Rough Idle

[redxemt]

I recently bought a 2006 Sierra 1500 Crew 4x4 with the 5.3 L Flex Fuel engine. The idle is rough. It's not horrible but isn't smooth like it should be.

 

I have checked and replaced vacuum lines and replaced the spark plugs and wires without success. MAF and throttle body have been cleaned. After this all, the computer was reset by disconnecting the battery for a while without any improvement after being driven.

 

I now have checked the fuel pressure at the Schrader valve on the passenger side fuel rail. Key on engine off I have 52 psi with no leak down noted. At idle the pressure is rapidly fluctuating (a couple times a second I would say) between 62-68 psi.

 

Because this is the 2006 Flex Fuel, the Fuel Pressure Regulator is in the tank and I don't want to replace the unit unless I have to. Is this what's next? Is the FPR a replaceable part or does the whole pump need to be replaced. Or maybe this fluctuating pressure is normal for these vehicles?

[redxemt]

Someone has to have put a fuel pressure gauge on a 5.3 before! Is fluctuation as defined below a normal thing? If not, does it mean the pressure regulator is shot? Other advice? Thanks in advance!

 

I recently bought a 2006 Sierra 1500 Crew 4x4 with the 5.3 L Flex Fuel engine. The idle is rough. It's not horrible but isn't smooth like it should be.

 

I have checked and replaced vacuum lines and replaced the spark plugs and wires without success. MAF and throttle body have been cleaned. After this all, the computer was reset by disconnecting the battery for a while without any improvement after being driven.

 

I now have checked the fuel pressure at the Schrader valve on the passenger side fuel rail. Key on engine off I have 52 psi with no leak down noted. At idle the pressure is rapidly fluctuating (a couple times a second I would say) between 62-68 psi.

 

Because this is the 2006 Flex Fuel, the Fuel Pressure Regulator is in the tank and I don't want to replace the unit unless I have to. Is this what's next? Is the FPR a replaceable part or does the whole pump need to be replaced. Or maybe this fluctuating pressure is normal for these vehicles?

[markw8]

What is the factory spec for fuel pressure versus what you have? You might be throwing parts at a problem you don't have. How many miles on the truck? Have you compared the idle to another flex fuel truck?

 

Mark

[00Silverado4x4]

I have the same truck as you (including flex fuel engine) & experienced similiar problem, not to that degree. I didn't ever pressure check my fuel system so this may be of no help, but I ran my tank down as far as I could & refill with some good quality (hopefully) gas with some fuel injection cleaner. It took care of my problems. Now if your burning e85 this will not work as you can not use treatments with e85 as per the owners manual. Once I started using e85 about 3 years ago I haven't had a recurr of this problem except when I've ran extended periods without e85 (road trips where not pumps available.) If this helps, great, if not, my apologies & hope you find a fix.

[redxemt]

I am not running E85 - just regular 87. I will try an injector cleaner, maybe that will help.

 

As far as pressures, those numbers are fine. I'm just wondering if the pressure is supposed to fluctuate very rapidly during idle/run or if it should stay very steady.

 

The truck has 90k miles. I don't have a truck to compare to.