Another P0171 P0174 Issue

[psi2rd]

I could use some help on this issue. I have the left and right banks reading lean. Has showed up and not gone away. I had the codes ran at an auto store. They told me it's an oxygen sensor but I know better. I have searched and read about this and seem to have an okay understanding. I am more looking for a check list of things to look at starting with most to least common. I am not 100% prepared as I ordered a scanner but do not have it till tomorrow. Back ground of what Info. I have is:
2004 4.0 79,000 miles
Just started Tuesday about 10 miles after I filled an unusually low fuel tank.
Never have had a SES light before on this vehicle
Trans replaced at dealer about 2k ago
Still drives normal but using what seems to be more fuel(have not had problem long enough to tell as about 6 miles is what I drive a day as I have a company vehicle)
Unplug MAF sensor it dies
Checked fairly thourghly for vacuum leak, none found or heard.
Did a starting fluid spray around intake gaskets, nothing found
This is all I have had time for so far but would like to take a close look at this weekend.
If anyone has specs of the items I need to be checking that would help too but I can always look those up.

Thanks in advance for any info. and going to continue the search now.

 

[TechGuru]

See if this helps:

http://files.mediahost.cf/DTC P0171-P0174 System Too Lean Diagnostic Aids.pdf

 

[psi2rd]

That does help, THANK YOU! and I did get my code reader today.
All 4 o2 sensors are reading ok at this point but did not do any WOT pulls.
I am not trying to run it in a lean condition as we all know what happens.
Fuel pressure is at 39ish at the regulator.
I am looking for the normal range for the MAF sensor if anyone knows.
Cat temps were around 1300 or so.
I am wondering if I may have had a blockage in the fuel filter due to running the fuel very low?
As an FYI I have an autel 619

Anything else I need to check?

 

[rrgone]

Have you read through this post:
http://www.explorerforum.com/forums//showthread.php?t=217062

The OP there has a 4.6 engine but other's chimed in with 4.0 engines with same issue.

 

[TechGuru]

 

[psi2rd]

Thanks for the chart!
I did read that post also. I actually pulled off a vacuum hose so I could hear what it would sound like. I have nothing like that and I have had time to check hoses for leaks now. Nothing found. I have reset the SES light and will see if it comes back. I am thinking it is an intermittent issue at this point so this will be some great "fun".