I apologize in advance for the length of this post:

Hi, I am new to the modern technology as the only stuff I ever work on has a carburetor like my '76 F-100 . I have learned quite a bit though lately but a friends 2006 f-150 with a 4.6L has us pulling our hair out. Its got 175k on the clock and ran like a sewing machine despite little maintenence other than oil changes. Recently it started running like crap; no power and missing so he borrowed a scanner and it was giving mulitple codes. Heres what we have done so far, not necessarily in this order :

1.Checked for vac leaks with carb cleaner (this can be tough as engine runs crappy and hard to detect minor changes in rpms while your under the hood) no leaks detected yet

2. Changed the plugs, all looked good except for one which was heavily fouled and the electrode ate away mostly, I wasnt there and he doesnt remember which one but have a suspicion, more on that in a min

3. Changed most of the COPs and checked them all with a spark tester, all are firing.

4.Cleaned the MAF sensor with MAF cleaner

5. Checked back pressure on the exhaust by removing an upstream o2 sensor and holding a plastic fitting hooked to a pressure gage long enough to get a reading, about 1 lb idling to maybe 2 max when engine is reved, gage is not the best and fluctuates a 1/2 lb or so. Exhaust does not smell of rotten eggs.

6. Changed the fuel filter, it was terrible

7. Ran a bottle of Seafoam in the tank

8. Took the throttle body and egr valve off and checked for carbon stoppage, the holes in the egr were not blocked

9. checked the PVC valve and line and both elbows

7. checked the injector connectors with a noid light for signal, they all flash, checked the injectors them selves with a multimeter set for ohms, all about from 13.5-14.5. This should mean they arent fried but could they still be stopped up? They all sound like they are pumping when you listen with a mechanics stethoscope

9. Changed all 4 o2 sensors as this had never been done anyway

10. Compression check on cylinders, all within 10% of each other at about 180 lbs. When we pulled the plugs they all looked good except for # 7 which was heavily fouled ( I suspect the same on the original plugs) and again with a bad electrode, the part coming out of the porcelin. Intrestingly, this was an autolite plug, the rest were motorcraft, I hoped this was somehow just a bad plug but no change with a new MC plug

11. Changed the injector on #7

The scanner reads lean condition on banks 1 and 2 and random misfires on #4 and # 7 still. Per a troubleshooting tip online, we sprayed some carb cleaner in a small vac line coming off the manifold to induce a rich condition and the scanner showed the o2 sensors go to .900 which is what they are supposed to do per the guide. This means they are functioning correctly and a bona fide lean condition exists. I am leaning towards a vacuum leak around the plastic manifold under the aluminum one, maybe the gaskets but would like to rule out the egr valve, could it be the culprit? I have even considered the possibilty that the PCM is bad, though not likely. I have read to detect a vac leak you can hook the scanner up and spray the carb cleaner around on the manifold and lines with the scanner hooked up watching the scanner PID for the o2 sensors and when they detect the cleaner, they will hit that .800-1.0 meaning the engine sucked the cleaner in and you have found your leak. The exhaust smells rich. If it is a vac leak, you would think it should be a massive leak and not hard to detect, as crappy as the truck runs. I have searched the forums for days and exhausted about all I know to do, does anyone have any ideas?

Edit: crap, left off an important note: early on I suspected low fuel pressure as a possibility; with no schrader valve on the fuel rail and no easy spot to T into the system, we were scratching our heads how were gonna measure psi but the scanner reads absolute fuel rail pressure, gives about 40-43 psi. I hope the scanner is telling us what we need to know there, would prefer a mechanical gage on the rail!

 

Do not assume that the fuel rail pressure sensor is good and giving an accurate reading. You have to mechanically check fuel pressure with an adapter that T's into the fuel line. Also, check to see if there is any fuel inside the vacuum line running to the sensor, if it is the type that has one.

How does it run with the MAF connector disconnected? Disconnect the connector, cycle the key to "on" three times, then start it up.

What is the value of the MAP and IAT pids?

 

Thanks for the reply! That is something I forgot to mention; we did pull the vacuum line off the FRPS and there is no gasoline in it, possibly the smallest hint of a gas vapor smell.....I have no idea how or where we would "T" into the fuel line to manually check the fuel pressure, are you thinking the FRPS could have failed and the reading is not accurate? We have released pressure on the system to work on the injector and when reassembled and hooked back up the pump whirrs for a few seconds and the truck cranks right up, it has never had any problem cranking up and does not stall. The scanner reads 35 psi on the rail after 30-40 mins of sitting, around 40-43 at idle. There is a new development, the miss fire codes have not returned but the lean condition on both banks is still there, but the engine has noticeably gained power without the miss fire naturally. Tonight I disconnected the MAF just to inspect and make sure there were no tears or rips in the intake tube. The engine ran ok but we did not cycle the key though, will try that tomorrow. Should we unplug the MAFS and drive it some, or just see how the system performs with out it; are you attempting here to determine if the MAF sensor has failed? This is my first go around with a scanner, what am I looking for with the MAP and IAT PIDS?