- XK8 - XKR Forum -

Short and Long Term Fuel Trim Error P0171 and P0174

Steven Albrecht
Jaguar Association of New England *

forum user since 2012-03-19

 

The other day I was driving along and the engine quit. It would restart only to quit again in a mile or so to where eventually it would not restart. After a 30 min rest it restarted and I bolted for the home stable - made it. Since it was below freezing I thought it might be water in the fuel line and added fuel treatment. Yesterday was in the 70s and the same thing happened. So, this morning I hooked up my decoder and started to monitor the PIDs. I was surprised to find a large difference between Bank 1 and Bank 2 short term fuel trim. At first, bank 1 was at 21 short and 11 long. Bank 2 was at 172 short and 10 long. I sat and monitored the changes at various rpm settings and the long term settings were stable. I was never getting any error codes. Then all of a sudden the codes appeared and I have a confirmed P0171, Fuel Trim System Lean Bank 1 and a possible P0174 Fuel Trim System Lean Bank 2. The stats now are: Short term bank 1 = 21.8%, Long term bank 1 = 19.5%, Short term bank 2 = 172.2% and Long term bank 2 = 17.2%. This is at 654 rpm and 14.5% calculated engine load. Coolant temp was 190.4.

My first thought from the start was either the fuel filter or fuel pump but, why the big difference between banks? Do you think the problem is the filter and / or pump?

Looking for ideas.
Best,
Steven A



Steven Albrecht
1999 XK8
2002 X-Type Standard 5 speed

Short and Long Term Fuel Trim Error P0171 and P0174

Steven Petry
Jaguar Association of Greater Indiana *

forum user since 2007-02-03

 

Steven,

Don't pay so much attention to the short term trim value. That one will immediately and constantly change according to what the O2 sensors measure. You need to pay attention to the long term trim. That's the one that will signal whether it is fueling more or less than normal. P0171 and P0174 will be recorded if long term trim remains roughly 10% or higher positive, meaning the ECM is ADDING fuel. If everything is normal the trims bounce just above and below 0%.

If that's the case, you have to trace things and see where it's getting excess air, making it add fuel, or not enough fuel making it do that.

Good luck!

S Petry
'95 XJR
'97 XK8 Conv.

Short and Long Term Fuel Trim Error P0171 and P0174

Steven Albrecht
Jaguar Association of New England *

forum user since 2012-03-19

 

Hi Steve,

It was good to hear from you.

I have done some further work on the XK and here is the list:
1. Replaced the fuel filter.
2. Replaced the vac hose that goes from the throttle induction elbow to the fuel pressure regulator because I found a small nick/possible hole in the hose.
3. Found that the breather pipes on both the left and right side were not fully seated. I could hear a slight hiss while the engine was running at idle.

One these items appears to have solved the problem. I am guessing the filter was not the problem and that was just preventive maintenance. (Just makes you feel better.) I don't believe the vac hose was the problem either; it really turned out to be a nick and not a hole. Again, replacing something that is not exactly right just makes you feel better. I think the problem was both breather hoses being slightly ajar from a fully seated position in the retaining sockets on both banks.

I ran the tests and have 0% and -0.78% on the short term fuel trims and 10.156% for the long term fuel trims on both banks. No lights and she is back purring.

Thanks for the ideas,
Best regards,


Steven Albrecht
1999 XK8
2002 X-Type Standard 5 speed

Short and Long Term Fuel Trim Error P0171 and P0174

Steven Petry
Jaguar Association of Greater Indiana *

forum user since 2007-02-03

 

That is still a little higher than we would like, but see how it goes for a few days. Then you might re-check the long term and see if it has settled any lower.

Those two fittings on the cam covers.......are you sure the "O" rings are still intact and not pinched?? They can be damaged if you are not very careful.

Good job, by the way!

S Petry
'95 XJR
'97 XK8 Conv.