Hi All, I am in need of assistance as I have tried everything from every forum that I have read and cannot figure out the P1071 error code.

I have not changed the DPFE / EGR because from what I have read that would / should cause a rough idle and I am idling very smoothly.

Vehicle Information:
1997 4.6L Vin 6 ~160K miles total ~30k miles on motor

Work that has been done to try to address:

• New Spark plugs / wires
• New coil packs
• New injectors
• New MAF
• New O2's
• New Fuel Filter
• New Air Filter
• New Fuel pump
• Ran smoke machine to check for vacuum leaks (no visible leaks)

OBD2 Data (Idle/2500rpm):

• Coolant 199
• IGN ADV 15.5/30
• MAF .6/2.2
• TPS 18.4
• Fuel Sys1 clsd
• ST FTRM1 ~ -2.4/3.6
• ST FTRM2 ~ 0.0/2.3
• LT FTRM1 24.2/18
• LT FTRM2 14.8/11.7

 

Check the PCV valve and make sure it is operational and the lines around it for any kind of smallish cracks. I've only ran into this code on GM's. I don't think I've ever seen it on a Ford 4.6. With GM, after cleaning the MAF, even if new, and checking or vac leaks after the MAF, then it was on to the PCV on 4.8/5.3/6.0 CHev's. One did have a bad fuel pressure regulator, but usually they were only small vac leaks or faulty PCV's. I didn't see where you change the PCV or anything with the fuel pressure regulator. Good luck.

 

PCV is new as well, forgot that on the list, will check the pressure regulator thanks .

 

Just went through receipts fuel pressure regulator is new as well

 

I'm having the same issue with our 5.4L 2003 Exped 150k. The P0171 - Bank 1 Lean code gets set, but never P0174 - Bank 2 Lean. I've been fiddling with this for months. The engine runs greats, idles smooth. All the vacuum lines have been replaced/upgraded, but I haven't run a smoke test. I've changed plugs, fuel filter, air filter, front O2 on Bank 1, cleaned MAF and throttle body. What I have noticed is I will get the P0171 when the engine gets up to operating temp, turn it off and let if sit for 10-15 minutes, then start the engine. If I start the engine in less than 10 min or greater than 15 min the code will not get set. The code will get set almost every time when the engine is started in the 10-15 min window. The code gets set after about 2 min. The code will not get set when the engine is started cold. I think the tests for P0171 and P0174 are done when the emission controls switch from open loop to closed loop. Is it possible I have a problem with the heater power for the Bank 1 O2 sensor? It has passed a CA smog test when I was careful after clearing the code to not restart the engine in the time window at the smog station. I may also have a small crack in the intake. I saw a post in another forum where changing the throttle position sensor fixed their P0171 problem.

 

What air filter are you using? Are you using a K&N or similar, or the regular paper filter? If you are using a K&N I'd check it for maybe too much oil, with will throw a code. If so, maybe try a regular paper filter and see if that cures your problem. Your sensors could be reading the oiled filter (if you use one). You do know, I'm sure, that certain silicones will make sensors go absolutely nuts. Permatex 6B (br also) will throw that sensor off, and any sensor that reads or senses air. There are others, so people have to make sure of which silicone they use. Thought I'd best throw that out there for some of the guys who are starting off or maybe didn't know. If it says "sensor safe", it's good to use. If it doesn't, play it safe, and don't use it.

 

The 171 code is a generic code, but should be isolated to the right side of the motor. You probably have some small vacuum leak or maybe a loose intake bolt, but you aren't setting a P030X code, so it may not be there. It's worth a check? If it was both codes, I'd look before intake, but since it a single, I'd bet at the intake, or some hose pertanent to the right side of the motor. Codes are generally specific, but the 171 and 174 codes seem to be one of the hardest to single out. There are numerous items that can throw this code. They do give which bank (luckily) so that gives you a specific area. Just with the 171 code, there can be lots of options to check, if you get my train of thought.

Here is a link you use. Very useful for quick reference.
http://www.obd-codes.com/p0171

Try spraying some B12 Berrymans with the engine running. You can find the smallest leak with this stuff. In 40 years, it is by far the best for this type of looking. When the engine rpms rise up some, spray it again. If it raises back up, you've found where the leak it. It is the simplist way I know to find a vac leak. It works better than fogging or smoke, IMO.

 

I will definitely try this.
Hadn't thought of a loose bolt which could easily be it, too.
I've been thinking my issue was something on the bank 1 side of the intake, maybe a crack in the plastic.
I just got an Android tablet working with a bluetooth OBDII adapter so I can see the RPMs while I try the B-12 Chemtool spray.
Next will be learning about long term fuel trims.

 

This is a mystery and everything I read on this post is good. Please post the fix when you find it.