On my 96 F150 (4.9) the check engine light is on. Had the codes read and the typical P0171 and P0174 too lean condition is present. I understand these are common failure code for the EEC-V v2.o on my six cylinder? At any rate, I've cleaned the entire intake, including lightly re-oiling the K&N filter. Still, the check engine light is on.....
So.....I reluctantly had the local Ford dealer diagnose that "the MAF is reading out of spec". So, I replaced that as well. Still, the light remains (and thanks to the Ford dealer for the incorrect shoot-from-the-hip diagnosis..)
Is there another common place to look for this common failure? I need to pass smog and it's not looking too good right now. Any help is sincerely appreciated! The vehicle runs really well, but very bad fuel mileage.
...Lastly, my OBD II (Acton mfr) code reader doesn't read or respond on the vehicle, any thoughts why? (it works fine on all other of my vehicles)

GAP
1996 F150, 4.9, auto, 4x4, (previously run on propane flex fuel), 119k

 

When is the last time you replaced the O2 sensors?

 

I've had the truck for a year and haven't replaced them myself. I was thinking about the O2 sensors as well, but thought that they would appear as a trouble code if bad. What do you think?

 

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If they haven't been replaced in a while, they might need replacement anyway and that could be the source of the code as well.

 

Since it's lean on BOTH sides, it sounds like a vacuum leak to me.

Try doing a forum search on vacuum leak & see what you come up with

 

A few other possibilities:

If you put too much oil on that K&N filter, it will get into the intake stream and contaminate the fine wires in the MAF sensor. This causes it to read too low at speed, which causes the computer to inject too little fuel, which causes the mixture to be too lean, and the computer can't figure out why it has to peg out the fuel trims trying to make it rich enough. Then it posts P0171, P0174.

If there is any leakage allowing air to get into the intake and around the MAF sensor, you will get unmetered air and P0171.

If your fuel pressure is too low, due to a failing fuel pump, bad regulator, or clogged fuel filter, then insufficient fuel will be supplied relative to the amount the computer commands. End result: code P0171, P0174.

With a MAF based system, I don't think that a clogged EGR valve could cause this. (The MAF should reflect the actual amount of oxgen coming in, regardless of whether the EGR works or not). But with the older MAP based system, if you had a blogged EGR passage but a functioning valve, the intake charge would have too much air and too little exhaust. The computer thinks some of the air is being displaced by inert exhaust and adjust the fuel mixtures. But the exhaust isn't actually coming in, so their is too much O2 for the fuel the computer wants to supply, again leading to codes of this sort.

 

My guess would be the O2 sensors too. I have found that Most sensors harnesses have a common wire linked to all sensors. For example I was working on a 4700 International truck with a 530 diesel engine. I was trouble shooting low oil pressure, change oil pressure sensor and checked oil pressure with a manual gauge, both were fine. traced wires and found there was a common wire to all sensors. Anyways it end up being the coolant level sensor causing the hole problem. Also I have seen ecms[eletronic control module] and sensor harness cause the same problems. I have also found problems communicating to the ecm is a good idicator of a ecm or harness problem, but I would replace the O2 sensors first and if that does not solve the problem I would consider trouble shooting the ecm and harness.

 

Thanks for all the good leads and tips. An update... I'd disconnected the battery in an attempt to reset the check engine light (after MAF replacement). The light went out. I promptly went to my local smog station, tested and passed!. On the way home the check engine light came back on... So,.... I'm back to troubleshooting, but at least for now (and for one whole year) there's no hurry. It seems to me that something vacuum related is failing and must be tracked down. It's very hot and dry here in Nevada and rubber products dry out and become brittle very quickly..

Thanks again...