Good afternoon all. I am in the process of trying to chase down a vacuum leak on my 2003 F150 with the 5.4. I have checked all lines and cannot find it. I decided to check the longterm fuel trim and noticed that my bank 1 is slightly higher than bank 2 (screenshot attached). Is this enough to assume the leak is on the bank 1 side?

 

chasing down vacuum leaks on these things is tough....might have better luck making/ borrowing or buying a smoke machine to really zero in on where it is at....or try some unlit propane (Like from a small plumbers tank or camp stove) run down a hose and systematically wave the hose over the engine ....while watching your short term fuel trims and when they spike that is where your leak is at.

 

From what I see you do not have any vacuum leak.
If the long tables were shifted 25% you would have a code to support it.
I don't see that in your data photos.
The absolute difference can be the Ox Sensors' sensitivity, age or contamination.
It could be some injectors are not dispensing as much fuel.
Bottom line, it's not worth chasing trying to make it perfect for the difference you see.
If it's worth anything, I have about the same difference on my 262,000 4.6L.
I know it's there but not going spend any time or money trying to make it perfect when it does not need to be.
Good luck.

 

Thanks for the advice! I was chasing the vacuum leak die to some HVAC issues. My EATC will not direct air to my floor vents, especially under load. I have already replaced the o-rings in the unit but still no fix. Still trying to determine what is causing this issue.

 

There is a faulty hose to the ETAC system.
Under higher load the engine vacuum will be lower because the throttle is open farther.
That leaves less vacuum for the ETAC system to function.
Use a hand vac pump to test that line and see where it loses vacuum.
It may very well contribute to higher LTFT tables you have.
Reminds me of the wind shield wipers on the 30s and 40s cars.
Going up a hill they would stop for a lack of good vacuum.

Good luck.

 

excuse my silly question, what is ETAC?
I'm also chasing a Po171, cleaned all sensors in intake. CEL went away for 280mi..

 

The EATC is the electronic air temperature controller. It is basically the automatic climate control unit available in these trucks.

 

Thank you, fortunately my truck didn't come with that luxury.
Are you getting a Po171 code?

 

No, I am having an issue where I get no air blowing out at my floor vents. I do recommend picking up a manual vacuum pump from the parts store. This is definitely helping me diagnose my vacuum leak.

 

No, if your actual symptoms are related to the climate control only.

..........

 

Using my vacuum pump I was able to determine that the issue was with the EATC. I then rebuilt the actuators in it again and now it seems all is well. Just yesterday I decided to rebuild all the vacuum lines on my truck using tubing I bought from MSC. I tested each of the old lines as I removed them and sure enough found a couple that had slow leaks not easily visible. This was a very easy and inexpensive repair and makes a huge difference!

 

Glad you got it tracked down!! and thanks for reporting back as to what was the culprit.....may times the forum doesn't hear back as what was the problem. To your credit you tracked it down where many wouldn't.

SO...did you replace the connections for the vacuum lines too?? or just lines?
and you wouldn't happen to know what that part number for the vacuum line is from MSC??

 

I checked all the factory connections as well. I replaced a few, but for the most part they were all good. I have attached a screenshot of the white line I used. They also have the other colors.

 

thanks.....you only got 1 foot?

 

No, I bought like 10 feet each color.... way too much. I would recommend 5 feet of each.