Thread: Low fuel pressure/0300 misfires

I have been trying to fix this problem for a long time now and I am stumped. Main thing is I am only getting 25-30 psi fuel pressure at the fuel rails and I am getting a flashing SES light with the 0300 code so I am not driving this car, but it is my only vehicle!

I want EVERYONES input because I am lost now. I have been checking everything I can and replacing a bunch also. I will tell you I was having this problem before I started replacing parts: I have replaced the Fuel filter, Spark plug wires (they needed it anyways), both fuel pump relays under the hood plus the fuel pump fuse, Installed PRJ fuel rails, Fuel pressure module, and there might be more but I can not think of it right now.

Before my mods with the fuel system are 42lb flow matched injectors from ZZP, Walbro fuel pump in the RaceTronix rewire kit. I already checked for vacuum leaks (fixed the SC gasket leak), and I can jump the relay to get power to the pump at all times but the fuel pressure still stays at 30 psi.

Could it be the pressure sensor on top of the fuel pump assembly?
Anyone take volt or ohm reading from there car for me to compare them to?
I need to get this car going and the mechanic I usually take my car to is booked up for weeks so he can not help me. Thanks.

got a kink in your line somewhere?

I did not see any kinks in the line, I also took the pump out and looked at it. The hose inside looked good, blew in it and did not find any holes or leaks and it is clamped up tight still.

The relay is kicking the power off quick so I think it is only going up to the 30 psi and stopping so it is hard to get a volt reading. I will jump the relay and try to get a reading...

The pump is a year old and I just replaced the regulator (sorry, I called it a module)

I just jumped the relay, connecting the 87 and 30 pins, and I got 12 volts back to the pump. But I also noticed that the PSI drops to 20 psi after the pump stops...

Would a stuck open injector cause this? I am thinking of by passing one rail at a time to see if I can get the PSI up...
I ask about the injector because the fuel PSI drops to 0 when sitting.

Originally Posted by Arkanzan Wheeler

I did not see any kinks in the line, I also took the pump out and looked at it. The hose inside looked good, blew in it and did not find any holes or leaks and it is clamped up tight still.

The relay is kicking the power off quick so I think it is only going up to the 30 psi and stopping so it is hard to get a volt reading. I will jump the relay and try to get a reading...

The pump is a year old and I just replaced the regulator (sorry, I called it a module)

I just jumped the relay, connecting the 87 and 30 pins, and I got 12 volts back to the pump. But I also noticed that the PSI drops to 20 psi after the pump stops...

If the pressure drops quickly after turning vehicle off the pump may be bleeding back. On another note is the pressure regulator leaking into the vacuum line? A pump would not be a huge surprise for a GM vehicle

There is no fuel getting into the regulator.

It is not a GM pump, it is a Walbro. They are suppose to be good...lol. It might be bleeding back, I will be able to find out if I loop the lines together to bypass the injectors...

I looped the fuel lines so they only go through the regulator block, the injectors are bypassed and it is doing the same thing...
I just swapped out a new fuel pump and still the same thing (injectors are still bypassed).

?!?!

just trying to get an image of the situation, did this all started to happen when u installed the prj fuel rails or the fuel rails were done a while ago?

The car was running fine for a long time, but I had the old Rollmaster timing chain and the car started running rough and less power but I thought the timing chain stretched so I planned on replacing that. Then it started to get worse, that was when I found the Fuel psi was low. Swapped a new regulator and fuel filter first because that was what I though of first. Still the same.

I wanted to get a set of fuel rails anyways (I/C later) so I got that hoping the problem was in the fuel rails but after the swap the problem did not go away. That was when we found the SC gasket had a vacuum leak. I also did the new Rollmaster timing chain at the same time.

Now I have looped the fuel lines (bypass the injectors) and replaced the fuel pump but everything is still the same. Both relays are new, fuse is new, resistor tab is bent out, I am stumped because the fuel pump runs up to 30 psi and then stops. I can bypass the resistor and it still only goes to 30psi.

Any ideas?

If it is a new pump, check the wiring, if there is a corroded connection or a lot of extra resistance in the electrical side of the pump, it may not have enough power to push above 30 psi, to check, unplug pump connector on top of cannister, hook up volt meter to power and ground in connector and turn key to run position, it should go to within 1.5V of batt voltage for 5 seconds, if it is less than 10V I'd say start looking at the wiring

I had 12.3 volts back at the pump, that should be enough... I was just jumping the relay.

Lol...If it was easy I would not be asking for help...lol. There has got to be something we are missing about this system...

is one of your injectors leaking?

Edit did you check the ground too, or only the power side?

Injectors are bypassed right now, it is just looped through the PRJ Fuel Pressure Regulator/Gauge block so I know it is not the injectors.

Yes I did check the ground, it looks good-all clean and tight. Still the same low PSI. I am looking for a higher psi regulator that will work right now...

I put a new pump in and it is filling up the bucket now so it over flows the bucket, the pump is submerged with fuel. That was one problem I had with the old pump, the bucket did not fill up. So that problem is fixed. It is like there is something else controlling the pressure and I can not find it...