I have a 2004 Tahoe Z71 with 222k miles. When I got it the only thing that had been changed was the water pump. I had to do a power steering pump and I did plugs/wires, K&N air filter, oil/filter, and fuel filter, and I had it tuned with HPtuners.
The problem im having is its hard to crank when the motor is cold. If you prime the fuel pump a couple of times it will crank right up, but still kinda idles rough until its semi warm. So I had a hunch that the check valve was bad in the pump and checked the fuel pressure with a gauge, If you turn it over once it comes right up to 48 psi, then if you crank it, it stays 48psi. I know thats about 10 psi to low but I figured if it was loosing prime it would be low the very first prime. While data logging with HPtuners, it seemed there was unmetered air like a vaccum leak or something. So I was thinking maybe intake gasket. I sprayed some seafoam all around the intake and couldnt find a leak. Also was getting some codes for running lean....any ideas?

 

You could have a bad MAF, MAP or coolant temp sensor. I'd go with the temp sensor myself as that causes all sorts of cold start issues.

 

Its not throwing a code for temp sensor, im actually was leaning toward MAF because when me and my tuner first started data logging it, the MAF was not reading near the incoming air a 5.3L should. We had a spare one at the shop and put it on and it was a world of difference but was still reading unmetered air. Is 48 psi enough fuel to crank a 5.3?

 

You have to hold the gas down to get it to crank when cold also.

 

If its 10 PSI to low for your year/make, then the pump is worn. You need to replace the pump. If it's not supplying the correct pressure to the injector you won't get the correct amount of fuel in the cylinder.

I.e. it will Run lean. These setups are very specific to fuel pressure. The injector data is tailored to the specific fuel Pressure spec.

 

Yeah I figured the pump is wore out but why would it only cause problems when the motor is cold and not hot?

 

Because when it first starts up its running on pre set values. As the engine warms up the sensors take over and the computer compensates for the fuel trim.

 

Yeah that's true I didn't think about that. Well I guess I'll go with fuel pump. I just didn't want to start throwing money at it and it be something else. I know the intake gaskets are a common issue also.

 

True they are common, but the only way to be 100% sure is to have them checked with a smoke machine. Sometimes they leak on the bottom side and it can't be detected by the common spray around the intake method. When the intake is filled with smoke you can visually see it coming out if there is a leak.

 

Well new fuel pump is in and its still hard to crank when cold. Ill be checking the new fuel pump pressure in the morning.