Engine P0171 Need Help

[Daniel Rosas]

So i bought my 96 gt a few months back, when i bought it it wasnt running, the intake manifold was leaking coolant, and the cats were torn to bits. Sense then i replaced the cats along with o2 sensors in both bank 1 and 2. I Also replaced the intake manifold. When i first started the car i couldnt help but smile, drove it around and BAM to kill my mood, comes on the CEL. I check the codes and p0171 bank 1 running lean. Okay so i quadruple check my work. All hoses are good i runn the engine and spary brake cleaner around. Near top left corner of the intake manifold had a slight leak and also the gasket from the EGR valve. I fix those two problems and clear the code. Spray another bottle of brake clean around and it seemed like it got the job done. Drove it for about a week and it throws the code again... After that i checked pressure on the fuel rail, cleaned the fuel injectors and replaced all the o-rings and pintle caps, also replaced the fuel regulator... Drove it around for another week and again throws bank 1 running lean.. I have no idea what im doing wrong and what could be the problem... Could it be the fuel pump? PLEAS HELP!

 

[wmburns]

First thing. Stop using brake clean as a leak finder. The harsh chemicals can degrade the gaskets used in the intake manifold thus trading (or creating) one problem for another. Best to use smoke or a vapor gas such as propane.


View: https://www.youtube.com/watch?v=ZRgOb9M_6tc


Note, an exhaust leak can also cause a lean code. How does the car run? How's the gas mileage?

Regarding if this "could" be a bad fuel pump. Why guess. Test! If the fuel pump is bad, this will show up a low fuel pressure. Besides the odd favor low fuel pressure affecting both banks (not just one).

What about the right hand (passenger's side) valve cover gasket and PCV grommet?

If you still suspect a fuel injector problem, consider an injector cleaning/flow test service such as Injectorrx.com.

 

[Daniel Rosas]

It runs pretty rough. Has 175,xxx+ miles on it ( odometer stopped reading miles) so not sure how many is on there. Cold start it idles above 1000 rpm and gradually drops back down to maybe 700 Rpm with a small increase. Not a steady idle... I did something like the video but i couldnt see any air leaks. I might do it again today just to make sure

 

[wmburns]

Cold start above 1000 RPM's is normal. Every Mustang I have ever owned does that.

The fact that the idle is higher when cold and then drops down as the motor warms indicates that the IAC valve is functioning.

It's also normal for the idle to "hang" in the 1100-1300 RPM range while the car is moving. This is called a fast idle. Once the car comes to a complete stop, the PCM activates a "slow" idle. This is done do make sure hydro-boost brakes work. The hanging idle is also normal.

What's not normal is a stopped idle above 1100 RPM when hot.

What's not normal is a fast idle above 1500 RPM when moving.

Suggest that you focus on why the motor is running rough in general. Look at ignition and fuel (clogged injectors) for starters.