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Does this help any. I tried making it as best as I could using torque pro so let me know if this gives you any different info. From what I see they all seem to balance with each other

 

In either case Your fuel trims are around 9%. That means ECU is prolonging the injection time for 9%. If it was only on idle, I'd say You may have a vacuum leak. But, as it occurs on wide variety of RPMs I'd convince to a fuel pressure regulator producing slightly lower fuel pressure than needed.

 

Fuel pressure regulator has been replaced. What are the odds of an ac delco failing out of the box?

 

I'd rather look for the answer on how to test the pressure regulator. I haven't been testing this particular one, so maybe someone else could be more accurate in this matter.
In general, thing that comes on my mind is to supply fuel line of a two spiders. Then use the pulse generator for driving injectors and compare the volume sprayed over a time. But that hardly makes sense, as while having two, You may swap them on the engine and check if the fuel trim changes.

 

FPRs on the SCFI/MFI systems VERY rarely fail. Your previously mentioned 55psi pressure test results should be sufficient for proper fuel delivery with the MFI spider. A higher pressure is typically desired with the SCFI spider due to the poppet nozzle, but I generally maintain that 55psi is the minimum for SCFI and normal for MFI. The observation that the fuel pressure does not hold could be a regulator, but to determine the cause, you need to test the unregulated pressure and leakdown from the pump assembly itself. This is accomplished by isolating the pump, placing the fuel pressure test gauge at the input of the fuel filter. Most often, when there is fuel pressure leak down after shutoff in excess of 10psi, it is a problem with the pump assembly that is the cause (check valve in the pump).

The intake is cleaner than most because a 2003 does not have an EGR valve. From the picture, it does not appear to be fuel washed which typically would show up as bright silver aluminum, not the dingy oil/dirt layer that can be seen in the picture.

As far as your problem, how did the plugs look? Are the misfires being reported on all cylinders or just a specific few? Have you done a compression & leakdown test yet (I think I saw you mention that)?

 

Plugs are new and compression was all above 140 at ceanking speed.

Id have to look at all the misfires again. If im remembering correctly it was not every cylinder but it was about 4 but clab should be able to clarify

 

I guess I should have been more clear... I know you said you replaced the plugs, but how did the old plugs look? Condition of the positive & negative electrodes? Color of the insulating cone? Were certain plugs dry or damp? The plugs can tell you a lot about what is going on in the engine and more specifically, differences plug to plug can indicate something amiss.

One thing that I want to go back to from the OP, you said that intake runner #6 was "completely full of fuel"... That should not happen under any circumstances and needs further clarification on your description. You said that there were no leaks internal to the plenum, yet fuel pressure does not hold. I'm wondering if you don't have a stuck injector, but your fuel trims do not agree with that as whichever side that injector is on should show lean (negative) trims, not rich (positive) trims.

I really think an unregulated fuel pressure test at the fuel filter inlet line is the next step here. Please let us know what the results are at that location for pressure both with the pump on and the leakdown rate when the pump shuts off.

 

Idle. Cylinders #'s 2&3 misfire

Few sec. After that caught cylinder 4 misfiring at an idle aswell

1500 rpms for the entire 16 sec you see here. Mostly cylinder #'s 2&4 but also was reading 2 count on cylinder #3
*note x axis changes derasticly*

Letting it go back to an idle just after the 1500 rpms


All the plugs were dry, electrodes all looked clean insulating cone has a dark purple spot.

 

I agree im leaning towards the check valve on fuel pump.

 

Counting up to 2 or 4 misfires before counters reset is pretty normal behavior. What you are seeing on cyl #4 and cyl #2 misfire counters is not normal, and this is happening only at speed and not at idle.

You say it has a new distributor in it, but does it still have the factory distributor hold down locking the distributor in place? Has the Cam Sensor Retard been checked? In addition to the unregulated FP testing that Swartlkk has requested, I would like to know the Cam Sensor Retard value (Torque Pro isn't going to do it). Timing advancing/retarding and jumping to the wrong place within a misadjusted distributor could possibly explain an intermittent misfire.

You say that a crank sensor relearn was performed, but how can this take place when a P0300 is setting. In my experience, the PCM won't complete the procedure if there are any misfire codes present - after all this procedure stores the reference the PCM for future determinations of misfire. Please explain how the crank sensor relearn was performed.

Another thing you should know is that both Torque Pro and Car Gauge Pro get two of the cylinders on the Blazers switched in the misfire counters. #1 cyl is one of them, but I can't remember the other. You should test your misfire detection anyways by pulling a plug wire on one cylinder at a time and starting the vehicle. If it is working correctly, misfires should rapidly count up on the cylinder where you have pulled the plug wire. If it doesn't your misfire detection is inoperative and cannot be trusted.

So first check the un-regulated fuel pressure and leak-down as Swartlkk says and report back to him. Procedures are in the sticky at the top of this forum.

If the fuel pressure angle doesn't work out, get either Car Gauge Pro or Dash Command with GM PIDs for your vehicle and check the cam sensor retard. Actually I think you should check it either way. In Car Gauge Pro use the single asterick (*) Cam Sensor Retard PID. In Dash Command the PID will be called CMPRET.

Good luck and best wishes for a successful repair!