Fuel Pressure dropping, attempting to diagnose and fix my truck

[GavinKBarnes]

I have a 2010 Silverado 5.3 LT 4x4 and my engine stalls when accelerating or revving, it doesn't get past 2000RPMs and starts making a deep almost rumble noise. I unplugged my MAF it almost kills my engine so I didn't believe it was that. I just replaced my TPS. After somebody recommending I test my fuel pressure, I did so and the results were as follows:
Fuel pressure at 60psi with power on (not started), about 57 idling, and once you press in the accelerator, almost immediately shakes between 40-43 and doesn't move from there until the engine stalls out. Is this my fuel pump or something else entirely? 
Thanks for the assistance.

[davester]

Yeah, it's the fuel pump.  It should only momentarily dip a little when hitting the throttle pedal, then return to about 60 psi and hold steady.

[swathdiver]

43.5 psi is normal commanded pump pressure for Flex Fuel 5.3 engines.  Does the pressure drop at WOT?  What are the Fuel Pump Trims?  Have you tested the injectors and fuel pressure regulator?

 

This is where a bi-directional scan tool is essential to quickly and accurately finding the problem.

[GavinKBarnes]

It stays at 41-43 at WOT, as far as injectors, pressure stays consistently at 60 with vehicle on, engine off. So they don't leak as far as I can tell. I'll try and check fuel trim once I get off of work tonight. 

[GavinKBarnes]

Also I have no idea how to test a pressure regulator on my truck, if I'm not mistaken that's built into the pump? How would I go about testing that?

[swathdiver]

22 minutes ago, GavinKBarnes said:

Also I have no idea how to test a pressure regulator on my truck, if I'm not mistaken that's built into the pump? How would I go about testing that?

With bi-directional scan tool.  But if pressure is holding for 2 minutes after key off and not losing more than 5 psi you're probably good on the pump, FPR and injectors.  Time to look elsewhere.

 

No codes at all?  No CEL?  Trans problems can sometimes do this too.  Get your hands on a Tech-2.  Where do you live?

[GavinKBarnes]

Just now, swathdiver said:

With bi-directional scan tool.  But if pressure is holding for 2 minutes after key off and not losing more than 5 psi you're probably good on the pump, FPR and injectors.  Time to look elsewhere.

 

No codes at all?  No CEL?  Trans problems can sometimes do this too.  Get your hands on a Tech-2.  Where do you live?

I live about 40 minutes outside of Manhattan, KS. I suppose it could be my trans, but man I hope it's not lol. I have a pretty generic ODB-II Scan tool, No CEL on currently, I keep scanning every time I'm out to try and figure it out, which is daily. No codes at all, I had a P0300 Random/Multiple misfire but the code went away on it's own. 

[swathdiver]

55 minutes ago, GavinKBarnes said:

I live about 40 minutes outside of Manhattan, KS. I suppose it could be my trans, but man I hope it's not lol. I have a pretty generic ODB-II Scan tool, No CEL on currently, I keep scanning every time I'm out to try and figure it out, which is daily. No codes at all, I had a P0300 Random/Multiple misfire but the code went away on it's own. 

Too far away from me here in Florida to put my Tech-2 on it!  

 

Well, that's a clue and I would check the coils and plugs and wires and see if any cylinders in particular are misfiring.  

[GavinKBarnes]

I'm checking coils and plugs now, but an update.. my odb-II scanner tells me (I'm sure it's not 100% accurate but it is all I have to go on for now) that my fuel trim was -2.3% before dropping back to 0%. Never saw it go below that, went all the way up to 1.6%. 

 

However, I realized I am missing a bolt where my manifold is attached to my engine, causing a small exhaust leak. I don't believe that could be causing this big of an issue but of course we need to consider all facts. 

[GavinKBarnes]

After some testing, it doesn't seem and of my cylinders are misfiring, code for each cylinder came on as I was testing them, as well as a serious difference in engine stability. Anything else you can think of I can test? I'm pretty frustrated with this truck right now lol

[davester]

At speed, with missing exhaust manifold bolts, it can suck in air, and that will mess up the O2 sensors

[GavinKBarnes]

I wish that were my issue, but this isn't even at speed. I can't get above 5mph currently

[sefiroxx]

Those are relatively normal fuel trim.

Does the engine rev normally while in neutral?

[GavinKBarnes]

Nope, tried that last night on a whim actually, exact same thing. Better way to describe the revving is it's almost like it cuts itself off, it'll start revving normally and once you hit about 1500-2000 RPMs it'll drop like a sack of bricks, and you'll be hard pressed to get it Above 1000 rpms afterwards until you restart the truck. 

[swathdiver]

13 hours ago, GavinKBarnes said:

Nope, tried that last night on a whim actually, exact same thing. Better way to describe the revving is it's almost like it cuts itself off, it'll start revving normally and once you hit about 1500-2000 RPMs it'll drop like a sack of bricks, and you'll be hard pressed to get it Above 1000 rpms afterwards until you restart the truck. 

And the fuel pressure is holding during this at the commanded rate?  

 

Can your scan tool check and test the transmission and torque converter?