Hi
2002 F-150, 4.2, 5-speed manual trans, 90,000 miles, Central Florida, original owner, 65 years old, speed limit driven, no burnouts.

I have codes P0171/P0174.

I cleaned the MAF sensor and cleared the codes. After 1-2 weeks the codes returned.
I put injector cleaner in the tank.

I sprayed starting fluid on the vacuum hoses and have not found a leak …. yet.

I bought a fuel filter and will install it today.

Is the intake plenum gasket fix the next step? Anything else before I order the parts?

Thank you

Harry

 

those are lean condition codes on bank 1 and 2. there is awhole thread and possible solutions to this problem alittle further down this forum under lean condition 01 4.2 are something.

hope this helps

 

Upper to lower intake gaskets and isolator bolts.

 

Do a quick check for exhaust leaks around or bufore the o2 sensors that will also throw those codes. Try checking when the motor is cold and then again after it is warm. That is cheaper and easier than the gaskets, but it is probably gaskets.

 

I fixed my 171 by replacing the master brake booster.It was leaking vacuum. Better brakes too !

 

Hi

I ordered the plenum gaskets and bolts last night. I will check all the other suggestions also.

Thank you

Harry

 

Hi

I started the plenum gaskets and bolts fix. WOW them bolts in the back are hard to reach. Any suggestions?

Also I'm going to replace the original spark plug wires. Any suggestions? Should I stay with Motorcraft?

Thanks

Harry

 

Haven't done it but heard you can pull the motor mounts out with a jack under the pan and drop the engine enough to get at them.

 

Stick with Motorcraft wires.

 

UPDATE

After 25 drive cycles. No codes. So far so good. Here’s a recap of steps taken:
1. Replaced the fuel filter.
2. Cleaned MAF sensor.
3. Check to make sure the correct 4.2 air cleaner was installed.
4. Replaced spark plugs with Motorcraft.
5. Replaced plug wires with Motorcraft.
6. Replaced the upper to lower plenum gaskets and bolts as per wchong4 fix below. http://sites.google.com/site/fordf15...p0174fix/Home/ The rubber on the original bolts was very hard.
7. Replaced the EGR heated valve and tube assemble and grommet on the passenger side. The o-ring was hard. Also two rubber pieces in the tube assembly were hard.
8. Replaced the EGR tube and grommet on the driver side.
9. Seafoam in the gas tank.
10. Check for exhaust leaks.
11. Check for intake leaks.

I spend 2 days alone cleaning the plenum and intake manifold.
Runs great.
21 mpg.
Knock wood.

Harry

 

I've done all this and my check eng codes are gone and truck runs much better. My question: My gas mileage dropped to 15 mpg for the three tankfuls since the fix. Anyone else have this?

I also did the IMRC bushings while I was in there.

 

I'd disconnect the battery for a while to clear out the adaptive learning from the PCM, see if that helps.

 

Just wanted to add what I did to resolve these error messages with a CEL on...first off, I have a 2002 F150 with 4.2L V-6 5 speed trans...I drove the truck for 2 years with the CEL on knowing the codes were being thrown. Then about 2 weeks ago my truck starting hesitating, bucking while in any gear and speed. I re-read the codes and a P0156 was a new code added to the other two. So, I changed the drive side aft cat O2 sensor and the problem persisted. So, I finally ordered the upper intake isolation bolts with gaskets and changed them on the upper intake plenum. Since I am a DYI kind of person, I had no way to clear the codes. I drove the truck for 2 more days with it hesitating and bucking and then probably after about 5 - 6 re-starts and driving all over the place my truck starting running like brand-new..! The CEL has now been off since the fix (you have to pull off the neg batt cable) and with confidence the truck drives like new. One thing I learned is all DIY people with just a simple scan tool cannot re-set the trouble codes and the codes hang in memory causing your vehicle to run bad until the old trouble codes are completely cleared out (re-starts). All the while new drive points are being built. I'm sure driving the past 2 years with the P0171/P0174 codes probably did not help the O2 sensors as well. I hope this helps someone..!

 

My cheap code reader will clear codes.

 

Isn't that code a vacuum leak usually? Mine was due to the PVC hose at the back of the intake on my old 97 with the 5.4.

Really old post I just saw... Oh well.. There you go.

Mitch