I'm getting only code P0171 on my 2003 5.4 Expy, any ideas? I thought if it was a vacuum leak I would get P0171 & P0174. The truck is still running and idling fine and fuel economy seems unchanged, I actually reset the code and it was off for about a week - now it's back.
Any ideas would be appreciated I've got a long road trip coming up for my son's football game, I'd hate to have problems hauling a bunch of 8th grade kids!

 

Check your pending codes and your long term fuel trims for both banks with the scan tool. Many times, it takes additional time to set the second "lean" code when a problem is just on the edge.

If bank 2 trims are within relatively normal limits (close to 0%, then the problem is isolated to bank one. If the bank 2 LTFTs are really close to the limit (25%, IIRC), then it's a problem that affects both banks.

 

No Pending codes, but the LT fuel trim % for both banks were high. So would this indicate I'm looking for a vacuum leak??

 

A vacuum leak would affect both banks not just one. I think you might just be looking at a bad passenger side front O2 sensor or wiring issue.

 

If they're both "high", then its something affecting both banks. See explanation above.

 

So then if both codes show up,p0171&p0174 its a vaccume leak? Is there a usual spot to find this or a trick to finding it?

 

Mine turned out to be on one of the vacuum lines coming off the pcv valve. It was hard to locate because it was pulling itself back together under vacuum but when I started moving stuff around I could here it. I just ran my hand along the vacuum lines and then I could feel the leak.

 

Found it. It was on the pass side valve cover. Rubber boot had a hole in it and it was so worn it had colapsed. Love these forums. Thanks

 

I know this is an old thread, but our 2003 5.4L had this exact problem and this discussion helped me find our problem.
The PCV elbow at 154k was is poor condition, but when replaced did not fix the problem.
There are 2 short sections of 1/4" vacuum hose near the front left corner of the throttle body that were also in poor condition. Replaced those with 1/4" fuel hose and no more code P0171.

 

i know this is old but i have a simmilar issue. p0171 only but my trim is high only on bank 1... bank 2 is l closer to 0.... now i have chancged all coils and plugs and sparks... removed cat conv, and still have the same code. fuel prssure is 28psi 2 ford mechanics and i have checked for air leaks in system and nothing yet. i have had this issue for over 3 months now and its driving me nuts please help....

 

Check the fuel trims for both banks. You *might* be just a whisker away from throwing the P0174.


Smoke it to verify there are NO vacuum leaks.

 

2 difrent shops did it already.. took it to one and they had the truck for a month then took it to another one and same thing they cant figure it out... and bank 2 stays lower than +10 and -10 but bank 1 starts at 25 and stays like that. did smoke and nothing came out. also did the carb cleaner near bank one to test for faulty intake manifold and nothing.

 

Your fuel pressure looks to be low. You didn't specify your vehicle so I looked up the chart for a 2003 which is what this thread is about.

 

sorry its a 99 f150 5.4 lt ke on ignition 10 psi
runinning 28-30

 

Then your fuel PSI is low, yours should be:
Engine running 28-50 psi
Key on engine off 35-45 psi

This could be due to a bad pump or a bad or leaking fuel regulator. Low PSI can set a P0171 lean code, so I would focus on solving this low pressure issue.