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Automatic Injector Switching... on-the-fly!

What if you could have a turbocharged or supercharged car that you could cruise around on the street with lower priced 87 octane and at the same time you could also have 116 octane ONLY WHEN UNDER BOOST?  Sounds almost to good to be true! Well, years ago I had an idea of having two separate fuel systems; one for 87 octane and one for 116 octane. I wanted something that switched immediately; such as "in a blink of an eye".  The only way to achieve immediate switching is to have two sets of injectors located in the intake manifold. This would allow each set to be electrically switched by a relay.  I didn't want a dual fuel system like pick-up trucks have that uses a mechanical switching valve on the fuel lines. The mechanical switching valve does not allow IMMEDIATE switching from 87 to 116. Mechanical switching also allowed the two fuels to mix together which would eventually dilute the 116 race gas and render it useless for high boosted engines. In theory, the Sequential Dual Fuel Injection (SDFI) will allow me to cruise around on 87 octane and still be able to run 20+ (or even 30+) pounds of boost at the same time! This will also eliminate having to drain the fuel tank and fill it up with high octane gas before going racing; then having to drain it again to put low octane back in for cruising around. This will also save money on fuel costs since the car doesn't have to use expensive race fuel for everyday commuting. In fact, it should save me 20 cents per gallon over 93 octane since I can use 87 octane to power the car under normal operating conditions. I figured I can save $3.40 for every 17 gallons of fuel used. That isn't much of a savings but it adds up every time I fill up! Another major bonus is it will conserve race fuel since it will be used only when needed. How many times have you put expensive race fuel in your car only to burn the majority of it out cruising to and from your favorite tuning spot or your local drag strip?  If you timed how long you are actually running the car under high boost conditions it would probably add up to 10 to 15 seconds at a time. 5 gallons of 116 race fuel will last a lot longer when it's only being injected a few seconds at a time. So if this system operates like I think it should, I will have my cake and eat it too!  In my opinion, it doesn't get any better than this! Read on and let me explain how this system actually became a reality!           1. It conserves expensive race fuel because it uses it only when it's needed. 2. It helps eliminate contamination of the 02 sensor by not having to run leaded race fuel during normal driving. 3. It eliminates the mixing of two different types of fuels that is always apparent when using mechanical switching valves on the fuel lines. 4. It provides INSTANT switching so there's no delay in getting race fuel into the engine. 5. This system will work with the stock ECM or AFTERMARKET units. 6. It allows use of cheaper 87 octane fuel for commuting when high octane isn't needed. (saves .20¢ per gallon over 93 octane) 7. TOTALLY automatic... no knobs to turn or switches to flip! 8. It can be made to work on almost any car with port fuel injection and ample room for installation! 9. It's VERY addictive!

 

     The main design of this system is to be able to "invisibly" switch between two different fuel systems without any engine skip or stutter. I has to be "instant" switching without any delays. To allow this to work properly it uses two separate fuel tanks with their own pressure feed line and return line. It uses two separate fuel rails with two separate fuel pressure regulators with 6 injectors per rail. Each set of injectors have their own injector wiring harness and each set of injectors are the same size.  In my case, since I have a V6 it uses twelve 84lb injectors and has two of them per cylinder. The 87 octane fuel system uses the stock fuel tank with a single electric fuel pump. The secondary 116 octane system uses a fuel cell with two electric fuel pumps and is located in the spare tire well in the trunk.

   Main Fuel System -   Low Octane:

 This system provides 87 octane fuel to the engine. It operates under normal driving conditions such as cruising down the highway.

 

   Secondary Fuel System -   High Octane:

This system provides 116 high octane fuel to the engine. It operates under high boost conditions such as drag racing or street racing. It provides very high octane fuel to the engine under extreme boost conditions. 

 

 

    Main Fuel System -    Low Octane Fuel Pump Operation:

     The ECM provides a fuel pump "signal" to the factory fuel pump relay and allows the pump to run when the engine starts. This fuel pump is running 100% of the time as long as the engine is running under all conditions.  This is the way it works from the factory. 

 

    Secondary Fuel System -   High Octane Fuel Pump(s) Operation:

     This fuel system has two fuel pumps...a primary and a secondary. It also has two relays, a primary and a secondary to provide power to each pump independently.

Primary Fuel Pump and Relay Operation:    

     The primary 116 octane fuel pump operates just like the factory pump except it's wired slightly different. When the ECM powers up the 87 octane fuel pump it also provides a "signal" to the primary 116 octane fuel pump relay. To get the primary 116 octane fuel pump to run, I tapped into the power B+ wire supplying the voltage to the 87 octane fuel pump. I used this wire as a "signal wire" to turn on the relay that powers the primary 116 octane fuel pump. After the engine starts the 87 octane and the "primary" 116 octane fuel pumps are running 100% of the time under all conditions. (see wiring diagram below)

Secondary Fuel Pump and Relay Operation:    

     The secondary fuel pump is NOT controlled by the ECM. It is a "stand alone" wiring system.  The secondary 116 octane fuel pump is controlled by an adjustable boost pressure switch and a relay. This boost pressure switch supplies the ground to the relay that turns on the secondary 116 fuel pump at a predetermined boost level.  This fuel pump runs ONLY WHEN THE BOOST IS ABOVE A CERTAIN LEVEL and turns off below a certain level. I have mine set to turn on/off at 3psi.

NOTE: It's not necessary to have two fuel pumps for the 116 secondary fuel system. A single external pump for very high HP engines would also work. However, it would have to run at all times to keep the fuel pressure up before the injectors switch over.

 

   Injectors - "Automatic Switching":

     The injectors are controlled by either the factory ECM or an aftermarket ECU like the F.A.S.T. XFI. Each set of injectors uses a separate harness that has its main 12V power source running through a 5 terminal dual contact relay. This relay provides the "switching" between each set of injectors and is controlled by an adjustable boost pressure switch.  Under cruising and low boost conditions, the 87 octane injectors function normal; just like the factory set-up. However, when the boost rises above a predetermined amount, the adjustable boost pressure switch applies a ground to the injector relay and switches the 12V power supply between each set of injectors. (On my car, I have the pressure switch set to 11psi.) Once this relay is tripped, the 12V power supply to the 87 octane injectors is switched over to the 116 octane injectors. This means the 87 octane injectors stop squirting and the 116 octane injectors are now providing the high octane fuel needed for high boost conditions. The 116 octane injectors will continue to provide fuel to the engine as long as the boost level is above a predetermined level; which in my case is 11psi. Once the boost level drops below 11psi the 87 octane injectors will again start providing the fuel to the engine and the 116 octane injectors will shut off. While this may sound complicated, the ECM continues to pulse the injectors normally and NEVER knows its being switched between 87 and 116 octane fuel. Also, since only one set of injectors will see 12v power, the ECM never pulses 2 injectors at one time!

 

     

The wiring harness that joins together both fuel systems is fairly simple. I've made it so it retains the factory injector harness connector for "plug-n-play" operation. No modifications are needed to the main ECM harness. Looking at the pictures below, there is 12 blocking diodes that are soldered in each injector wire.  6 MUST used to eliminate two injectors from firing at the same time. Without them both injectors on the same cylinder would fire. That definitely would not work so they MUST be installed for this system to operate properly.

Wiring for STOCK ECM #1227148

 

Wiring for F.A.S.T XFI ECU.

 This wiring system is the same as above except it provides a "fail-safe" or "back-up" system just in case if the ECU or boost pressure switches fail. It's unlikely that both will fail at the same time. However, it's nice to know you have a failsafe procedure to prevent major engine damage should something go wrong. For this to work properly, the parameters must be set correct in the FAST XFI ECU.

 

 

 

The small gray wire in the pictures below attaches to an adjustable boost pressure switch (not pictured). It provides the ground to the relay that switches the main power B+ supply between each injector harness. You can make the injectors "switch over" from 87 octane to 116 octane at any boost level you want but I wouldn't recommend anything over 10 to 13psi when using 87 octane in the main fuel system. I personally have mine switching at 13psi and it's unnoticeable. 

   

 

The Beginning Stages: 

This is how the unmodified aftermarket intake manifold looked without any modifications:

 

 

After installing injector bungs on the outer part of the intake runners:

         

 

Test fitting injectors:

   

 

Beginning stages of first fuel rail:

 

 

Fuel rails finished and installed on intake with injectors:

     

     

 

Bench Testing:

Here is a couple of video's so you can see the system in action while bench testing before installation on the car.

Bench test 1: Dual Fuel Demo 1.WMV 17MB
Bench test 2: Dual Fuel Demo 2.WMV 11MB

 

On Vehicle Testing:

After installing the system on the car I shot some more video footage. Here you can see the switching routine with the engine running under low boost conditions. Since this unit was still in the prototype stages I had mismatched injectors...55s and 60s.  There was some change in exhaust tone when I switched the system between each set of injectors.   While looking at the video you can see they switched with just a slight change in exhaust tone. When the injectors switched there was no missing or hesitation and the engine kept running like normal.

 Below is a full unedited 5.1 surround sound DVD quality video of it in action while under load. Two noid lights are located on both #3 injector harnesses meaning that the engine is running on 5 cylinders in this video. The upper light is for the low octane injectors and the lower light is for the high octane injectors.  The final testing will have the same size injectors on both fuel rails.

Sorry about the file size but I wanted it to be full quality with the best sound as possible so you can actually hear the engine while the switching is being done. Also, I am manually switching the relay to show you how it works.
Dual Fuel System on car under load. - 44MB 5.1 Surround Sound

     Below is the same video for the 56k guys. PLEASE NOTE .... in this compressed video you can hear what sounds like an engine stumble just before it switches. You can NOT hear this in the 44MB video above. I don't know why but I think it's the video compression I used to make the file size smaller. If you are a non believer please download both videos and see that it switches just fine. You can also hear this same "glitch" in the other video's I have posted on the "video's" page.
Dual Fuel System on car under load. 5MB

 

On Road Testing:

Here is a video of the system switching under full throttle at 50mph. You can see the two green LED's near the boost gauge light up at the exact time the system switches over. The first green LED near the 3psi mark on the boost gauge is when the second fuel pump turns on in the 116 tank. The other green LED near the 11psi mark is when the 116 octane injectors turns on. I have never had a engine skip, pop or stutter when it switches. in fact, I've NEVER felt it change over at all! This is why I put the green LED's in place...just to show me when it does!

50 MPH Roll  - 600KB
50 MPH Roll- -  5.1 Surround Sound - 5.2MB (Right click and "Save Target As")

Close up of the boost gauge on the dyno. Not a very good video but you can see the lights light up. - 4.22MB

 

Dyno and Drag Strip Video's

Here's a couple of videos of the car on the dyno and at the drag strip with the SDFI fully operational. The first video is the car on the dyno. It made 580 rear wheel horsepower at 25psi of boost. In this video, as the boost was rising I locked the torque converter clutch manually so you hear the engine rpm's decrease for a second or two. The second video is a run down the drag strip. The car had a 1.52 sixty foot and ran a 6.69 at 104 in the 8th mile. Both of these video's was with my 3.8L engine.

See if you tell when the SDFI switches from low octane to high octane!

   

 

 

   

 

On October 25th 2006... The SEQUENTIAL DUAL FUEL INJECTION SYSTEM is functioning full time!  No knobs to turn...no switches to flip...no adjustments needed after initial set-up and best of all....it's 100% AUTOMATIC! What more can you ask for?  This has been a successful project for me and am proud to say it works very well...no...EXTREMELY WELL! 

 

 

 UPDATE: 

April 3rd 2009, absolutely NO PROBLEMS at all since this system has been operating!

 

DISCLAIMER: Custom designing is just that...CUSTOM. Your design may be different than the one I provided on this page. I provided information on what I seen while I was designing and testing this system. If you attempt this, be aware of the  "trial and errors" you may encounter when doing such custom projects. As always, I am not responsible if you screw up. Anyone...ANYONE who claims this system does not function properly has NOT taken a ride in my car. Non believers are more than welcome to stop by for a demonstration.