Ok here is the story and where im at at the present moment...i picked up a used truck (2000 silverado 3/4 ton) specifically for work and its a good looking truck and was maintained with 150k on a 6.0L, 4l80e and got it for a steal.

It through these two codes PO171, PO174 Lean banks 1,2 at the same time , I knew this before i purchased the truck.

Cleared them and came back. The truck sat for some time before the purchase and on a cold start would sputter and hesistate to go if i punched the gas.

So i started where a lot of people would. And with the miles i figured i might as well replace these essential things now so i dont have to worry about them.

Put 50.00s in 91 octane and Lucas fuel injector cleaner
-new fuel filter
- cleaned the maf (which looks to be very new gm delphi)

nothing still

-new Bosch 02s Pre cat (left,right)

nothing still

- so today i replaced the intake gaskets (cleaned everything) which were leaking and not sealing (they where indeed the orginal ones) and seems like the stutter on a cold start went away. cleared the codes and came back after about 20 mins.

IAT sensor was cleaned, TB cleaned, no holes or cracks in the air intake, or lines. Only mods are k&n drop in filter and flowmaster exhaust.

Tonight i went to autozone and rented a fuel pressure tester and on position (truck not running) it went to 22psi when it was running it stayed at 28psi.


When i drive the truck there is no misfire and drives completely normal and pulls fine.
I just cant figure out if its a colgged injector ,bad pump, or the regulator ??? anyone expierence anything like this or from personal knowlege give me some insight?

i havent cleaned or taken the fuel pressure regulator out ...i need no CEL on as i need to get it smogged for my tags so i need to have this issue over and done with and is frustrating me at the current moment






I am going to change the pcv since its cheap and not sure it has been replaced tomarrow and try to figure this out

 

Fuel issue. I had a friends truck that ran about 30psi and had trouble starting(lost its prime). I recalibrate the maf sensor a hundred times trying to fix the cold start issues. Just needed a new pump. I would check the fuel pressure again driving. Unplug the vacuum line for the regulator and it should read 58 solid.

If you think the problem is a vacuum leak, then a scanner to show iac counts can be very handy as well as a can of Carb cleaner.

 

Your Fuel pressure should be around 48 Psi at Idle and 58 at Idle with the vacuum regulator on the fuel rail unplugged.

 

thats exactly what is does first start of the day after priming 3x was still hard to start and was at 22 psi. while running is was at 28psi once again. i checked the regulator and its very clean not clogged and reinstalled it. started again and unplugged the vacum line and was still at 28psi with no drop at all .

 

Check your intake for leaks, and clean the MAF sensor. If you have an aftermarket MAF, like the Grantelli, they're out of GM spec and run LEAN.

 

Un- pluging the vacuum should raise the pressure not drop it.

Your fuel pump is no good.

 

fursure man thanks I'll get that taken care of and keep this thread updated

 

This is were you should be with a healthy pump.

The pressure spec may very within 4-5 PSI from pump to pump and gauge to gauge.

The Pressure difference from regulated to un-regulated should be around 8-10 PSI difference.