Been working on a 93 civic si hatchback for a friend of mine. So fuel pump wasn't priming or anything and I checked for power. At the plug it has 12.48 volts while the key is at "acc" position for about 2-3 seconds as if it was priming then kills out. Naturally I rule the fuel pump is bad and we buy another one. Install it and still no priming so I figure maybe a bad sending unit. I check for power at the plug that goes into the fuel pump itself and same thing 12.48 volts for 2-3 seconds while it would be priming. So I figured maybe I just had a bad pump again. Hooked the pump up to the battery, which had 12.8 volts and it spun up like it should. So my question is what could the issue be? The main relay has to be good if it is pushing power to the pump. I know the pump was good because I hooked it up to the battery. I know the pump is getting the required 12volts.

TL/DR: Fuel pump has 12.48 volts of power at the sending unit plug and still won't prime even though it will run hooked straight to battery with 12.8 volts.

 

Not sure if the fuel pump is the same but most of the things in these old Hondas that I've seen are ground switched. So you have positive power but is the fuel relay switching the ground to complete the circuit? You might check for ground continuity in those 2-3 seconds.

 

Wouldn't it be fine though since I used I used my volt meter probes on the ground and power at the plug, like I didn't ground at the chassis I actually grounded at the plug.

 

Okay, then I can not think of a reason the pump would not run if the plug has ground, and the plug has 12v. That just doesn't correlate.

 

That is why I am stumped. I thought maybe it was a ground but I am using the ground at the plug it is weird..