I need help with some diagnostic advice ... we have a 2005 Fiat Panda 1.2 4x4 which has been a great little car since we've had it. However it has recently been using much more petrol than before - about an extra liter per 100km. There was not a specific event where the car misbehaved and it happened all of a sudden, it just seems to have crept in and be that way now.

I noticed a big hole in the exhaust and replaced it - thinking that might be the source but it does not seem to have changed things much if at all.

I have taken the car to a garage for a engine diagnostic and they seem to think that all the data coming from the ODB port looks normal. The car is not burning oil and the engine sounds and feels its usual underpowered self. The clutch feels a bit 'grabby' in higher gears but I don't think that would have anything to do with the fuel economy?

I'm now scratching my head with where to look next ... could it be:
1. The drivetrain? If the drivetrain got stuck in all wheel drive it would probably be using more fuel? The odd feeling clutch could be linked to this?
2. The MAP sensor? Would the diagnostic tool not see the MAP sensor reading?
3. A break on the fuel line? But I can't smell or see anything?

Any genius ideas or advice where to look would be appreciated.

Don't know how much colder South Africa is in the winter (probably not too much since the equator is rather close), but overhere consumption always rises when the outside temperature drops.
How's your thermostat? If it'sw not closing properly, consumption rises significantly too.

gr J

Thanks A3jeroen - but we're in the middle of summer here at the moment! I initially thought it might have been that I was running the A/C but alas even with the A/C on it still seems to be using more fuel.

Having said that, a check of the thermostat is a good idea irrespective of season.

bpalmer said:

Thanks A3jeroen - but we're in the middle of summer here at the moment! I initially thought it might have been that I was running the A/C but alas even with the A/C on it still seems to be using more fuel.

Having said that, a check of the thermostat is a good idea irrespective of season.

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I read it as you've either got mechanical drag, or an overfuelling problem,

do you have acess to an exhaust gas analyser ??,
that should tell if the vehicle is over-fuelling,


I know you've tried reading with MES to see basic lambda reading..,

have you confirmed there is no major oil / water consumption.?

also firing correctly on all 4.. it's amazing how the electronics can mask a fault nowadays..engine will run MUCH better than it should woith a specified fault,

good luck,
do let us know what you find..,

Charlie

Thanks Charlie, good advice ... No major oil or water consumption at the moment. I will hunt around for an exhaust analyser, at least then I'll know which area to focus my search on.

our FIRE engine will run quite happily with the cam-belt 2 teeth out of sync,

the elctronics obviously just adjust all settings up 1 end to compensate..!!,

Charlie

Any problems when starting from cold?

Unpleasant 4x4 rear disc brakes seized and increasing friction.

Thanks Andy - no problems starting from cold, engine sounds good.

doctorchris said:

Unpleasant 4x4 rear disc brakes seized and increasing friction.

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Thanks Chris - will definitely be worth a look. I can actually hear the rear brakes from inside the car when I'm braking.

I'd tend to look at the rear discs too, as they can seize up and drag. Try a few quick tests;

- Try lifting off power and knocking car into neutral - does it still roll along OK or feel like it's slowing unusually quickly?

- Drive normally and try not to use the brakes for a while. Pull over and then feel how hot the discs are (any of them) - if they're too hot to touch then that's the problem.

Clean the tailpipe and then run the car for a few 100 miles and see how much soot builds up - too much too quickly (thick black mess on a clean rag) and it is probably running too rich. In which case try lambda sensors (first one is the important one - rear does relatively little).

A bit of an update ... I finally managed to get the car up on a lift today and have a look in more detail.

Firstly I noticed that the exhaust looked fine - the benefit of fitting a new one is that I can see that it's not too sooty after a few hundred km's - so hopefully the engine is running well.

With the wheels off, the rear brakes did look quite different to the front ones ... the pads had worn down past the wear indicator and the discs themselves looked to have some fine cracks on them, perhaps a sign of excessive heat? Either way, I'm going to replace the discs and pads ASAP - I just hope it is the only potential source of drag on the drive train.

While up, I also spun the wheels individually to see if the all wheel drive was engaged or stuck etc ... when I span the front wheels, the rear wheels also rotated a small amount, that eased up depending on how vigorously I span the individual wheels. I assume that this is normal behavior for the 4x4, as the system should engage all wheels if a single wheel spins (i.e. loses traction)

I didn't want to do the brakes there and then (need to get some quotes first!) so I had them re-assemble the calipers and off I went. Then, the odd thing is that the cars economy returned to normal on the way home ... as economical as last year and perceptibly so. I briefly stopped at the shops on the way home and after reversing out of my parking space, the economy had dropped off again and I was back where I started.

So ... could my use of the brakes on the way home have 're-gripped' the disc after that short period of time ... or did reversing the car possibly lock the all wheel drive system up? Either way, I'll know as soon as I've replaced the back brakes ... and hopefully that's all it takes to get my economy back

Thanks again for all the help and advice - greatly appreciated. :worship:

How are you measuring the change in fuel consumption so quickly - via the dash info display? Those things are not hugely accurate - particularly over short distances - so you should keep a full brim-to-brim log ideally.

To answer your question, it's unlikely that moving back and forth would change the drag from a sticky brake, but it is possible. However, if a binding brake IS the root cause of a significant change in consumption, then it will generate a lot of heat in doing so. Go for a decent drive, try not to brake very hard during that drive and ideally find a decent road where you can stop and then have a feel of each brake caliper. If you are suffering binding losses, then the culprit will be too hot to touch. Simples!

A bit of an update ... Just replaced the rear brakes and had all the calipers serviced etc. The brake guys were quite confident that the brakes were not binding, even though the pads and discs needed to be replaced. Unfortunately since doing that the car still feels a bit held back - and the onboard computer seems to be backing that diagnosis.

I'm going to get the car into a gearbox and 4x4 drivetrain specialist - for a bit of a look underneath to see what's happening.

I'll let you know how it goes - fingers crossed because we're doing a trip through Africa with her at the end of the month!

Good news and bad. :bang:

I took the car out for a longer spin and it seems that now the brakes have bedded in properly that everything seems to be back to normal. On a mixed cycle of half highway, half urban that I was getting 6.8 l/100 which is pretty much as good as she was before - so very big thanks to all of you for the advice about the rear brakes being the source of the problem.

Just to be sure I took the car into a specialist 4x4 drive train company who gave the underside the once over and confirmed that all was running well. While I was there, they noticed that the gearbox and diff oils had never been inspected so they thought I should get them checked while I was there - which sounded like a good idea as we're taking the little lady up into Namibia next week for a bit of a off-road holiday.

They said that the levels were quite low, so they did a bit of a top up with 80w90 oil and I left with a smile on my face as everything was now fixed. This morning however, when popping to the shops the gearbox felt a bit different to last week and I'm having a bit of difficulty moving through the gears - especially into 2nd. Ironically the quirky 3rd gear issues (rapid downshifting was not it's favorite thing to do) have now dissipated.

Doing a bit of Google research, there are quite a few horror stories about the wrong oil killing gearboxes, over filling etc. (But when I have a little headache and Google it I always come to the conclusion I've got a terminal brain injury!) So now I probably have to go all the way back and get the 4x4 specialists to sort it out (Parow Gearbox Exchange).

I'm wondering what should I say to them? Have they even done anything wrong and am I being paranoid? I don't want to kill the gearbox when I'm stuck in the middle of Africa. Can I just get them to drain the system and replace with proper grade Fiat oil if they've made a mistake or have I just broken my gearbox now? Should I get it towed to them or can I drive it to the workshop on Tuesday? As always - any advice from this great group of enthusiasts is appreciated. Thanks. :worship:

are you sure it is not a clutch problem ?. also what specification of oil does your owner manual say ?

From the 4x4 owners manual:

Gearbox/differential 2.7L SAE 75W-85 synthetic oil that passes API GL4 PLUS, MIL - L - 2105 D Lev specifications

Rear differential 0.6 SAE 75W-85 synthetic oil that passes API GL5, MIL - L - 2105 D Lev specifications

The only proper grade for the box is Fiat stuff from what I've seen, Castrol do the right grade for the rear diff.

306maxi said:

The only proper grade for the box is Fiat stuff from what I've seen, Castrol do the right grade for the rear diff.

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There are stacks of oils that meet the specification. Providing they meet it, they are absolutely fine. (and the oil spec for a SA car may be different - but same applies - if it meets the spec, it is absolutey fine.)

Show me all these oils that meet the gearbox specs.....