Technical Fuel Consumption issue??

[JKR74]

Hello there,

I'm a newbie in this forum, but have a question:

A week ago I cross-connected a friend's low battery with mine. (his battery would not start his car...) The wires were connected with the correct polarity, but since disconnected, I noticed a slight change on the consumption behaviour of my GP.

IC increased from 17lt/100 km to 23lt/100 km on first gear, to 24lt /100 km on second, and I can now hear the engine sound like it pumps in too much gasoline. But the idle rate is normal (no suspicious variations), and no sign on my warning panel LEDs, whatsoever. The car was sent to the local FIAT dealer to be checked, and nothing was detected (I saw the report, it was OK).
The Tech. Supervisor instructed me that I should be carefull with the gasoline I put (unfortunately one cannot be sure about the quality these days ).
But still, the problem persists. I get increased consumption.
I made a rather harsh test, by driving in high rpm s, testing it hard and fast, but the results were the same: absolutely normal behaviour on 140-150 km/h (120 mph).
I know there is something wrong there.

Any ideas? Could it be the spark plug wires, or else?

FYI my GP is 1.4 16V Racing Edition, 2008.

TIA!!

 

[georgios1976]

I do not always trust what the on-board computer tells me about fuel consumption. Best way of doing it is measure fuel consumption yourself, this way you will know if your car is using more petrol than before. Might be some fault with your computer after all, not the engine!

Each time I fill up my car and do my normal driving routine, I expect the fuel warning light to come on at 320-350 miles. On the motorway, the light comes on at 420-450 miles.

Why can you not be sure about the quality of petrol out there? Thought all EU countries have the same standards on fuel quality!

 

[Aircooledbug]

The onboard computer can give you a variation in what it reckons you can get. My ST is a bitc* for it. If I drive along for an hour and I finish with 160 miles, turn the engine off, leave for 5 minutes then turn it back on it will shoot up to about 167 miles. There was a test done on Top Gear that their onboard computer's said 0 miles left, but they went on for another 20 miles. It does this so you will panic and fill up before actually running out.
To regards to the fuel, I stick to the same garage and same premium in my local area. But if I was out and about I always use Shell same as my local area.

 

[JKR74]

Well, I didn't mean the milage fuel consumption, which is generally true. I can get variable indications the same way you all described, so I don't really trust this. I only take a general overview, of what's left in my fuel tank
What I meant was actually the reprise of the car, so that is why I described the Instant Consumption meter. This meter indicates the pre-calculated consumption based on your gas pedal pressing, the velocity of the car, and the rpm s given. I have found it very usefull myself.
So I put it this way: I can feel the reprise a bit 'heavy', and the engine sounds and reacts as if it tries to pump in more fuel than it should. But no indication of injection malfunction or other, is shown on my panel LEDs. Imagine like leaving your A/C on, and try to accelerate. As I already mentionned, the computer was checked and found OK, by the local FIAT Service (Meanwhile I checked the A/C on/off and no problems found)
What could be the issue?...

*Regarding fuel quality, I'm afraid that in some cases you may not be sure. Some years ago, I had to clean my carburator (it was an old car I was using) due to gasoline mixed with... baby powder!!!!!!!!!

 

[Caravadossi]

The car was sent to the local FIAT dealer to be checked, and nothing was detected (I saw the report, it was OK) ... I know there is something wrong there.

I think you need to provide more evidence - that is, more data. It would help if you gave ALL of your computer readings - & not just `instant’ fuel consumption. What was your range & trip mileage & what was your av. speed readout etc? If we have this data, then we have something to work with – we don’t need to know how fast (or “harsh”) you have driven, as the evidence will be in the data.

You’ve had the computer checked by the dealer – with no fault detected. But you question that diagnosis.

I find the computer `reasonably’ accurate. I check my fuel consumption via the computer & manual calculation, from the same position – that is, fill-to-fill. Effectively then I’m checking my computer (& calculations) every 400 miles.

When do you check your computer readings? Every trip or after every fill?

Can you provide ALL of your computer readings for (say) after 160km or so? Or from a fill-to-fill situation?

How did you know your fuel was contaminated with “baby powder”?

A few other points. At `idle’ revs when the car is stationery – then the `instant fuel consumption’ reading is `zero’ … as you’re doing `zero’ km/h. The range & av. consumption are `estimates’ based on `past’ (yesterday) driving – it cannot predict how you will drive tomorrow. A difference in range from 160 to 167 is only a 4% change - & that figure will be constantly recalculated depending on how you are driving.

/

 

[Caravadossi]

A few other points. At `idle’ revs when the car is stationery – then the `instant fuel consumption’ reading is `zero’ … as you’re doing `zero’ km/h. The range & av. consumption are `estimates’ based on `past’ (yesterday) driving – it cannot predict how you will drive tomorrow. A difference in range from 160 to 167 is only a 4% change - & that figure will be constantly recalculated depending on how you are driving.

I could have put the above better.

The range is an `estimate' - the av. mpg (or av.km/h) is an `actual' reading. The estimated range will obviously reduce as you drive - but can show an increase if you throttle-back.

 

[JKR74]

Well, regarding the 'baby powder', I saw it myself, when the tech guy opened up the carburator and showed it to me. It was back in 1996, travelling a 550 km distance. I filled the tank from an 'underground' gas station... It was my only option before I go empty... And after 10 km, the engine went down.

Now, regarding the data you mentionned, I can provide them but I sure need time, in order to arrange a short trip, or wait till the tank is empty ("fill-to-fill" case).
I insist: there is something wrong with the fuel pumping and mixture. As I described it is like ""leaving your A/C full on, and try to accelerate."", the engine feels like it pumps in too much fuel. I see the IC indications, I can hear the difference as well (engine sounds lower, and unflexible) no matter where or when I am driving. I know this happened right after I removed the cables from the battery (see thread #1), because I noticed the difference right away.
It is not a matter of an overall consumption, eventhough your remarks are true. It's much like having a faulty carburator or similar. (I can't think of another way to describe it... and I am not a car modder... sorry! )
I've been using my GP, for 2 years, almost 50km per day, and made 15 medium/long distance trips. I know how it behaves, and trust me, this is not it!

 

[JKR74]

OK, so now I update: today I was driving a lot. It has now made clear, that it is a fuel-air mixture problem. The engine definately pumps more fuel, and the car cannot accelerate as it did before. It jams and shakes at around 3-3500 rpms. And still no sign on the panel.
It is quite like having a jammed carburator (old tech cars), or worn up spark cables...

I can't figure it out!

 

[Aircooledbug]

Have you contacted your dealer about this?

 

[JKR74]

Yes, I've already done that (see post #1), and I am going to visit them again, and explain the problem, as well as taking the car to another technician I know and have a second opinion on the matter.

 

[Aircooledbug]

Do you get a foul smell from your exhaust?

 

[JKR74]

Nope, all exhausts are measured and nothing's wrong with them.
I visited the Fiat Service again today. Test drove the car on maximum power, accelerations, etc, and no issue was noticed. The technician could not detect anything abnormal, which eventually made me look like stupid!!
The only possibility (quite rare, I'd say..) is that the program cannot recognize a false data to the springler that controls the mixture. In any case since there is no electronic evidence, I cannot go on by guessing...
Both techs (one service post I know nearby, and FIAT) came to the same test results, using same methods. Error report null, all clear and exhaust metrics normal as it should.
Maybe I shall have to wait, and see...

Will a computer upgrade fix the possible issue?

 

[JKR74]

Edit:

The issue is fixed, just by removing the negative battery contact for 15' . Then the computer was OK, and back to normal. Only bug is that I nearly lost the idle rpms for a while, and gave me the creeps, but after 10 mins of constant idle mode, the car was back to business. Ran it on a highway, high rpms and 150 km, and it's now smooth.

Thanx for all the support!

 

[georgios1976]

Edit:

The issue is fixed, just by removing the negative battery contact for 15' . Then the computer was OK, and back to normal. Only bug is that I nearly lost the idle rpms for a while, and gave me the creeps, but after 10 mins of constant idle mode, the car was back to business. Ran it on a highway, high rpms and 150 km, and it's now smooth.

Thanx for all the support!

Truly bizzare fault. I'm glad it disappeared, I'd love to get an explanation for it though...

 

[JKR74]

A tech guy I know told me that it might be a random change of values in the car's pc, due to amperage interferance.
He stated that it is possible, sometimes, the computer can be affected from voltage alternations of that nature (e.g. battery jump), and change its factory values having impact on how the car reacts on the driving sequence. This will not have impact on basic functions like fuel injection or similar, but the 'Smart Drive' values may be changed.
Last info was that in some serious cases, one must leave the battery contacts out for maybe 1 day, in order for the computer to reset itself and get back to normal.

I don't know if this is true, I only heard it from this guy, working at a car service store...