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Anybody know what open loop fault Misfire could be?

Silverado07wt

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Silverado07wt New Member

Silverado07wt

Posted
Posted

2007 silverado 4.8l 1500 new body style wt.

 

So I have a problem where at idle my fuel pressure goes up from the factory spec 43psi in to 59psi and my engine starts misfiring and a p0300 stores.

 

At this time using my live data scanner I see that I'm in open loop fault on both fuel system 1 and 2 and also both my upstream oxygen sensors start reading high voltage and fuel pressure is up to 59psi which is out of spec. To get the engine to come back down in fuel pressure back to 43psi spec, I simply rev the engine a couple seconds and it jumps back down and no misfire blinking anymore. I manually checked the fuel pressure and it's accurate to my scanner as well as did key on engine off and leakdown and it passed. Fuel trims are at 0 at this open loop fault time.

 

However, as I keep the engine idling for a long period of time the system enters closed loop and my fuel pressure stays constantly normal at 43psi with no misfire and oxygen sensors reading normally. Why does my system take so long to get to closed loop and what is open loop fault?

  • 1 year later...
Hillwood Enthusiast

Hillwood

Posted
Posted

The HO2 sensors have to get hot before they can work right.. Open loop is when the sensors are still heating up and have no control on fuel..Closed loop sensors are hot and controlling fuel.
No other codes?
Fuel pressure is normal.. If the engine is running rough, the vacuum is low and the regulator will increase the pressure.
You running factory spark plugs?

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