jreich85

About a week ago I threw the engine lean codes on my '02 5.4L, and have been reading this forum and searching for answers ever since. Yesterday I took my battery and battery holder out and found a smaller, black, stiff vacuum-hose looking thingy that had an open end. It was grouped with a couple of other hoses that did not seem to be as stiff. I searched everywhere to see where it may have connected to with no luck. Does any tube just dead end back here or am I missing something? I may be able to get a pic of it if it helps with a diagnosis. Thanks for any help you can offer.

RLXXI

The vacuum reservoir is part of the battery box and those vacuum lines are for your hvac plenum functions, vent/defrost/floor.

Turn the air on and find an open stretch of road and floor it, you will experience air flow changes. It will also cause lean codes.

Just repair them and no worries.


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jreich85

That does make perfect sense. My AC has been acting up and been very unwilling to shoot out of anything other than the defrost vents. The problem is, I have no idea where this vac line goes to. Any ideas? The hose is in the middle of the picture, which is on the passenger side of the truck looking towards the firewall (battery and tray removed). Thanks for any help.

RLXXI

That black box looking thing is the vacuum reservoir, the hose attached to it needs to connect to the intake manifold, follow the line thru any other connections like a vacuum tree where multiple lines connect. It all eventually terminates to the intake manifold. (vacuum source) Repair any leaks you find.

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jreich85

I spent some time tracing all these lines to the manifold and to my knowledge they all check out. The only one that bothers me is the one in the background of the picture that seems to have nowhere to go. It is in the same conduit as the red vac line and greenish vac line, which both have destinations. I'm stumped...

Marc D

OK. I just looked under my hood. Although I have a V6 the hose configuration is similar. The red, green and white hoses all involve the manifold vacuum sensors. The black hose appears to be the A/C control that is attached below the sensors at the fire wall. Yours looks like it will be below the sensor closest to the motor. Use a mirror to look carefully below the sensors. The attachment point is a thick rubber sleeve a 1/4"x1/2", not another tube. Before you do that start the truck and see if the hose even has vacuum to it. At the very least put a cap in it at test drive the truck for performance, then check the A/C to see if it switches from floor to dash to defrost.

RLXXI

The black line is the a/c plenum control vacuum, it goes inside thru the firewall. the other end may be broken off flush with the firewall, look for a small hole, if this is the case your going to need to go inside under the dash and see if you can find the other end and get some new line to span the gap.

Marc D

It seems strange that the plastic hose is not factory bent. You might try cutting the plastic cover off the hoses on fender side where the black, green and red hose go and see if there's a hose inside that's disconnected.

RLXXI

It is pre formed, that line is broken.

jreich85

Thanks a bunch for the input guys. I've carefully checked all around the area of those hoses in the picture and so far have only found one rubber grommet that carries a vacuum line into the cab (it's located a little low and to the right of the sensors that the other lines go into). It's hard to tell but it doesn't look like it was designed to take this extra hose. Is there anything I should be looking for? I feel like I'm missing something here...