1996 Ford F-150 Pickup Code P171 and P172

Reader Question: Austin,

I have a 1996 Ford F-150 Truck with a 4.9L inline 6-engine. I have been struggling with a P171 P172 system to lean Bank 1 and Bank 2 since I was at 100k miles.

No mechanic seems to be able to help me. I have replaced the O2 sensors.

Recently, now at 160k miles, I am having a problem with very rough starts where the entire truck shakes while starting. This is very random. It happens with the engine sometimes when it is cold and sometimes when it is hot.

Now my inspection is coming due again soon and my check engine light is not functional. The bulb has gone out before but now the light will not come on to do a check when the truck starts.

Does all this sound related? Can this lead back to a computer problem? Can the computer be replaced without special equipment and tools? Any suggestions you might have would be wonderful.



Hey Kenny,

If you were in my shop, I would first start with cleaning the MAF (Mass Air Flow) Sensor. You can buy a can of cleaner at your local auto parts store just for this repair. Try to spray inside the sensor so the cleaner runs out and not accumulates inside the sensor.

On the check engine light, it sounds like you have a burnt out bulb to me, and I think you are on to that as well.

If you still have this running problem, I would check the fuel pressure at the engine with a manual fuel pressure gauge, which you can usually rent at your local auto parts store.

Austin Davis

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