It's a Toyota Forklift, Model 7FGCU15, with a propane gas system. The Lift won't start consistantly. Once the gas (propane) system is hooked up by not opened the lift turns on. But once I open the propane valve and try to start again, no good. The regulator is good to go. The solenoid for the gas flow on the regulator works great when the propane isn't hooked up and turned on. Once I open the valve for the propane, I can't feel the solenoid working anymore. The volts are good going into the solenoid. I would like to check the vacuum sensor, but I can't get a reading with my meter. I may be doing it wrong, (the testing on said vacuum sensor) The vacuum sensor is a Denso 5volt 079800-4410. Any ideas or hints please.