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The fuel tank sender has no voltage to measure. It can only be tested as resistance using an Ohm meter. As the float moves up and down the resistance changes. Best way to test is to remove it. This is the same thing you would do to test the oil and temp senders. You don't want to introduce any sort of voltage for testing. The ICVR provides the voltage to the gauge and the senders provide the ground. Spark and fuel is not your friend here.
Basically if the factory gauge itself pegs to the high side when the hot wire at the tank is grounded momentarily, then the gauge is probably good. Just do this for a second to make sure it's OK.
Then with the sender unit in hand run the float arm through full travel lock to lock as it were, and see if the gauge display is corresponding to that. When the float arm is at the top of its travel, the gauge should read above "F". If not, that's a problem. It may just need an adjustment. The aftermarket senders have a set screw that will allow for calibration. I don't really care how many ohms it is, I just want the gauge to read close. Small adjustments make big changes in the gauge indication.
An easier or at least quicker way to calibrate is if the tank itself is known to be 1/2 full, adjust the float arm set screw (if it has one) and float arm so the fuel quantity gauge displays at 1/2 full, in the center of its range.
Which ICVR did you install? A solid state one will put out a constant 5 to 5.5 volts, an electro mechanical one will pulse.
The only reliable way to test these gauges is to follow the manual instructions. Disregard the 8.5 ohm resistor and radio choke they aren't used in your truck.
I bought and installed this a few years ago. I thought I might have bought the wrong one, but it fits the description of NPD and Dennis Carpenters website.
OK, I see they have "improved" the quality of construction. The arm is just crimped on to the rotor. Nice. So no adjustment is possible.
Note the gauge indication while moving the arm to either end of the stops. Might be able to bend the arm to change the degree of rotation and therefore the gauge indication, but the bend would have to be sharp and inside bracket before the stops. Or take your dremel and remove a slot to alter the travel range. If it is only pegging 1/2 when full though, it may not be salvageable. It's early and Coffee hasn't kicked in, but adding a resistor wouldn't help here I don't believe, unless it was reading too high.
No offense to you, but that's a POS! Guess we're lucky somebody makes 'em.
That IVR could be either one. Have you put a volt meter on it? You have an NPD sticker on top of a DC sticker. NPD sells both the solid state and the electro mechanical under the same part number. The things are all made in China some work, some don't.
Just follow the procedure in those shop manual pages I posted and you will find the problem. You might have to order the resistors from e-bay if there isn't an electronics store near you. And If you don't own an analog multimeter it's time to buy one. As Tedster said in a previous post digital multimeters are nearly worthless on these old systems.
When doing any of the testing the wire needs to be unplugged from the sender.
It sounds like maybe the wire is still hooked to the sender?
Wire with test light to ground light should blink.
Ohm meter to sender and to ground should read resistance of the sender.
Also if using a test light it has to be old school and not the new LED type.
Being the oil & temp use the same IVR and if working right could unplug them and test the wire with a test light to ground and see if it blinks.
Dave -----
When doing any of the testing the wire needs to be unplugged from the sender.
It sounds like maybe the wire is still hooked to the sender?
Wire with test light to ground light should blink.
Ohm meter to sender and to ground should read resistance of the sender.
Also if using a test light it has to be old school and not the new LED type.
Being the oil & temp use the same IVR and if working right could unplug them and test the wire with a test light to ground and see if it blinks.
Dave -----
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