Hello fellow Jag owners, I have a question, I am getting the codes P0171 System too lean Bank 1 and P0174 System too lean Bank 2 - based upon this forum, I believe I have a vacuum leak. At first the check engine light would come on once every couple of days. Now it comes on every 30 mins to an hour of running.

I tried to find the leak using the old carb cleaner around the vacuum hoses when the engine was running trick but could not find it. No difference in the idle.

With that being said, is there an area that you all recommend that I should look that seems to be a place most common for a vacuum leak?

Any help or suggestions on where to find the leak or a better way to find the leak would be appreciated.
Dave

 

I had the same codes that I chased for a while. Carb cleaner didn't work. Found with a homemade smoke machine. I have a thread on making one. Also used to find a leak in EVAP system.

 

I second the smoke machine idea. I bought one from Amazon (I think), and I have used it several times over the years. Saves a lot of guess work. I only have direct experience with the supercharged V8 on my 98 XJR, so this may not apply to your car, but: the part load breather tube runs under the intake and plugs into the front left cam cover on one end, T's into the throttle body and runs on past the throttle body. That tube is the most brittle thing on planet earth, and probably leaks if you sneezed on it. Another possibility: The brake assist vacuum line plugs into the right side of the throttle body. The O rings inside that fitting can crack and allow a vacuum leak. Mine did anyway. But if you've sprayed carb cleaner around there and didn't notice anything, then my vote is the part load tube under the intake, if the VDP has a part load tube.

A smoke machine will find it for sure!

 

Throughly clean the MAF sensor.

 

A dirty MAF sensor was the cause of my lean codes. I thought I had cleaned mine after spraying the glass-like bulb that hangs down - not realizing there are electronics on wires up inside the cylindrical plastic tube that extends into the airstream. Be sure to spray/flood this area with cleaner and dry with compressed air.

 

Gently tighten the bolts on the cam covers; check all fitting to the throttle body, including the rubber seal; examine all rubber hoses for broken or dried ends; clean or replace the MAF sensor; clean the throttle plate and bore; check the seal on the dipstick; run a can of good fuel system cleaner through a tank of gas (always fixed the problem on my RRS/SC); find or build a smoke unit. How old are the plugs? Can you read the short and long term fuel trims on your OBD II reader?