MPG getting worse - Civinfo
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post #1 of 51 (permalink) Old 4th January 2018, 20:18 Thread Starter
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MPG getting worse

I know there are lots of threads and lots of possibilities but I wanted to start one that hopefully will stay on track and highlight what to check and when, if this problem arises for anyone in the future.

Firstly, my Ep3 has been my daily since early September since selling my Fn2. It started with a similar mpg to the Fn2 of around 31mpg but has slowly got worse, I'm guessing it's around 24mpg at the moment. Oil usage is a bit more than normal, but I have changed the oil and transmission fluid since September.
90% of my driving is the commute which is 18 miles each way on an open A road with a mile or two of city driving (stop/start). Speeds average 45mph, a few bursts of vtec from junctions etc
No EML, no loss of power, no misfire or rough idle. Tyres are good and set right, no brakes binding although I am getting a whiff after driving which leads me onto possible problem number 1. One of the o2 sensors could be on it's way out. Number 2, it could be the cat on it's way out.
Other causes could be....
3. Bad spark plugs - I checked when I bought the car and they looked recent
4. Faulty injectors - I need to pulse test and also check with multimeter
5. Dirty Air Filter - the air filter on the teg was clean when I installed it, don't think it will be this
6. Throttle body - need to check it's clean/not stuck open
7. Valve clearance - I really need to get this done, could be a cause, especially when the oil consumption is up too

I'm going to do a compression test when I re-check through plugs, it can't hurt

Any other causes or opinions? Please add
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post #2 of 51 (permalink) Old 4th January 2018, 20:26
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Change the PCV just in case.

Has the chain been given a clean bill of health?

Make sure theyre also the right spark plugs.
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post #3 of 51 (permalink) Old 4th January 2018, 20:30 Thread Starter
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Pcv done, plugs are correct, haven't checked the chain it's on 89k and I have no history of valve clearance being done. It's my Saturday task
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post #4 of 51 (permalink) Old 4th January 2018, 20:32
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Binding caliper(s)?
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post #5 of 51 (permalink) Old 4th January 2018, 20:37 Thread Starter
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Binding caliper(s)?
Nope, all fine
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post #6 of 51 (permalink) Old 4th January 2018, 20:38
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Handbrake left on?!
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post #7 of 51 (permalink) Old 4th January 2018, 20:58 Thread Starter
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Handbrake left on?!
nope, and no hole in the fuel tank
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post #8 of 51 (permalink) Old 4th January 2018, 21:00
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Dang, you answered my next question.

Might it just be the winter cold affecting mpg? Although the change does seem excessive, my guzzler has only dropped a few mpg since summer.
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post #9 of 51 (permalink) Old 4th January 2018, 22:06
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Are all manifolds and vacuum pipes seated fully?
Possible coil breaking down or faulty spark plug/s
Have you changed fuel station recently or fuel type/RON?
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post #10 of 51 (permalink) Old 4th January 2018, 23:15 Thread Starter
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I used to 50/50 between fill ups with V Power and Momentum, but mostly momentum now. All pipes etc seem OK, can't imagine it's electrical as everything seems smooth. A manifold leak might explain the whiff.
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post #11 of 51 (permalink) Old 4th January 2018, 23:20
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Flashy.... on our CRV.
Changed the front tyres, still in legal limit and pressures are checked every other week.. we found in the same new brand/make, same psi (just newer) that mpg has improved by 4mpg.
Weird I know, just wanted to throw that in the mix as a FYI..
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post #12 of 51 (permalink) Old 4th January 2018, 23:48 Thread Starter
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I will do the valve clearance on Saturday and put on the new rocker cover kit which includes plug seals. When I checked the plugs they had a bit of an oil banding, not enough to concern me but nonetheless. If excess oil is getting in the plug tube it will eventually damage the coil boot, may cause a short/weakness. This could explain the oil consumption and poor mpg. No misfire though.
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post #13 of 51 (permalink) Old 5th January 2018, 07:52
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Could be valve stem seal or worn piston ring which is passing oil, you compression test should show this. if compress is lower than should be then you may be using more fuel to compensate?
If it helps, I'm getting 27 MPG out of my FN2 on my daily commute of 10 mile
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post #14 of 51 (permalink) Old 5th January 2018, 08:39 Thread Starter
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I'm going to start by removing and checking plugs and doing a compression test. Funnily enough I checked the oil level this morning and it was still on the max. Bit of a puzzler this car
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post #15 of 51 (permalink) Old 5th January 2018, 09:30
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My FN2 started around 20mpg.

PCV netted me a 1-2 mpg back.
One or more of my injectors must've been leaking as fitting the RDX saw it rise to an average 28-32mpg now.

Unsure if the Teg is going to affect it much untuned but could be leaning it out so ECU is just dumping more fuel in to compensate. Hard to say without datalogs. Same could be on the other end with the O2 sensors.

It's also winter and mine tanked but now it's warmer but wet I'm getting normal mpg again.
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post #16 of 51 (permalink) Old 5th January 2018, 09:34 Thread Starter
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I miss my Flashpro would an obd2 show anything other than codes? Got one in the car.
The Teg may be coming off

Last edited by flashy; 5th January 2018 at 09:38.
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post #17 of 51 (permalink) Old 5th January 2018, 09:58
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Argh, have you just changed exhaust?
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post #18 of 51 (permalink) Old 5th January 2018, 09:59
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Quote:
Originally Posted by musegroove View Post
My FN2 started around 20mpg.

PCV netted me a 1-2 mpg back.
One or more of my injectors must've been leaking as fitting the RDX saw it rise to an average 28-32mpg now.

Unsure if the Teg is going to affect it much untuned but could be leaning it out so ECU is just dumping more fuel in to compensate. Hard to say without datalogs. Same could be on the other end with the O2 sensors.

It's also winter and mine tanked but now it's warmer but wet I'm getting normal mpg again.
Sorry, retard question time again. Whats PCV and RDX please
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post #19 of 51 (permalink) Old 5th January 2018, 10:02 Thread Starter
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Pcv = positive crankcase ventilation. There is a valve on the k20 that can fail over time and need replacing
RDX = aftermarket injectors
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post #20 of 51 (permalink) Old 5th January 2018, 10:04 Thread Starter
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Argh, have you just changed exhaust?
Not yet. Still in the garage
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