Throttle body modification for new ECU

Last update: 10/29/09

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Using a normal vented fuel tank caused strong gas odors in my garage after a ride. I installed an emissions control carbon canister on my car and the smells are gone. One of the requirements of using the canister is that it has to be "purged" when the motor is running.  

Purging is accomplished by connecting the purge port on the canister to a source of vacuum. The vacuum draws fresh air through the canister to get rid of the gas fumes stored in the canister. After the gas fumes are purged fresh air is continued to be drawn into the vacuum source. Typically the fumes are injected into the intake manifold to be burned in the engine.

On my GSXR there is a vacuum source available by using the PAIR valves. These reed valves basically use the vacuum created at the exhaust pipe side of the exhaust valves when they close. Normally this is done to draw fresh air through the air cleaner and inject it into the exhaust system as a form of emission control.

The plan:

The PAIR system uses an independent vacuum port on the #4 throttle body to operate the PAIR valve. The port is located below the throttle butterfly valve and has vacuum on it whenever the engine is running.

My plan is to disable and not use the PAIR system. The purge vacuum line from the canister will be re-routed to another common vacuum system connected to the throttle bodies. There is already one vacuum system connected to all the throttle bodies that it is used for the IAP sensor. This vacuum system should not be combined with the purge system. The IAP sensor reading would be drastically affected if the purge system was connected to it.

If the canister purge hose was connected to only the #4 vacuum port, the mixture on that one cylinder would be slightly leaner than the other three cylinders after all the gas fumes were removed from the canister. By installing a new and separate vacuum system on all the throttle bodies I will have a separate vacuum system for purging. In affect all the cylinders will tend to run slightly leaner but the new ECU using the o2 sensor can correct that condition since the second vacuum system will be on the intake side of the engine.

The new vacuum system required that I create  new vacuum ports similar to the one on the #4 cylinder on each of the other throttle bodies. Luckily each of the other throttle bodies has a casing boss for a vacuum port on them. California motorcycles use an emissions canister and have the purge system working with two vacuum systems. So it's not completely an original idea on my part.  "All" I had to do was drill the ports through and install short metal tubes to attach the vacuum hose to the individual throttle bodies.  

Interconnecting the throttle bodies this way actually will help balance the intake system. For instance, if one throttle is a little more closed than another at low speeds, the vacuum on that body will be greater which will tend to draw some air from the other bodies. This will tend to balance the load on each cylinder. The vacuum tubes I've added have a .040" restriction hole in each metal tube to restrict the amount of air that is drawn into the intake system.  A 0.40" size hole was already used on the #4 PAIR vacuum connection.

To see an enlarged view of most pictures, left click on a picture or right click and select "View Image".
Thottle bodies 3 & 4

These views show the throttle bodies upside down. This a view of throttle body #3 on the left and #4 on the right.

Note that #3 body has only the one IAP sensor vacuum connection and #4 body has TWO vacuum ports.

You can see how the right side IAP hose connections are in parallel to create the balanced condition.
throttle #4

This is a close up of the #4 throttle body vacuum connections. The vacuum tube on the left is the PAIR valve vacuum tube.

I was surprised to see that the vacuum tubes project into the air stream.

My new vacuum tubes will not project into the air stream for ease of making them.

throttle #3

This is a close up of the single #3 throttle body vacuum connection. Throttle bodies #1 & #2 are similar. The fuel injector is located at the dark circle to the left of the vacuum tube.

If you look where the vacuum tube on the left will be located you can see the boss on the outside edge of the body.  The picture below shows the vacuum boss in greater detail.

As a point of information concerning the bore size of  the 2002 GSXR-1000 throttle bodies.

At this point the throttle bore is straight and is 42 mm in diameter. The air cleaner side of the throttle body is 49.8 mm tapering down to the 42 mm dimension above the throttle butterfly.
Vacuum tube

This is a close up of one the vacuum tubes I made. The metal tube started out in life as a 1" long threaded spacer. The spacers were not drilled completely through.

I drilled in from each side with so that there was ~.125" thickness of metal not drilled through. I then drilled a 0.040" diameter hole through the remaining metal.

I also slightly tapered one end of the spacer using my lathe and a flat file.

The metal spacer is ~.003 larger in diameter than the holes I drilled in the throttle bodies. The taper will allow me to press the tubes into the holes in throttle bodies.

About to drill

This fellow car part mutilators is a moment of truth. I am about to drill the new #3 vacuum boss. The boss is very visible in this picture.

There is a hole cast into the boss but it is smaller than required and doesn't extend into the casting very far. But it made an excellent centering hole. I'm purposely not giving any drill sizes because your throttles will more than likely require different size holes depending upon the tube you use.

After this picture was taken I leveled the throttle bodies left to right and horizontally before drilling.

I drilled to within ~1/8" of the open portion of the throttle body and then completed the hole with a smaller 1/8" drill.
3 & with hoses

After drilling the 1/8" hole completely through to the throttle plate area, I used a hand tapered reamer to slightly enlarge the holes.

The smaller portion of the drilled hole centered the hand reamer. The small hole was slightly enlarged as I reamed the hole to fit the tapered portion of the spacer.

I tapered the drilled hole just enough so the end of the spacer just above the tapered portion would enter the hole. This allowed the maximum diameter portion of the spacer to just enter the tapered hole. (Easier done than described.)

I then put a little sealer on the tapered end of the spacer, placed it into the hole and gave the end a light tap with a hammer to seat it in the hole.

throttle all done

Here is a picture of the complete new vacuum system. The new system is the set of  tubes on the left side of each throttle body.

The IAP vacuum system uses the "T" fitting between throttle bodies #2 and #3. The curved hose goes to the IAP sensor.  The purge vacuum system has the "Y" fitting between throttle bodies #2 and #3.  The short straight hose will be connected to the purge system through an electrical vacuum solenoid to control when the purge takes place. Until the Megasquirt is installed, the "Y" hose is connected to control the PAIR valve.

The Megasquirt ECU will output a signal to the solenoid when the engine is running above ~2000 RPM to allow the purge to take place. By using the solenoid in this fashion the engine will idle without additional air being added through the purge system. Above 2000 RPM the engine will try to run slightly faster than the throttle setting. The driver will just set the throttle for the speed desired and should be unnoticeable to the driver.

The metal 90 degree tube at the upper left of the picture is the high pressure fuel line to the injector rail. All the electrical wiring is for the TPS and the secondary throttle sensor and control motor. The secondary throttle motor is also used for the fast idle on the Suzuki throttle bodies.