Technical Fiat Panda 169/2005 High Fuel Consumption on idle/stationary

[marinosg]

Hi all,

I've been reading many interesting threads in this forum and couple days ago I decided to register myself and reach out to you all for some help with a challenge I am facing. Meaning... I am new in the forum (this is my first post) so let me start by saying a big HELLO to everyone

coming to my challenge...
I have a Fiat Panda 169 (which I really love), 2005, petrol 1242cc 60HP with 125000km on it, and lately I am facing some issues with high fuel consumption on idle - or I should better say when the car is stationary (or moving very very slowly).

let me try to better explain:
overall speaking, the car engine seems to be running fine (it idles at 800RPM stable, accelerates fine, no engine lights on...), but when I monitor the fuel consumption I see some crazy figures the moment I start to move the car (from being stationary). The car's onboard measurement for (instant) fuel consumption has a maximum reading of 25 lt/100km, and this is the figure I see when I move the car (from being stationary). This reading stays as such for few seconds and then begins to drop. When I am driving the car, the fuel consumption reading is normal (e.g. an average of 5 lt/100km). If I stop at a red traffic light, the moment I will accelerate and start driving the car, I get the the reading of 25 lt/100km (for 2-3-4 seconds).
Please note that I am 46 years old and my "racing days" are long gone... meaning that I am not flooring the gas pedal that could probably justify such reading.
I tried one more thing: to start driving just by releasing the clutch (without having my foot on the gas pedal) however, I still get the same reading on fuel consumption.
I also tried one more thing: I was parked on a hill, and I released the hand-break and let my panda to roll down the hill (having neutral gear and no foot on the gas pedal). I still got the same reading in the fuel consumption... (for 3-4 seconds, and then started to drop)
Just to mention here that the reading of 25 lt/100km is the maximum value on the car's onboard measurement system. I tried with an ODBII device and the reading I got was even higher. It was 39 lt/100km but this value was again the maximum of that OBDII device I used. The real value may even higher than that...

One comment I received from some friends, is that this value may not be realistic. It may be just the way the ECU is measuring on idle - which may not reflect the real fuel consumption. My response to this comment is 2 dimensional:
- That was not the measurement I was having previously. The car is 17 years old, and as I remember over the last 16-16,5 years I was getting a reading of 8-13 lt/100km when I was starting to drive from being stationary. Why this changed over the last months?
- This high value of fuel consumption is also reflected in my actual fuel. The tank gets empty incredibly fast. Previously, I was able to run approx. 400-500km by driving within the city with a full tank. Now I get approx.150-200km with a full tank by driving within the city.

so far, I have performed following actions trying to resolve it:
- cleaned the throttle body (and partially the IACV - without removing it)
- cleaned the MAP sensor
- checked and cleaned the spark plugs
- cleaned the injectors (I got professional help for this)
- cleaned both O2 sensors (and swapped positions with each-other)

Apologies for the long post, but this thing is driving me crazy. I can't figure it out...
any suggestion will be highly appreciated.

thank you,
Marinos

 

[mjc506]

Right, let's do some maths

The engine will use some (small) amount of fuel when idling, even in neutral - it's driving the alternator, there are plenty of pumping losses, and internal friction is significant.

When you're stationary, the distance you're travelling is by definition 0.

Measuring fuel consumption in litres per km (or anything similar, mpg etc etc).

You've got a non-zero amount of fuel used, divided by 0 km travelled. No matter how high or low the amount of fuel used (so long as it's above 0, which it will be with the engine running, unless on overrun), you get infinity lt/km...

The car won't display that (or even try calculating it, dividing by 0 is bad...) so freezes the display, unfreezing when you start moving again. When you start moving again, distance increases above zero, the calculation runs, but it's still logged the amount of fuel used while sat still. Resulting in a high number displayed.

This doesn't indicate anything wrong with the vehicle

Previous readings being so much better might be a result of 'rose-tinted glasses', but your full-tank range does sound low. Unless you do a massive amount of idling, most of the fuel consumption comes while you're moving. I'd be tempted to check for brakes rubbing, alignment etc, anything that might be slowing the car down (roof bars? anything else fitted?). Also bear in mind that the alternator will put more load on the engine while charging so an old battery could feasibly increase fuel consumption (this should be a small effect though).

Is there a possibility that your fuel gauge is miscalibrated? If it's showing 'empty' when you've still got half a tank this would appear to reduce your range. Should show up during fill-ups though - less litres would fit.

 

[marinosg]

Right, let's do some maths

The engine will use some (small) amount of fuel when idling, even in neutral - it's driving the alternator, there are plenty of pumping losses, and internal friction is significant.

When you're stationary, the distance you're travelling is by definition 0.

Measuring fuel consumption in litres per km (or anything similar, mpg etc etc).

You've got a non-zero amount of fuel used, divided by 0 km travelled. No matter how high or low the amount of fuel used (so long as it's above 0, which it will be with the engine running, unless on overrun), you get infinity lt/km...

The car won't display that (or even try calculating it, dividing by 0 is bad...) so freezes the display, unfreezing when you start moving again. When you start moving again, distance increases above zero, the calculation runs, but it's still logged the amount of fuel used while sat still. Resulting in a high number displayed.

This doesn't indicate anything wrong with the vehicle

thanks mjc506 for your reply.

The logic you describe in your post is absolutely correct, and I know some cars' ECUs follow this approach when measuring the fuel consumption, however, I strongly believe this does not apply for my issue.
as I mentioned in my original post:
One comment I received from some friends, is that this value may not be realistic. It may be just the way the ECU is measuring on idle - which may not reflect the real fuel consumption. My response to this comment is 2 dimensional:
- That was not the measurement I was having previously. The car is 17 years old, and as I remember over the last 16-16,5 years I was getting a reading of 8-13 lt/100km when I was starting to drive from being stationary. Why this changed over the last months?
- This high value of fuel consumption is also reflected in my actual fuel. The tank gets empty incredibly fast. Previously, I was able to run approx. 400-500km by driving within the city with a full tank. Now I get approx.150-200km with a full tank by driving within the city.

My Panda when stationary on idle shows "------" on fuel consumption reading. --> and this reflects what you mention as infinite.
It will only start to show some reading when the car starts to move.
honestly, I own the car for 17 years. All previous 16 years I was getting a reading of 8-13 lt/100km when I started to move the car from stationary. Why this changed now? I did not do any update in the ECU software...

 

[mjc506]

Sorry, I edited while you were writing apparently.

If it was just the display being 'wrong' then I wouldn't worry - the ECU can only measure how much fuel is being used by measuring how long it opens the injectors. If fuel pressure drops or flow reduces for any reason, the ECU will 'correct' by opening the injectors longer in response to the O2 sensors, but will think it's using more fuel when it's not.

However, range dropping significantly does point to another issue. Check for things like rubbing brakes, low tyres, recently fitted roof bars etc that will slow the car. I assume you've not noticed the amount of fuel going in when filling up reducing significantly? Any problems starting the car if it's been sat for a few days? (perhaps a large electrical load that's working the alternator hard to keep up)

 

[marinosg]

yes, very good thoughts.
I also had similar thoughts, but please share your view on how I see...

a massive amount of idling:
I would not call it massive... just normal traffic jam and stopping at red traffic lights. Because of this issue that I am facing, I now adaped a habit of switching off the engine if I need to stay idle for more than 10 seconds in traffic jam or red traffic light.

fuel pressure:
a potential vacuum leak could impact the fuel/air ratio and could make the ECU to drop more fuel, however, I think this would impact also the enging idling (it would not be at 800RPM stable as is now in my case). It would be idling rough and either going higher than 800RPM or lower (am I right?)

rubbing brakes, low tyres, recently fitted roof bars etc that will slow the car:
This was my first thought, but I would experience similar fuel consumption even on when on a trip road, wouldn't I. When I am driving outside the city (on a road trip where I am not continuously stopping because of traffic lights), the fuel consumption is on a normal level (average of 4.5 lt/100km). I am able to drive a distance of 550-600 km with a full fuel tank when driving on a road-trip outside the city.

I assume you've not noticed the amount of fuel going in when filling up reducing significantly:
Unfortunately, this is not just a matter of wrong fuel gauge or display issue. It is actual fuel consumption (or fuel loss?). When I go to the gas station and fill-up, I start thinking of finding a second job... (fuel prices are way to high nowadays)

Any problems starting the car if it's been sat for a few days? (perhaps a large electrical load that's working the alternator hard to keep up):
I do not experience any problems when starting the car (even if sat for few days).... however, I am having some thoughts about the battery itself (or maybe even ground issues). The battery is providing 12.06 volts when engine is not running. If I start the car, then I am able to measure 13,6 - 13,8 volts on the battery (should this be 14,0 - 14,2 volts?). Also to mention that, at the very moment I ingite the engine, the battery drops to 10Volts (and I believe this is the bare minimum acceptable voltage?) which potentially shows the battery may be coming to end of life (if not there already).
I read somewhere that a battery may be able to start (ignite) a car engine, but not able to properly run it. If this is true, could a bad battery cause misreadings in some sensors or maybe cause the ECU itself to behave abnormal? Does this make any sense?

I forgot to mention that sometimes (not always though) I smell gasoline when I am stationary and my windows are open.

 

[koalar]

Is the temperature gauge reading correctly

 

[koalar]

Read the long term fuel trim at idle

Is it maxed out

Or report back at what the O2 sensors voltages are at idle

 

[koalar]

Fully charged battery should be
12.6V
12.4V is still okay

Doesn’t fall below 11V when cranking and the battery is new

You can normally solder on for a bit longer even if it drops to 8V

If I remember correctly if you use a MultiECUscan to read the battery voltage it read approximately .5V lower than the true voltage on a meter

The three pandas I have had pump out 14.1V at idle and no load on a volt meter

 

[varesecrazy]

Hi

Only thing I can question..

How long has Greece run E10 fuel..?

That is a change that you might not have experienced until recently

Other things you have checked all sound great..
We kept our 1108cc 169 from 2004/2019

They are great cars..
and Batteries was the one thing that I had regularly fail ( failing to start the cars engine)..
and YES you would notice it running better with a new battery

 

[marinosg]

I was measuring my battery voltage using a voltmeter (not via OBDII) but nice to know this info, thank you

yes, the temperature gauge is reading correctly.
actually I replaced the temperature sensor approx. 1,5 year back because of problem I experienced: While I was driving at a mountain full of snow (winter time), all the sudden the temperature gauge dropped at minimum reading and I got an engine light on on my dashboard. I drove my panda to the garage and there was an error code related to temperature sensor, so I replaced the sensor. Last winter I faced again the exact same issue. Finally, the issue was caused by faulty thermostat so I replaced the thermostat as well. Now the temperature gauge reading is ok.

the long term fuel trim at idle is not maxed out... but I do not remember by hard what is the actual reading. I will check and get back on this.

O2 sensors voltages at idle:
I connected by OBDII device and collected some snapshots - hope these help to provide needed information.
the first part (the long graph) is from starting the car being cold over night until it starts to warm up.
the second part (the random snapshots) is once the car is somewhat warmed up (but not fully)

I was wondering...
if someone in the forum might have a similar panda to mine, could he/she please check what is the reading he/she gets for instant fuel consumption when starting to move the car from being stationary? it would be nice to check and confirm...

 

[marinosg]

Hi

Only thing I can question..

How long has Greece run E10 fuel..?

That is a change that you might not have experienced until recently

Other things you have checked all sound great..
We kept our 1108cc 169 from 2004/2019

They are great cars..
and Batteries was the one thing that I had regularly fail ( failing to start the cars engine)..
and YES you would notice it running better with a new battery

I... do not know...
honestly, I have not tracked this at all. Do you believe that E10 fuel could relate to this (potentially)?
should I try to run it with E5 or other for some time?

 

[varesecrazy]

If youve had good numbers on E10 than that isnt your problem...

I just hadnt seen fuel mentioned

 

[DaveMcT]

E10 has less calorific value than E zero but its not much. Ethanol has about 70% of that offered by normal gasoline. So we are losing 30% of 10% - about 3%. However ethanol contains oxygen so we gain a slight boost f efficiency. E10 has probably 2% less energy per litre than plain gasoline.

Reasons for poor fuel consumption
(a) Engine running cool (stuck thermostat) prevents the ECU from properly using the oxygen sensors - engine runs rich.
(b) Inlet side air leak confuses the ECU so engine runs rich to avoid damage. However this will usually raise an error code.
(c) Fuel has a lower than expected octane rating. The knock sensor retards ignition timing when knock is detected. This puts more heat into the exhaust so less is available to turn the engine. Power is reduced and fuel consumption increases. Test with known high octane fuel (or octane booster) and check for any difference in consumption.

Check the engine for faults e.g. (a) and (b) then run the octane tests (c) and see what happens.

 

[marinosg]

thanks for suggestions.

(a) I had a problem in past with the thermostat - but now replaced/fixed. Now the engine warms-up (very) quickly. So this should not be the case...
(b) this could be a reason... but wouldn't this increase the idle speed besides from raising an error code? I have no error codes visible...
(c) I've tried using couple gasoline additives (i.e. liqui moly injector cleaner, wynn's catalytic converter and oxygen sensor cleaner) but didn't help. I can try using some 100 octane gasoline and I can try E5 fuel, E85... This is easy to try

no engine error codes visible in my OBDII device...

 

[mjc506]

Hmm. Bad fuel consumption in the city, but ok fuel consumption on long drives?

That would support some problem reducing engine power (less noticeable cruising, but you'll put your foot down further subconsciously when accelerating away from the lights)

Here's a left-field idea - any problem shifting gear when stationary with the engine running? Is the clutch releasing all the way?

 

[DaveMcT]

A slipping clutch usually IMPROVES fuel consumption because you have to drive very carefully and can't use the power. I also think a slightly contaminated clutch would slip more at highway speeds than around town. The clutch would judder on pulling away but seem ok at low power. More torque is transmitted when you go fast in top gear so that's when slippage is most likely. Initially you might not notice but eventually you'll struggle to get home as the heat makes the clutch plate even more slippery.

The additives you have tried are not octane boosters. I would go with the 100 Octane fuel and see what happens.

Comment on the "left field idea" - A worn Panda clutch tends to get heavy to operate with a bouncy pedal feel and poor control that gets worse. eventually you can't select gears, because it's not releasing properly.

 

[The Panda Nut]

Whats the overall consumption like? If thats still OK it will be electronic nanny issues. If its really overall usingn more fuel then there is an issue. If you can smell fuel some times its a concern... I wouldalso check the breathers and fuel lines are all secure and the that and the flame arrestor (mesh in the breather pipe is OK. Go back to first principles and do the simplest checks first! Good luck

 

[marinosg]

Whats the overall consumption like? If thats still OK it will be electronic nanny issues. If its really overall usingn more fuel then there is an issue. If you can smell fuel some times its a concern... I wouldalso check the breathers and fuel lines are all secure and the that and the flame arrestor (mesh in the breather pipe is OK. Go back to first principles and do the simplest checks first! Good luck

short summary on the consumption is:
- if I am stationary or moving very very slowly (up to 10-15km per hour) I see a high ratio in the instant fuel consumption reading.
- if I am moving faster (above 15-20km per hour) the fuel consumption reading is normal
one very strange observation is that I face this issue even if I am just rolling down a hill (no gear selected, no gas pedal used),
I somehow lean towards some electronic issue, this is reason I was previously asking about the battery (or ground)...

but... you have some good point about breathers, fuel lines, flame arrestor... I need to better check these thoroughly, yes

 

[Txuchin]

I have a problem, which although it is not the same, may be related.
The CO2 reading on my Panda (1.2 2005) was always high, with apparent over fueling.
After passing through several workshops, I ended up discovering that the problem was the solenoid valve of the canister system, which was always open.
It is easy to check. You just have to release the ventilation tube from the tank and check that there is absorption.
Here is the valve:

 

[koalar]

I take it the bottom half of the screen is the post catalytic O2 sensor

Doesn’t look right to me. Should be over half way most of the time from memory.