My fuel gauge is an idiot - Alfa Romeo Forum
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(Post Link) post #1 of 16 Old 07-07-17 Thread Starter
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My fuel gauge is an idiot

Is this normal? (147 1.9 16v JTDM)

Set off on 150ml round trip, with ~2/3 tank showing
Get back from 150ml round trip, with ~1/3 tank showing
It was indicating 205ml range shortly before I parked.

Next time I start the car, it's showing FA fuel and indicating restricted range. Idiot.

This isn't the first time and it is telling lies. Once the gauge gets below 1/3 it loses its marbles once parked. There is a bit of a camber, but not 1/3-tank worth. I know that if I fill it up it will prove to be 1/3 full.

I don't particularly care, but last time it claimed to be running on fumes, I did 50mls then turned off and filled up because I was worried it would run out, only to find there were still 11L in the tank.

OK, that's better than pretending there is fuel when there isn't, but 11L is beyond sensible caution.

I don't understand how the gauge goes from 1/3 (correct) to buggerall, just through being parked. It seems the tank sensor is working, but I suspect there's some insanity being applied by the ECU. Anyone know more?
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mine does the exact same
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(Post Link) post #3 of 16 Old 08-07-17 Thread Starter
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Interesting!. I am struggling to understand how a gauge can go from 1/3 full to reserve just through turning the ignition off then on again. I sort-of assume it's like the temp gauge, lie-by-wire, and there is some condition that makes the ECU insist reserve is now appropriate even though it's not. Unfortunately, once that has happened it's not smart enough to recognise the fuel level is higher than it thought.

I probably won't be using the car for a few days, will fill it to the brim next week and see how much fuel is actually remaining. I suspect it will be at least 15L.
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Originally Posted by halftone View Post
Is this normal? (147 1.9 16v JTDM)

Set off on 150ml round trip, with ~2/3 tank showing
Get back from 150ml round trip, with ~1/3 tank showing
It was indicating 205ml range shortly before I parked.

Next time I start the car, it's showing FA fuel and indicating restricted range. Idiot.

This isn't the first time and it is telling lies. Once the gauge gets below 1/3 it loses its marbles once parked. There is a bit of a camber, but not 1/3-tank worth. I know that if I fill it up it will prove to be 1/3 full.

I don't particularly care, but last time it claimed to be running on fumes, I did 50mls then turned off and filled up because I was worried it would run out, only to find there were still 11L in the tank.

OK, that's better than pretending there is fuel when there isn't, but 11L is beyond sensible caution.

I don't understand how the gauge goes from 1/3 (correct) to buggerall, just through being parked. It seems the tank sensor is working, but I suspect there's some insanity being applied by the ECU. Anyone know more?
Mine does this too, I've replaced the fuel pump unit with a new sensor and the fuel gauge, neither of there were for this issue, it still does it, it will usually remember where it's supposed to be after 5 to 10 mins of driving. I guess it's just one of those Alfa thing we all love

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(Post Link) post #5 of 16 Old 09-07-17 Thread Starter
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Thanks all, I guess I can live with knowing that I sometimes have a reserve of about 150mls
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Mine does this too, I've replaced the fuel pump unit with a new sensor and the fuel gauge, neither of there were for this issue, it still does it, it will usually remember where it's supposed to be after 5 to 10 mins of driving. I guess it's just one of those Alfa thing we all love
Yep, when I had a 1.9 156 I found it did exactly that. The level would drop massively after engine off, but then gradually creep up over ten minutes or so until it got back to where it had been the night before. My twinspark does a similar thing, but less of a drop and a correspondingly quicker return to where it was. No idea what causes it!
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As has been said, it is an Alfa trait...

My previous 156 TS used to read 1/4 tank if it was parked on a slope, but then sorted itself out soon afterwards. My current 156JTDM 150 never does that, so I guess it's just an Alfa thing! I suppose that you could zero the trip every time you fill it up, then you would have more of an idea ?
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(Post Link) post #8 of 16 Old 14-07-17 Thread Starter
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I perhaps owe my 147 a bit of an apology. When I filled it up it took 53.1 litres, so had gone onto reserve with 7L in the tank. Which is not at all unreasonable, really. In fact I think it's what the owner's manual says.

However it's not really that simple.The implication is that the gauge had been lieing about there being more fuel than there was, until I turned off the ignition and turned it on again. Whereupon it showed me pretty much the true level.
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My 2008 GT has just run out of fuel on the autoroute whilst still showing just below a 1/4 tank ..... any ideas on how to fix the gauge anyone?
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My 2008 GT has just run out of fuel on the autoroute whilst still showing just below a 1/4 tank ..... any ideas on how to fix the gauge anyone?
Mine does exactly the same....when it hits the quarter full mark....just fill it up again....and smile that you have an Alfa

Who wants boring ?
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Mine does exactly the same....when it hits the quarter full mark....just fill it up again....and smile that you have an Alfa

Who wants boring ?
Yes who wants boring, eh? My GT Q2 is anything but, but I would rather fix the problem!
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The fuel gauge in any car tends to show less when cold (as in low ambient temperatures) and higher when warm (as in warm cabin).

Offhand, I can't remember if sender has high resistance when empty (which seems logical) or high resistance when full (illogical) but I'll take measurements with 2 different 156s at some point tomorrow (one is near empty, the other has 1/2 tank and very accurate gauge apart from over-reading when full).

I'll post results and try to advise.
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Have fuel tanks/senders evolved any, or do they still work with a system similar to the one in a cistern!?
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Have fuel tanks/senders evolved any, or do they still work with a system similar to the one in a cistern!?
Most cars still operate with the cistern as you call it (funny too ), cheap and cheerful, if it ain't broke don't fix it. Where I park there is a very adverse camber in the street, with the 7L's (or less) depending on the direction I park, the car won't start.

I believe the fuel sender is on the left hand side of the car/tank and regardless of sensor or ecu if there's no fuel that can get to the fuel pump the car ain't going to start.

So I always park with the camber to the left and the car starts every time. As Fruity said above the ambient temperature can also affect components on any cars, my brothers Merc doesn't like the cold at all.

There's the wrong opinion, and my opinion.
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Have fuel tanks/senders evolved any, or do they still work with a system similar to the one in a cistern!?
Most cars still operate with the cistern as you call it (funny too [IMG class=inlineimg]https://www.alfaowner.com/Forum/images/smilies/blabla.gif[/IMG]), cheap and cheerful, if it ain't broke don't fix it. Where I park there is a very adverse camber in the street, with the 7L's (or less) depending on the direction I park, the car won't start.

I believe the fuel sender is on the left hand side of the car/tank and regardless of sensor or ecu if there's no fuel that can get to the fuel pump the car ain't going to start.

So I always park with the camber to the left and the car starts every time. As Fruity said above the ambient temperature can also affect components on any cars, my brothers Merc doesn't like the cold at all.
Lolol....in that case im thinking at 12+ years old for most if our cars, the actual pivot is bound to start getting sticky and may give inaccurate or inconsistent readings at times. As well as all the other external influences mentioned. Over time, a full tank will give roughly the same miles, assuming driving conditions dont change dramatically.
If its 420 then refill at 390 to be safe and forget the gauge.
If you, like me, do short-ish journeys and then do a 400mile motorway round trip, you should expect a bit more.
Im at around 360-370 at the moment. I woyld easily get 500 though if i did some longer and more consistent journeys
Fuel gauge is a guide with live data being sent to/from the ecu. If u have 2galoons left and stuck in traffic doing 20mpg it'll shout at you to put more in asap. If you're doing 65mph down the m74 it'll leave you alone coz it calculates yoy have 90+miles left in the tank
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I have had fair share problems with the fuel gauge in my 156, first it was reading 1/4 when the car actually running on fume after living with that for a few months the problem goes away. Then it came back a year later and fix itself again, and a year after that it just goes crazy, bouncing from empty to over full(further than a little over F when it is working correctly) all the time, so the limited range alarm screaming at me every 15-30 second. I tried cleaning every connector I thought related to the fuel system and nothing has worked, after a week I finally figured out that the loose wire in the speedo plug caused the problem, 1 cable tie on the wires at the base of the plug fixed the problem I have had on and off with the fuel gauge since I own the car.

2002 Alfa Romeo 156TS Selespeed
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