1991 - 1997 Ford F-150 & Bronco

Posted by Diesel Conversion on Oct 15th 2020

1991 – 1997 Ford F-150 Conversion Overview

Information for all F-150 and Bronco models 1991 - 1997: 

If you’re looking to maximize fuel economy in your F-150 or Bronco then you have come to the right place.  The professionals at Diesel Conversion Specialists have created a kit that is full of components to help you place a Cummins engine into your truck and retain factory functions at the same time.

Cummins 4BT Engine Information

Essentially a 4 cylinder version of the 6BT, the 4BT Cummins shares the same pistons, injectors, connecting rods, & valve train design as the 5.9L 12v Cummins.
Cummins currently manufacturers the 4BT engines for delivery trucks, marine, construction, agriculture, & other off-highway applications.
4BT stands for: 4 cylinders, B-Series engine, Turbocharged. 


3.9 Liters or 239 Cubic Inches

Inline 4 Cylinder

Turbo Charged

800 lb. engine weight (Approx.) 

105-130 HP (Stock)

265-327 Lb.-Ft. (Stock)

Typical Governed RPM-2,500 / 2,700

The 4BT is the best option, compared to the 6BT, for the F-150 and Bronco.  There are many factors that make this the best engine for the half-ton chassis.  Just to name a few….

Simplicity- The simplistic nature of this all mechanical engine is world renowned for being low maintenance and highly reliable.  Relatively inexpensive maintenance costs are another benefit.

Engine Weight- Much better suited for a ½ ton truck because it weighs about as much as a Big Block V-8 gasoline engine. No need to modify suspension, reinforce or  “box” frame & cross member, axle swap or braking system. If a 4 cylinder engine weighs as much as a Big Block V-8, we hope you realize that this is an industrial engine capable of serving all of your needs even if you tow a bit.

Power- Some basic fuel upgrades can make this engine produce as much or more torque as a stock 6BT engine. Although results vary based on engine tuning, fuel upgrades can help improve fuel economy because your foot isn’t into the pedal as much.  Turbo upgrades are often needed as well to keep the air-fuel ratio correct, but the good news is that you can often find an early 6BT turbo cheaply and they work great on a modified 4BT.

Fuel Economy- The 4BT engine is well known to consistently achieve Middle to upper 20’s for MPG. That’s why the engines are often found in box trucks and delivery vans.  Some folks have used these engines in Jeep conversions and tout Mid 30’s for fuel mileage however we haven’t been able to verify that.  Of course driving style, gearing, and tire size all play a role in fuel economy.

Transmission Information:

Some folks find an engine and transmission combination from a delivery van.  Can you make this work? Yes.  Is the combination ideal in an automotive application? No! Here’s why. 

              Manual transmission: These transmissions lack an overdrive.  This greatly limits your on road drivability by quickly maxing out your RPM range.  Maximum fuel economy RPM is 1,800 – 2,000.  This combination may work for a vehicle that operates strictly off road however the overdrive transmission can prove to be handy for those “unexpected” times that the truck is operated at highway speeds.

              Automatic transmission: The automatics also lack an overdrive and lack a torque converter lock-up.  There is no comparing an older turbo-hydromatic transmission to today’s newer electronically controlled transmissions for efficiency in power transfer and economy. 

Beyond lacking an overdrive you will also be faced with a good bit of fabrication work to make a transmission mount.  If your truck is 4WD you would also need to find a divorced transfer case, or purchase a transfer case adapter, if available, to marry the transmission to your existing transfer case.  All of the previously mentioned options are an additional cost some of which are substantial.  Custom drive shafts will more than likely come into play as well.  Your factory speedometer can be a hurdle as well because most of the trucks in this year range use a manual speedometer cable rather than an electronic sensor.  There may be other issues to work through as well.

In summary the easiest route is to use the drivetrain already equipped in your truck or similar Ford transmission.






One of the benefits of using these transmissions is that they are completely non-electronic so an aftermarket transmission controller is not needed. The down side is that you will need to rework the governor and or valve body. You will also have to use an adjustable vacuum modulator delete plug or use a throttle vacuum valve and keep the vacuum modulator. These items control transmission line pressure and shift points, which will need to be changed, because the Cummins engine has a much lower RPM “Power Band.”  Because these transmissions lack an overdrive, less the AOD, you fuel economy and power transfer will not be as good as it could be compared to an electronically controlled transmission.


This new generation electronic transmission does have an overdrive and a torque converter lockup.  Our automatic transmission conversion kits were designed  based on the E4OD.  Some may think that the need for a transmission control module (TCM) is a drawback because they desire simple (mechanical) transmissions.  This is valid only to the extent that the E4OD is mechanical 1st through 3rd gear and only overdrive is electronically controlled. It does cost a little more money to convert, because of the need for an aftermarket TCM, but saves a good bit of work by not having to change the valve body, Vacuum modulator, etc.  Today’s transmission control modules are very reliable, have a high level of user adjustability, and require only basic wiring to integrate into your truck.  Due to the high level of user adjustability this is a very viable option for those of you that plan on using your truck for a multitude of functions. 


NP435 / T-18: Some call this 4 speed transmission “The Rock Crusher.”  This is a fine transmission for off road or agriculture use however not so good for on road or highway travel.  If you don’t mind a top speed of 55 – 60 MPH, at maximum engine RPM, on the highway then certainly stick with this transmission and plan on changing ring & pinion gears.  Your fuel economy will not be as good as it could be as compared to one of the transmissions listed below.

Mazda 5:  Found behind the 300 I-6 and 302 gasoline engines.  This is a fine transmission with the same size input shaft as the “Rock Crusher” and also has a beneficial overdrive gear. 

ZF5:  This is specifically for 351 Windsor or Cleveland engines (351W) or (351C).  Basically the same as the Mazda 5 with different gear splits.  The small block ZF5 has a “Big Brother” used behind the 7.5L gas and 7.3L diesel engines.  This is a great transmission upgrade for those with the 4 speed manual transmissions.

Parts Information:

Adapter plates:

DCS adapter plates, for automatic transmissions, require a custom flex plate to adapt to a Diesel E4OD torque converter and also require the use of a Ford 6.0L Power Stroke starter.  We used a 1997 7.3L Power Stroke torque converter and it works great.  The manual transmission adapter plate also uses a Ford 6.0L Power Stroke starter.

Engine Mounts:

Bolt in replacement engine mounts take fabrication and guesswork out of the equation.  These engine mounts support all F-150 and Bronco frames from 1991 - 1997.  Please Note: The engine mounts were designed for use with the DCS transmission adapter. If you are attempting to use any other adapter plate you will encounter fitment issues.  Engine mounts are a non-returnable item.

 Sensor Adapters:

Adapt the Ford Oil pressure and water temperature sending units into the Cummins engine. This allows you to have your factory dashboard functioning.  The kit includes a coupler to tie the Ford power steering line to the Dodge Cummins pressure line.  Also included is a Tee line to tie your or vacuum lines into the Dodge Vacuum pump for vacuum assisted brakes. 

Tachometer kit:

These parts are necessary to make your factory tachometer work (if you have one). This kit consists of a sensor, spacer, mount, and a tone ring that bolts to the front of a Cummins harmonic damper (a.k.a. cranshaft balancer)  The tone rings work best with 6BT balancers, which is a nice addition anyway considering most 4BT engines just have a pulley on the crankshaft not a harmonic damper.

Transmission Control Modules (Automatics):

You will need a throttle position sensor.  Please click the link for more information.

Flywheel and Clutch (Manuals):

DCS offers kit includes a flywheel and clutch to bolt onto the Cummins engine and the pressure plate and clutch disc that will work with the Ford transmission.  The clutch kit Includes Flywheel, Clutch Disc, Pressure Plate, Release bearing, and the pressure plate bolts.

Some other parts you will need to get on your own are:

Intercooler- A 1999 Super Duty diesel intercooler can be added to your truck. Just a little bit of angle iron and drilling is all that’s required.  Not all engines are intercooled however it’s not a bad idea to install an intercooler during the conversion process.  The entire theory behind intercooling an engine is simply a matter of efficient use of the fuel.  Intercooling the engine is almost mandatory if you add fuel upgrades to keep exhaust temperatures in check. 

Additional battery- Not required but it’s certainly not a bad idea

High capacity radiator – Extra cooling capacity as the OEM radiators are fairly small

Intercooler pipes- Your local exhaust shop can be a great resource

Radiator hoses- This will consist of upper and lower radiator as well as heater core hoses

Engine Components:

Most 4BT engines do not have the amenities of an automotive engine.  An example of this specifically is the lack of an A/C compressor and bracket.  Because there are many applications for the 4BT engine these specific components vary greatly.  A 4BT from a delivery van is configured much differently than one from a Gen-Set, which is also different from a Marine engine.  We mention this so you can “dress” your conversion engine accordingly to achieve complete functionality after the conversion.