2009 F150 Fuel Trim Help

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Got my 5.4 3V replaced a couple months back due to a dropped valve.

Since I got it back, I’ve had a rough idle, a little shutter in drive when I let off the brake and then it runs great.

I’ve used numerous code readers and scanner and there are no active codes. Just left the engine builder and he is thinking I have a clogged or leaking hector. After plotting the short term fuel trims there is a strange difference between the two.

On the same time scale the bank one trim bounces up and down around 2-3x more then bank 2. Bank 2 is consistent with a couple higher spots when the a/c compressor kicks on and off. Bank one is a jagged up and down with essentially no smooth section.

I’ll work on sharing a picture of what I plotted but what would make the short term fuel trim on one bank bounce 2-3x more then the other bank. I have all new coils and the engine runs great at higher RPM. Is it time for new fuel injectors? There are 166k on the truck.
 
Have you compared front o2 sensor readings for the 2 banks? If bank one isn't jumping around with the fuel trim, it could be in the process of failing and sending incorrect data to the pcm.
 
Wouldn’t a vacuum leak effect both banks? It’s only one side of the engine to me whose is what is so strange.

I don’t think the pcv is serviceable on my truck.
 
Originally Posted By: PReal
Wouldn’t a vacuum leak effect both banks? It’s only one side of the engine to me whose is what is so strange.

I don’t think the pcv is serviceable on my truck.


PCv is a metered orifice in the valve cover on the 5.4 3v. A vacuum leak from an intake gasket could affect only one cylinder bank.
 
Also, even with a vacuum leak on one side, wouldn’t I get a consistent fuel trim but just a richer percentage to compensate for the additional air?
 
Originally Posted By: PReal
Also, even with a vacuum leak on one side, wouldn’t I get a consistent fuel trim but just a richer percentage to compensate for the additional air?


Likely, although I'm not familiar with monitoring fuel trims on a snap on scanner I'm only familiar with IDS. So that readout looks Greek to me.

Easiest way to rule out a vacuum leak is if the fuel trims return to around 0 when opening up the throttle. As the engine will overcome the vacuum leak with
the throttle opened. Smoke testing the intake or spraying brake cleaner around the plenum will also find it.
 
I’ve stayed the plenum with brake cleaner and didn’t see any rise in rpm.

That dang fuel trim is crazy. I can’t comprehend anything that would’ve the fuel adjust 2-3x more often then the other side except a partially bad injector. Since the O2 reads all 4 on that bank, one cylinder rich/lean would drive it to more adjustment. If all cylinders were lean/rush id get a code due to multiple misfires.
 
Fuel trims will be different depending on if its ported or manifold vacuum. Manifold vacuum will be higher at idle and low rpm causing fuel to be added in that range, ported vacuum will increase with rpm and have the the opposite effect on trims.

Yes a vacuum leak can effect one bang more than the other depending on the location of the leak if there is in fact one.
An intake leak near 2 adjacent ports for example with drive the mixture lean on those 2 only but because you have only one wide band on each bank it will adjust the trim for the whole bank they are on.

What are the exact readings for bank 1 and bank 2? For example bank 1 +10 and fluctuating and bank 2 +3 more stable.
Spraying brake fluid all over isn't the best way, the reading may be too short lived, try (unlit) propane with a nozzle and extension hose and watch the trims for a few seconds as you move along the manifold, plenum, hoses and connections, keep the flow wide open or almost at the valve.

https://www.homedepot.com/p/Bernzomatic-WH0159-Universal-Torch-Extension-Hose-361542/202539579
 
Both the trims stay on the same range between about negative 1 and 3.


The issue is the frequency at which the trim changes the trim on bank one is 4 times more often. The trim was changing due to my AC compressor kicking on and off. For ever cycle between -1 to 3 on bank 2, bank 1 when through 4 smaller cycles from -1 to 3. On back one the graph looks like a close together mountain range and on bank 2 it looks like a skyscraper in the middle of a field.
 
Not sure so sure I would put much stock in those short term readings, If you were to draw a line across the screen at 0%......They both dip a little negative the rise a little positive, Min/Max readings being pretty close.

Paying to much attention to "graphed" data can lead you down the wrong rabbit hole.

Keep in mind that fuel trims are reactionary to AFR/O2 sensor input, The Bank 2 AFR sensor may be a little lazy but the ECM can still maintain Stoich.

What are the Long Term Trim's doing? Short Term Trim's can read close to 0% with a vacuum leak because the Long Term has corrected them. This overall correction will show-up in the long term percentages.
 
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Long term fuel trim for bank 1 is bouncing between -1.6 and -2.3. It will stay steady at one of the values, mainly -2.4 for a while.

Long term fouel trim for bank 2 is steady at -0.8
 
That sounds fine to me, With overall trim running a little rich.....A vacuum leak wouldn't be high on my list of possible causes.

What brand coils are you running? Ford uses "multiple spark discharge" at low engine speeds and some aftermarket coils don't handle it well.

Were the Motor/Trans Mounts replaced? Performing an engine swap can stress/ruin original high-mileage mounts & cause vibrations.
 
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It’s got 4 duralast could and 4 from rock auto. They are all new and made no difference.

According to the paperwork the motor mounts were replaced and they look like they were.
 
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