The fuel gage on this `99 Grand Prix is very unstable. I think it gives n accurate reading when you first start it, but as soon as one stars driving it the needle goes all the way past full. When one comes to a stop, the needle very slowly starts to decline. If I put it in park and get my foot off the brake pedal it will go down a lot faster. The needle will not move untill one stars driving. I did the basics, checked all connections and grounds and tested the fuel gage sender with a multi-meter, checks out fine. Any other sujestions are welcome.

 

if the guage isn't PCM controlled (i don't think it is but don't have access to wire diagrams from home) it sounds like a sending unit. when you checked it with a meter, you checked it probaby without the car moving. the fuel moving around in the tank can cause the connection on the rheostat to make and break. this is most common...what you could do to further test the wiring and guage connections is this. the guage operates on a 0-90 ohm rheostat on the ground side of the circuit. try disconnecting the guage sender wire (purple) and connecting a resistor (1/4 watt will work) to the wire end and then to ground. drive it and see what it does. if the guage doesn't fluxuate, i'd feel pretty good about replacing the sending unit in the tank.

 

In addition I will say that some fuels have a high sulfer content and that also affects the electrical contineuity at the sender. You may want to try a gasoline additive that is designed for this problem. GM dealers have an additive that may correct this problem without having to replace the sender.

 

right you are SLJ! my bad...and thanks for the addendum...

 

The Fuel Level Sensor consists of the following components: float, the wire float arm, and the ceramic resistor card. The Fuel Level Sensor is mounted on the Modular Fuel Sender Assembly and is used as an input to the PCM. The PCM uses this information as a fuel level input for Various diagnostics. The PCM controls the Fuel Level Gauge by grounding the Fuel Gauge Control circuit.

Some customers may comment on the following conditions:

• The fuel gauge reads incorrectly.

• The low fuel chime sounds prematurely. For example, the chime may sound when 19-22 L (5-6 gallons) of fuel remains in the tank.

• The fuel gauge may fluctuate from full to empty and then back to full after a fill up and a hot soak.

Cause
These conditions may be caused by several factors which are vehicle specific:

• Fuel contamination to the resistor board (sender card) of the fuel level sensor in the fuel tank.

• Calibration changes within the EEPROM of the PCM.

• Software revisions to the I/P cluster.

Each of these factors affect the accuracy of the fuel gauge and/or the low fuel warning system.

Correction
1998 Oldsmobile Intrigue vehicles built prior to May 7, 1998.
Request an exchange I/P cluster from the A-C Delco® Service Center. This cluster must contain the software modifications in Delco Electronics Bulletin #98 IDPD07ISA.

Installing this new cluster will result in the elimination of the low fuel chime.

Important: You must advise the customer about the elimination of the low fuel chime, as this is a change to the Owner's Manual information.

All 1997, 1998 and 1999 vehicles built prior to December 1, 1998.
In order to improve the accuracy of the fuel gauge, replace the fuel level sensor in the fuel tank. Refer to the procedure in the Engine Controls sub-section of the Service Manual.

1998-99 Oldsmobile and Pontiac vehicles built prior to October 1, 1998.
Reprogram the EEPROM using any Techline CD numbered higher than CD #21 for 1998 or the TIS 2000 #12 CD or higher.

 

Thank you everyone, most of this info and tips are new to me. I will give it a try and get back with results later. Thanks again.

 

pulled the pump and cleaned contact between float and sending unit and worked fine. Tanx evereyone