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Do It Yourself Exhaust Brake

Source:
Jonathan Ryan


Updated April 5, 2002

The following article was updated due to a possible problem with the torque converter lockup circuit described in the original article. Please do not utilize any automatic transmission information from this article that was published prior to this Update. Damage to the automatic transmission and or electrical circuits in the Ford F-Series Truck may result if the lockup circuit outlined in the previous version is employed.

Sorry for any inconvenience.


The Engine Exhaust Back Pressure Valve (EBPV) is a butterfly type valve located on the outlet of the turbocharger, between the turbine and the downpipe. It is controlled by the Powertrain Control Module (PCM), and activated by engine oil pressure. Its purpose is to decrease engine warm up time in cold weather by restricting exhaust flow out of the engine. It can be very easily and very inexpensively converted into an engine exhaust brake by adding some simple wiring and a switch.

The valve is very practical for assisting braking. When used correctly its braking effect can be compared to the restriction gained by downshifting one gear while descending a hill. The valve is most valuable to braking when engine speed is between 2500 and 3000 RPM. Unfortunately, it will lose the engine braking abilities when engine speed drops below 2000 RPM.

The following method outlines the manner in which the EBPV can be converted to a braking device. The brake will function better in a vehicle equipped with a Manual Transmission. Vehicles equipped with Automatic Transmissions will have good braking effect, while the torque converter stays locked, but will lose braking effect when the torque converter unlocks. The unlocked converter will allow a reduction of engine speed, which will inevitably reduce the desired engine braking effect.


Click on Schematic for Larger Format

In order to control the function of the EBPV, I recommend using a 3-position switch. This type of switch will control the Valve in the following manner:

Switch in the OFF Position (center position): The EBPV will function normally, as it would for a stock vehicle. This means that the valve will only actuate in order to warm up the engine.

Switch in the "A" ON Position: the EBPV closes and remains closed until the switch is turned OFF.

Switch in the “B” ON Position: the EBPV will close whenever the brake pedal is pressed, and will open when the pedal is released. There will be a 2-3 second lag for the exhaust valve to close upon stepping on the brake. Thus, it is important to understand that when using it in the "B" ON position to push the pedal and hold it down with steady pressure. The reason for keeping pedal pressure is that the EBPV actuator is receiving power from the brake light circuit when the switch is in this position. Thus, pumping the brakes or releasing the pedal will cause the valve to deactivate or open. Furthermore, once the brake is applied again it will take another two seconds for the EBPV to activate again. Unfortunately, pumping the brake pedal will result in the exhaust valve remaining in a constant open position. This will provide ZERO engine braking force. To prevent this less than desirable phenomenon from happening, it is important the operator keep his foot on the brake lightly enough that the brake light switch is continually activated. I prefer touching and holding my pedal just hard enough for the brake lights to come on; then, when I hear the EBPV close (it makes a distinct hissing), I begin applying additional pressure to the brake pedal. Reducing brake pedal pressure can be done without losing exhaust-braking force, as long as there is enough pedal pressure maintained to keep the brake lights on.

Materials:

  • (1) ON-OFF-ON type Heavy Duty Double-Pole Double-Throw (DPDT) toggle switch. It will have connections for 6 wires on the back, and the switch will have 3 positions UP=ON, CENTER=OFF, DOWN=ON. RS (Radio Shack)# 275-1533A $2.49 or 275-710 $2.99
  • 25'-30' of 18 gauge wire. 5'-7' each of 4 different colors is best.
  • (10-12) Ring or Spade terminals for wire connections. 18-22 gauge are red. RS# 64-3032A or 64-3033A $1.49 (4-6) Butt connectors for wires. 18-22 gauge are red. RS# 64-3037A $1.49
  • (2) Rectifier Diodes. A diode is the equivalent on an electrical check valve, allowing current to flow in only one direction. RS#
  • (2) Optional Mini Indicator lamps. RS# 276-085A (red) 276-084A (green) $1.99 each. (By using the switch indicator lights, the operator immediately knows how the EBPV is activated or not.)
  • 10' Split loom for protecting wires. RS# 278-1264 $3.99
  • (10) Wire ties.
  • (1) Inline fuse holder. RS# 270-1213 $1.99
  • Electrical tape. I recommend Liquid Electrical Tape as being better for almost everything.
  • Tape and Marker (In order to label wires.)

Tools:

  • Wire cutters/strippers
  • Screw Drivers
  • Drill w/ bits up to 7/16"
  • Volt/Ohm Meter, or at least a test light.
  • Soldering Iron is recommended but not essential.
  • Torx bits &/or 1/4" drive metric sockets to remove dashboard trim to install switch.

Procedure:

Decide on a place in the dash to install the switch. I installed mine in the black panel just to the right of the "Wait to Start" light. There is room for 2-3 switches there.

Remove the necessary trim and molding around the steering column / instrument panel to access the reverse side of where you want the switch. Drill a 1/2" hole, and install the switch. Re-install the molding to make sure it fits into place when the switch is installed. Then, remove the switch and the molding again for ease of access while wiring.

Wire #1: Decide what you will use for a positive power source. Insure that this source is one that is "ON" only when the ignition is in the “ON” position. I recommend the 8 gauge, gray/yellow wire in the bundle under the steering column. You can also tap a fuse in the fuse panel. Run wire [#1] from the source to the switch, connecting it to terminal A2. I numbered the terminals as viewed from the back of the switch Install the inline fuse holder on this line. Make sure to leave 6"-12" or more of slack on all the wires. You can always bundle them up later.

Wire #2: Decide placement of a negative power point or ground, and run a wire from this to the switch, connecting it to terminal C1.

Connect one light to terminals A1 and C2; this is light A. Connect the other light to terminals B1 and C2; this is light B. Drill holes for the lights just above and below the switch. Install the lights with B in the top hole, and A in the bottom. I recommend this because when the switch is down, contact is made between A+C; when the switch is up, contact is between B+C. For simplicity, the diagram does not show the lights "crossed" like this.

Remove the black-hinged cover from over the fuel filter area in the engine compartment.

Wires#3 & #4: Run two wires from the switch through the firewall into the engine compartment. Connect one [#3] to terminal C2 and run it to the front of the engine. Connect the other [#4] to terminal B2 and run it to the brake master cylinder. If you have a horizontal diamond shaped plate about 2.5" wide just to the passenger's side of the clutch cylinder, remove the screws and run the wires through it. Otherwise, you may need to drill a hole. I always find that running the wires is the hardest part of any wiring project.

There should be a green wire by the driver's side of the master cylinder in the group of 4 marked "Center High Mount Stop Lamp Feed." This wire most likely will not be connected to anything. This wire is only energized when the brake lights come on. Connect wire [#4] to this one. If this wire is not present, use a voltmeter or test light to find a wire that is hot only when the brake lights are on and connect to that wire instead.

Locate the wires that travel from the PCM to the EBPV. There should be a 2-wire plug just under the turbo compressor. It is located towards the front of the engine between the turbocharger and the fuel pump on the intake side of the turbocharger. The plug is attached to the turbo pedestal. Disconnect this plug, and remove the loom (protective plastic shielding) on the plug side moving away from the turbo, to expose the wires inside. Slide off the loom until it reaches the intersection of the larger wire bundle. This will expose both wires; one wire is black w/gray, the other gray w/red.

The Two Rectifier Diodes that are required will each have a silver band around one end. Twist the wires from the "silver" ends together making a "Y.” The "black" ends will be at the top and the silver ends at the bottom of the "Y.” Cut the gray w/red wire 2"-3" before the plug, strip the insulation back 1/2" or so, and solder the black end on one diode to the end of the cut wire that does NOT go into the plug. Solder the black end on the other diode to wire [#3]; solder the two silver ends to the gray w/red wire that goes into the plug. The diodes are necessary to prevent the brake lights from coming on when the PCM operates the EBPV, and to prevent the PCM from receiving a 12v signal from wire [#1]. If you don't have a soldering iron, you can use crimp connectors.

Coat all the wire connections with several coats of Liquid Electrical Tape, then wrap them with regular electrical tape, and replace the loom. Also, cover wires [#3 & #4] with loom, all the way to the switch. Bundle up any excess wire with wire ties, and secure them all to prevent chafing. Install the switch in its hole, and replace the dash trim.

Testing:

To test, start the engine. With the switch in the up position, the upper light should come on when you press the brake pedal, and you should hear a distinct hissing or swooshing sound when the EBPV closes, after 2-3 seconds. With the switch down, the bottom light should come on and stay on, and the EBPV will close immediately.

Conclusions:

I find no advantage to using the EBPV brake with an unloaded truck during normal driving. However, when I am hauling a heavy load, it is worth its weight in gold. During normal hauling, I leave it in the up position, so I will have extra braking power when I need it. For exit ramps and long or steep downgrades, I put it in the down position and leave it on as long as practical. When the truck is parked, you can leave the switch in the down position, as it is useful as an anti-theft device. The activated valve will not allow the truck to go much over 33 mph. This is also very useful for very fast warm-ups in winter.

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