Hello,
Still working to clear the DTC codes on my 2003 XJR. I'm now down to these two codes: P0171 & P0174; "System too lean bank 1" "System too lean bank 2". Besides vacuum leaks,, is there any other reason for the car to throw these codes? The fuel trims are tolerable in idle but the short trim especially goes high on acceleration. I had tried a smoke test though probably the smoker did not have enough volume to really press a large quantity into the throttle body but still, did not see any smoke coming from anywhere. The O2 sensors seem to be showing some numbers when the accelerator is pressed so I'm not convinced there's anything wrong there. Besides, I'd get a code if any were failing.
Not sure what else to check at this point.
Lastly, I hear a very faint high frequency squeal coming from the brake booster while the car is running. I removed the vacuum line and taped it shut to test to see if the trims would settle down. There was no noticeable FT change at all with the vacuum line closed.
Has anyone ever had an issue with the booster failing? Even though the trims did not change, is there any reason to suspect the booster is causing the problem?
Thanks much, Dave

 

Fuel pumps good? Pressure at the rail valve should be 40psi give or take a couple.
Fuel pressure regulator faulty
Unmetered air leak...if the other end of the vac line is loose? it's connected to the TB.

 

The DTC PDF has a full list that's quite long.

If high idle trims don't reduce when revving it's not likely (or mainly) an air leak.

 

The following thread about this same issue seems to have quite a few ideas to offer:
https://www.jaguarforums.com/forum/x...solved-117387/

 

In another source I found a recommendation to change the fuel cap on my 2013 Jaguar XF AWD 3.0L (X250) with a genuine Jaguar fuel cap, no generic after market units. I thought, what the heck, I've tried everything else. Immediately after I installed the new fuel cap, and deleted the previous codes, the problem went away. Interesting at best. I would gather this is due to the pressurization of the fuel tank. Just an idea.

 

X308s don't vent via the cap, there's a charcoal canaster, associated pipe work & valve in the left rear wheel arch. So I doubt a cap would work in this case, it's an idea though. Leave the cap off & rev it to see if anything changes.

 

Leave the cap off? Expect a new code. Don't do it!

 

Well, you are the SFT trim winner! I had replaced the fuel pressure regulator last fall with an adjustable after market unit. When you mentioned the regulator, I increased the pressure to 41Lbs and that settled the SFT numbers into normal range! Now all the DTCs have been resolved on my XJR! Wow!
Really great advice from this group! Can't thank you all enough....

 

curious which aftermarket one you selected and why

 

Well, there is no brand name on the box; it's one of those ubiquitous units on Ebay for about $50. Black body with a gauge and comes with connectors but needed to buy the manifold and fuel line fitting. Thanks to guys one this forum that pointed me to the correct parts.