Tech 2 fuel gauge calibration

[carrera]

Right, I've run in out of fuel twice in the silver car, about 10 miles or so after the reserve light comes on, when the needle is only just starting its descent town to the end of reserve. The gauge is not working like I expect it to so I have been messing in Tech 2.

The activation of the needle by Tech 2 correctly places its position

I understand there is a global adjustment, and then individual calibration adjustment at certain points.

Anybody know how the "increase" / "decrease" translate into the reading of the gauge, or how to interpret "Fuel level (ECM)"  and  "Fuel level (Calibrated)"

So in other words I can see where to make the adjustments, but am unable to observe a visible change in the fuel gauge, so don't know if I making things better or worse.

I am trying to avoid draining the tank to go through the WIS procedure ....... but in a sense that's a bit of a false objection as I have obviously already done this twice 

I have already read that there may be an issue with baffles coming loose, but these symptoms would not seem to fit with a physical blockage, as the point where the reserve light comes on would seem to be correct.

For reference I just looked at the green car and the settings there are 2 0 1 0 0, reading top to bottom.

Thoughts ?

[phoenix]

If you know your mpg figure is accurate (on a couple of brim to brim fills) then you can start from a full tank and work out the fuel consumed, read the actual values at the theoretical set points and then set a suitable offset.

[carrera]

The problem is I don't understand which way the adjustment works.

If I was to set the adjustment to +5, which of these statements is true?

A, Resistance reading indicates there is 20 litres in the tank, +5 means show 25 litres on the gauge; or
B, Resistance reading indicates there is 20 litres in the tank, +5 means the gauge is over-reading by 5 so move the needle to where 15 litres should be

I was hoping I could just go to the extreme and see a difference, but that cunning plan has not worked 

Bright idea. Does ECM mean Engine Control Module ?  (as I just think ECU), so ECM is the base reading from the resistance, and calibrated is where the needle should point to on the gauge ?

[phoenix]

IIRC there are two values that you see on the "read" display- actual and filtered. So I guess you just try the offset plus or minus and see what it does to the filtered value (which is the one the display and DTE uses)

[carrera]

Messing about on a different car now, ignition on engine not running:

Starting point, set to -1, sender showing 3.0v

ECM:    62 litres
Filtered 62 litres

Changed from -1 to +3

ECM   : 66 litres
Filtered 62 litres

Distance to empty did not change, unsurprisingly, at that part of the fuel gauge scale 4 litres is not visible.

My logic tells me that the MIU is getting a "filtered" value from the sender, and it is then telling the T7 ECU a different, bigger value, and also making consequential changes to the needle position.  I expected DTE to change, as I see DTE as litres remaining x miles per litre. Looks like T7 does not.

That would seem to be the "wrong" way to go if you don't want to run out of fuel ?

[Audax]

My logic tells me that the MIU is getting a "filtered" value from the sender, and it is then telling the T7 ECU a different, bigger value, and also making consequential changes to the needle position.  I expected DTE to change, as I see DTE as litres remaining x miles per litre. Looks like T7 does not.

With T7 that the DTE is only calculated periodically when driving, the reason is that if the value changed constantly it would mean as you accelerated your DTE would drop massively and then if you went down a steep hill it would go to infinity. I can't remember the update interval though but did you actually take the car for a drive after changing the value and resetting the DTE?

[carrera]

It does drop massively when I boot it 

Experience tells me that the DTE is updated fairly regularly, but with a smoothed recent average MPG, rather than instantaneous.

It's also fun to clear the calculation when you are doing say 60, then let the car coast and suddenly you can see 99.9 mpg on the SID. Little games

I didn't take the car out for a run as I didn't want to change the test conditions, as soon as the car was started the internal mpg would have started dropping DTE dropping and then would go up again as the engine got warm. Probably just an invalid expectation from me for the DTE to immediately change with the fuel level "change". 

Maybe a bit of overthinking or logic overload 

[sgould]

I was working on my car, and the engine had been ticking over for a while.  I got in to turn the engine off when I saw a photo opportunity.  It was not long after I bought the car.  The mileage is over 150,000 miles higher now...

[sgould]

I did read the bit in WIS on the DTE.  It's an accumulation of weighted averages.  A bit of instant, a fairly large % of  the last 10 mins, and other %ages of older consumption.  Something like that.

[carrera]

Thanks for that.... fits with my gut feel too. However is this a start of a competition for the worst mpg on a car 

Postie still hasn't been so I might end up doing a tank drain over the weekend after all

[sgould]

The post seems to be a mess at the moment.  I ordered a new battery charger/conditioner on Good Friday. It was listed as "dispatched by First Class post" by the seller on Saturday.  It's still not here.   The sharkfin I ordered a week or so back took nearly a week to get here by First Class post.

The sharkfin seller has since posted that he leaves the packages at his local post office, but he found out that the Royal Mail are only collecting from the PO three times a week, rather than twice a day.  Mine was left at lunchtime on a Friday, but not collected until the following Tuesday...

The package that is currently awaited, may have been left at a PO on Saturday, but due to Easter holidays, it may not have been collected from there until the following Wednesday...

[sgould]

I've found the DTE info from the WIS. It's not as I remember it.

The SID uses the following sources: Fuel level, Miles travelled, Fuel consumed (from ECU), Coolant temperature.  It's updated every 16 seconds.

but... no update takes place when starting from cold or when the speed speed is below 5km/hr.  When reset, the starting value is calculated using 1 litre/10 km.

[sgould]

Postman brought the package this morning.  So a whole week from posting to arrival for First Class post.  Battery is now on charge.

[carrera]

Postman brought two packages this morning

Power supply is in the car and does clear error P0826, so later TCM's can be used in a 2002 car with this mod.

I'm about to shuffle cars about and will look at the fuel gauge again, then it'll be a siren repair with the other package.

[carrera]

I decided to drain the fuel off.

Believe it or not, the first time I tried this on a 9-5 I managed to syphon it off. no luck this time, so as I don't have the tool to disconnect the fuel lines easily I decided to remove the pump to put the drain pipe in.

Wise choice !

Someone has been in here before, and the pump body was no longer attached to the cover plate by the spring plate. So, resting on the botton of the tank probably, and probably stopping the float moving fully down.

I cleaned the contacts and it has a nice full range from 50 ohms to 425 ohms.

Now I just have to try and reassemble it, and hope no damage was done in the previous bodgery

I think that's the problem anyway, need to find a decent picture of a good one