HVACBILL

I just got service engine soon light on and checked code to find PO171 system too lean (bank one) and PO174 system too lean (bank two). Can anyone help by telling me what can cause this fault.

foggysail

Try cleaning the mass air flow sensor. I had that fault in my 96 Cougar and was able to get rid of it. BUT YOU WILL HAVE BIG PROBLEMS WITH GETTING THE SPECIAL TOOL to take the sensor off!! Check Google for the tool.

I forgot where I purchased the set but they have security features (WHY????) and without the right tool, I don't know how to pull the sensor.

BE CAREFUL! There are two very fine platinum wires that can easily be broken. Get some electronic spray cleaner, spray the dirt off the wires and you might be in good shape. OH--- some air filters can cause the mass air flow sensor to get dirty also.

Foggy

HVACBILL

Thanks for the tip Foggy, I will try that. It also happened soon after I replaced a clogged PCV valve and the new one fit loosely in bottom larger tube and I also replaced top short 90 degree tube with a homemade piece because I could not find replacement tube yet. Someone else had these codes from a loose fitting or leaky PCV valve fitting.

fold_em83

They also make a special cleaner now for cleaning the MAF. If that doesn't help, I'd check out the O2 sensors.

__________________
94 Thunderbird LX

tbird100636

The upstream O2 sensors are a possibility but with a fuel system lean code on both banks the more likely cause is a fuel pressure issue. Check the fuel pressure first.

HVACBILL

I replaced the fuel filter but have not had a chance to drive the car much since resetting codes. I will post if this worked.

00gtr1

What year is the car? what engine 12v or DOHC? how many miles?

foggysail

Good luck. It will not take long to find out, 2 trips long or short will flag the light circuit if you have a fault pending.

If that is the the problem though and you have fixed it, 3 cheers! If not, you should clean the mass air flow sensor, cleaning it is a 2 minute job, a piece of cake after you get the security tool.

Foggy

HVACBILL

Thank for tips. I believe the problem is gone. I ordered some parts from a local ford dealer while I was repairing their boiler (my real job). I got a new PCV valve and the tube it fits into plus the top tube that connects to PCV. After installing new parts I found a cracked rubber hose that is connected from throttle body to manifold. I replace this 3/8 hose with a new piece 2 inches long and everything seems to be working fine again. Ford mechanics said it was a vacuum leak.

foggysail

YUP! A leaky vacuum hose will do it. Good job Bill--

Foggy