2002 Dodge Ram 1500 Van, 3.9 V6, 150k, Fresh valve job, uses no oil.

Problem: Throws codes: p0300, p0301, p0303, p0305. P0301 pops right away. Misfires at idle and under moderate load, seems almost normal at very light throttle, and under heavy throttle. Does not act like a spark miss. Spark plugs are very light, almost white. I tried replacing the #1 injector, had no effect. Of course I have done all the obvious, plugs, wires, cap, rotor, coil, cam sensor, etc. I'm wondering if I have a fuel pressure issue. I replaced the fuel pump with a lo mile one I had a few thousand miles ago, when I noticed the pressure seemed on the low side (48psi, bouncy needle) I noticed last night that the pressure was only 45psi, so I swapped out the regulator with a spare I had (not new), and got 50psi with a very bouncy needle, from 45-55psi. Is this a defective regulator? Should the fuel pressure be very steady? I tried two different guages, they both show the same. Could this cause the misfiring? Thanks for any help you guys can provide.

 

I have the same problem except that for me it the #3 that misfires almost immediately. A couple of other people have also posted this problem. It's odd that everyone only has the problem with the drivers side (odd cylinders). I was considering the problem to be a cracked head, but since you're having the problem after a fresh valve job, I'm now thinking of ruling that out.

Did you have this problem before the valve job?

 

It misfired before the valve job, but on #2, 5, and 4. Those cylinders had badly worn valves. After the valve job it seemed fine till this problem cropped up. I've heard somewhere that when fuel pressure is iffy, #1, 3, and 5 misfire first, because they get the least fuel flow, due to the layout of the fuel rail.

 

That's a new one on me. Not saying it isn't true, just that I haven't heard it before. I thought the fuel pressure regulator was built into the fuel pumps on these vans. Where was the regulator located that you swapped out?

 

The regulator is at the top of the fuel pump. It is removable and available as a separate part. I have a port in the vehicle floor for access, a trick learned years ago dealing with fuel pumps in vans.