[sn]

Gidday crew,

About 6 weeks ago I serviced our 2013 GD wagon, 1.6 litre, auto

Engine oil and filter, air filter, fresh iridium plugs [clearance same as the old iridium plugs / as per the book]
Cabin filter, skimmed the front disks, new brake pads all corners, fresh brake fluid etc.

Since then, my petrol consumption has worsened markedly.

Even to the point that when I refill the tank [to the second "click"], the "range predictor" in the dash now estimates a bit over 500km with the full tank, instead of the previous being between 590 / 625ish.

Previously, half a tank would last me a week, now nowhere near that.


Same routes, same traffic, same tyre pressure, same load in the car, same 98 octane petrol from same servo - normally refilling when the gauge is at 50%.

Could it be a dud sensor of some type?
Would this show up with an OBD scan?

Any ideas?

Thanks,

Stephen

[sn]

OBD scan at Supercheap found nothing

[TerryT]

OBD scan at Supercheap found nothing

Sorry, I'm late reading your thread as I don't browse the forum as much as previously.  You seemed to have done many of the things that needed doing.  I thought of a defective O2 sensor; or a clogged/defective fuel injector/s; or a faulty catalytic converter; or problems with the muffler/resonator restricting flow...but your OBD2 scanner should have detected something if the testing equipment and operator were good.

How many miles (km) has the car engine done and has the engine been regularly and properly serviced? Lots of mileage = carbon starts to build up on the injectors, cylinder walls, pistons and valves [leaky valves], all bad for fuel consumption.   

Have you considered doing a engine compression test; a engine leak-down test; and a exhaust back pressure test, to help determine the overall health of your engine.  Although it sounds like your problem just appeared and was not a gradual decline over time.  And you have not suffered any noticeable sudden loss of power  .

I'm no mechanic and cannot offer any more but was just throwing out some random thoughts in the hope that our more experienced/knowledgeable members might  be tempted to involve themselves.  (Plus, I do love a mystery ).

[Greyhound]

new brake pads all corners

I assume you have checked that new brakes are running free and not binding at all when not applied.

[Aye30]

Hi, range to empty seems to be calculated from the previous average drive cycle mpg (on mine at least)  and tank filled level. So with the same filling behavior, the difference would be the previous  mpg figure. I have noted they sometimes reset the automatic transmission  adaptive driving values and also the ecu, which then means the car is learning the new driving style. Try resetting the mpg trip, if yours has one  and drive around a bit, they may have run the engine a lot without moving at the dealership which would throw the mpg figures out. ( sorry just re-read and saw it wasn't dealership).  But mpg is still calculated on duty cycle of injectors and distance travelled.

[Greyhound]

Perhaps do some manual consumption measurements in parallel with what the car is telling you.
Record odometer km and litres at each fill-up. Do this over time and then manually calculate consumption. Use a spreadsheet to calculate average consumption.

[Aye30]

new brake pads all corners

I assume you have checked that new brakes are running free and not binding at all when not applied.

With new pads on the rears, I assume the handbrake was adjusted?

[Aye30]

Out of curiosity, what method and tool did you use to compress the caliper pistons in the brakes?  Also did you remove and reapply the caliper slide pins with fresh guide pin grease?

[sn]

How many miles (km) has the car engine done and has the engine been regularly and properly serviced? [/quote]

125000km,
serviced every 10000km as per the logbook - easy stuff by me / awkward stuff by John Hughes mobile mech.

[sn]

I assume you have checked that new brakes are running free and not binding at all when not applied.

all 4 corners running free when up on jack stands / no sign of drag or binding

[sn]

With new pads on the rears, I assume the handbrake was adjusted?

yep - I adjusted the handbrake when I replaced the pads, checked again a week later, no binding or dragging

[sn]

Out of curiosity, what method and tool did you use to compress the caliper pistons in the brakes?  Also did you remove and reapply the caliper slide pins with fresh guide pin grease?

I used a caliper piston compressor tool from Repco, basic flat plate with a bolt running through a captive nut, has been in the family since the 1960's, back when one of the few cars on the road with disks was a lowly FIAT, and yes - pins were lubed up 

[sn]

Perhaps do some manual consumption measurements in parallel with what the car is telling you.
Record odometer km and litres at each fill-up. Do this over time and then manually calculate consumption. Use a spreadsheet to calculate average consumption.

Sounds good - except for the spreadsheet bit [I am a proud techno-peasant]

[The Gonz]

Perhaps do some manual consumption measurements in parallel with what the car is telling you.
Record odometer km and litres at each fill-up. Do this over time and then manually calculate consumption. Use a spreadsheet to calculate average consumption.

Sounds good - except for the spreadsheet bit [I am a proud techno-peasant]

Don't let the spreadsheet scare you - it's overkill anyway.
Just solve ([final odometer] - [starting odometer]) / [litres used] for distance travelled per volume of fuel. Invert for fuel per distance.

[TerryT]

How many miles (km) has the car engine done and has the engine been regularly and properly serviced?

125000km,
serviced every 10000km as per the logbook - easy stuff by me / awkward stuff by John Hughes mobile mech.
[/quote]

Okay, thanks for the info, it could help with a diagnosis.  Your other replies seem to rule out brake/handbrake issues e.g. binding etc.

Do you see any value in any of the tests I first suggested (compression, leakdown, exh backpressure)?