Finishing up my 3100 swap. The new oil pressure sender is about 1/3rd the size of the old Fiero unit (which is giant!). New one has 3 pins also, just a smaller connector, so the question is: Is the unit compatable with the Fiero gauges and fuel pump relay? Which pins are which? Larry

Outside pin - Orange or Orange/Black or Red - +12v unswitched

Middle pin - Tan or Tan/Black - Gauge

Outside Pin - Tan/White or Gray - To fuel pump

So assuming you have a 3 pin connector just connect the 3 pin 88 2.5 or 2.8 sender. It should work fine. Or if you wish cut and splice the pre-88 connector onto your harness. Pin for pin. Outside pins are the fuel pump switch. Middle pin is the gauge.

Your stock 3100 sender most likey gave you proper fuel pump operation but pegged the oil pressure gauge high as soon as the oil pressure built.

You can use the oil pressure switch solely to control your fuel pump since you are carbed. The engine will fire from the fuel in the bowl. If your engine is reasonably sound you will also have oil pressure right after you start cranking. This means you will have fuel under pressure most likely quicker than you would have with a mechanical pump.

[This message has been edited by phonedawgz (edited 08-20-2013).]

Sounds good, is the resistance of the gauge part of the sensor different on the smaller units than on the giant ones on the Fiero 2.8 engines? Larry

GM units from that era should all be the 0-90 ohm (low-high pressure) units

Also, I am just moving the fuel pump relay to the area that the computer used to be located in, I will install a "prime" button next to the lighter socket just to get fuel moving if I need to. I have built a nice little fuel bypass regulator, I will post some pictures of the assemble, very easy and cheap to do. Think I will set it to about 12 to 15 PSI? what do you thik? Larry