I'm looking for some help with my 97 F250 2WD 5.4. 2 days ago, driving home, my truck started to misfire. At first, it would only do it when going uphill around 40 mph with a 20+ mph headwind in Overdrive. It has now accelerated to the point of most anything above 1/4 throttle makes the engine miss horribly. I pulled the data off it, and I only got a P0171 code. It had the freeze frame data with it, and bank one long term fuel trim was +16.7%, and bank 2 LTFT was +.6%. Obviously, I know there is a problem with bank one, as its running very lean. I pulled the number 1 plug(haven't had much time yet), and it didn't look bad, just a lil oil burning.

The truck has 224,000 miles on it now, timing chain replaced 10K miles ago, along with new MAF, throttle position sensor, O2 sensors, air filter & fuel filter. The truck has a slightly rough idle. When it misfires, the whole truck will shudder. Is it possible that when the timing chain was done, bank 1's cam was put in with one tooth advanced? I did most of the work with the chains, however, i had a ford guru there helping with the timing, and he thought the cams were right. any way to tell with out tearing the motor apart if thats what it is? As big as the LTFT is between banks, it allmost has to be something mechanical.

I have also tried to run the truck misfiring to set another code, and the PO171 is the only one I can get!

 

Ok... I just was outside playing with it before I leave it for a few days, and I reset the pcm(with a scantool), started the truck, hooked a vac. gauge to the fuel pressure vacuum line(fpr had no vacuum as a result), put the truck in reverse, held the brake as hard as possible, and slowly opened the throttle. once it reached near zero inches, the engine started missing, the vacuum never flinched. after 30 seconds, it finally lit the light! I got a P0308. Cylinder 8 misfire detected.... WTF! thats on the wrong F#$%ING bank! Well, Im outta time tonight, Ill be back to the truck on tuesday, hopefully FTE can help me out by then.

BTW, Idling, the truck had a nice smooth 19 inches of vacuum. no bobbing, or anything. What do I look for with the lean issue on bank 1?

 

Either the PCV valve is shot or the elbow on the pcv hose going into the back of the intake is cracked??

 

well, i know its not the pcv valve...... I had removed that and plugged the vacuum port on the back side of the intake. no leak there! Any other ideas?