I just bought my first Jag Wednesday after the Jag dealer did a $250 prepurchase inspection. Drove it home 2.5 hours from the dealer. Took it to the tinting shop Thursday morning. Thursday evening, check engine light "Restricted Performance" Code P0171 and P1111. Welcome to Jag ownership I guess.

Anyways. I have done my research on the forums and it seems if you get the P0171 and the P0174 at the same time chances are you have a bad or dirty MAFS, a vacuum leak, gas cap not closed, bad dipstick o-ring, manifold gasket leak, etc. But since I only have the P0171 and the P1111, is it not more likely that it is in fact the O2 sensor? That or the "Full breather" hose?

Let me know if I am interpreting my finding correctly.

Robert

2004 XJ8

 

I've been through this one...

First of all, you can put the items that affect both banks on the back burner for now. So don't worry about the MAFS, gas cap, and dipstick, or fuel filter.

The P1111 just means the system has completed all its checks...so that will display until you clear the P0171. After you clear all codes, the 1111 will change to a P1000...which means it has not finished running all checks. That will go back to P1111 after 50 miles of driving or so.

Also, there are 4 O2 sensors, so they cross check each other and know when one is bad. Your code says you have a lean condition, so that means both sensors in the right bank are agreeing that you have a lean condition. So, not an O2 sensor.

Now, concentrate on items that only affect the right bank. This includes:

An exhaust leak on the right side before the O2 sensors, which could be as subtle as a crack in a pipe...but usually easy to find.

Vacuum leak, like a hose that is pulled off or cracked. This engine uses a lot of those corregated plastic hoses which tend to crack when they get old...and they also make a hissing noise all the time, so hard to hear a real vacuum leak because they are so loud.

If you don't find any of these items...burn your current tank of fuel to near empty and refill with a good premium gas. Not from 7-11 or some no-name station. Then clear the code and see if it returns. Many times a code can be temporarily triggered from a tank of bad gas. If it stays out, you are good.

If the code returns, we need to start looking at the harder items, like fuel filter and injectors on the right bank...

 

If you can do live data, check LTFTs to see if it's just one bank or the other is close behind (nearer zero so hasn't flagged P0174). If banks are alike you're looking for a leak that would affect both banks, which means fairly early (in terms of air path) or the like. But first... rev to about 2500 and check the LTFTs head towards 0. That shows it's an air leak rather than something else (they head down as the leak is swamped by the main air in).

 

Ok, I took the car to a local mechanic that works on imports as I am just not ready to start tearing apart a 1 day old to me car. The list of codes they pulled was extensive but they cleared them and were not able to pop any codes again. I have since taken the car back and have driven it a couple of times with no check engine lights so I believe I will do as suggested and refill with a good tank of premium and go from there. Do I dare try any injector cleaner or fuel treatment?

Here's the code list btw.
P0171
P0174
P0300
P0301
P0306
P0101
P0829
P1226 <- He wrote down P01266 but this is what made sense
P1316
P1582

The car never did anything but run smoothly so I'm not sure when all that misfiring happened.

 

You often won't feel or hear misfiring even though it's reducing mpg, increasing emissions and busy destroying the cats

An elm327 is only a few $$$ and will let you check the fuel trims as posted.

 

Well, that changes everything! Hopefully those were just spurious. I'd like to hear if any come back...

 

I will be driving her from west Kentucky to Miami on Tuesday. I'm guessing if a code is going to pop, it will pop sometime on that trip. If all is good by the end of the Thanksgiving holidays I will close this thread with a big smile on my face and plenty of thanks to give. If not, I guess I will post a list of codes and start writing Santa a parts list. Lol

 

Well back from my trip. I put 1500 miles on the car before I got a check engine light. I did a little poking around and it seems I have the dreaded busted air filter box like so many others. Check engine light came on in the rain so I am guessing I got some water up through there. I did a temporary fix with foil duct tape because the previous owner fixed it with regular duck tape and the heat had made it droop. I also cleaned the MAF with MAF cleaner and the throttle body with throttle body cleaner. Seems this made things worse. Not only did the check engine light stay on but now, every time I started the car, I got restriced performance that would persist until I got the car up to 55 mph then it would go away until the next time I shut off the car.

Well, this went on the entire 1100 mile drive back to Kentucky. Once on the highway though, I was getting 28 average mpg and performance was fine. The morning after I got home I took the MAF out and sprayed it well with the MAF cleaner. Dried it out and put it back in the car. I prayed to the motor gods and turned the key. No restricted performance message. Drove the car to the self car wash and gave her a bath. Started her again, still nothing. Drove her across town and half a mile out, the check engine light that had been on for the last 1100 miles went out. I have knocked on every pice of wood in the car but it seems I have fixed my issues with a $6 can of MAF cleaner.

We shall see.