Part 3: Wiring and Plumbing for Our Ford/Cummins/Allison Swap
Big-3 Blend: Part 3
Our Ford/Cummins/Allison project has been a long haul, and there have been plenty of dips and bumps along the road to swapping our ’01 Ford F-250’s worn-out 7.3L powertrain for a 24-valve, 5.9L Cummins and a GM Allison 1000 six-speed automatic transmission. It isn’t easy, as a lot of adapting is required to make the Big Three’s best attributes work together as if they were meant to.
Thankfully, the special adapters and custom parts offered by DeStroked and GOS Performance make the challenge considerably easier than trying to piecemeal such a project together for the first time. The two aftermarket companies have been doing custom Cummins/Ford conversions for 15 years, so they know exactly how to handle the multitude of obstacles and glitches that pop up when undertaking such a swap.
There are no formal “kits” for this 7.3L-Power-Stroke-to-5.9L-Cummins swap. However, as we mentioned earlier, there’s a lot of knowledge available when issues arise. Believe us, you will encounter issues.
We were fortunate to have the expertise of GOS owner Aden McDonnell available to us for the custom parts and troubleshooting suggestions, especially for wiring the Allison 1000 six-speed automatic transmission’s electronics and plumbing the Cummins for compatibility with the Ford Super Duty platform. Along the way, Aden recommended ways to significantly improve the power and performance of the “new” engine and transmission package, which we covered in Part 2 of this series.
Radiator ModificationsNow that the ’01 24-valve Cummins is hitched to our performance-built six-speed Allison, and the Super Duty’s crew cab body is set back in place, it’s time for Shawn Smalley and Mat Johnson of Mobile Diesel Service to focus their attention on the final wiring and plumbing.
This stage of the conversion process is far more complicated than the mechanical side of mating the Cummins engine to the Allison transmission to the Ford transfer case. Our first order of business—and the easiest—is improving the engine and transmission’s cooling. The 7.3L Ford radiator and transmission cooler are woefully inadequate, as coolant flows through 3/8-inch tubing. The truck’s original hardware is replaced with pieces for a 6.0L-powered ’04 Super Duty, which has ½-inch tubing in the transmission cooler, and the radiator’s surface cooling area is double that of the 7.3L. The components also bolt right into the older truck without any modifications.
Selecting the right fan is also critical—more so than the radiator. The fan from a ’99-to-’02 5.9L Cummins has a special offset toward the radiator that allows the blades to clear the tach sensor that’s mounted on the front of the block, as well as bolts holding the reluctor wheel to the crank. Our salvage-yard ’01 engine didn’t come with the fan, and now we know why: These fans are very hard to find because they are no longer made. After a lot of searching, we were in business—albeit $500 lighter in the wallet. Lesson learned.
More Plumbing ChangesMat also relocated the truck’s stock vacuum reservoir, moving it forward and down on the passenger-side inner fender. Then he put a 6.0L degas canister where the reservoir once sat and used two 90-degree Ford degas hoses to make the turn into the nipple on the custom steel lower radiator tube from DeStroked. This helps keep the engine bay clean and tidy.
He also used the ’04’s hard transmission cooler lines to simplify that part of the plumbing, cutting off the hose on the passenger side to run new ½-inch high-pressure, high-temp line to the Allison and then back to the cooler.
Connecting the cooler lines requires a pair of 90-degree #10 Boss-to-#8 JIC fittings, which enable the ½-inch hoses to clear the downpipe and exhaust. (The transmission is a lot larger than the F-250’s stock Ford 4R100, so side-to-side clearances between the body and frame are much tighter.)
While Mat reworked the cooling system, Shawn ran ½-inch hoses from the remote engine-oil-cooler adapter on the Cummins to the new oil filter’s location on the opposite side of the block (where the stock lift pump is located). Doing this puts the oil filter in the same location it’s found in on the 7.3L.
Shawn took a Cummins fuel-pump bracket, bent it into a “U”-shape, and used the existing bolts covering the lift-pump cover plate to mount the filter in place. Positioning the remote oil filter in this manner makes doing oil changes easier, and it keeps the remote filter out of harm’s way.
Shawn used DeStroked’s CNC-machined, custom-made manifold and hoses to connect the Ford’s A/C system to the Cummins compressor. Using these parts saves a lot of time trying to cobble together something that works.
Handling the Electrical SystemThe electrical side of the swap is rather involved, even using wiring harnesses and diagrams from DeStroked and GOS Performance as references. All three elements—the engine, transmission, and truck—have separate computer systems that need power and grounds, and each has its own OBD-II port for programming and troubleshooting.
The two technicians quickly learned that neither the Ford nor the Cummins factory alternators will work, requiring the use of a modified, internally regulated alternator from GOS to charge the batteries. The Mobile Diesel Service crew also realized that additional ground straps from the Cummins and Allison to the Super Duty frame are needed to ensure good grounds.
Figuring out exactly how to wire the power and grounds for the Allison, routing the three separate wiring harnesses so they look factory installed, mounting the three OBD-II ports under the dash, and installing a “Check Transmission” light in the dash all requires a lot of time to accomplish.
Mat replaced the Ford’s shifter handle with a customized tap shifter from an ’08-to-’17 Super Duty, courtesy of a kit GOS Performance offers for such swaps. It makes driving with the Allison seem like it does in a heavy-duty Chevrolet or GMC, sans the shift-position indicator in the instrument cluster (GOS uses a remote-mount digital readout gauge that mounts on the dash).
More UpgradesTo clean up the engine bay, Mat removed the truck’s stock airbox and, in its place, he installed a CNC-machined aluminum battery tray from DeStroked, designed to hold a pair of Optima RedTop cells. Tucked neatly between the batteries and the inner fender is the computer for the Allison six-speed automatic transmission.
Mat also swapped the stock Cummins air intake with Banks Power’s 3-inch High-Ram Intake, which is said to add another pound of boost while greatly improving airflow between the intercooler and intake manifold.
On the opposite end of the Industrial Injection PhatShaft turbocharger, Mat used a Holset HX10 flange from Industrial Injection to mate with a Diamond Eye Performance 4-inch downpipe that’s designed to fit ’04½-to-’07 5.9L-powered Dodge Rams. The remainder of the 16-year-old Ford exhaust was replaced with a Diamond Eye muffler and aluminized 4-inch exhaust back to the tips.
The new exhaust gives our healthy 24-valve Cummins a deep, throaty growl, without drowning out the occupants’ conversation when cruising down the highway with a big toy hauler in tow.
Performance TuningThe Allison transmission is controlled by a standalone computer system, which is programmed specifically for this Allison/Cummins application. Aden is an expert in this area, and the distance between shops wasn’t an issue in handling the job. Aden was able to “remote tune” from his shop in Montana—900 miles away from Mobile Diesel’s shop in Oakland, Oregon—handling the critical aspects of tuning.
With that taken care of, Shawn did a little white-glove hot-rodding to the Cummins engine by using the newest Juice with Attitude CTS2 programmer from Edge Products (for ’01-to-’02 5.9L Cummins engines). The Competition version of the device has seven power modes, and on Level 7 it is said to add 150 hp and 380 lb-ft of torque.
The CTS2 provides more aggressive fueling in the bottom end and more timing adjustments than the standard Juice with Attitude CTS programmer. It also allows the driver to switch between power modes (including Economy and Tow modes) on the fly, while monitoring more than a dozen engine and transmission parameters on the multiple gauges displayed on its LCD touch screen.
We Have Ignition!It took more than a month for the Mobile Diesel Service team to bring this Cummins-powered, Allison-shifted Ford F-250 to tire-frying life, thanks in no small part to a lot of help from DeStroked and GOS Performance.
Mobile Diesel’s Shawn Smalley and Mat Johnson didn’t cut any corners in the conversion process. They took their time to ensure every modification looks stock and that quality parts were used.
What we learned from this merging of the Big Three’s most lauded diesel components into the ’01 Super Duty is that even with custom parts and experts doing the work, such an undertaking always takes a lot more time—and generally a little more money—than a person may initially estimate. There are unexpected glitches to overcome and spur-of-the-moment modifications that arise.
But, with patience and the right mindset, slipping a 5.9L Cummins engine and Allison 1000 six-speed automatic transmission into an older F-250 can be done. The result is a big step up in power and performance over the 7.3L Power Stroke engine. Let’s just say the drivetrain swap creates a kick-in-the-pants tow rig that’ll be around for a half-million miles or more. It’s fun to watch heads turn when people hear a Cummins and see a Super Duty roll by.
Edge ProductsOgden, UT 84404
Gale Banks EngineeringAzusa, CA 91702
Industrial InjectionSalt Lake City, UT 84104
BD Diesel PerformanceSumas, WA 98295
Diamond Eye PerformanceAthena, OR 97813
DestrokedWheat Ridge, CO 80033
FuelabLitchfield, IL 62056
Mobile Diesel Service541-459-8939
Automatic Transmission Specialists406-222-3992