Don't know what else to do
 

So been lurkin around the forum quite abit here the last month or so and the info here has helped quite a bit but i cant seem to figure out this problem with my truck. i got a 2000 F150 5.4 automatic, its got 348,000km on it or roughly 217,000miles. im currently gettin 1131 and 1151 lean codes and it idles really rough majority of the time when u stop at light or whatever, best way to describe it is almost like its running out of fuel. truck runs otherwise quite well while ur drivin it just not when its idling. ive changed the fuel filter, spark plugs, DPFE sensor and hoses, checked for vacum leaks and cant find any, air sensor seems to work fine soooo im sorta at a loss. one thing i should note is i do have an exhaust leak somewhere its either the donut or the manifold itself on the passanger side cant pinpoint where its leaking from. i really dont think its my 02 sensors cause while they probably need to be changed i dont think they would cause the severe running problems im experiencing could be wrong tho i guess.


anyone got any ideas or sujestions cause im outa ideas with this thing... :smoke:

You'd be surprised what O2 sensors will do to the running of a vehicle...they are made to tell the computer ho lean and rich the exhaust is...if they don't work properly, u can never tell what the engine will do....I would say replace them for sure....clean ur maf sensor and make sure ur fuel pressure is up properly...other then that, might be an internal problem. Good luck dood!! And wow, 350k.....impressive :)

sounds like a vac leak

thats what i thought as well but i have spent many hrs tryin to find a leak and as far i can see there isnt any leaks.

Here is another case where the fault codes are not interpeted for discription of the action.
Both sensors are responding to the same fault. It's not the sensors, they only report the problem.
The codes are the same for both banks.
They are telling you the PCM has tried to correct for an "over rich" condition.
When the fuel tables are 'out of limits', the codes are set.
.
Causes can be an air leak in the intake at some location, leaking fuel regulator allowing gas to be sucked into the intake, fuel pressure to high, leaking injectors.
Also look at the OX sensor harness for a burn against the exhaust at some point.
.
To go on further, if you were to look at the fuel tables live values in the computer program, with a scanner, they would show out of limit values to support the codes you see.
The rough idle result's because the PCM has shut down most of the fuel causing the idle to be rough just like closeing down the needles on a carb would do.
Good luck. Go gitum!
Happy Holidays.

how would a person check the fuel regulator?

fuel pressure gauge...if your FPR, fuel pressure regulator is over pressurizing...it will read somewhere over 40psi.

normal pressure should be 30-38psi

A check for a leaking diaphram is to pull the vacuum hose off the regulator and check if you see/smell gas in it. It should be dry.
Pressure test with a pressure gage attached to the test port fitting.
Engine running should net about 35 psi +/- a few psi.
Good luck.

One key here is the exhaust leak. Find it, fix it, clear the codes and go at it again. The 02 can't get a good reading if what it is supposed to be checking is leaking out and not being tested (the exhaust).

Have you made any progress on this? I have the same issue on the wife's expy with the same drivetrain. After putting $86 bucks worth of low-test gas in it today I realized it's getting 9.5 MPG. I've cleaned the MAF and put on a new IAC and checked for vac leaks and got no where. I can hear the converter guts rattling around in the case which isn't good either. I checked the vacuum line on the fuel regulator and it's dry. If i cure it,i'll let you know.

Stewy, if you have junk rattling in the cats it can also travel into the muffler and clog it. Better get those cats replaced soon.

Yes sir. As soon as i can have it out of service to spend some quality time with it. Gotta put in a heater blend door too so it's gonna be ALOT of quality time.