With the Chevy Venture, Oldsmobile Silhouette, Pontiac Montana they seem to have issues with the fuel gauges appearing to malfunction. The gauge jumps all over the place and you can not seem to determine how much fuel you have in the tank. OR It will just read empty or full at any given time.
There are a Multitude of things that can be causing this, but most likely it is the fuel level sending unit(FLSU), located inside the gas tank on the fuel pump assembly is opening up.
The FLSU an open-contact variable resistor hooked to a float. As the float moves, it changes the resistance measured by the Powertrain control module(PCM). The PCM reads this signal, and adjusts the fuel gauge accordingly.
What you can do yourself if you are technical enough to handle this. If you do not feel comfortable then we suggest you find a good mechanic and allow them to perform the tests and repairs. GMTruckHQ.com does not take responsibility for any failures or problems that may arise from performing the actions in this post. If you wish to perform the below steps then you take these steps under your own actions and anything that may happen negatively or positively are not the responsibilities of GMTruckHQ.com.
Basically we are telling you that if you mess it up you are solely responsible for the mistakes.
Now on with the information.
If you have a voltmeter, you can check the signal from the PCM through the electrical harness located on the driver's side, underneath the van. It is where your feet would sit if you were in the middle row seats. There are a total of three connectors, one is for the fuel tank.
With the van off, unplug the white connector with six wires. Locate the Purple wire and Black/White (black with a white trace) wire and then determine the corresponding pins on the van.
Hook your voltmeter to the pins on the van, and turn the ignition to "Run" !!!!NOT "Start"!!!
You should see 5 volts DC. If not, you have other problems and can locate a response in this forum for that too....but on with what we started.
Turn the van off.
If you have an ohmmeter, or are using a multi-meter, measure the resistance of the sending unit. On '98 and later Ventures, you should read 40 ohms empty, 250 full. If you read more than 250, or unlimited or OL on your meter, then it is reading "open."
One thing I have done was to hook up the meter and shake the van to see what the fuel did as it moved. The unit would go from 80 ohms to open, so the PCM was not getting a consistent signal, and caused the faulty readings on my gauge. I confirmed this by hooking up a 500 ohm variable resistor in place of the sending unit and turning the van to "Run". This allowed me to vary the resistance that the PCM was seeing and confirm that the sending unit is the problem. If you try this, be sure you are on the right wires, and don't drop the resistance below 40 ohms, as this low resistance may allow too much current into the PCM. In addition, you will notice a lag time between moving the resistor and gauge movement. This is okay. The PCM takes a measurement of the fuel level resistance, and then adjusts the gauge. It's not like the old way of doing it, where the sending unit goes straight to the gauge. If you try this and the gauge doesn't move where or how you want it to, your problem may be something else. If it does work, then it's definitely the sending unit.
Make sure you don't have a wire problem (broken, corroded, etc.). If not, then I would suggest replacing the fuel sending unit. They are only available from GM, part number 88964333. I would suggest you check and make sure this is the right part number for you. I will update this thread with part numbers later.
To replace it, you have to drop the fuel tank. This is not a quick and easy thing to do. It can be done in your back yard or garage. There are two fuel lines to disconnect, two EVAP lines and one filler hose.
The fuel lines disconnect by pinching the clips on the lines and pulling apart.
The EVAP lines have a ring that you have to pinch.
The filler hose has a plain old hose clamp (screw type).
WARNING: When disconnecting these lines, and working with the fuel tank in general, you WILL spill gasoline. Gasoline is highly flammable and can be explosive, so BE CAREFUL. If you are prone to accidents, or are generally inattentive when working, don't even try this. Take it to a shop. I am not responsible if you get yourself hurt!
The fuel lines and first EVAP line disconnect at the front end of the tank, just beneath the driver's seat.
The second EVAP line disconnects behind the rear driver's wheel, along with the filler hose.
Once the lines are disconnected, you can remove the three straps that hold the tank in place. Use a floor jack to hold the tank in place. A bolt on the inboard side and a t-slot on the outboard side hold the straps. Remove the bolts, and take the straps out of the slots. *** Remember where they go.
Now, slide the tank out from under the van.
Clean off the dirt around the fuel pump assembly before you take it out. Disconnect the lines and electrical connectors. There is either a plastic or a metal retaining ring holding the pump in place, depending on the model year. If it is metal you will have to tap it out of place with a brass punch, which is non-sparking. REMEMBER -- Steel on steel is not safe around gas. Sparks cause fires! Once the ring is loose, lift the pump assembly out. You will have to lift and angle it over, in order to clear the strainer and sending unit float arm through the hole.
Remove the old sending unit, and replace with the new one. Make sure all your electrical connections are correct before you put it back in the tank. Check twice as you don't want to repeat this job.
Return the pump assembly back to the tank, making sure that the o-ring is in place (THIS IS CRITICAL). Lock the retaining ring back in place and re-connect all lines and electrical connectors as you removed them.
Putting the tank back in place is essentially the reversal of the removal. However, be careful not to pinch, break, or lose your fuel or EVAP lines. Reconnect everything and start the van. It will take a couple of tries to start it as there is no fuel in the lines yet. Once it is running, get out, and check for leaks. If you find one, kill the engine and fix the leak.
BE CAREFUL with this procedure!