Error Code P0171
In a 1996 Bronco 5.0L the engine light is on because of the Error Code P0171 and/or P0174. It starts and runs fine, the mileage is the same since it was new. How can the MAF be tested to see if it is working?
Are there any other sensors that can trigger the Engine Light?
It passes the Smog test easy, as long as the Engine Light is not on.
What else can cause the Engine light to come on?

 

First off, welcome to FTE and the Big Bronco Forum. We will do our best to get you the most accurate info we can dig up.

As to Codes PO171 and PO174... these are BOTH indicative of a lean condition. 171 indicates a lean condition on bank one (driver's side cylinders) and 174 indicates a lean condition on bank two (passenger side cylinders). Given that you are getting both, I'd start looking for vacuum leaks. Lean conditions that the computer cannot compensate for are typically caused by excessive air in the induction system that the computer cannot control. These codes are triggered when the computer has exhausted all means of adjusting what it can to correct the problem. As a result, at the moment your mileage will most likely suffer because the computer is dumping more fuel to compensate for the lean condition it is "seeing" in the system. The sensors triggering these codes are the O2 sensors int he exhaust system. Your truck should have three of them. One for the left bank of cylinders, one for the right, and one down stream of the catalytic converter (behind it).

As for what can cause the "check engine" light to trigger, there are a host of conditions and sensors that will cause it to come on and there will always be some fault code associated with it. With that said, not all codes will cause the CEL to come on either. However, IF the CEL comes on and there is a loss of power/performance associated with it as well, it is not recommended that you continue to drive the truck. If the CEL comes on and there is no loss pf power/performance, you can keep going but look into the cause for it coming on a soon as possible.

 

Thanks for the welcome and your input.

I read yesterday that one code was about the right side & the other was the left after just thinking is was the M.A.F. Hopefully it's not all 3 or 4.

My mileage has not changed since the Engine Light has been on or years prior to that. The power seems the same and it starts up quick every time. The only exception during startup is that once in a long while after it starts it struggles and hesitates. If I turn it off, turn into on position until the fuel pump sound is off, it starts perfect. That doesn't happen very often.

I'd like to find out if the air filter might have the ability to encourage the error code. I have been an AMSOIL dealer for a long time and changed to our easy breathing Bronco Advanced Air Filter. I'm wondering if it is too easy breathing or low restriction air flow that it might contribute to too much air, or more than the fuel injector computer can adjust for. If you want, you can get a Free Catalog and to read more about the filters etc.

I am going to try changing back to a MotorCraft or FRAM air filter to see if a stock airflow restriction will set it back to standard air flow and the M.A.F. sensor will now show too lean or to easy of an airflow.

Considering how clean even the original tail pipe is, I'm pretty sure all of the sensors must be in great shape.

Thanks again!

- Alan

p.s. I'm glad the "Only stupid question is the one you(I) don't ask"

www.AdvancedMotorOil.com

 

no, do what greystreak92 said and check for vacuum and intake leaks

 

That's another thing I was thinking about trying with a lite trickle of water around the connections to vacuum hoses and the intake manifold on a cool engine.

Thanks

- Alan

www.AdvancedMotorOil.com

 

The ECM can adjust for ANY amount of airflow as long as it has some way of regulating it at idle. You could have NO air filter in the box or no plumbing in front of the throttle body and the ECM can still run the engine because it still has control over the airflow. (NO air filter flows TOO well, such a filter would just not block enough crud) At the throttle, the flow is controlled by the IAC at idle. At the EGR ports the flow is controlled at the EGR valve. These are the ONLY two locations that air should be introduced into the induction system. Anywhere else and the ECM cannot control the flow of the air into the engine at idle. So if you have a lean condition, (as indicated by Codes 171 and 174) the ECM cannot control one of these two things OR you have air getting in at some location it shouldn't be. Since you haven't gotten any fault codes indicating there is a problem with the EGR or the IAC, process of elimination would dictate a vacuum leak somewhere.

The other very remote possibility is an exhaust leak UPSTREAM of BOTH the left and right bank O2 sensors. This would allow fresh air to "contaminate" the exhaust before it gets to the sensors causing the "lean" reading. But if I recall where those O2 sensors are located, you would have to have either manifold leaks or loose manifold to Y-pipe connections. You would hear either of those.

 

OK. Thanks.

The next thing I probably should try is while idling, to run water around the intake manifold before it's hot to see if the idle is affected or the engine dies.

The other possibility is that the MAF sensor or left or right exhaust sensors are bad.

Thanks again.

- Alan

 

I wonder why this thread sounds so much as advertising... Is this company an FTE sponsor?.

 

It does??? What kind of advertising does it sound like?

 

That pretty much sounds like advertising

I'm pretty sure that's advertising also, even the username is advertising. Lets do something, i'll report this to the administrators and they'll call it.

 

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