Retrofitting 16.6 Gallon tank (late model) in early model chassis

[jlevie]

ahh i see. is there any way to test out the sensors? I am still having trouble visualizing the 2 tier system with the late model tanks (siphoning, dual sensors, etc) utilize

You can pull each sensor, drain it of gas and check it's resistance when the sensor is right side up (empty tank) and upside down (full tank). The full tank resistance should be zero and the empty tank resistance should be about 60 ohms.

The problem I face right now is that when my gas neeedle is on the red mark, I know the tank still has 6 gallons left (because filling up at the gas station stops at 10 gallons) despite the indicator suggesting I have a lot less. However, it has no trouble recognizing when the tank is full. I suspect one of the sensors are faulty but am confused as to which one it owuld be.

That sounds like a bad left (driver's side) sensor. But it could be a weak fuel pump or a clogged filter that is reducing the system fuel flow rate to the point that the siphon isn't working well. That would leave more fuel in the left side of the tank than should be there. The flow rate test is in the Bentley manual.

[bmwstephen]

You can pull each sensor, drain it of gas and check it's resistance when the sensor is right side up (empty tank) and upside down (full tank). The full tank resistance should be zero and the empty tank resistance should be about 60 ohms.

That sounds like a bad left (driver's side) sensor. But it could be a weak fuel pump or a clogged filter that is reducing the system fuel flow rate to the point that the siphon isn't working well. That would leave more fuel in the left side of the tank than should be there. The flow rate test is in the Bentley manual.

I'm going to have to go with bad sensor because the point and time where the gauge is misread is always between the red mark and half way mark. I recently had my fuel filter replaced and before and after the install, the shop was required to check the fuel system pressure all the way up to the injectors to see if the numbers were different from the old filter (needless to say, it was a waste of 70 bucks because the numbers were no different despite the filter being 10 years old ). On top of that, my car starts fine everytime never has any hesitation or bucking in terms of fuel pressure

but based on my description, would it also have anything to do with the cluster? I've heard some members mentioned that there are nuts/grounds on the gas gauge that comes loose over time. but i find it hard to believe that thats my issue

[jlevie]

Bad connections in the cluster usually result in the gauge needle bouncing erratically. It wouldn't hurt to refresh the connections for the fuel and temp gauges by reflowing solder on the pads, but it doesn't sound to me like that is your problem. A worn pump can produce sufficient pressure/flow for the rail pressure to be correct, but still not produce rated flow. Once you know that the rail pressure is correct the next test is to measure the flow rate from the FPR.