Error Codes

Assuming your 4.0L is the SOHC and not the OHV. If so, the most common cause of the P0171 & P0714 codes along with difficulty starting when the temperature drops below 50F or so is leaking lower intake manifold o-rings. Ford extended the warranty on them to 6 years 72K miles so if you have less than 72K on it, Ford will replace them for free once they've verified that that is indeed the problem. If you have more than 72K miles then expect to pay from $150-$400 depending on where you take it.

Its the OHV. Have they had any problems with the o-rings? (I'm way out of warranty :-( Murray

I haven't heard of any intake manifold o-ring problems on the OHV. One other problem that wasn't quite as prevalent on the SOHC was a contaminated Mass Air Flow Sensor (MAF or MAS depending on who you talk to ). I don't remember if it also applied to the OHV but might be worth looking in to. If the sensor wires on the MAF get dirty, they will not read the correct amount of air going in to the engine which will cause the engine to run lean. Basically since the problem is on both banks, you are looking for anything that might introduce more air into the cylinders than the sensors have read (air leaks, dirty MAF, contaminated O2 sensors).

Actually, I have seen several problems regarding lower manifold seal on the OHVs..... The centre cylinder(s) will develop leaks partially masked by the intake/valve area relationship. Fouling plugs is an early sign....

YMMV

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