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Poor mpg and Car performance feels a bit 'flat'

JensenA

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Car: 2009 Accord Tourer i-dtec Type S

My car is achieving terrible mpg figures all of a sudden, to stave off all the usual comments about what to check, here are the details.

Tyres: Continental Sport contact 5's 235/40x 19 all round. Pressure 33psi all round
Wheels: HPF 19" alloys
Callipers: No binding, I've just jacked the car up and checked.
Outside Temperature 9 deg C
Fuel: Shell V power diesel
New Honda OEM Air filter
I know people will say the on board computer isn't 100% accurate, but it's been checked and its accurate as dammit.

I've just done a steady run on a flat motorway for 19 miles, engine temp on normal, no acceleration, just a rock steady 70mph on cruise, and my mpg is 38.2.

Any ideas?
 

F6HAD

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Hi Alan, fuel filter replaced recently? Are you carrying much load at all?
 

JensenA

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The car's empty Fahad, just me in it, and 1/4 tank of fuel. I'm not sure about the filter.


PS - Just remembered, yes, I fitted an OEM filter a few days after I bought it.
 

BazCW3

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I Had same problem with MPG and it was down to sticky EGR wasn't showing fault when plugged in just that it was sticky closing got it blanked and mapped out and MPG returned to mid 44's on city driving and seems more responsive.
 

JensenA

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All that has been done Baz. 2 weeks ago, driving it steadily I was getting 50+ easily. Suddenly, with me driving carefully to try and achieve good mpg, it has plummeted to below 40!
 

F6HAD

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Worth trying a battery reset. Leave it disconnected overnight.
 

nokia

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Would a low battery give poor performance? Not being sarcastic - genuine question
 

F6HAD

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Nope it shouldn’t
 

nokia

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Apologies Fahad, I misread "battery reset" as "battery test"
 

Gozzy

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Did you resolve this mate? I had a similar issue and it turned out to be a cracked EGR pipe. Have you noticed a smell of diesel fumes in the cabin at all?
 

edgeoftime

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Mines an auto tourer, never seen better than 41.5 mpg on the puter, but what I have seen is an improvement the further I go i.e. 20 miles not so good check again at 50 miles getting better??? and an average speed of never greater than 38mph, even though I cover 50 miles under the hour, so who can trust a computer???
 

stellamon

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My 2010 idtec es gt manual is only doing 37 mpg average. Had a remap, and egr delete. How would the fuel filter affect mpg?
 

F6HAD

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Blocked fuel filter will restrict flow of fuel which basically alters the operating conditions causing the ecu to try and send more fuel in to compensate. Basically the engine won’t be running optimally. Please also check for evidence of binding brakes, I see it all the time on hondas. Normally the rear wheels, just feel if one is hotter than the others.
 

stellamon

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F6HAD said:
Worth trying a battery reset. Leave it disconnected overnight.
Would this actually change any parameters involving fuel economy. I'm beginning to think that 37 mpg is about all I'm going to get the way I drive.
 

F6HAD

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What it will do is reset any of the adaptation values, so effectively allowing the ecu to learn from scratch. But I’m in agreement with you, 37mpg might be about right for mixed driving with a relatively heavy right foot.
 

stellamon

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Had a spin up the M54 earlier today, did @ 50 miles there n back and she averaged @ 51mpg.
Nice to see a new figure on the computer and restored my faith a bit.
 

F6HAD

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That’s great Nick and shows there’s nothing wrong with the car. Just your led foot!
 

Richard B

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On a long drive I did the car settled on 63/ 64 mpg driving conservatively. On a fresh reset, I can "drag" the average mpg all the way into 70's by staying out of city traffic, ****ing off people behind my by accelerating reaaaally slowly and coasting with my foot off the pedal as much as possible.

Coasting in gear uses no fuel, and drags up the MPG average. But it also seems to skew the algorithm. When I measured the amount of fuel pumped into the tank against distance travelled, the figure was around 50mpg, with the dash showing 64.

During the last few summer months it's been warm and humid and the air con ends up eating into fuel efficiency, making the dash figure float around 54.
 

Camsti

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Is it totally safe to unplug the battery for a night only loosing the clock and preset radio stations? I feel that my ECU have a lot to learn ....!
 

DazTheMe

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Yep all good. Fahad wouldn't recommend it otherwise. As you said, you'll just have to enter your radio code again.
 

Camsti

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Great - it´s a desperate try - but desperate tries are needed!

It keeps showing the particle filter clogged-symbol with an exclamation mark and enters an emergency program - but all testers says there is no errors whatsoever ...
 

DazTheMe

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Then you need a new DPF. A battery reset won't fix anything like that.

And what "testers" say there are no errors? An OBD2 reader won't pick up any errors from a blocked for, you'll need a forced regen to reset that message.
 
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