I seem to be having an unusual problem with my 2002 Navigator with the 5.4L DOHC engine (which seems to be an all together different engine from the 5.4L in the Expedition).

After driving for a couple of hours and stopping (for a food or restroom break), when I get back in the vehicle and start it up (it always runs flawlessly) and drive a few hundred feet the SES light comes on!

It is always a P0174 (Bank #2 is too lean). That is the ONLY code - never the famed P0171/P0174 combination that the search function shows is so often discussed in this forum.

The freeze frame always shows the Long Term Fuel Trim for bank #1 to be in the -3% to +3% range, while the LTFT for Bank #2 will be in the 14% to 20% range.

I have also run while data logging the fuel trims and bank #1 will sometimes get as high as 8%, while Bank #2 hovers in the 10-14% range with spikes as high as 25-27% !

There is a vacuum hose that comes off the driver's side of the upper intake manifold and goes over to what I t-h-i-n-k is the EVAP purge valve on the firewall by the brake booster. This vacuum line looks a little swollen and is hard. I disconnected this line frome the intake manifold and applied a vacuum with my vacuum pump and it holds a vacuum just fine, but I think I'll replace it 'just in case'.

Has anyone experienced this problem on this engine? And what was the solution?

Thanks in advance for your comments . . . . .

 

Sounds like it could be a leaking injector on the bank 1 side. This would cause the computer to lean out the mixture, at which point the bank 2 side goes lean.

 

Bank #1 seems to be within spec (Bank #1 LTFT is under 10%), but Bank #2's fuel trim in the 20+% range indicates the computer is trying to richen up bank #2 and it is still running too lean. Maybe a bank #2 fuel injector o-ring is causing a vacuum leak. Is there any way to isolate which injector it might be, as it appears that the upper and lower intake manifolds must be removed to access the injectors on the Intech engines?