I have a 2000 F150 4.2L and I have 2 codes PO304 & PO174 so far I have changed my plugs & wires,fuel filter,mass air flow sensor, and coil pack...it is still running rough under a load and a little rough on idle.. any suggestions?

 

Your miss fire and lean code are on the same bank.I would look closely at # 4 cylinder.If you have a misfire the o2 sensor will still read lean regardless of raw fuel from that cyld.It senses o2 and can't detect raw fuel, so my thoughts are the 2 codes are the result of the same problem.
Maybe low compression at #4?
Hope this helps

 

Thanks for the reply.But I am not understanding what the advice includes.,I was thinking of checking the O2 sensor.....not knowing how to check compression or so forth ..... On cylinder 4 I have checked the fire with a test light and have good fire through the plug wires to the plug...

 

You will need live stream data or a volt meter to check the o2 sensors,live stream data scan is best by far.I still think your problem is with the misfire on #4.
Do you have the misfire at open loop (within first minute after starting cold)? If you do that pretty much eliminates a lazy or bad o2 sensor.

Do you have freeze frame data with the codes( does your scanner store freeze frame data)?

Since you have already changed plugs/coil pack/wires ect you need to find out why#4 is misfiring.
Could be a fouled fuel injector,major intake gasket leak at that cylinder, low compression.
The next thing I would do is a compression test.If compression is lower than 90psi the cylinder will not fire.
I am not an expert on the 4.2 but these systems are basically the same.
Keep us posted and good luck....anyone else has some input please feel free!

 

I know on my 98 4.6 I had to change the IAC valve, have you tried cleaning it with a q tip?

 

Sunday good,the 1st thing I did tonight was put the old coil pack back on it still has a heaitation

 

Sorry,that was all bad,Idle air ctrl.? I have changed it before but it has probably been 2 years but the truck wanted to actually stall when that was the problem , I put the old coil pack on and it still has a hesitation but soothes out a little better, so next I am going to exchange it out and lets see how that does .....thanks,Cnichols

 

Yes, Idle Air Control Valve. Mine was on the back of the engine on my 4.6 if I remember correctly. Not sure on a 4.2.

 

So would IACV cause a
no-fire an running to lean? I put a 2nd
coil pack on and that wasn't it...

 

I don't know about the lean, but the rough idle might be caused by it.