Engine Performance problem
2003 Ford F150 V8 Two Wheel Drive Automatic 108500 miles
2003 Ford F150 4.6l V8 W engine with reoccurring P0171 and P0174 codes, with engine idling rough at normal temp and dying when idling at normal temp. Engine seems to perform OK when given gas, and seems to run smooth at cold temp right when you crank it.
Air filter has been cleaned (it's a K& N CAI)
MAF sensor has been cleaned and replaced
No sounds of leaks anywhere when examined with stethoscope
PCV valve and hose has good suction when disconnected
Following procedures in Haynes book:
EGR vacuum regulator is receiving voltage, and ohms measured within range
DPFE has good reference voltage and signal voltage is within range at cold and warm temps
This is what I think:
According to the Haynes book, the EGR doesn't operate when the engine is cold. That's when the engine seems to run OK. It's only after the engine reaches normal temp that it begins to run rough. Also according to the book, too much EGR will cause the engine to run rough.
So, the next step is to replace the EGR valve? Should I go ahead and replace the oxygen sensors even though they're not throwing codes?
You may have a vacuum leak, get a can of spray throttle body cleaner, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs! If it has any misfire codes, especially P0301, could be the intake is clogged with carbon, you would need to remove the upper intake and clean the ports.
May, 17, 2009 AT 4:55 PM
I am unsure that you read my full post.
I've been over the intake manifold and hoses that connect to it for leaks 4 or 5 times, I've lost count. I've used soapy water, the manifold cleaner you suggested, a stethoscope and my bare fingers. I've tightened all the bolts, and tightening the lose two bolts I found made no difference.
I'm not getting any misfire codes, just P0171 and P0174.
May, 18, 2009 AT 2:46 AM
OK sorry I didnt see that you had srpayed the soap! Test fuel pump pressure. If you need to un plug the vac to the EGR this may set an egr code, but you can test the performance this way.
June, 30, 2009 AT 7:58 PM
Pressure test came back 35 psi at cold idle, 36 psi at warm idle. The needle danced 1-2 psi when the engine ran rough during the test.