Fuel consumption... looooong post

fooesboy · Post by **fooesboy** » Fri Sep 13, 2013 11:54 am

I drive from Te Aroha to Hamilton every day, about 90km of open road and 15km of town driving.

I cruse at about 105kph and rev up to about 4000 in the open road and about 3000 in town, to overtake I (might) drop down to 4th

With the weather how it has been the roof has stayed up almost all the time. Aircon does not work so that has not been used.

My other car is a twin turbo Legacy and I get about 9.4 liters per 100km driving the same.

When I first bought the car I was getting 7.8 liters per 100km and I have not changed my driving style.

SLYDIT · Post by **SLYDIT** » Fri Sep 13, 2013 3:22 pm

When warmed up the car is running on the o2 sensor so it would adjust out any extra fuel. Looks like you have one of those faults that needs a full run down and check of all components. Afm. Coolant temp sensor, TPS. Fuel pressure. Etc.maybe worth a clean of the afm contacts with CO contact cleaner or Maybe book it in at autoways in Frankton and get him to swap in one of his chipped ecu with the crystal mod.

tomtikki · Post by **tomtikki** » Fri Sep 13, 2013 11:01 pm

Don't get me wrong I'm all about saving money/not wasting gas but I just hope you have run the numbers as to how much 'extra' per tank you will save by spending money to fix this issue.
At some point this is going to be an uneconomic exercise, you have already dished money & time on a new O2 sensor...

Just a thought. Good luck none the less mate.

WideOpenThrottle · Post by **WideOpenThrottle** » Sat Sep 14, 2013 7:06 am

Could be in the timing,fuel line pressure or ECU among other things.

SLYDIT · Post by **SLYDIT** » Sat Sep 14, 2013 5:27 pm

whats your air filter like? have you cleaned it lately? if you have re-oiled it have you put too much oil on it?

authentic · Post by **authentic** » Sat Sep 14, 2013 10:28 pm

Speaking of air filter oil, which is the best to use for a foam panel filter? Its a Jackson Racing one so they don't sell their product over here.

fooesboy · Post by **fooesboy** » Sun Sep 15, 2013 10:20 am

I replaced the K&N filter with a stock one during the last service. This was one of the first things I changed trying to sort out this problem. Then watched the MCM video on performance gains using after market air filters giving no performance difference I decided to leave it off.

I changed the plugs on Friday night, you where right SLYDIT they where carbon'd up pretty bad.

Today I will reset the timing, when I bought the car it was set at 7° and I changed it to 12°. I will change it to the stock 10°. I'll do a tyre pressure check at the same time.

fooesboy · Post by **fooesboy** » Sun Sep 15, 2013 10:23 am

I called into Autoways last week (or the week before) and was told the main guy who knows all about MX5's was away on holiday for a month and would be back around the 5th of October. I wend through all that I had done with the guys there and they had no suggestions.

fooesboy · Post by **fooesboy** » Sun Sep 15, 2013 10:39 am

tomtikki wrote:Don't get me wrong I'm all about saving money/not wasting gas but I just hope you have run the numbers as to how much 'extra' per tank you will save by spending money to fix this issue.
At some point this is going to be an uneconomic exercise, you have already dished money & time on a new O2 sensor...

Just a thought. Good luck none the less mate.

You are dead right mate!
With fuel prices as they are at the moment the car is costing me an extra $27.60 per tank.
I drive a minim of 550km per week = 28,600km per year
If the car is using an extra 3 litres per 100km then there is an extra cost of $1,973.40 per year.
That is not an insignificant amount, but what I'm more interested in is the health of my motor.... you see, I'd like to fit a turbo a some stage in the next 12 - 18 months and I am concerned that there might be a larger fault. It seams logical (to me at least) to make sure the motor is working just like it should before bolting on a turbo.

And yes I know that with a turbo it will be using a lot more fuel!

WideOpenThrottle · Post by **WideOpenThrottle** » Sun Sep 15, 2013 4:42 pm

Why don't you do a compression test?...it will tell you the state of your engine...low compression will mean its working harder & using more fuel.

If its all good then providing your turbo is tuned properly then fuel use will be sorted or it may highlight where the problem lies.

Snapfrozen · Post by **Snapfrozen** » Sun Sep 15, 2013 8:24 pm

Being honest, considering the cost it's almost worth a full rebuild of the long block if you are wasting 2k per year on gas...

binarypunk · Post by **binarypunk** » Sun Sep 15, 2013 10:01 pm

Sorry to butt in... But I've been through this with my '93 1.6 (edit: I can't tell what model you have, this only applies to the early 1.6 with the 'gate type' AFM)

Check the obvious things (o2 sensor, ECU temp sensor, AFM wiring) first

If no luck, I had great results adjusting the clock spring tension on the AFM. You should be able to find a guide online - I made one on the UK owners club forum, but I can't post a link...but if you search for the username victormeldrew and 'calibrating the AFM' you should find it.

NicF · Post by **NicF** » Mon Sep 16, 2013 8:22 am

I do a similar mileage in mine, which is why I'm going to a megasquirt soon. Even if the car doesn't have fuel consumption problems like OP, being able to tune out the rich setting the OEM fuel management has will pay for it in a year's driving.

Donovan · Post by **Donovan** » Mon Sep 16, 2013 3:43 pm

I get about 8.5l/100 on a trip to the Coromandel and back again with a little bit of tootering around, so that should be the benchmark to bet considering the size of the motor in mine

marcellarius · Post by **marcellarius** » Mon Sep 16, 2013 5:25 pm

Have you checked for ECU fault codes?

The JDM cars don't have a check engine light, and while primitive, the onboard diagnostics might pick up really broken sensors.

SLYDIT · Post by **SLYDIT** » Wed Oct 23, 2013 7:08 pm

any update on this??

fooesboy · Post by **fooesboy** » Wed Oct 23, 2013 8:36 pm

I had the engine temperature sensor replaced last week, just need to go through this tank to see where I'm at. The previous tank was 10.14l per 100km.

Next step that the garage has suggested is to send the air flow meter to Tauranga to be checked. Does this sound reasonable?

warrior · Post by **warrior** » Wed Oct 23, 2013 9:57 pm

I have a air flow meter you can borrow if you want to try it

SLYDIT · Post by **SLYDIT** » Thu Oct 24, 2013 10:35 am

Probably cheaper to get another afm then check your one.

Fuel consumption... looooong post

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