Quest for good fuel economy. 5 litre auto

[Haydz]

Hey guys.

since getting my exemption. i have realized its been using a fair bit more fuel than what other people have reported their cars of the same type use.

so here is what i have done so far.

1. Cleaned the Throttle body IAC etc
2. Replaced the oxygen sensor
3. Got 10mm leads
4. New Spark Plugs

Still yet to put the new plugs/leads in. and i have a bottle of Nulon injector Cleaner to go in.

since replacing the oxygen sensor my fuel economy has gone from 20.5l/100km down to 18.4l/100km

so im hoping the rest will fix it up to a more normal level.
just wondering if there is anything else anyone can suggest to make it a bit better.

the car is also going to get a wheel alignment. as it pulls to the left a bit.
this is also for anyone who needs to cure there fuel economy problem.

[hsvpunk]

WTF 20 per 100.
Something is seriously wrong with your car dude. (hence thats why your here)

I still cant belive 20 per 100,sorry 18.4 per 100.
How do you drive, road wise highway, country?

Im lucky to hit 14 per 100, and i do atleast 300-350kms a week. and thats highway, and stop start trips to amtes houses and shops.
I cant say ive seen anyones that high.

Maybe Mr Foam could share his thoughts, could be tune?

[greenfoam]

The standard tune will do alot better than 18l/100. With a tune you can see a improvement of 1-2L/100 maybe 2L but 1.5 would be more typical I'd say. The whole Coolant sensor/ECU coolant circuit and thermostat areas are where you want to be looking for the problem and also the fuel pressure regulator. It _should_ use *just* under 10l/100 on a tune on the highway and maybe 11 without one, worst case. If it's 12 or 13 on the highway then it has issues that need some fixing, My VP goes about 650kms on a tank, mostly highway so it does still chew the juice considering the size of the tanks in these things but they are a bit thirsty engine after all

[Haydz]

ok guys.

well my driving is

most of the time under a quarter throttle. maybe 25-50 kays of the 350 or so. under heavy acceleration.

greeny. i spoke to wavez about getting a tune from you. probably be next pay day now. i splurged and bought new plugs and leads.

Ok. anyone know how to test the coolant temp sensor? or just buy another one and hope that was the problem?


not much highway in sydney.











that was reset with a full tank of petrol.

[VrWagz1]

Haydz just buy a new coolant temp sender unit, its not worth the effort to test them and its a fair chance it will be the problem. But thats bad fuel economy, im doing heaps better than that in my wagon which would be a similar weight. Do the plugs definatly, you will notice a nice little power increase if your old ones are worn and make sure they are gapped to specs too.

If your running non stock wheels, do a check on your cluster to make sure the k's are clocking up close to what they should be. You got any of those 1 - 5km odometer check things on the freeways near you. If its out you can calibrate the dash to read right again pretty easy. It will help make sure you fuel readings are accurate.

[clubby_you]

with alot of city driving (ie me going to work ) was pretty common for my clubby to be around 18l per 100 with full throttle being used like 3 times a week in traffic these things are terrible since putting the manual in i have been driving a bit harder and am now around 14.7 to the 100
I have seen 20 - 100 km when i was sick one week and i was just driving in peek hour to and from home to pick my missus up

My advise get a manual

[Haydz]

this traffic was not peak hour. as indicated by my average speed. its a bit of both. traffic lights to 60-70 kay roads. with a bit of a blat in for good measure.

im going to call peps now and get a price for a temperature sensor. and if its not to costly ill buy it if not it will have to wait till later



Edit: 25 bucks from Peps auto spares

[greenfoam]

I see your speed average is 30 ks, my average speed is about 80 for lifetime of the car while I've had it, so that's a pretty big difference. Not sure how I would go putting around in heavy traffic like that, I don't think I'd have a car over about 1.8 litres if that's all I was doing

[paulsautoelec]

put negative lead of multi meter on neg battery clamp pos in radiator water/coolant with engine running . a reading of no more than 500mv should be observed. any higher voltage and youhave electrolisis problems. flush cooling system replace with gm coolant and distilled water. you will be surprised at the difference it can make

[STEALTHY™]

Convert to manual. Job done.

[KyleBrown92]

i dont have an 8 but, does it see, to be rivving higher than it should be?
ever changed the dif?

[clubby_you]

Convert to manual. Job done.

2nd that 1 million times better to drive to

[Nanos]

buy a ls1. lol

currently my average speed is 47.2km's average fule is 12.7.

i would be doing what everyone sugest's also i have noticed that no one has asked when you last changed your air cleaner or last time you cleaned it.

[STEALTHY™]

12.7 is good, under 10 is better

I'll stick to my 5L thanks.....(and to think the 6 speed will be lower than that)

[clazzza commy]

try and replace your fuel filter,it can stuff your economy if its realy blocked

[Haydz]

Hey guys. well some progress has been made.


replaced the temp sensor. replaced the plugs and leads. and now gets 12 ish babying it. and 14ish normal driving. still on the quest to improve it a little. but now that its manageable im happy. and to the other posters.

i cleaned the air filter just over a month ago. and fuel filter was replaced last week.



and manual. i done that with my old car. if it werent my daily i probably would. but i just get sick of changing gears when you can be doing better things

best time driving i ever had in a 3 seater auto ute

[Cobez]

I average about 16.5L / 100kms city driving stop starting all the time. Pretty average, not bad, not fantastic. That's with a Foam tune, 3" cat back, HSV headers, the factory HSV CAI with an aftermarket flat panel.

[Haydz]

well after a few months. normal driving is now around 14 -15 with an average speed of 60ish. thats with a greenfoam tune and on 98 fuel.

just wondering if there is anything else i could try to improve it a bit more? anythings worth a shot really.


would the coil or dissy cap/rotor button cause excess fuel usage?

[Vee-ard]

Haydz quick question, did you replace the temp sensor itself or the temp sender unit? Im getting about 17L/100kms at the moment, and thats all highway driving. Its suddenly got shit after being about 15/100kms not too long ago, and nothing has changed with the driving style.

[Wombles]

Maybe high flow filter, CAI..
Other than that no clue what else you can do...

[Haydz]

hey man i replaced the temp sensor. the 2 wire one that goes to the ecu. it was about 40 bucks. at the same time i also replaced the thermostat. thinking it may be the wrong temp etc. but now that works perfect. sits at a quarter on the guage and goes up to half in traffic.

also wombles i have a K&N Panel and a CAI also pacemaker extractors and a 2.5 inch cat back.

i think i have an exhaust leak at anything above 3000rpm though. could this cause shit economy? depending on where its coming from?

[Asmodai78]

i do drive the V8 from Sunshine (vic) to Albury every 2nd week and i get my fuel average down to 10/100, thats with a greenfoam tune, Pacemaker extractors, 2 1/2 cat back and standered 3.08 diff. Mate of mine who does the same trip only he dosent have a foamy tune but he has 2.93? diff and he gets 8.8L/100.

[levymetal]

well after a few months. normal driving is now around 14 -15 with an average speed of 60ish. thats with a greenfoam tune and on 98 fuel.

man, that's pretty good. i wouldn't expect to get too much better than that really. some cars are better than others after all. you would probably spend more money trying to save 1l/100 than it's really worth in petrol money

[greenfoam]

With my VP when the coolant temp circuit in the ecu broke my economy when to crap. That's the only time it's been bad. I mostly drive on the highway but I get just a little under 10l/100 on a straight run on the highway and with my normal 80% highway/town driving I get 12.3L/100, it can't do any better than that any everythings in good condtion etc.

I don't run a tune with lean cruise on it. My friend has a VS stato, with the typical VR/S tune I do he makes 9.5l/100 on the highway (tested at the pump). Without the tune (which I lean out lean cruise a bit further and exented it's range) he makes about 10.5l/100 which we tested back to back on the same road. Droping 1 litre is about typical, but then again the base timing on other cars could be wrong or anything, there's alot of variables but It should allways improve a little bit with a tune.

Anyway, on the highway depending on the car anywhere from 9.5 to 10.5 is normal with the VR and VS's. If you can't get it into the 10's then there must be something wrong with the car somewhere. Around the city averaging 60 km/h I would have thought 14 was pretty good for a 5 litre, that's a big heavy car with a big iron engine that takes a long lonnnng time to warm up after all.

With the manuals you can drop a litre of two out of those figures

[Haydz]

ill give it a test on pure freeway tonight and let you know how i go. im not really complaining about the amount of petrol it uses. but hey why not make the car the most economical it can be.