Testing electric FP sender?

[RBSOB]

Replaced a lift pump recently due to fluctuating pressures, sometimes on ZERO. The new pump showed steady pressures for a while [1 week,500 miles] now fluctuation is back. Any way to test the sending unit, which is remote mounted,rubber isolated and only 16 mos. in use, or just replace it? Testing will be a trick because the problem is intermittant. Thanks guys, JimG

 

[Deezul1]

Usually those units complete the ground circuit to the gauge so use a OHM meter to check from battery ground to the case of the sending unit for a zero reading inicating a good ground. The other thing you could do is run an extra wire from the sending unit into the cab so you can check the reading with the meter going down the road and see if the meter reads erratic along with the gauge which would inicate all is well with the gauge.