You’ve got questions. We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re helping to diagnose some fuel level and oil pressure gauge troubles.
W.K. Lucama, NC
Q: I own a 1950 Ford F-1 pickup with Flathead V8 engine. I have changed the truck over to a 12-volt electrical system, and put a set of Auto Meter gauges in the dash. I have a new float assembly in the gas tank, with all the wires hooked up correctly. However, the gas gauge will not register anything. When I turn the truck on, the needle on the gauge moves slightly, indicating that it receives power. I am also having a problem with the oil pressure gauge. It shows only 10 psi at idle, and 22 psi at 50 miles-per-hour. My manual pressure gauge shows 20 to 25 psi at idle and 40 to 45 psi at 50 miles-per-hour. Do I need a special sender for this oil gauge?
A: Let’s start with your fuel gauge. There are three possibilities: bad ground, bad gauge, or wrong sending unit. Due to different ohm readings and ranges, you could well have a mismatched sending unit. You can check for a bad gauge by disconnecting the ground wire from the sender and put the gauge directly to ground. The gauge should then read full; if it doesn’t, the gauge is bad. As for your oil pressure gauge, did you use PTFE tape on the sending unit? If you did, this can cause a poor ground connection against the block, which will throw off our readings. Remove the tape and see if that fixes the problem.