Vacuum operated valve on intake?

[tonyroc14]

I've searched and cant figure it out? What is the vacuum operated valve on top of the intake in the center/rear. I have a vacuum leak there and wondering what it's for. Any help would be appreciated.

 

[Maniak]

I can't think of a valve on the top of the intake. Can you grab a pic of it? close up, and farther back so we can see exactly where it is.

The only thing I can think of that would even look like a valve is the EGR/dpfe, but I don't remember it being at the top of the intake.

Also, which motor is this? 5.0, 4.0 ohv, or 4.0 sohc?

~Mark

 

[2000StreetRod]

Sohc vis?

Do you have the SOHC V6? The 1997 and some of the 1998models have a variable induction system (VIS). It changes the length of the intake runners at around 3,000 rpm. A solenoid controlled vacuum motor actuates a control rod.

 

[Carguy3J]

My '99 also has that, so I don't think it was '97-'98 only.

 

[2000StreetRod]

Wiring changes

My '99 also has that, so I don't think it was '97-'98 only.

That's good to know. You're the only member I'm aware of that has reported having VIS on a 99. Do you have the original engine? Is your VIS functional? I know there were electrical wiring changes in 99 but don't have the wiring diagrams. On my 2000 wiring diagrams the PCM pin 46that used to control the VIS is now connected to the fuel cap indicator.

 

[tonyroc14]

Yea that's it, so if I fix it will I see an improvement in performance and or fuel economy. Right now the valve is actually broken, looks like a retaining clip is missing or something. Sorry for my noob mistake of not mentioning drivetrain, yesterday was a long day. Thanks for the help

 

[2000StreetRod]

common problem

It's common for the VIS rod to be separated from the lever. Many owners don't even notice the difference since they seldom rev the engine above 3,000 rpm. If you fix it you may notice a performance improvement. If you have a vacuum leak then fixing that may result in more optimum fuel trims and avoid a lean condition. Make sure the lever can rotate from stop to stop before connecting the control rod. Carbon builds up in the intake runners causing the lever to stick.

 

[tonyroc14]

It's common for the VIS rod to be separated from the lever. Many owners don't even notice the difference since they seldom rev the engine above 3,000 rpm. If you fix it you may notice a performance improvement. If you have a vacuum leak then fixing that may result in more optimum fuel trims and avoid a lean condition. Make sure the lever can rotate from stop to stop before connecting the control rod. Carbon builds up in the intake runners causing the lever to stick.

Well I'm not sure there is a vac leak. I'm assuming there is an electronic solenoid that controls the vacuum to that valve. If thats correct than there should be no vacuum while at idle, only 3000+rpms, so I might not have a vac leak.

If im in neutral and give it gas it will hold at say 2000 rpm for maybe a second after I left off the gas. Not sure if this is normal or not for this engine.