Strange fuel gauge, reserve light, sending unit question.

Hi_Fi_Guy · Hi_Fi_Guy's Garage

Out for a drive this morning and reserve light starts flashing on the fuel gauge with the needle reading 1/2 full. I'm in some twisty mountain roads and don't think much about it... just fuel sloshing I assume. But when I get back to the level roads the gauge continues to read 1/2 full and the reserve light on. At this point I know I am at least 30-40 minutes from the nearest fuel station and start to worry a bit. Then it happens fuel gauge needle flickers from half to empty, back to half again. I start driving very gingerly using "one-toe" throttle inputs and manage to make it to the gas station. Fuel gauge is still reading 1/2 full when the car drinks 15.3 Gallons!

Based on this scenario does anyone know if the culprit is the sending unit or the gauge? Does the same float inside the sending unit trigger the gauge needle and the reserve light or is there a separate trigger for the reserve light?

Thanks in advance for any and all responses.

tirwin · tirwin's Garage

I’ve been trying to diagnose a strange problem — or I think it’s a problem — with my fuel gauge.

I was on a road trip with some other Porsches. We stopped for gas and while I was filling up I heard a clunk like when you squeeze a metal can. I thought it was strange but didn’t think much about it. Then later I realized the gas gauge wasn’t reading right. I filled the car up again and it was only reading 1/2.

Got home and started to troubleshoot. Took a rubber mallet and tapped the sender. I heard the float rise. Turned the key and it read full so I thought I had the problem licked.

Later it seemed like it was still not reading accurately again. It was full or half and nothing else. I pulled the sender and tested it following the Bentley. It ohmed out slightly out of spec so I got a new sender. Didn’t change anything.

When the float was upright out of the car, the light was on. I had a hard time getting it to slide enough to read anywhere in between the extremes.

Try tapping on the sender to see if the float is stuck.