Engine Bank 1 Lean PO171

[Flyboy87]

I have a 2000 Protege ES with the 1.8L and the 5spd manual. Im getting the PO171 code (Engine Bank 1 Lean). The car has no driveablity issues so Im not sure if Im getting a false reading or not. Im going to replace the fuel filter and ohm the 02 sensors. Is there anyway to test the fuel pump to see if its making enough pressure? If I had an exhaust leak upstream of the 02 sensors could that be allowing oxygen causing the reading? Ive been driving around with a precat efficiency below threshold code for awhile now however it goes on and off so Im not sure whats going on with it.

[99es]

Flyboy,
Before you go replacing parts, check and make sure that the intake manifold gasket is all there. My daughter's 99 ES also had a code P0171, which was due to a vacuum leak caused by a piece of the gasket going AWOL between cylinders #3 & 4. This was common enough that Mazda had a TSB on it, I don't recall if it also covered MY 2000. The car still ran fine, but the fuel trim was maxed out. Take a can of carb cleaner and spray along the gasket - if suddenly the car "hiccups", you found your problem.

[Flyboy87]

99ES you are my hero!!!! That was the EXACT problem. Did you replace the gasket yourself and if you did how hard was it?

[99es]

Flyboy,
Glad you found the problem. How this happens is beyond me. Yes, I fixed it myself, took an afternoon to do with the help of a Haynes manual - it is a bit of a PITA, but I figure I saved a couple of hundred bucks. It has been fine ever since (almost 4 years now), I think Mazda updated the gasket design. BTW, her car also throws the occasional catalyst efficiency below theshold (P0421) - I think it's a weak point on these cars.

[13thghost]

very nice good diagnosis skill .

[Flyboy87]

-99ES

I am about to fix the car this upcoming week. I have www.alldatadiy.com for my manuals. The specify removing the following:

1.) Fresh Air Duct
2.) Resonace Chamber
3.) FUEL INJECTORS & RAIL
4.) Air Cleaner
5.) Air Cleaner Element
6.) MAF Sensor
7.) Air Hose
8.) Accelerator Cable
9.) THROTTLE BODY (This may be an issue because I cant find the gasket anywhere online... I'm going to see if I can get it from the dealer)
10.) VICS solenoid valve bracket
11.) VICS solenoid valve
12.) Dynamic Chamber
13.) Intake Manifold
14.) Intake Manifold Gasket
15.) Dynamic Chamber Gasket


Did you remove all this as well? Or did Haynes specify a different approach??

Any help would be great!

-Flyboy87

[99es]

Flyboy,
The procedure sounds about the same. I don't remember removing either the throttle body or MAF sensor, I think I left it as an assembly. I did not remove the support bracket underneath the manifold, only loosened it enough to back the manifold off the head so I could replace the gasket. It's been awhile, so I don't remember every detail. Good luck-

[lsman]

Have you fix the problem, Flyboy?

[kenmac]

. BTW, her car also throws the occasional catalyst efficiency below theshold (P0421) - I think it's a weak point on these cars.

I also had this code . Someone told me to use anti fouling adapter in the exhaust. I did & now no p0421 code