Fuel Gauge Malfunction

[Kelvin 996]

The fuel gauge of my 98 C2 was malfuctioned, i had the oil sensor(Sensor in the fuel tank) problem before and replaced earlier in February and since than it was ok until last week the gauge was failure when i was driving 30mins later. At first the fuel gauge needle was suddenly dropped to bottom together with the warning light flashing. I was then stopped the car and restarted the engine, the needle was moved right up to the top and station for few seconds than dropped with warning light flashing again and this condition was still the same on return home.

On next day i took the car to my local garage, the mechanic was detail looked at the sensor with some measurment carried out and said to me the senor was ok, the possibility casuing the failure this time is the fuel gauge on the instrument panel(Speedometer Panel). He also told me that the whole instrument panel need to be replaced and cannot just replace the fuel gauge individually. I had checked the price for a complete new panel with my local Porsche dealer it cost HK$24,000 which is US$3000.

Now the needle was pointed to the top (no warning light flashing) looks like there are full tank of fuel and needle never get down even there is only 1/4 fuel inside the tank.

I have a few questions below and hope all experts here can direct me with some advices.

1. It is true that i have to replace the whole panel not just the fuel gauge only.

2. I found there are few second hand instrument panels on ebay but they are all Mile version not KM on the speeometer. Is the mile/km surface indicator can be easy dismentled and changed.

3. By observing the failure is there any other possibilty causing the malfuction.

Very much appreciated and looking foward to have your valuable advices soon.

Kelvin

[JFP in PA]

When your fuel gauge was replaced, did they perform the fuel system level calibration with a PIWIS? This requires totally draining the tank, installing and checking the new gauge, and then putting measured amounts of fuel in the tank to test and set its calibration......................... If they did not, there may be nothing wrong with the gauge itself.

Edited August 19, 2011 by JFP in PA

[Kelvin 996]

When your fuel gauge was replaced, did they perform the fuel system level calibration with a PIWIS? This requires totally draining the tank, installing and checking the new gauge, and then putting measured amounts of fuel in the tank to test and set its calibration......................... If they did not, there may be nothing wrong with the gauge itself.

First of all, thanks for your quick response. I believe they did not performed the PIWIS calibration, i think what they have done in February was took out the leveling sensor and replace the new one. May i ask is the PIWIS calibration a must when replacing the new leveling sensors and what is PIWIS.

After the replcement in February the reading of the fuel gauge on the instrument panel was corrected and the fuel needle was working fine each time when the fuel was top up. The malfuction of the needle suddenly dropped down with warning light flashing happened last week, does it related to the PIWIS?

I have top up the fuel in full today and i will drive again tomorrow to observe the needle movement to see for the sudden drop occur or not. Now the needle is pointing to the top and no sudden drop for the 4km driving since the fuel added this aftrnoon.

Thanks again

Kelvin

[JFP in PA]

A PIWIS is the Porsche diagnostic computer system, mandatory for many types of work on these cars. When the fuel level sensor is replaced, they are supposed to run the level calibration diagnostic, otherwise the fuel gauge will not read correctly. Even a prolonged disconnect of the battery can require this calibration. I would suggest you get the car checked out by someone with the correct equipement.

Edited August 19, 2011 by JFP in PA

[MountShasta]

I'm interested in the comment on the consequence of having had the battery disconnected for a while. I had some alternator problems about a month ago and during the time in the shop, the battery was no doubt disconnected. Shortly after i started to notice the inaccurate reading on the fuel gauge. It would show low, and i go to fill up expecting to put in maybe 12-14 gallons (have 2001 Carrera: 16.9 gallon tank), but only taking 5 or 6 gallons. I top off and needle only show maybe 4/5ths full. The trip computer was giving me inconistent "messages"...the MPG calculation appeared normal, but the RANGE seemed to synch up with what the needle was telling you - which was lower than actual and therefore the RANGE showed less than what you could actually do.

So, I have to assume that this does NOT somehow self correct once the battery is reconnected? Is then the potential fix the diagnostics, and then fill up some, re-calibrate; fill up some more; re-calibrate...

[JFP in PA]

Normally, fuel level calibration is supposed to only needed if the tank and/or sending unit is replaced, or the instrument cluster had been changed. That said, we have encountered instances where prolonged battery disconnection has also led to this type of problem.

While time consuming, the procedure is not overly complicated. The tank sender has to be removed, and the tank completely drained of fuel, being careful to get all the fuel in the 4WD cars with saddle style tanks. Once drained, reinstall the sender, return 28 liters (7.3 gallons US) of fuel to the tank, and run the “tank calibration” function in the instrument cluster section of the Porsche computer system and you are done.

[EleCTriCT]

Additionally...... you can run the calibration with a piwiz using a resistor of 251ohms or use a trim pot jumpering the 2 middle wires on the connector.

Some might argue this is inaccurate but it is a method used at the dealer to save time - i was told. (you dont have to drain tank and fill with exact amount of fuel this way)

d.

[MountShasta]

Thanks for the feedback. Funny timing. I had talked to my mechanic about replacing the fuel sender unit - scheduled to bring car in tomorrow. I had assumed that is was only one possible issue - faulty sender, and had asked him to foucs on that only once i brough the car in. Then this morning, thought i'd search this forum for some feedback. I will now first talk to him about these two alternatives. Labor cost might still be about the same (assuming going with standard methodology), but at least i can potentially save $$ on the replacement for the fuel sender.

[EleCTriCT]

there is also a tech bulletin explaining this issue for the turbo and c4 i beleive, and most likely available on renntech!