Hello everyone,
First off, a big thanks to all the quality contributors to this forum. None of us could successfully finish these conversions without the help and advice from the members posting positive and helpful information. That said, I wanted to showcase my first “Fummins” build.
Let’s get right down to it. We started with a 4wd Crew Cab Short bed 2000 Ford F250 Superduty with a worn out 7.3L diesel and a ZF6 manual 6 speed.
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We named the project “Tom.” That’s for two reasons:
First, we bought the truck from a stylish guy named … you guessed it … Tom. He drove the truck out to us in the Pacific NW all the way from Maryland. Thanks Tom!
![]()
And the second reason this truck will forever more be called Tom is this: The school bus that gave up its engine was a Thomas Built Bus (#425 for those keeping track of how to get home after school) which was bought at a GOV deals auction from a local school district. Bus #425 had approximately 9000K hours and 156K miles.
![]()
The truck was in surprisingly good condition, considering that the Superduty had north of 300K on the clock and having spent its days in a rust-prone part of the USA. It even made that cross-country drive without issue, other than the expected dirt and wear and tear. The truck ticked all the boxes needed for my first Fummins swap, namely that it was a running, driving truck.
The goal for this build was straight forward: Create a “forever” truck. We decided to tackle this in two phases:
Phase 1
Phase 2
Because I know everyone wants to see photos, I tried to document the build with the details that would be most interesting and helpful to everyone that reads these posts. Here we go:
We started by dismantling Bus #425 and removing the engine. For any of you considering this, let me just say, it’s a major undertaking requiring a lot of work and equipment. I would never attempt to remove the engine without the use of a suitable forklift or a very big tractor with a loader. Everything on the school bus is big and heavy.
I had excellent help courtesy of a sawsall and a good pack of blades:
![]()
While in process, make sure you keep track of the required wires as well as the gauges and the gas pedal. You’re going to need to keep those. Also, if you intend to reuse the bus air system, make sure to keep the governor as well as the dryer and some of the air tanks. We also kept all of the battery cables, fuse holders, and switches. There are a ton of good parts on the bus that we tried to keep for future use.
![]()
We finally had both the engine out and the parts we wanted to keep. It was time to send the rest of the bus to the recycler. We were glad that part of the project was over. Working on gravel sucks!!!!
Once we had the engine in the shop, on a workbench, we could really see what we had. Have I mentioned working gravel is the worst? I was so glad to be back in the shop.
![]()
In the shop, we first added the SN of the Cummins to Quickserve and unlocked a lot of very useful information, everything from wiring diagrams, service manuals as well as air system diagrams. If you have not set up a quickserve account for your Cummins, I highly recommend you do so.
![]()
Our engine is rated at approximately 250 HP, so our plan for 350hp is doable with a set of 100hp injectors and no tuning. We sent the injectors out to our local turbo and injector shop for them to be resized. It appears that our VP44 pump, as well as the lift pump, were recently replaced. Great news for us! One great thing about buying a bus from a big school district is that you can be confident the buses were maintained. As a bonus, the buses aren’t necessarily going to auction because there’s something wrong with them; we learned from the helpful shop manager at the bus depot that most of the auction buses are just old. They just need to make room for new ones.
![]()
Our turbo is an HX35W and was in great shape. As a result, our plan is to run it and if the black smoke is bad with the upgraded 100HP injectors, we will swap it with something bigger.
![]()
Here you can see the two ECM connectors. Thanks to Quickserve, we have a great wiring diagram for the ECM connector as well as the 23 pin connector that is used for all the power, ground, and switched power connections. Because the School bus engine is modular, the wiring is simpler than it looks. In most cases the harness comes apart in big sections with bulkhead connectors as well as a lot of weather pak connections.
![]()
Our engine did have an exhaust leak on the rear cylinder, so we sent the manifold to the machine shop and had it surfaced. The bolt was just loose when we removed the manifold but better to be safe and have it surfaced than to risk an exhaust leak.
First off, a big thanks to all the quality contributors to this forum. None of us could successfully finish these conversions without the help and advice from the members posting positive and helpful information. That said, I wanted to showcase my first “Fummins” build.
Let’s get right down to it. We started with a 4wd Crew Cab Short bed 2000 Ford F250 Superduty with a worn out 7.3L diesel and a ZF6 manual 6 speed.
We named the project “Tom.” That’s for two reasons:
First, we bought the truck from a stylish guy named … you guessed it … Tom. He drove the truck out to us in the Pacific NW all the way from Maryland. Thanks Tom!
And the second reason this truck will forever more be called Tom is this: The school bus that gave up its engine was a Thomas Built Bus (#425 for those keeping track of how to get home after school) which was bought at a GOV deals auction from a local school district. Bus #425 had approximately 9000K hours and 156K miles.
The truck was in surprisingly good condition, considering that the Superduty had north of 300K on the clock and having spent its days in a rust-prone part of the USA. It even made that cross-country drive without issue, other than the expected dirt and wear and tear. The truck ticked all the boxes needed for my first Fummins swap, namely that it was a running, driving truck.
The goal for this build was straight forward: Create a “forever” truck. We decided to tackle this in two phases:
Phase 1
- Freshen the 24 valve Cummins and boost the power output to approximately 350 HP
- Install a School Bus ISB 24 valve Cummins out of a 2000 Thomas School Bus
- Plumb the compressed air system from the School bus to run air bags and air tools as needed
- Retain the ZF6 manual transmission
- Install an exhaust brake
- Repair and stop any rust as needed on the body and or chassis
- Rewire engine and accessories to ensure the body can be removed easily in case of future repairs.
- Test drive, test drive, and more test drives
Phase 2
- Install larger Turbo if more power is needed or if it smokes too much due to the larger injectors
- Fix anything that need to be replaced after all the testing in Phase 1
- Repaint Paint exterior body
- Replace the interior with leather from Leather Seats.com
- Fabricated and install custom bumpers from MOVE
Because I know everyone wants to see photos, I tried to document the build with the details that would be most interesting and helpful to everyone that reads these posts. Here we go:
We started by dismantling Bus #425 and removing the engine. For any of you considering this, let me just say, it’s a major undertaking requiring a lot of work and equipment. I would never attempt to remove the engine without the use of a suitable forklift or a very big tractor with a loader. Everything on the school bus is big and heavy.
I had excellent help courtesy of a sawsall and a good pack of blades:
While in process, make sure you keep track of the required wires as well as the gauges and the gas pedal. You’re going to need to keep those. Also, if you intend to reuse the bus air system, make sure to keep the governor as well as the dryer and some of the air tanks. We also kept all of the battery cables, fuse holders, and switches. There are a ton of good parts on the bus that we tried to keep for future use.
We finally had both the engine out and the parts we wanted to keep. It was time to send the rest of the bus to the recycler. We were glad that part of the project was over. Working on gravel sucks!!!!
Once we had the engine in the shop, on a workbench, we could really see what we had. Have I mentioned working gravel is the worst? I was so glad to be back in the shop.
In the shop, we first added the SN of the Cummins to Quickserve and unlocked a lot of very useful information, everything from wiring diagrams, service manuals as well as air system diagrams. If you have not set up a quickserve account for your Cummins, I highly recommend you do so.
Our engine is rated at approximately 250 HP, so our plan for 350hp is doable with a set of 100hp injectors and no tuning. We sent the injectors out to our local turbo and injector shop for them to be resized. It appears that our VP44 pump, as well as the lift pump, were recently replaced. Great news for us! One great thing about buying a bus from a big school district is that you can be confident the buses were maintained. As a bonus, the buses aren’t necessarily going to auction because there’s something wrong with them; we learned from the helpful shop manager at the bus depot that most of the auction buses are just old. They just need to make room for new ones.
Our turbo is an HX35W and was in great shape. As a result, our plan is to run it and if the black smoke is bad with the upgraded 100HP injectors, we will swap it with something bigger.
Here you can see the two ECM connectors. Thanks to Quickserve, we have a great wiring diagram for the ECM connector as well as the 23 pin connector that is used for all the power, ground, and switched power connections. Because the School bus engine is modular, the wiring is simpler than it looks. In most cases the harness comes apart in big sections with bulkhead connectors as well as a lot of weather pak connections.
Our engine did have an exhaust leak on the rear cylinder, so we sent the manifold to the machine shop and had it surfaced. The bolt was just loose when we removed the manifold but better to be safe and have it surfaced than to risk an exhaust leak.
