I have a VDO gas gauge in my 40 coupe which has a 16 gallon poly tank. When tank was near empty yesterday, the needle pegged over FULL. I then put 10 gallons of non oxy fuel in and the needle settled at HALF full. Is this a sender problem or is it possible the wiring is reversed or bad ground? Getting to the sender on this car is tuff as the trunk is highly upholstered and builder wanted floor totally flat so laid down a piece of flat sheet stock before padding and carpet. Any suggestions, as replacing sender on a stock 40 is a piece of cake but not this rod. Thank you in advance. Mr.34
Make SURE that the ground on the gauge is at the same potential as the ground on the sender. VERY important, especially with a poly tank.
+1 If the ground is lost or weak it will change the resistance of the sending unit causing it to give bizarre readings.
No ground ,the sending unit goes to full mark on the gauge ! Run a jumper wire (alligator clip) from the sending unit screws to the frame (bare metal ) That should show you some type of reading ! To test the gauge and see if its working , Go to the gauge and disconnect the sending wire and put a test wire on it and ground it ,the gauge should go to empty when you turn the key on !
i believe you have the wrong sender. it appears your gauge is trying to read backwards. a VDO gauge uses a sender that is 10 ohms empty and 180 ohms full. is there a chance that there is a Stewart Warner sender in the tank? SW is 240 ohms empty and 33 full...almost the opposite
I would bet a paycheck that what Dbradley said is correct... When a VDO sending unit fails or the ground goes bad the guage fails to full (pegged at full actually) I chased a sending unit problem in my VDO guages when all it turned out to be was a crappy ground (metal tank too...those rubber gaskets messed me over I guess)
The sender is VDO and I have only owned car since last winter as it was in storage since built fresh on 2000. Everyone is suggesting the ground which makes sense, so once I get the car back up in the air for the winter I will check that as well as the clever check on the gauge that was suggested. Thanks guys.
still can be wrong sender... We just went through this last week with a guage from TPI. Different OHMS....even though it was new from TPI.. If you turn the key on and it goes to full, usually a ground We did all the normal stuff and ended up with a guage that read full when empty and 1/2 full when full. Called TPI and found out the sender was wrong for the gauge shipped... Bad part....they have no more senders available...
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