fuel pump no prime

SC02gmc · August 23, 2020

Hello group I'm new to this site and I'm having issues with 2002 gmc sierra 4.8 1500. Mods are Magnuson supercharger/4l80e swap/external pump for more fuel and its been mod over ten years ago. Its cranking over but not starting and also fuel pump not doing its 3 sec prime like its should before turning over. Checked relays and fuse even swap out with i know are working in other sections and no solution. Then checked all grounds from cab/rear engine and engine bay. Also did test light and all good but no light when did prime test? Also did fuel pump which i knew that was not issue but I did it any way. Also fuel regulator is dry not wet so no issues there. Some kind on electrical problem I think but I can't pin point. Could it be a ppm issue.

davester · August 23, 2020

So the fuel pump isn't working. Test the plug to the pump to see if it's getting power & ground when the key is on.

But it wouldn't surprise me if the pump's gone bad after 10 years...

SC02gmc · September 3, 2020

So far I have checked fuses and relay even switch around and no. Checked and cleaned all grounds. Did a test to see if I had a break in the wire using ohm meter from harness to about were mid of cab and got reading. Did I mentioned new pump from telescope brand. No codes. No vats issue. Could it be a bad pump. I can turn on pump by bypassing it using car battery and connecting to grey wire. Any help

davester · September 3, 2020

Sure, new parts can be bad, right out of the box. But, you say that directly providing power and ground to the pump turns it on.

If that's true, then you have a electrical problem. I would find a connector that's fairly easy to access & unplug, that has the wires that eventually go to the fuel pump, and apply power and ground directly to the pins in the connector, and see if the pump works or not. Then go closer to the pump if it doesn't work, or further away from the pump if it does.

riverbanks · September 3, 2020

Do a search for fuel pump relay wiring,it's here somewhere, just thinking you need to check the power feed at relay and pump enable from pcm at relay

SC02gmc · September 3, 2020

I believe I did a test at fuse box looking for power feed when key is turned on but no luck light wouldn’t turn on. I’ll check under neath fuse box for issue

SC02gmc · September 4, 2020

Update did the security relearn 30min key on 20sec key off repeat twice more no luck. Used battery to bypass relay and pump turned on. Also did an ohms test from connection to mid way of cab and got readings. New pump is a top scope brand.