks for your personal mpg readings. I'm from the UK so I'm not too sure if our miles are the same, I know USA miles are different in distance to UK miles. Where are you from buddy?
I got my mpg from a 'Official Chart in UK mpg' I can't find the link but I believe it was from Mercedes Benz Club or somewhere on this site members posted charts. If, I find it I'll post it.
Nevertheless! Its really good to have your figures, because it lessens my expectations at the top end by 5 mpg which would indicate the problem not to be too severe, hopefully!

It would be nice for it just to be a plug or coil bud.
Although, I noticed yoir worst mpg to return in low 20's around town in traffic I guess. My worst was and is currently 8 mpg. I think we can both agree that this is very bad mpg regardless of any available mpg record/chart.

Anyway, it is great to have your records, it makes me feel that my slk problem might not be quite as bad as I had previously thought.

Steve

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