I have a 1997 5.4 with 135,000 mi and the check engine light came on the other day. The codes or 0171 and 0174 which means lean mixture on right and left bank. I changed the o2 sensors that are in front of the cat on the left and right side. this didn't help I have dumped two cans of injector cleaner in the tank but this hasn't help either.It runs fine but the idle is rough. Checked for air or vacum leaks and don't know where to look next has anyone had a problem like this and if so what did you do to fix thanks for any advice .

 

Hey janvan,

I have the exact same problem. Here is where I posted the same thing awhile back.
https://www.f150online.com/forums/sh...hreadid=120663

I found that cleaning hte MAF helped with the rough running condition but I still have the CEL on. I think it was 98SCREAMER that suggested changing it, which I hope to get around to doing before too long. Also it was suggested to confirm that the IAC is postioned correctly. If you search for IAC you should find the thread on the IAC with instructions.

I just noticed that yours is the 5.4, a very common cause of the problem is the PCV elbow at the back of the intake. Follow the PCV hose around to the back of the engine and there is an elbow that leads it into the intake. that is possible leaking causing the CEL on yours


Godd luck
Stan

 

I agree. This is the most common cause of those codes. Unfortunately people get talked into replacing the oxygen sensors when it is really an elbow that has deteriorated.

 

Thanks to everyone who responded. I changed the elbow as suggested. When I tried to remove the elbow it was real gummy and it tore while removing I replaced and the truck seem to be running fine. I need to get it to Auto Zone and get the codes cleared and see what happens but I beleive that the elbow was the problem.thanks again

 

Just disconnect the neg terminal on the battery, and turn on the head lamp switch for about 5 min.

After that, turn off the headlamp switch, hook the neg back up, and start the truck and let it idle in place for ~ 10 to 15 min. Then take it for a drive, the way you are going to normally drive it on and off highway for a few miles.

That will reset the PCM, and start the learning mode for the PCM as well.

If this fixed the code, the CEL will stay off.

 

also you'll need to exceed 48 miles an hour during your drive and go for longer than 70 miles. this is ussualy about the time that the PCM decides whether or not a problem exists. it a took 75 mile test ride for my CEL light to come back on. thats after I had idled (25-40mph) around town for a week.

and according to the book it takes 3 driving cycles (cold start, warm up, drive at better than 48mph, highway / city, shut down, cool to cold = 1 cycle) for the PCM to decide the condition does not exist and shut off the CEL on it's own.