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Monday, October 19, 2020

Bypass the FPCM : My GT-R Fuel Pump won't work

Blues. Neither car was happy right here. 

So the other night I went to startup the #bluecar and it just cranked, and cranked. I didn't think I heard the fuel pump run/prime.  I felt the fuel lines under the hood, and they felt like no pressure. 

"Shit, E85 killed the Hellcat pump." was my thought.  Oh well. Maybe E85 is harsher than I thought.  I did just get some gas/E85 maybe it was bad stuff.    So I reserved myself to pulling the top of the tank off.   

The two wire connector is for the pump.  The ground is the white wire. It turns brown in the harness, and is shielded. Black with the yellow trace is the positive. 

I plugged my meter in to the two wire connector and saw 12 v at the pump. I checked all the fuses. I did try the pump with a small 19.2 battery, and it ran for a few seconds, but then seemed to stop.  Maybe its just binding up with some time. Run and stop, run and stop.   I had sort of already convinced myself I had to pull the top of the tank off, so doing some other logical things wasn't in my wheelhouse. 

I pulled the pump. Everything was clean in the tank. E85 smells good. Its a little harsh on your hands, but then again so is gasoline. Either way. Once I got the pump out, I used my jump box, and the pump ran great. No issues. Everything inside super clean, no corrosion, no weirdness, Actually everything was probably cleaner than when I took it out last time.  Slammed it back in, figured, must be FPCM. Let me bypass it, by grounding the FPCM wire, and see how it goes. 

The two wire connector is for the pump.  The ground is the white wire. It turns brown in the harness, and is shielded. Black with the yellow trace is the positive. 

Brown wire in this harness has the white wire in it. It is shielded. You can see the shield wires on the outside there. I did trim these later. 

By grounding the white wire, you are grounding the fuel pump, creating a complete circuit. The FPCM, or fuel pump control module is what I call a complicated ground. 

Fuel pump control module R32 GT-R FPCM
FPCM or fuel pump control module for an R32 GT-R

The fuel pump control module puts resistance on the ground side of the fuel pump circuit to slow the fuel pump down at low speed, or low demand times. Its for NVH or noise, vibration, and harshness. You don't probably want or need it in 2020.    Car started up, ran, and I took it to two events on Sunday. No more noise than it had before. Since its an in tank pump, and my car has an exhaust, and a stereo, for sure nothing I will ever notice. 




They do fail, and they can leave you stranded.  You can be pre-emptive and go and do it now, you can do something like the PPR fuel pump relay kit, or you can leave it as stock, but keep a jumper wire in the car, for that time that it does fail. 


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