Check/service Engine Light

[tlocus]

Greetings,

The engine service light just came on and when I hooked up my scanner I recieved the following codes:

 

1) System too lean (Bank 1) P0171

 

2) System too lean (Bank 2) P0174

 

I was wondering if you guys can give me a few suggestions on what may be the cause.

 

BTW, I replaced the catalytic converter about a year and 1/2 ago. Also replaced all 4 O2 sensors (around the same time).

 

The truck has around 170,000 miles, it's a 5.3L V8. There's no rough idle or hesitation.

 

t

[minibike132]

Try cleaning the throttle body first but it will probably end up being an intake gasket

[tlocus]

Try cleaning the throttle body first but it will probably end up being an intake gasket

OK will do, thanks

[harleyhoghead]

I have been working through the same problem for the past 3 months. I was told the intake manifold on my 2002 'burb was probably bad, but I used starting fluid (spray) all around the manifold when the engine was cold and there was no change in the idle speed, so I figured it could not be the intake. I cleaned the MAF and that helped, but cleaning the throttle body really did the trick and cleared the check engine light.

[minibike132]

Cool glad it worked for you. On a side note it can be misleading if your spraying the intake and waiting for a swing in idle. I used to do that without my scanner to watch weather it went rich or lean. It only took getting burned one time, I sprayed and the pcm adjusted so fast I never noticed an uptick in the idle. Since then I watch my fuel trim while spraying.

[rjirvine]

Have you replaced the fuel filter lately?

[spartus]

Fuel filter, fuel pump, dirty MAF, and dirty injectors can all cause lean conditions. If your O2's are original, they may also need replacing.

 

You need a good data log on all your sensors with that high of mileage.

[tlocus]

The O2 sensors are fairly new (under 2 years old).

The fuel filter is probably 2 years old.

Since I had the truck (2 years) I haven't clean or replaced the MAF

Same goes for fuel pump....which I really hope is not the cause

 

I noticed that the throttle 'sticks' a little when you first start pressing the gas peddle.

 

I guess I'll start by replacing the fuel filter and cleaning the throttle body. BTW, how difficult is cleaning the TB?

And as far as the MAF, should I attempt to clean it or just get a new one?

 

thanks again guys

 

 

p.s. *Just remembered* A while back I was told I had a very small leak in the exhaust manifold I believe. When I first start the engine you can hear a slight PFFFt Pffft type of sound, then after it warms up it goes away. But would an exhaust manifold leak cause a lean condition (And I was told this way before the light came on)?

 

t

[minibike132]

Just take off the plastic air horn where it goes into the throttle body open the throttle all the way and spray some top engine cleaner or carb clean (I prefer top engine cleaner but the stuff is expensive and mine is free). If your plate is sticking you'll probably need to scrub with a tooth brush, do not use anything harsher than that you do not want to scratch it. As for an exhaust leak it can trick the o2 into thinking things are lean by introducing more oxygen into the system before the sensor but I think you said both banks are coming up lean so unless both sides leak its a no for you.