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I am working on a 2003 F-150 with a 4.6L engine. Bank 1 has a long term fuel trim of -25, Bank 2 has a long term fuel trim of +19. Computer is sending an engine code PO172 (rich condition bank 1). O2 sensors both send good oscillating data (0.8-0.01 on a 3 second interval) and have been replaced for good measure. Vacuume test shows good, fuel pressure test shows good, all coils test good and new spark plugs, smoke test intake mannifold no leaks, new egr, MAF send good signal, PCV new hose ends and valve (no leaks). Also replaced all injectors just to rule out plugged and leaking problems.
This truck is running OK (slight rich miss at idle) but definitely gets bad gas mileage (12 mpg HWY). the only problem I can find is that the computer is opening the purge solenoid all the time even at idle. I unplug it but the rich fuel trim problem continues and makes no difference in fuel economy.
What exactly is "good vacuum"? You got numbers? Can you do a cylinder contribution test with a scantool? Did you PLUG the evap line to the intake manifold instead of unplugging it electrically? Maybe the purge solenoid is stuck open? What is the compression? Can you do a relative compression test in order to compare bank to bank?
Rich and lean codes at the same time do have 3 main causes:
1- timing jumped ( on one bank)
2 - plugged exhaust on dual systems
3 - evap purge solenoid stuck open ( this affects both banks equally, not
differentially)
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
The vacuum test is steady at 20 at idle, drops to 5 with throttle snap. stays steady at 24 at 3000 rpm. Plugged into the brake booster port. This rules out intake manifold leak, timing problems, burnt valves, and a plugged cat.
Problems I notice
1. goes into CL with in 30 sec's of starting no matter how cold temperature is. (engine temp sensor accurate and test good)
2. Will not pass evap test. " PCM unable to control engine RPM" So I replaced IAC and got the same problem only worse drivablity. Computer would randomly hold RPM above 1500 (like having cruise control stuck on). Had to use brake and clutch to stall engine then it returns to normal RPM. Cleaned and put old IAC back on and it works better than the new one but will not pass test for evap.
3. this truck has old school timing. Not variable valve timing. I can't imagine it going mechanically out and still be able to run at all.
Purge solenoid test good (dose not leak and I can turn it on and off electrically). I plugged the line just to make sure and it did not change fuel trims.
sorry my messages are so broke up I tried typing this out in one post and it logged me out.
The rest of the Evap system seems to be good from the carbon canister to vent valve to vacuum testing the tank sensor and cap.
the other mechanics in the shop believe that the computer is messed up and I should replace that next. I have wasted so much time and parts on this truck I want to make sure I have exhausted all other options before I get a computer.
Parts that I have replaced: Spark plugs, coils, fuel injectors, O2 sensors, IAC (but put the old one back on), fuel filter, oil change (was not fuel contaminated), EGR, Air filter (was very dirty), cleaned throttle body and MAF sensor (sends good signal), reset KAM three separate times, replace PCV and hose ends ( the hose end on the back of the manifold was bad and this is the original problem the truck came in with besides the dirty air cleaner).
I also checked all my grounds (seem to be clean, tight, and not corroded) and put new battery and battery cable ends on (professional solder on HD cable ends NOT clamp-on's)
To add insult to injury. The hood and the roof of the cab of this truck got lightly damaged, by a piece of metal roofing blowing around, while in my care, so I ended up buying the truck from the customer to make them happy and not have to turn it over to insurance. So now I'm not getting paid for this job, I"m only losing more money and feeling kinda dumb.
I also looked at cylinder balance and they all are with in tolerance, #1 and #4 take turns missing at idle (some times). Some times there is no miss at all, and sometimes #6 misses all by it's self a little at idle. Its not all the time and it is very random so it leads me to believe that fuel is being turned on the rich side creating a rich miss that can only be felt at idle, and maybe #1 is a lean miss sometimes.
Fuel pressure tests good and does not bled off when turned off
What is your maf readings at idle warm engine and a 1st/2nd gear wide open throttle run you should idle see between 5 and 6 grams at idle and on that engine I expect to see close to 200 grams on a wide open throttle run
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