I have a 1999 4runner limited with the 3.4L engine. I was having issues with rough idle and hesitation while driving. I had recently placed new wires, ignition pack and plugs (less then 6 months). I had also had the timing belt, water pump, pulleys and belts replaced. It finally gave two codes p0300 and p0302. I understood this to be a problem with my fuel injectors but before changing them I cleaned my MAF, Idle control Valve, and replaced any worn vacuum hoses. When this didn't work, we tested the injectors and #2 failed, so I replaced all injectors. This didn't solve the issue either. We tested the fuel pressure and found it to be extremely low, so we replaced the fuel pump. After the fuel pump we were getting good pressures, but it now wouldn't stay running. Okay, we replaced the fuel regulator (twice) and it still won't stay running. I also swap the evap canister and vapor purge valve (just in case) but this didn't help either. We figured out that if we clamped the fuel return line the truck would run fine, but we are aware this is dangerous and it can't be driven this way. I'm at a loss and so is my mechanic buddy, any insight would be greatly appreciated.

 

Was it just not mentioned or was the fuel filter never changed ??

What fuel pressure are you getting now??

Voltage at the fuel pump ?? Was this checked before replacing the first fuel pump

What brand fuel pump ?? Quite possible the new one is about to quit already .

Electrical side of the fuel pump in good shape ?? Circuiting opening relay working like it should ??

 

The fuel filter was replaced. The new fuel pump is a denso with strainer. We didn't replace the sending unit though. I will check the fuel pressure and voltage myself because my friend checked it while I wasn't around and stated he was getting 40psi at idle. I will reach back out after I test voltage and fuel pressure. Thanks for the response.

 

I tested the voltage at the fuel pump and it's reading 5 volts. The battery is reading 12v and the EFI relay is reading 11.99v. So, I know now I'm having a issue with wiring, COR, or ECU/ECM. I'm expecting my fuel pressure gauge tomorrow, so I will send that information as soon as I'm done. Any ideas would be greatly appreciated.