Fuel Gauge Failure

Wentworth · Post by **Wentworth** » 17 Mar 2004, 11:53

MY fuel gauge randomly cuts out but sometimes with carefull percussion maintenance on the dash it bolts back to life. The yellow low light still works always though Its a 940 Wentworth 1994.

Any ideas. Volvo have replaced the gauge and the wiring to it. No change from

Volvord · Post by **Volvord** » 17 Mar 2004, 14:34

You have posted two problems this one and the cut-out thread) that could be related. In the fuel tank there is a low pressure fuel pump that feeds the maij high pressure pump. I have run across several instances where the ground wire at the fuel tank that grounds both the pump and the sending unit had broken or was loose. This would cause both gauge and drivability problems.

Access is inthe trunk on a sedan and under the cargo area carpet on the wagon. There is a plate on the floor on the drivers side that will provide access when removed.

Wentworth · Post by **Wentworth** » 18 Mar 2004, 04:02

Thanks Volvord, I'll check. But how would me tapping the gauge on the dash fix that sometimes. Volvo don't believe this bit.

For the cut out problem its always when I put my foot back on the accelerator gently after having eased off for some reason whilst driving. It can do it 10 times in one afternoon then nothing for days/weeks.

Volvord · Post by **Volvord** » 18 Mar 2004, 08:03

Wentworth wrote:Thanks Volvord, I'll check. But how would me tapping the gauge on the dash fix that sometimes. Volvo don't believe this bit.

For the cut out problem its always when I put my foot back on the accelerator gently after having eased off for some reason whilst driving. It can do it 10 times in one afternoon then nothing for days/weeks.

Well tapping on the gauge may just be a coincidence, but don't know. As for your Volvo dealer believing, well as a mechanic you have to look at all the symptoms ... too often they jump to conclusions, this wmay work some of the time, experience does play a role, but car problems are not consistent and don't always follow the rules. In diagnosing a problem a systematic and logical approach must be followed.

Look for bad grounds, fuel pressures, loose, cracked, or leaking intake hose connections. My 765TI also had a similar problem with the "cut-out" a while back, it was a real PITA to diagnose because it occured so seldom. In the end the solution was replacing the knock sensor, any application of gas would cause the sensor to trigger which rapidly causes the engine ECU to retard the timing, this cause a seriour hesitation. Replacing the knock sensor cured the problem.

Good luck

Wentworth · Post by **Wentworth** » 22 Mar 2004, 04:29

Can you give me more info on this knock sensor. Where to find it is easy / cheap to change. It is possibly the right area as I had noticed that the gauge dropped off after accelerating and then easing of the gas. It's an automatic.
Cheers

Wentworth · Post by **Wentworth** » 07 Apr 2004, 06:13

I replaced the Fuel pump relay in the dash and no more cut outs.
Still looking for the fuel gauge problem

LaRy · Post by **LaRy** » 07 Apr 2004, 11:48

I would take out the instrument cluster if it helps to hit the dashboard. It is fastened by two hidden screews in the lower front corners, and then you can tilt it out if the solution is similar to the 740. You say that the gauge meter is changed and the fault is still there. The gauge meter and the principle is very easy, so it must be a bad connection. Then it must be somewhere in the instrument cluster. I just suppose that they have the same solution on a 940 as in the 740's with a electrical soft filmsheet connecting different components and that principle has some problems. Take out the cluster, MAKE NOTES WHAT ELECTRICAL PLUGS YOU DISCONNECT AND THE POSITIONS!
I have been reparing similar kind of problems by checking all connections used for the not working unit. The connections are made by some sort of clamp pressing the electrical film against the gauge meter terminals. Loosen the clamp, scratch the cupper connetion area in this film carefully by a sharp knife (or use a fine sand paper) to get rid of the oxidation. After that clean all connection points with spirit.

I would also use good light and follow the "wires" in this electrical soft film all the way from the gauge sensor to the connector, using a magnifying glass. If it is cut by vibrations it will just look like a very thin line. If you find that, remove the insulation and solder som cupper wires over the crack. Good luck!