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MK2 Focus Horrible MPG After Full Service [1.6 100ps]


Mark89
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Hi,

I do 80 miles a day every day 6 days a week all year round. I reset my MPG every fill up, and I constantly average 36MPG which is fine as its 50% city 50% carriage way.

Anyway, on the last service I thought I'd treat the car to a proper service with all OEM Filters - Spark Plugs - Full Synthetic etc

I also replaced both front discs and pads with the service. Now here is it interesting part, the last three tanks I've done 29 MPG !!! Worried about the brakes being stuck I removed both sides and nothing seems to look out of the ordinary, all properly greased up, with no uneven wear. I checked the sparks which are torqued correctly and the leads seem fine.

I was hoping for an MPG increase not a dramatic decrease. Bare in mind I've owned the car a while now and this has NEVER happened - winter, summer you name it, the MPG has been fairly consistent.

This difference will equate to £600 over the course of a year which is a massive hit to my wallet!

Any clues as to whats gone wrong?

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I don't know the engine variant that well, but does anyone know if an air leak downstream of the MAF couldnt result in poor mpg? I.e. if the filter housing wasn't fully sealed?

Just thinking of things that could be off after the work you have done.

I agree with the above, excess windage can result from too much oil in sump (mixing of the oil and air in the crankcase by the crank) can cause loss of mpg.

As a not for interested parties, on the oposite end of the scale, we used to underfill the MX-5 of my buddy's race car, by about 0.75 litres (if I recall correctly) and this resulted in a 3-4hp gain. This was carefully tested and gradually increased over months, with monitoring to ensure no oil starvation occured. Final power difference from back to back dyno run at two oil levels. ) 0.75 left you just under minimum fill level on that car.

 

 

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It would be worth re-checking the oil level just to make sure the initial level wasn't a mis-reading, just in case? Had you run the engine and let it drain down when it as checked?

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Dont trust the computer, do a couple of brim to brim mileage checks, also if the car had been electrically shut down the ecu may well have gone back to learning mode and you may find that your recorded mpg figure will increase, but as i first said brim to brim checks, the other thought is these readings may be right and yoy old ones wrong.

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Thanks for all the replies.

The airbox is an interesting one. I will definitely check it when I set off home.

Yep definitely oil is at the correct level I checked it on 3 seperate days when cold.

My MPG calculation is light to light and I have crunched the numbers , over 1000's of miles the trip is accurate (for anyone wondering, the Focus trip seems solid.)

 

Thanks

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Light to light is not accurate enough, there is hysteresis in any sensing system, and inaccuracy, and also you cant pull over the moment it comes on, even if the above were not true.

You need to record mileage at fill, to the brim, and the same the next time. This is as accurate as you can get in real world situation, without a fuel flow meter.

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Guys I appreciate the replies but I've been recording my mileage / fuel consumption for a good part of a decade now (for tax purposes) I was simply pointing out my real life MPG would always reflect what the trip was displaying per tank, thats all.

My MPG has fallen to 25.6 MPG (real life) and 26.1 MPG on the trip computer.

Something has obviously gone terribly wrong at this point if I am burning over 30% more fuel per fill up. I usually fill up on Sunday evenings, however I had to fill up Friday on the way home from work.

I'm open to any and all wild theories at this point, I want to sort this out tomorrow as its my only day off and my only chance at saving my sanity. I am going to remove the brakes ONCE AGAIN to see if something is binding. I've checked the airbox clamps etc, everything is in good order. I've checked the leads, there are no cracks. Could it be the spark plugs?!

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Our old Mk1.5 took a mpg hit when one of the front caliper pistons started sticking. The sudden reduction in mpg was the only clue that something was wrong, there was no noticeable effect on the steering or braking,

Out of all the work you've done I'd say the brakes are the most likely suspect. One thing worth trying is to place your hand on the wheel hubs after a run and see if one is hot, or warmer than the others.

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On 10/9/2018 at 12:43 PM, Mark89 said:

Thanks for all the replies.

The airbox is an interesting one. I will definitely check it when I set off home.

Yep definitely oil is at the correct level I checked it on 3 seperate days when cold.

My MPG calculation is light to light and I have crunched the numbers , over 1000's of miles the trip is accurate (for anyone wondering, the Focus trip seems solid.)

 

Thanks

My Focus routinely tells me i'm getting 33-35mpg when in fact i'm getting 36-38mpg if I work it out manually from fillups. Fuelio (app) echos this too.

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On 10/13/2018 at 4:42 PM, mjt said:

Our old Mk1.5 took a mpg hit when one of the front caliper pistons started sticking. The sudden reduction in mpg was the only clue that something was wrong, there was no noticeable effect on the steering or braking,

Out of all the work you've done I'd say the brakes are the most likely suspect. One thing worth trying is to place your hand on the wheel hubs after a run and see if one is hot, or warmer than the others.

+1

It only takes 1 caliper not be retracting properly/fully and that little bit of extra pressure of the brake pad being pushed into the brake disc can make a big difference to performance/MPG, especially on the less powerful engines.

At the beginning of the year I noticed my MK2 1.8 TDCi felt a bit sluggish compared to normal and the MPG on my regular 1 hour run to/from work had nosedived from 64 MPG to 51 MPG.  I'd been meaning to do the calipers anyway (144K miles at that point in time) so 4 replacement calipers later and I was back to 60+ MPG.  Other than the car feeling a bit sluggish when accelerating I really couldn't feel any other signs that something was wrong.  @mjt advice/suggestion about checking the temperature of each disc is exactly what I used to identify the root cause, it was actually just the rear passenger side caliper that was sticking but the others were of the same age so I ended up doing them all (got a decent deal so it didn't cost as much as you might think).

Hopefully your issue is just a sticking caliper as this would be a relatively cheap issue to fix.

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