Hi guys,

Is it possible to reflash the ECU for better fuel economy in a KJ?

In short its really not worth it unless you have quite a few mods

I was only really interested for a stock car.
I read here that a free flowing muffler gives better economy?

Straight through muffler gives tiny bit of better economy, but it will take years in terms of savings in petrol and the price of the muffler itself.

Assuming you don't already have a a VRX, Sport or Ralliart, I'd suggest buying a straight through rear muffler (which those models already have) and getting a tune for a bit of go as well as fuel efficiency.

This way you get a more fuel efficient car and a good boost in performance.

If all you're interested in is economy and don't care about performance then you have to figure out if the cost of a tune and muffler is worth the petrol savings over the long run.

To answer your question, yes you can retune your ECU to make your car more fuel efficient.
I don't know exactly what people have seen in improvement but I believe it is a significant amount.

Tune your right foot? :P

Ditch any excess weight you can from the car - total cost = $0.00 if you just clean the car out (Can cost money if you get serious.). Maybe ditch that roof rack and/or tow bar if you don't need them?
Check tyre pressures - Total cost = $0.00
Clean air filter, throttle body, MAF - Total Cost $60 (new filter, can of TB cleaner and can of contact cleaner)

Doing these things might improve economy as much as fitting a free flowing muffler, but they don't cost as much.

I'm a real tight arse with cash, so I always attack problems without spending any money unless I absolutely have to.

Having said all of that, an exhaust upgrade can reduce weight as well as give some benefit to economy by being less restrictive.

Is it possible to reflash the ECU for better fuel economy in a KJ?

With a standard ECU in a car that spends most of its life in closed loop mode, only minor fuel economy gains are likely to be achieved with tuning, simply because closed loop mode sticks close to stoichiometric AFRs (14.7:1 for petrol). Any gains are a consequence of extracting more power from a given amount of fuel by increasing the ignition advance. Despite some claims I've seen, Magna ignition maps don't appear to be grossly conservative in the RPM/load ranges where most cars spend 80% or more of their operating life - certainly not as conservative as some other vehicles anyway - so huge economy gains are unlikely to be made this way.

It is possible to achieve better fuel economy by getting the ECU to always run in open loop mode and then carefully leaning out the fuel map (and adjusting the ignition map appropriately) at cruise RPM/load. But there is a limit to what can be achieved, perhaps in the order of 10% for standard engines based on info I've come across.

The Mitsubishi GDI engines took this to extremes, with AFRs of 40-50:1 under some circumstances (if the info I recall on Wikipedia is reliable), but they also used high compression ratiios and lots of EGR too. The original Honda hybrid is another example of this approach, leaning out to around 25:1 or so for short bursts when cruising.

If your car spends a large part of its running time with the engine below normal coolant temps, forget the above...

just note tuning is always a gamble for fuel eco. i know mine isn't really any better after my tune. but hard to tell. i seriously wouldn't bother. best change for fuel economy is having a manual rather then an auto.

WytWun, can you tell me how many L/100km you use? As I live in the ACT as well and traffic there is not such an issue.

I have not bought the car yet and to be honest as of late I am a bit skeptical due to the fuel consumption. I was hoping that a tune could just be loaded on the ECU for fairly cheap and save me 1-2 L/100km but I guess this is overly ambitious.

just note tuning is always a gamble for fuel eco. i know mine isn't really any better after my tune. but hard to tell. i seriously wouldn't bother. best change for fuel economy is having a manual rather then an auto.

Very true, I lost 2l/100k just by going to manual.

WytWun, can you tell me how many L/100km you use? As I live in the ACT as well and traffic there is not such an issue.

I have not bought the car yet and to be honest as of late I am a bit skeptical due to the fuel consumption. I was hoping that a tune could just be loaded on the ECU for fairly cheap and save me 1-2 L/100km but I guess this is overly ambitious.

Keeping in mind I'm driving an AWD with mods & tune running on Shell 94 RON E10, my current trip computer reading (over a number of tank fills and multiple weeks) is 13.8l/100km. While this is better than I was getting before the tune (about 14.2l/100km), it isn't as good as I was getting when the car was stock and I was running 91 RON ULP and the car was shod with Michelin Energy XM1 tyres (13.7l/100km). Using E10 lowers fuel economy by about 4% compared to using ULP, so if I were running 95 RON ULP I would expect to be getting 13.2-13.3k/100km.

To put this in context, my normal daily drive to & from work just sees the engine reach operating temp at journey's end so for most of these trips a fair bit of extra fuel is being used compared to doing the same tip with a warmed up engine. Offsetting this, I usually do 1 or 2 trips a week to events that are typically 25-30km each way.

My personal record highway fuel economy of 9.2l/100km was also when the car was stock on the Michelin tyres, on a Canberra to Port Macquarie run via Sydney. Around 10l/100km is my more usual average highway economy at 100-110kmh; nearly 11l/100km at 130kmh in the Northern Territory.

Based on my experience, if you care for economy be very selective with tyres and keep them in optimum condition. If you are a keen DIYer, advancing the timing of the stock #6 camshafts is about the least expensive performance mod you can do for an auto - power delivery can be modestly improved and fuel economy can be slightly improved.

WytWun, what would you expect your economy to be if you were running a stock KJ 5 speed FWD auto?

To be honest because I am not in Canberra yet and do not know where I will be living/working I don't know what my drive will be like.

Initially I was pretty sure I would get a KJ but recently I am having my doubts. Fuel economy is one of the biggest concerns and when I was there last (5-6 weeks ago) petrol was 1.48 or so, so 13L/100km @ 1.48 = $18.20 and I know I can easily drive around 500km+ a week in Canberra due to the large distances, so this can easily reach $400+ a month if not more, assuming petrol does not rise in cost that is...

The only experience I have of driving an FWD was a rented TL 4 speed in 2004, for a trip to Sydney with several days there - all told about 1000km with a trip computer calculated average of 8.5l/100km as I recall. As best I can estimate, in stock trim my AWD would have recorded 10-10.5l/100km for the same trip. As best I recall, the instantaneous consumption readout in similar places around Canberra was typically 1.5-2l/100km lower than my AWD.

Best guess for a FWD KJ? somewhere around 11-12l/100km. A lot will depend on your trips and how you drive of course...

BTW, if the usual trips involve any significant amount of idling at traffic lights etc the trip computer will be excessively pessimistic about fuel use. This seems to be because it doesn't compensate for the effect of injector latency at low injector pulse widths (ie at idle). My normal trips don't involve much idling so the trip computer is only mildly pessimistic (my actual fuel economy is a bit better than the trip computer indicates).

Thanks WytWun,
The other issue is to somewhat accurately gauge and compare how much fuel other cars would use.
It seems that the accuracy of Redbook for fuel consumption is not so good and I don't even know if I should use it as a basis for comparison

General rules about low fuel consumption:

The newer the car the better.
The lighter the car the better.
The more aerodynamic the car the better.
Diesels do better than petrol engines.
The longer the trip the better the average fuel consumption.
Steady speed beats stop-start traffic.
A light foot beats a heavy foot.

etc, ad nauseam. I'm sure others can add to this list.

So, in short, a small car like a Mitsu Colt driven sedately will get great economy.

Hell, My TS V6 is sh#t on fuel, short trips every time, $50 can maybe get me close to 200 Km if I'm lucky. Everyone's finances suffer due to fuel costs.
Fact of life.
I've stopped fretting over it.

I have a series II 5 speed KJ verada..It has done 130000,it is run on either 95 or 98 ron petrol..18 x 235 tyres that I run 45 pounds of air in..The car averages about 11 litres per 100km around town when I drive and about 11.5 when the wife drives it..She seems to believe you have to get as quickly to the next car or round about then plant your foot on the brake over and over..
This is around Gosford and mainly running to work or kids to school..
On the highway I have averaged 8.2 litres per hundred on a long trip but usually it will easily run under 9 litres per hundred with out trying with the family in it..You should be able to get between 9.5 and 10 around Canberra with a little careful driving pretty easy I reckon,unless you live in the traffic lights..

Thanks guys for the help.
10L/100km sounds pretty reasonable.
Another car I am considering is a 1998 model C class Mercedes, but I am unsure what to expect in the fuel consumption department (for a 2L 4 cyl 5 speed auto).

Mate if you are doing vast distances around Canberra your economy should be alright with a magna, i do 70/30 -highway/city with my auto 3L and on average it uses 10/100.
This drops to 9.1/9.2/100 when i put in 98.

Doing a trip from Syd to mid north coast i got down to 8.2/100 for the average of the 500 or so kms travelled, and that was with the family on board and the back loaded up etc.


There is a whole thread on here about economy, have a look in there, try not to be scared of with the other above posts stating 13/100km's, mine has NEVER gone anywhere near this high, im not saying these guys are lying, not at all, but maybe they do a lot of stop/start driving and have heavy right foots.


Driven sensibly, magna's are great on fuel given there size/power.

I average 11L/100km doing the daily commute in Canberra in my TL.

Thanks, it seems that I should be expecting about 11L/100km as well. I wish I could get more reliable data on some other cars I am considering.
Anyone know how much attention I should be paying to the Redbook fuel consumption figures?

Well they are most likely taken straight from manufacturers claims so are probably higher then what they state...

Real world figures from switched on drivers would give a better indication.

The only experience I have of driving an FWD was a rented TL 4 speed in 2004, for a trip to Sydney with several days there - all told about 1000km with a trip computer calculated average of 8.5l/100km as I recall. As best I can estimate, in stock trim my AWD would have recorded 10-10.5l/100km for the same trip. As best I recall, the instantaneous consumption readout in similar places around Canberra was typically 1.5-2l/100km lower than my AWD.

Best guess for a FWD KJ? somewhere around 11-12l/100km. A lot will depend on your trips and how you drive of course...

BTW, if the usual trips involve any significant amount of idling at traffic lights etc the trip computer will be excessively pessimistic about fuel use. This seems to be because it doesn't compensate for the effect of injector latency at low injector pulse widths (ie at idle). My normal trips don't involve much idling so the trip computer is only mildly pessimistic (my actual fuel economy is a bit better than the trip computer indicates).

Advancing the timing on 380 or ralliart cams can this give u a gain like the number 6 cams or no?

Advancing the timing on 380 or ralliart cams can this give u a gain like the number 6 cams or no?

What advancing the camshaft timing does is to bolster the low and mid-range power/torque at the expense of the top end - its not an overall gain as such. If you want the power delivered lower, as I do in my AWD, then advancing the Ralliart/380 cams does help. Probably not as attractive a mod in a manual without extensive dyno work to optimise it.