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Technical Petrol consumption for mk2b Punto

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Technical Petrol consumption for mk2b Punto

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judderbar

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Hi

I am doing many short journies but my petrol consumption via the dash trip gadget is showing 24 miles per UK gallon.

The car runs quite well. There is the occasional flat spot on accelerating but otherwise it starts first time, idles evenly and shows no obvious problems. Here in Finland it is getting a bit colder but is above freezing and we drive constantly with the lights on main beam. The Car is kept in a basement garage under the house.

So far I cannot get a graph of my lambda or look at the fuel trims but the voltage via my voltmeter is from .1 to about .75 The maximum reading i have noticed was a tiny bit over .8. My voltmeter has a bar chart and the voltage cycles up and down in what seems like a typical manner.

I just passed the Finnish MOT and emissions test without comment.

I am going to go thru the various systems and try to see what is going on but has anybody got any suggestions so far? The last time i checked the plugs I saw no problems.

I have so far paid no attention to the amount of fuel i have been using and since it is displayed in km per liter it has never got my attention until i converted it to miles per uk gallon.

What should I expect to get in miles per UK gallon?
 
judderbar said:
How free should the front wheels become after you apply the brakes and jack the car up? If there is resistance there caused by the pads is that normal?
Click to expand...

no its not, the wheels should turn fairly easy and smooth once off the ground, try to push the caliper piston back manually and see if it moves freely.
 
I seem to have got very muddled up:eek:

Earlier today the car was doing at least 8.1 liter per 100km which is 34mpg. The consumption figure was improving but I thought it was getting worse because I thought the display was showing km per liter.:eek:

I had a look at the car and it seemed to me while using a new plug and lead the spark at the plug seemed very weak. So I got a new coil pack but the spark seemed even weaker but I ran the car with it and found I am now supposedly getting 4.7 liter per 100km at 80km per hour which is 60mpg.

I had a look at the front brakes and there do not appear to be any problems there.
 
Last edited:
samperry209 said:
I get 43 to 48mpg but I have just had a new exhaust so that may improve
Click to expand...

Very little unless you had major leaks affecting the back pressure

Crappy sparks result in poor mpg as the car trys to compensate, due to a poor flame spread inside the combustion chamber

I never trust the mpg read out
Mines very much 3 - 5 mpg out according to fuelly


Fill the car uo from empty
Drive 1 whole tank noting the before and after mileage to give the total trip (just incase you get flat battery)

When refilling work out miles vs fuel used


Fuelly is a great website to track mpg and stuff

It shows my driving style is poor and my driving distancr aint helping to my low mpg

Cars sweet as a nut though :)


Ziggy
 
Ziggy122 said:
Very little unless you had major leaks affecting the back pressure

Crappy sparks result in poor mpg as the car trys to compensate, due to a poor flame spread inside the combustion chamber

I never trust the mpg read out
Mines very much 3 - 5 mpg out according to fuelly


Fill the car uo from empty
Drive 1 whole tank noting the before and after mileage to give the total trip (just incase you get flat battery)

When refilling work out miles vs fuel used


Fuelly is a great website to track mpg and stuff

It shows my driving style is poor and my driving distancr aint helping to my low mpg

Cars sweet as a nut though :)


Ziggy
Click to expand...

I will start using fuelly im intrigued im gonna get crimbo done and then im gonna get it serviced. Sure the sparks need doing. Clutch is poss next thing to sort it feels like its slipping slightly again blame my crap new driver style driving lol. Oil was done in june so thats still alright ive only done about 1500k since change.

Im blaming partly corroded exhaust.. yeah it failed mot my exhaust was corroded and lambda readings came back to high but im all good now 140 quid later.

But as i say i normally shove 20 quid in and i came get roughly 150 miles covered with that or 9 days tooing and throwing from work

Let you know fella what fuelly says!
 
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Ziggy122 said:
Crappy sparks result in poor mpg as the car trys to compensate, due to a poor flame spread inside the combustion chamber
Ziggy
Click to expand...

Hi Ziggy,

I think you mentioned the spark from the coil should be one inch long? I thought my spark was a bit pathetic. I was able to get one cm with a spare new lead and a new plug and it gave a good click as it went off but it was still a thinner spark than i was expecting. I have not seen a car spark for about 30 years or more though. With the old aluminium cylinder things i seem to recall they were fairly juicy.

I am noting too that my plugs are not eroding after 30,000km and seem like new.

However otherwise there are no faults reported and the consumption at the moment seems very good. It could be I just got totally confused with my old persons eyes and old persons memory combining to totally confuse me as i was working out the consumption:eek:. Just about to drive about 30 miles there and back nearly all on motorway. So will do that at 80km all the way and see what happens.

I tested the old coil with a battery and could get no spark at all. Presumably it was on its last legs and full current for longer than the ECU would ever provide even when new blew what was remaining to bits?? I have started hacking the old coil into bits to have a look but it is resisting my efforts so far
 
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Now I am really curious to know what consumption the car is really doing.

On the same section of motorway doing 13km in both directions at 90km per hour the trip calculator is giving me 4.8l per 100km which is 59mpg.

And I learnt also the computer gives me current consumption as well! Obviously i have not been paying much attention to that dash board!
 
At this point in time I still do not know if my 'pathetic' spark is a sign of some weakness in the ECU or some other component or even a weakness in my far older eyes.

The car seems to be running ok but that does not really satisfy me. Unfortunately I dont know anybody in Finland who messes around with cars.

As I recall in NZ even on a bright day you can easily see a spark on a sparkplug even in sunlight?
 
Our car averages 15 km per liter ( 42 mpg imperial , 35 mpg US) or 6.6 litres per 100 km.
As Ziggy said don't trust the on board display. I am sure that our 6.6 l/100 km varies between 4 and 9 l/100 km depending on the conditions.
Get an accurate figure by filling the tank and using the odometer and refilling. Until you have a good number for that you could be wasting time chasing a phantom problem. If the car was over fueling I would expect to see it as sooty plugs and maybe even smoke on acceleration.
Whether or not there is a problem the basic rules still apply. Connections and earths will only get worse with time and can only get better by cleaning. Two in particular are the ecu earth to the throttle body and the main earth strap from the top of the gearbox.
After that there is the coil supply and the injector plugs.
If you feel comfortable opening the two ecu plugs you could also spray them with electrical contact cleaner.
While you are in the connection mood, the earth, black wire, in the plug for the rear light clusters corrodes and apart from causing the lights at the back to behave funny can also cause other electrical problems elsewhere in the car.
 
The trip computer is terribly inaccurate on short trips.

But... are you sure that it's not 24 kilometers per litre instead of mpg.imp? Finland is both LHD and metric, isn't it.
 
Last edited:
Yiiiiieeeeehaw said:
The trip computer is terribly inaccurate on short trips.

But... are you sure that it's not 24 kilometers per litre instead of mpg.imp? Finland is both LHD and metric, isn't it.
Click to expand...

I got muddled up. The trip computer was displaying 8.1 l per 100km since I filled up for the displayed trip km of I think 180km.

After resetting the computer and changing the coils the computer displayed 4.7l per 100km while travelling on a 5km round trip as near as 80km per hour as I could do.

At the moment for the same computer trip with 120km travelled the trip computer shows 6km per 100 liter. 47 UK MPG

I get that the trip computer provides confusing results when focused upon in real time. I am though assuming a car with computerised fuel injection can build a reliable comparison measure of fuel consumed so that last months similar driving can be compared to this months similar driving.

So for example did changing the coils make such a big difference? I am not so sure yet. Normally i make many small journies. Idling for example definately eats into the petrol MPG consumption surprisingly quickly.
 
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