VIS Conversion

[2000StreetRod]

The 1997 and 1998 Explorer with the SOHC V6 came with a variable intake system (VIS) - also known as intake manifold runner control (IMRC). It was also available on some years of the Mustang with the DOHC V8 engine. I have found minimal documentation on the operation and performance of VIS. When the PCM determines that the engine revolutions exceed 3,000 rpm it energizes a vacuum solenoid (air control valve) that activates a vacuum motor mechanically linked to a lever that shortens the length of the intake runners. In the photo below the vacuum motor and the lever are shown just aft of the IAC valve.

Since the vacuum motor must reliably operate at wide open throttle (WOT) when vacuum in reduced there is a VIS dedicated vacuum reservoir (cylinder) located between the uppper and lower intake manifolds. In the photo below the reservoir can be seen on the passenger side adjacent to the lower intake manifold.

The VIS lower intake manifold is identical to the one on my 2000 Sport.

The 1999 and later Explorer PCMs do not support VIS and incorporate fixed length intake runners. The PCM pin formerly used to activate the VIS vacuum solenoid was instead used to illuminate the fuel cap indicator in the instrument cluster.

Since purchasing my Sport in May, 2009 I have wished that it came with VIS since it has the potential to increase torque (and fuel economy) at low engine speeds and increase performance at high engine speeds. I have decided to convert my engine to VIS and evaluate it.

 

[2000StreetRod]

manifold similarities

A top view of my fixed length runner intake manifold is shown below.

A top view of a 1998 VIS intake manifold is shown below for comparison.

(photo courtesy of boominXplorer)
The manifolds are fairly similar except for the intake runner control, the vacuum motor and the IAC valve mounting orientation. I have a spare IAC valve for my 2000 but unfortunately the 1998 requires a different part.

A bottom view of my fixed length runner intake manifold is shown below.

A bottom view of a 1998 VIS intake manifold is shown below for comparison.

(photo courtesy of boominXplorer)
The manifolds are very similar except for the VIS vacuum solenoid next to the EGR vacuum regulator (lower right) and the large diameter tube that extends from a Y fitting at the IAC valve to the rear of the manifold where it is capped. I'm guessing that the tube may be for export models with a different crankcase breather or PCV valve configuration.

 

[2000StreetRod]

Reservoir & O ring

The photo below shows the VIS vacuum reservoir and the numerous vacuum hoses associated with the intake manifold.

(photo courtesy of boominXplorer)

Yesterday I received a new EGR tube O ring from Rock Auto.

I noticed when I installed my 00m12 kit that the O ring had become brittle so I did not chance removing it since I didn't have a replacement. This O ring is a source of vacuum leak that is often overlooked because it is hidden within the intake manifold.

 

[2000StreetRod]

knock sensor first

I've decided to install the new knock sensor coming from Rock Auto before performing the VIS conversion. It means pulling off and installing the intake manifolds an additional time but will allow me to establish a baseline with the fixed intake runner manifold. Once I get fuel economy results and possibly dynamometer results with a fully functional knock sensor then I'll convert to VIS for comparison testing. That will also give me time to fully decarbon the VIS manifolds before installation.

 

[crazymind]

I've been looking into doing this to my 99 as well. Although now discouraged now with the pin out used on another function

 

[2000StreetRod]

RPM switch

About 2 years ago I purchased an MSD RPM activated switch at a bargain price.

At the time I did not consider the fact that my SOHC V6 has a distributorless ignition system that incorporates three ignition coils. The switch is designed to work with an MSD ignition system or a single coil ignition system. For the MSD ignition system configuration the RPM switch module white wire is connected to the MSD ignition system Tach Output terminal.

The module is configured for 6 cylinder operation by cutting the red wire loop. Ignition switch controlled battery voltage is connected to the long red wire and vehicle ground is connected to the black wire. A user selected RPM "chip" plugs into the switch module to determine when the switch activates. The RPM switch module counts trigger pulses for a predetermined time interval. When the RPM set by the "chip" is reached an internal switch is activated and the yellow wire normally open path to ground is closed. The yellow wire can be used to activate the vacuum motor solenoid.

On my Sport the tachometer in the instrument cluster is driven by an output from the PCM (pin 48). I suspect the signal is an analog voltage that represents the engine speed and is not compatible with the MSD RPM switch.

For a conventional ignition system the white wire is connected to the negative terminal of the ignition coil primary. The voltage at the negative terminal would normally be ground except when the distributor points break. For the Explorer there are three primary coil negative terminals that are controlled by the PCM. In order to obtain the correct number of sparks per revolution while maintaining the proper firing order each primary pulse must be counted while being isolated from the other two. I'm hoping that connecting a diode between the white wire and each of the three PCM trigger wires will work.

 

[crazymind]

To try and make the wiring a little cleaner could you go off the crank position sensor? That way you would have only a single wire to worry about. Or does the rpm switch need more of a halifec sort of switch to tell the rpm?

 

[2000StreetRod]

12 volt wave form

To try and make the wiring a little cleaner could you go off the crank position sensor? That way you would have only a single wire to worry about. Or does the rpm switch need more of a halifec sort of switch to tell the rpm?

The RPM switch requires a 12 volt waveform to count which is not available from the crankshaft position (CKP) sensor. Also, the CKP has 35 pulses (1 tooth is missing) per revolution instead of the needed 3.

Snoranger sent me a PM to just use one coil primary and get a chip for 1,000 rpm. A very good and easy solution but I want to look at other options.

 

[snoranger]

I'm also looking into some other options for you.

MSD Tach adapter #9117 should work for what you are trying to do.

 

[2000StreetRod]

Auto Meter tach adapter 9117

I'm also looking into some other options for you.

MSD Tach adapter #9117 should work for what you are trying to do.

Thanks Kevin. I assume you meant the Auto Meter tach adapter 9117. After reading the installation instructions: http://www.autometer.com/productPDF/0561B.pdf
I agree that it should work with the MSD rpm switch. However, it has the limitation of 18 volts which means it can't be used when a capacitive discharge high voltage source is applied to the coilpack primary. I just happen to have one that I built from a kit about 45 years ago that I might want to try out. Also, the 9117 costs about $85 after shipping is added.

I'm going to investigate further the PCM tach out signal. I remembered this afternoon that when I was an amateur radio operator (20 years ago) I had a transmitted signal monitor scope. I found it in my storage room and the instruction manual that states it has a limited oscilloscope capability. When I turned it on I was pleased to see that it still works. I plan to fabricate a long cable with probes and observe the PCM tach output waveform.

 

[Sedition]

VIS Information

I have some information and pictures of the Variable Intake System and upper intake manifold from my 1998 SOHC Explorer that you may find interesting.

The VIS unit is attached to the top of the upper intake manifold along with the IAC. The IAC is attached to the VIS via a conduit on this particular model. The VIS unit consists of a vacuum actuator (blue line) which is connected to a butterfly type valve, like a throttle body.

The operation of the VIS is actually quite simple. When the VIS is closed each cylinder bank is fed air seperately from the upper intake manifold. When the VIS is open both cylinder banks are fed air via both sides of the upper intake manifold simultaneously.

The VIS opens at engine speeds above 3000 RPM or when a surge of power is required at any lower RPM. The VIS can be opened at lower RPM by applying 3/4 to WOT after a 0.5 second delay. The VIS is either open or closed, it has no in between positions and it opens immediately.

When the VIS opens it is accompanied with an immediate burst of accelleration. Sometimes I get bogged down in soft sand at low speed and RPM but once I open the VIS the truck will just get up and run.

Here are some pictures of my upper intake manifold with the VIS removed and the VIS unit.

Now I have a question for people without the VIS. Is the passage between the two cylinder banks on the upper intake manifold - open, partically open or closed?

 

[Bashir]

Please help me identify where the short vaccum pipe from the VIS in my 1997 Ford Explorer V6 goes. It is hanging and I cannot find where it should go. I have very poor gas mileage (5km/l) and read in other parts of the forum that it can be caused by vaccum leak. My engine search identified the above pipe. Thanks.

 

[Sedition]

If it's a blue vacuum line it plugs into the back of the diaphragm on the very back of the upper intake manifold. You'll have to remove the top cover first.

 

[Sedition]

Also The pics just above your first post show the VIS and the blue vacuum line. I deleted my VIS as it is a POS power robbing system.

 

[rb142]

On my Sport the tachometer in the instrument cluster is driven by an output from the PCM (pin 48). I suspect the signal is an analog voltage that represents the engine speed and is not compatible with the MSD RPM switch.

Dale, check pin 48 with your scope. I looked at the wiring diagrams for this car, and things are clear as mud, but in this vintage of vehicle, pin 48 should be CTO instead of an analog voltage. CTO is clean tach out, which is an inverted version of the PIP signal which used to be used to drive the ignition coil primary. CTO is a square wave that will go low at 10 degrees before TDC every cylinder, and will rise roughly half way between cylinders. You get a pulse for every cylinder, and it should be able to drive any normal tach without problem. That was standard for a long time. If this car actually has a real analog signal there, that would be very unusual.

You could pick up a signal off the coil primaries, but you are going to have a huge noise problem to deal with.

 

[Bashir]

Thanks Sedition for your reply. The line is black and not blue. I couldn't upload the pic. Nevertheless, I will check for the plug in the cover. I will keep you posted. Thanks once again.

 

[2000StreetRod]

no longer needed

Dale, check pin 48 with your scope. . . You get a pulse for every cylinder, and it should be able to drive any normal tach without problem. . . You could pick up a signal off the coil primaries, but you are going to have a huge noise problem to deal with.

Thanks for the information but I installed an M90 with a matching intake manifold so no longer need to worry about VIS implementation.

 

[rb142]

Thanks for the information but I installed an M90 with a matching intake manifold so no longer need to worry about VIS implementation.
View attachment 82106

Yeah, I just noticed the date on that part of the thread. Nevermind.

 

[kcampbe]

I know this is an old thread, but hoping someone can help me.

While replacing the upper and lower manifold gaskets today I ripped the "Y" hose that I've highlighted in the picture below.

I've tried searching the part number on those with no luck. Any guidance or ideas on finding a replacement? One further question, there's a plastic tube that connects to is that goes down somewhere on the passenger side of the engine, but I don't know where. Any help would be appreciated.

Thanks!

 

[angstrom08]

I know this is an old thread, but hoping someone can help me.

While replacing the upper and lower manifold gaskets today I ripped the "Y" hose that I've highlighted in the picture below.

I've tried searching the part number on those with no luck. Any guidance or ideas on finding a replacement? One further question, there's a plastic tube that connects to is that goes down somewhere on the passenger side of the engine, but I don't know where. Any help would be appreciated.

Thanks!

Are you certain you properly attached a photo below?

There are two Y hoses I can think of: the PCV valve has a tee on it with hoses to the rear of each side of the tubular upper intake and, second, the evap hose which connects to downward aimed fittings on the bottom of the tubular upper intake. The first is easier to replace than the second. Good Luck.