The CEL came on and I had several codes display on my reader. With 64K miles on the truck and after reading the forum I decided to replace the plugs, wires and ignition coils. All the codes cleared and the truck ran much better, not like new but better. It still seems a little sluggish. After a few hundred miles the CEL came on again with code PO171, Bank 1 system too lean. I'm not a mechanic and not sure where to go from here. Any suggestions would be appreciated. Also, how can you determine if all the plugs are fireing or if the engine is missing?

Michael

 

Ck ur MassAir Flow Sensor. Might be that you need to clean it.

Problem might also be inside your manifold.

 

I have a 1997 F150 4.6L and have been chasing PO171 and PO174 codes for a long time. It ran fine for a long time and didnt worry about the CEL since it was running fine. I recently had a new muffler and tailpipe put on and noticed an exhaust leak at the exhaust manifold. Turned out that one of the studs connecting the flange was rusted out. I had that bolt replaced without removing the exhaust manifold. This cleared up the PO171 and PO174 codes for a long trip of about 600 miles, until I entered the highway on an on ramp and the CEL came back on. I had left the gas cap off and figured it just got air back in the system, reset with removing the negative cable. It did not come on again until about 600 miles later when getting on highway at on ramp. Had the codes checked and found now only PO171. After reading previous posts I changed the PCV valve and tubing to that valve and back of intake. I recently started having a low idle and it almost dies at stop lights. I started changing the DPFE sensor and in the process noticed that the EGR tube is broke at the nut to the exhaust manifold. The tube still lined up and decided to try some JB weld before replacing the manifold and egr tube. Seems to be running better but still an occasional low idle, but only driven about 10 miles so far. Will this take time for the computer to realign the fuel trim tabs or should it have corrected immediately upon fixing the leak and pcv leak at back of intake?

 

It is now dropping the rpms down to like 2-300 when coming to a stop at the light. Should I give the computer more time to catch up and learn new idle, or is this possibly an IAC or DPFE problem?

 

I removed the air cleaner box and to my surprise I didn't need to remove the MAF. The wires protrude into the air duct. I cleaned the MAF with MAF spary cleaner. I took it out for a spin and it runs well. No CEL so far. It still seems a bit sluggish though.

Thanks for your help.