Hello again have my Jaguar XJ8 running almost great except for the P0171 code. I have smoked tested the engine and found the Intake leaking between upper and lower plenum. Replaced the Intake with new gaskets and cured that issue. Replaced the PCV Valve Also. I have no leaks at the intake or in the vacuum tubes.

What type of readings should I look for with a reader that gives me O2 sensor readings and Fuel Trims?

Also I am going to check one more thing is the exhaust manifold to the Cat. Converter bolts and ensure that the flange is good and the bolts are tight but not He-man Tight.

Would anyone have any other suggestions as I have plenty of fuel in the rail and the car idles very smoothly.

This code only shows up when I back out of hard acceleration so I think I am looking in the right place as the exhaust is sucking outside air past the O2 sensor possibly.

 

Having only P0171 or P0174 and not both does indicate a fault that is specific to only one cylinder bank, and an exhaust leak is a definite possibility. In addition to checking the manifold-to-cat joint, check for leaks at the manifold/cylinder head gasket and for cracks in the manifold itself.

Another possibility is a problem with one of the O2 sensors or its wiring harness. There are plenty of tutorials online for interpreting Live Data O2S voltages and fuel trims (STFT & LTFT) so I won't try to repeat them here.

Please keep us informed.

Cheers,

Don

 

Everyone I checked the exhaust and everything looks good and no cracks at this point and everything is sealed.

When I start the car and about 3 minutes after idle Engine light comes on and restricted performance shows up. I drive it down the street about 5 miles the restricted performance goes away and the amber light goes off. What would this possibly indicate.

I am going to purchase a reader for the STFT and LTFT as to me it is possibly fuel related or O2 sensor related now.

 

Keep in mind, one of the things that will get you P0171 is a problem of air getting introduced after the MAF sensor in the inlet tube. (unmetered air)

 

Box I agree with that to a point, both banks should run lean if it is after the MAF and before the heads.

I have at this point sealed all of that tight according to a smoke test. So at this point I am going to get a good OBD2 scanner and inspect the O2 sensors as I think this is a bad read. The sensors by my knowledge have 250K miles on them. So it is a good possibility.

 

I have a question for everyone if I have long enough leads I can swap O2 sensors upstream and downstream. If it changes to bank #2 would it be a good test to prove that it is an O2 sensor?

 

Along that line I should have mentioned that it is possible for both banks to be running lean due to an air intake leak, but for the O2 sensor responses to differ just enough that the lean code is triggered for only one bank. Being able to view the Live Data and fuel trims will let you know if both banks are actually running lean.

 

+1 trims should show if you've both banks or just one lean

 

I had this code ended up being a coil on the left bank (no cylinder misfire code set think it has a high threshold)

 

Having similar problems as yours Joe . Presently working with my mechanic to solve.Identified wiring harness as suspect( previous owner did a bad job of baking the car on paint job)- put a relay in. Managed to clean only 2 of the oxygen sensors(might need a torch to loosen & get at the other 2.) Now only intermittently getting a restricted performance code. Will be flushing the radiator ( full of gunk) which we think maybe affecting the thermostat resulting in the code being thrown.
Recently acquired Super v8 so can't trust history too much.

 

Okay everyone I got my Bluetooth OBDII Reader.

STFT 1 0.8 %
STFT 2 -0.8 %
LTFT 1 18.8%
LTFT 2 10.2%

Inches of HG is 22.

Fuel Pressure 47 PSI

I only measured this at idle at this time.

By what I understand I see a large vacuum leak on the #1 Bank henceforth the P0171 lean code.

I have purchased all the gaskets to rebuild the intake and reapply it with all new gaskets. I will keep everyone informed on what I find after this fix.

 

Everyone,

Rebuilt my complete intake with all new gaskets. About $200 in gaskets. Fuel Injector o-rings also.

Put it together and fires it up, P0171 code is gone.

STFT 1 and 2 identical at less than 5% at idle. LTFT 1 and 2 are reducing percentages exponentially now that the top of the motor is sealed up.

Makes for a Happy Saturday

 

Joe, I'm glad you got it sorted out.

 

Joe,

If I read this thread correctly you performed a smoke test, found the intake leak, replaced gaskets and then still had the 0171 code. Then, using the OBD reader saw the fuel trim indicated a leak on bank one then replaced the gaskets again? After then replacing the intake manifold gaskets (between engine and aluminum section of the manifold?) the problem was solved.

I am fighting the 0171, 0174 wars and would appreciate your insight. Best,

 

This issue spans a couple of threads actually. As I understand it, it was disassembled and reassembled without gasket replacement on the upper plenum first time.