Hey all, NightHawk (Jesse) here! I have a P0171 system too lean code showing from bank 1. With my lack of experience, I admit I do not know if it is paired to a P0174 because I don't know how to check bank 2. Last night I attempted to replace my fuel filter but I can't find it! I have already cleaned my MAFS, got the car to run slightly better but there wasn't much change. The engine struggles a bit with acceleration (pulsing feeling) and when idling it will dip and rise in RPM by about 50-100. I apologize if this is a repost. Anything you can do to help is greatly appreciated!! 2007 XJ8 4.2L 135,000km runs royal purple oil and filter. SAJXA71B27SH15398

 

First thing take the cover off the engine and look for any cracked or broken hoses around the area of the throttle body. Look around and listen for leak or suction noise while engine is idling. Search this forum with the trouble codes you described and see what other posts have found.

I had the 171 & 174 codes and chased the vacuum leak angle for weeks and discovered it was a faulty MAF sensor, even though there was no MAF code. Read the link below.

https://www.jaguarforums.com/forum/x...-tires-131991/

 

Thanks edobernig! Very useful stuff! So I've taken to collecting and replacing pieces on the car in attempts to cure my CEL and P0171. First was my MAF sensor, which gave me a few hours of somewhat normal driving. Whilst waiting for my PCV and connecting hose to come in, I started experiencing very rough idles. At this point I decided to park her and not drive until the problem is solved. Valve and hose have now been replaced, though I want to be very thorough with this. I don't know what hose to pull off for a smoke test (cigar method, don't really want to spring for a several hundred dollar smoke machine) so I'm attaching a photo, if someone could steal the image and highlight what I should remove, it would be greatly appreciated!

 

Take a look here
https://www.jaguarforums.com/forum/x...-leaks-117917/

I made a smoke machine for a few bucks

Cheers
34by151

 

Thank you 34by151! That's a great little machine you made there! I'm working on making one today, any suggestions on where to inject the smoke from? OBDII only reads P0171, not paired to a P0174.

 

NightHawk, im glad to help

Remove the intake tube from the airbox/maf and plug the end

A plastic lid from a bottle will do but a quick search of the kitchen (while the misses is not looking) will yield a perfect cap.

Punch a hole in the cap and inject the smoke there
This is also the same bank as the P0171 so it will show the leak quicker thank bank2

Remember to check the smoke output now and then as well incase the oil runs low

This will show up most vac leaks fairly quickly however I have had to resort to using a vac pump to chase down some leaks.
The process is longer and slower but will always get to the leak
Basically you attach a vac pump and gauge, same a charging an a/c system
Vac down the system and leave it 30 mins, if it looses vac you have a leak.
Tricky part is hinting it down by blocking tubes or testing off the car

Cheers
34by151

 

If you read the fuel trims you'll know how different (or not) the 2 banks are - you might be near a P0174.