SonexBuilders.net

Have any of you bench tested a VDO? When this one is installed it reads 999 all the time, engine on or off. I put the old one back in, it was getting erratic, and it reads a solid 45. When I take a ohm reading it reads open. Have you used air pressure and what was the result?

Yes, can use air pressure with a regulator to check the sender. The resistance changes with the pressure. For my own future reference I took the following readings from a brand new vdo 5 bar 80psi sender before I installed it a few months ago.

5psi / 32 ohms, 10psi / 46 ohms, 15psi / 55 ohms, 20psi / 64 ohms, 25psi / 76 ohms, 30psi / 85 ohms, 35psi / 96 ohms, 40 psi / 108 ohms,
45psi / 110 ohms, 50 psi / 127 ohms, 55psi /137 ohms. 60psi / 148 ohms, 65psi / 156 ohms, 70psi / 164ohms

Onex107 wrote:Have any of you bench tested a VDO? When this one is installed it reads 999 all the time, engine on or off. I put the old one back in, it was getting erratic, and it reads a solid 45. When I take a ohm reading it reads open. Have you used air pressure and what was the result?

Open would mean nearly infinitely high OHMs (i.e. air resistance) if I'm correct, so it's pegged on the high side. Sounds like a bad sensor. I can tell you from my experience (of the lead wire grounding out on my baffles) that low OHMs would give a low/zero pressure reading. The circuit should be closed with very little resistance when the pressure is zero.