Hello I have a 2001 5.4 and I have had for the past year a hit and miss lean code on both banks. The pcv checked out from the elbow to the valve cover I fixed a line behind the battery and I replaced a dry line going to the purge valve. I found a grommet in the cai for the iat sensor to be loose and messed up so I fixed it and did a propane test on the entire motor and got zero rpm change from the manifold to the lines and everywhere in between. The idle dropped back down from 850-90p back to 750 and it's not giving me little engine jerks at idle like it subtly was. Could the grommet I found have caused this? In a day or 2 I'm going to use my step dad's scanner and check the fuel trims as they were around 24 to 25 on long term months ago. Is the propane test a good reliable method? I have no coolant crossover leaks and even stuck the hose attached to my torch under the intake manifold to see if it was leaking under it on the insides at the gasket and got no rpm change. My fan clutch does cycle quite a bit but I would leave the hose sitting g and check the tach and still nothing. Thanks for any ideas or replies

 

Can you post us the exact codes? Please.

 

As you reported doing it, no. The computer is simply too fast most of the time and there will be no discernible change in the engine's operation.

You need to use the scanner and monitor the short term fuel trims in real time or the O2 sensor voltages for the old propane or spray procedure to work reliably.

 

P0171 p0174

 

Before chasing anymore leaks, have the MAF sensor checked including the barometric signal. A faulty MAF can cause those codes too.

If the MAF checks out OK then look for leaks. I recommend doing a smoke test over the propane test.

 

Thanks for the replies everyone. My local shop I trust can't get me in for another week for a diagnostic and I only have access to a live data scanner no smoke machine unless the shop has one wich I'm sure they do. I cleaned the maf with the specific cleaner 4 months ago and I run an oil less filter in it. I will look if the scanner I use will log data on the maf or show it. What numbers am I looking for on a good vs bad maf?

 

Chris Fix has a video where he uses a shop vacuum connected to the exhaust pipe with tape and reverses the flow to blow into the exhaust pipe. He then uses a soap/water mix to spray on the vacuum lines and suspected leak locations to blow bubbles is there is a leak. If you have a shop vac, it might be worth a try.

 

Back in the summer my ltft was 24 on both banks. I fixed a grommet issue and now in 37 degree weather at hot idle their consistently 19.5 and driving down the interstate at 1900 rpm their the same. I used a scanner with live data. Maf reads .82 lb/min at idle and will climb up to 4 or 5 and some change as I'm driving. Any thoughts? I have an appointment for a diagnostic run in 3 days if I could figure this out before then I'd love to save 80 dollars

 

 

 

18.2 was cold start then worked up to 19.5 and those numbers would drop down to 14 or so give or take as I would throttle down without kicking the transmission down a gear

 

A new maf sensor evened out my fuel trims to normal. The shop smoke tested the entire engine and nothing then tested fuel pressure then tried a known good maf and within a few minutes it was all back down to normal. It did leave me with 292 dollars for a bill but i guess it's the price to pay for a thorough diagnostic