UPDATE-Codes P0171 & P0174 - could it be the petrol?
 

So had a great trip from Yorkshire to Stratford on Avon to see Henry IV at the RSC - even had the top down all the way back :icon_smile:

However, noticed the yellow engine light come on - nothing else no limp home mode etc. Car going perfectly - temp fine so i just ignored it. Got home and took the codes before turning engine off and this is what I got P0171 (system too lean bank 1) & P0174 (system too lean bank 2). Switched off and restarted - light gone off.

Anyway, it occurred that I noticed the yellow engine light about 30 miles or so after I had filled up - 1/2 tank of Shell V-max. Never used this fuel before and never had these codes before so just wondering if it could be the additives making the engine run too lean? :icon_confused:

The pleasing thing was that there were no other fault codes showing after a 160 mile trip. Got about 26 mpg.

Update:
So on searching the threads it seems these codes are often due to leak from air hoses/MAF etc. I have had a good look around the engine bay and can't see anything obvious but have not checked with "propane" - not sure I fancy that idea - I do have some stuff I use for checking for LPG gas leaks on my boat but probably not useful here. The only thin I have notices is that the clips on 2 of the vacuum hoses are broken but i can't fathom where they would normally clip too anyway. The air box lid is tight and the fuel filler cap likewise.

The overflow pipe from the coolant expansion tank has a repair where it goes back into the engine - I have a complete replacement pipe ready to fit but I can't see that this would cause an air leak.

White arrows on pipes copy.jpg show broken clips and the repair to the overflow hose

Any advice gratefully accepted - in the meantime I'll just wait and see if the codes come back.

Steve

Steve

Since you have both codes, it's reasonable to assume that whatever the problem is, it affects BOTH banks of cylinders. I certainly would have expected you to find a leak in the corrugated tube between the air filter and throttle body. Pretty common with age. Next I would look at the hard plastic main vacuum line coming off the right rear of the lower intake. They sometimes break, or pull out. Another thought would be that one of your fuel pumps has failed, and the car has to rely on just one. A third thing would be the Mass Air Flow Sensor. These will sometimes seem fine, but just don't allow a rich enough mixture under load. If your scanner will read data, pull up MAF in g/s, and watch the reading under a full load at peak revs. You should see close to 200 g/s. If it is, say "150", you may need to look at a replacement. The XKR and XK8 MAF sensors are different. I do not believe that it is the fuel, o2 sensors, vvt's or anything internal.

You can try cleaning the MAF (easy to do with sensor cleaner) which I've done with success. I also once found the connectors for the Maf to be dirty and simply pulling and reconnecting them cured the problem. Good Luck.

Since it is both banks, the most likely cause is the dirty MAF or a small air leak.

If your meter can show live data, then you can set it to monitor STFT and spray MAF cleaner around the engine bay. Similar idea to the propane but safer and more sensitive when reading the fuel trims.

If you hit a spot with a bad seal or air leak you should see the trims go wild.

Thanks for the advice - there seem to be numerous MAF cleaner products out there - is any one better than the others? I also see some recommending brake cleaner or carb cleaner?

Steve

Look at LTFT as well, should be within about 5 of zero, parked, hot engine, at idle and 2500rpm.

Will do. I'll clean the MAF sensor this weekend and see if that sorts things.

Be aware that the MAF signal has to be very wrong to trigger a trouble code and that cleaning doesn't always help.


Mine was reading about 13% low when I was searching for a leak and marginally worse after cleaning. But at no time did it cause any fault codes to be registered.


Old MAF peak was 195g/s


Replacement MAF 225g/s

Taken the MAF off today. The "main" sensor wires are a little mucky but the 2 "hidden" ones deep inside are filthy with loads of goo all around. I've ordered a can of CRC cleaner so hopefully will make a difference when they are all clean and shiny.

So cleaned the MAF sensor (the "hidden" wires were very dirty) and all fault codes gone and no yellow warning light. Seems to be running smoother vas well but might just be my imagination. Also prompted me to clean the MAF sensors in the other cars so every cloud and all that ....

Just got a new code reader that could read STFT & LTFT and just hooked up to give it a try really. Car was started from cold as not run for a few days. STFT varied between -1.8% & 0% and LTFT was round about 5% at idle and 7% at 1000rpm (didn't take it higher as still "cold"). I'll do the readings again next time I've had a run. Both banks gave the same readings. Still no return of the previous fault codes or yellow engine light so does seem to point to a dirty MAF sensor.

Steve

If similar with hot engine you've no signs of any air leak :)

Thanks
Coolant temp got up to 83c so I reckon will be fine but will test after run anyway.
This new OBD II wifi scanner for the iPhone is pretty nifty.

Steve

Looking good - 0% and +7% STFT & LTFT when hot after run

Just a reminder that there are two banks to read STFT and LTFT you gave one set of numbers were both banks identical ?

Yes, both identical

I live in dallas, Tx. Gas stations out here go through a four times a year shift of summer blend to winter blend formulas. Most gas stations will let their massive tanks of either blend run to nearly empty which results in the new batch collecting a lot of residue from the bottom of the tank of the old blend. This residue can easily find itself into your gas.
When I had the issue, I took it to a Jag dealer, who had 11 cars in for the same codes.
He suggested adding an injector cleaner to my gas. I bought some BG44K on EBAY,
(much cheaper than at any dealer or store). The codes quickly disappeared. good luck, Ed.