Ranger Biodiesel Swap - Automatic Transmission Control Wiring Bypass

In addition to the engine, I also planned to swap the original Ford 4R44E automatic transmission for a 4- or 5-speed manual, such as an M50D. Besides the better fuel economy, this would greatly simplify the conversion by eliminating the need for integrating the shift controls into the VW engine.

However, the automatic transmission cannot simply be unplugged without making additional modifications to the wiring harness. Otherwise, the truck's ECU would throw multiple OBD2 codes, and several crucial functions would be disabled. The common recommendations to avoid this are to simply convert a manual truck instead of an automatic, swap in a manual truck's wiring harness and ECU, or reprogram the ECU itself.

Instead, after studying the wiring diagrams, I designed a bypass box that tricks the original ECU into thinking that an automatic transmission is still installed, and that it is permanently locked into the Neutral position. I chose Neutral because:

1. The starter is normally enabled in both Neutral and Park.

2. The fewest internal shift solenoids are operated in Neutral.

3. The ECU won't compare the input and output rpm in Neutral, so I don't have to mimic those sensors.

Pages 29-3 through 29-5 of the Ford Wiring Diagram Manual provided most of the necessary information. The transmission is equipped with a "Digital Transmission Range (DTR) Sensor, which is a multiple-pole rotary switch attached to the gear selector lever. The diagram on page 29-3 shows the wiring connections that are engaged in each discrete gear position, and page 29-4 shows the wiring connections to each of the internal shift solenoids and sensors. Finally, page 29-5 presents a pinout diagram of the two harness connectors attached to the transmission, including wire color codes, pin numbers, and circuit functions.

By focusing on the connections specific to Neutral position, and determining which solenoids are actually called for in Neutral, I designed a jumper box in a waterproof case. Several wires are simply connected, whereas a few others are joined by resistors with specific OHM values. The large resistors imitate the presence of the internal shift solenoids, so the ECU self-check doesn't detect any faults and trigger a code.

 

Ranger Biodiesel Swap - Fuel Pump Override Switch

My Ranger is a 1999 model, equipped with a standard OBD2 system that monitors emissions and onboard mechanical diagnostics. To avoid this added complexity, most diesel swaps are performed on pre-OBD2 vehicles, or the builders will seek to remove/bypass/reprogram the ECU. 

For my build, I'm trying to retain as much of the ECU functionality as possible, and my goal is to pass the NJ MVC inspection honestly, with minimum codes and without an illuminated check engine light. 

In preparation for the swap, I'm making a number of modifications to the truck's electrical, fuel, and exhaust systems. The first of these will be described below, where I'm installing a fuel pump override switch.

The Ford Ranger ECU is programmed to run the fuel pump for approximately two seconds when the ignition is switched on, to prime the fuel injection system in preparation for engine startup. After this, the pump is shut-off until the ECU detects that the engine is running at sustained idle.

I'm replacing the original fuel system (single fuel line, regulator/return inside the tank, internal fuel pump) with a complete recirculating system featuring both sending and return lines, an external pump, and a water separator/filter. 

This type of system requires sustained operation of the fuel pump prior to startup, to circulate fuel and purge all trapped air from the lines. Rather than bypass the original fuel pump controls and wiring, I decided to install an override switch.

As shown on page 24-1 of the Ford Ranger Electrical Manual, the fuel pump is powered by the switched-side of the Fuel Pump Relay, through the Inertia Fuel Shutoff Switch, and on to connector C422 on page 24-7. 

The coil-side of the Fuel Pump Relay is connected to +12VDC on one side, and ECU Pin 80 on the -12VDC (Ground) side. To run the pump, ECU Pin 80 is switched to ground (logic output 0), which completes the circuit and triggers the relay coil. Therefore, an override switch simply needs to connect the existing Pin 80/Fuel Pump Relay wire to a switch, which can manually ground the circuit. 

Step 1: Shut off the truck, remove the connector from the ECU (engine bay on top of firewall), remove the protective covers and tape, and identify the wire connected to Pin 80.

Step 2: Carefully remove a 1/2" stretch of insulation from the wire on Pin 80 (do not cut the wire!!), wrap the stripped end of a new override switch wire around it, solder the joint thoroughly, and wrap the exposed conductors with electrical tape.

Step 3: Tuck the wires back inside the protective covers, including the new override switch wire. Route the new wire along the original harness and through the firewall of the truck, and rewrap the covers with electrical tape.

Step 4: Install a SPST toggle switch in the cab, and connect one side to the override switch wire that was just pulled though the firewall. Connect the other side to a wire that is grounded to the truck chassis.

This switch will now allow the driver to manually override the fuel pump at any time, without altering the original wiring or throwing any OBD2 codes.

1999 Ford Ranger Biodiesel Swap

Nearly 4 years since I've posted to this blog, and a lot has changed! 

New job, moved to a new state, bought a house, adopted a dog, and got married, most of which occurred during the coronavirus pandemic. Needless to say, I had....other priorities and projects to attend to since 2018.

I don't know if this attempted revival will stick, but I'll try to keep up with it as often as I can.

And with (re)introductions out of the way, here's a summary of my new biodiesel project:

In October 2021, I bought a 1999 Ford Ranger 3.0L 2WD long bed off Facebook Marketplace, with a seized engine and clean title. I've pulled and sold-off the original drivetrain, and plan to swap it with a VW 1.6NA diesel engine (55hp), Ford M50D manual transmission, and 5.13:1 rear gears. The primary goal of this swap will be to maximize fuel economy, and optimize the truck for backroad 55-60mph commuting.

Dragged home from the junkyard.

Interior stripped for rust repairs and upholstery reconditioning.

The refurbished interior, including modifications for a manual transmission.

Pulling the seized engine for scrapping.

I bought and installed a relatively rare Leer long-bed cap.

Major suspension work, replacing the leaf spring shackles, brackets, and bushings.

Original "Rabbit Diesel" badge