Know your IDI History, Ford Diesel - 101
While not a true technical article in the wrench and socket set sense, the below information compiled and authored by Tom Brewer, represents the point of reference from which all other technical articles of relevance here are drawn.
Vintage Ford Diesel Truck History - By Tom Brewer
Depending on which definition you go by, the term “classic”, as it applies to automobiles, can be anything from 25 years old to anything produced before World War II. Antiques are typically anything over 50 years old. For the sake of confusion, this article will refer to the first series of diesel powered Ford trucks as “vintage.”
Ford began putting diesel engines in its light duty truck line in 1983 and continues with that heritage through present day. Beginning with the 1983 model year, Ford introduced the Indirect Injected Diesel (IDI) to its light duty truck lineup. The term indirect injection refers to the fact that the fuel is injected and initial combustion takes place in a pre-combustion chamber then transfers to the cylinder for complete combustion and power stroke. This engine started life as a 6.9 liter (420 cid) displacement engine and was later expanded to 7.3 liters (444 cid). The IDI was the diesel mainstay in Ford pickups for 11 years. Then in midyear 1994, the Powerstroke was introduced. This engine also displaced 7.3 liters, but was a redesigned engine, implementing computer controlled technology, reduced compression, turbocharging, and a high pressure oil activated, electronically controlled direct injected (DI) fuel injection system. The old style pre-combustion chamber was eliminated and fuel was now directly injected into the cylinder. This engine would remain in production until 2003. Some may argue that the engine became another generation with the introduction of the Super Duty line in 1999 due to the addition of factory intercooling, but basically it was the same engine. Ford is now running its third (or fourth depending on how you look at it) generation of diesel engine, also a Powerstroke, displacing 6.0 liters.
The “F” series moniker first appeared on Ford pickup trucks for the 1948
model year when the F-1, F-2, and F-3 were introduced. Jump ahead 32 years to 1980. The Ford F series pickup is still going strong. As a matter of fact, Ford trucks were the best selling vehicle in America, cars and trucks included. Entering the ‘80’s, Ford trucks went through a major design change, bringing on the seventh generation in its history. The new design sported a squarer look, with sharper lines and flatter panels. The face of the hood slanted back and the grill had a cleaner look to it. The truck could be had as a regular cab, super cab (which were split for a twin window effect), and crew cab (F-350 only). They were available with trim levels Custom, XL, XLT, and XLT Lariat. It’s interesting to note that the Ranger trim line was dropped in 1982 to make way for that name to be applied to the new compact pickup that Ford was about to introduce. Another noteworthy change was that of the switch from F-100 to F-150 for the half ton designator for 1983 model year.
During the 1981 model year, Ford signed an agreement with International Harvester to develop and supply diesel engines to Ford for the light duty truck line. The result of this 1981 agreement was the development of the 6.9 liter indirect injected diesel engine to be supplied to Ford Motor Company and for use in its own product line. Then in late 1984 Tenneco Inc., owner of “Case” and “David Brown” brands, declares its intention to purchase certain assets of International Harvesters 153 year old Agricultural Division. The deal is completed in 1985 to the tune of $488 million and Harvester is placed under the control of “Tenneco’s” Case division. The remainder of what was International Harvester is renamed Navistar. The split and sell off enabled Navistar to eliminate debt and concentrate on engine, medium and heavy truck development.
The new 6.9 liter normally aspirated IDI diesel engine first appeared in the 1983 model lineup. Was this an answer to the introduction to the 6.2 liter IDI diesel engine introduced into its pickup truck line by General Motors for 1982? Possibly. And why did Ford out source its diesel engine instead of developing its own? Maybe to avoid the pitfalls GM encountered as a result of the catastrophic failure of the Oldsmobile 350 engine that was converted to diesel in the late ‘70’s. Many believe this was the engine (Olds 350) , or a derivative thereof, that GM put in its light duty trucks. Actually, the 6.2 liter diesel was a new product of GM’s own Detroit Diesel Allison Division. But that’s a whole ‘nother story.
There is some debate that the 6.9 was a dieselized version of International’s 446 cid gasoline engine that was widely used in the 1970’s. The 6.9 did mimic the appearance and manufacturing technology of the 446, but was a whole new design. It implemented improvements such as oil squirters to cool the pistons, hardened nodular iron crankshaft, four bolt main crank caps, and roller lifters to name a few. The new 6.9 had 30% more power than GM’s 6.2 diesel. Demand for it grew to the point that by 1985, Navistar’s Indianapolis manufacturing facility, where it was produced, was at capacity and looking to expand.
Specifications for the 6.9 are as follows:
Editors note: Horsepower ratings advertised on the valve covers varied from as little as 155hp, to 175 depending on pump calibration.
Max HP 175 @ 3300 RPM
Max torque 318 ft/lb @ 1800 RPM
Cylinder bore 4.00”
Displacement 6.9 liters or 420 cubic inches
Comp ratio 21.5:1
Top deck thickness .500”
Oil drain back holes 3/8”
Cylinder head bolts 7/16” -14UNC 5.25” long
Head bolt washers .105” thick
Head bolt torque 75ft/lbs new
Head gasket fire ring ID 4.14”
Glow plugs centered in pre-cup
Pre-combustion chamber volume 18.34 cubic cm
Injector Pump Stanadyne DB2 High altitude 1807568C91
Low altitude 1807560C91
*The oil cooler design was improved during the 1985 model year to change the number of sealing O rings from 6 to 4. The early ones had 2 large and 4 small O rings which they changed to 4 large ones.
* Head gaskets also went though several changes to improve oil and coolant sealing.
Unlike GM, Ford chose to only offer the diesel engine option in trucks with a gross vehicle weight (GFW) rating of 8600 pounds or greater. The standard F-250 with its lighter chassis and semi-float rear axle, and 6600 pound GVW wasn’t thought to be strong enough. This meant that only the F-250 HD and F-350 got the diesel engine option. Even though the F-250 was not identified as an HD, the higher GVW package came with full-floater Dana 61 rear axles (Dana 70's in many cases. Ed.). In February of 1985, the switch was made to the Sterling 10.25 inch ring gear rear axle. Higher capacity F-350’s came with the Dana 70 rear axle and late in 1985 the F-350 4X4 dually option was added to the lineup.
Prior to 1985, all F-250 HD and F-350 4X4’s came with the Twin Traction Beam (TTB) front axle. The F-250’s had reverse cut Dana 44’s up until 1987 with the Dana 50 optional. Most F-250 SuperCabs came with the D50 due to the added weight. The D50 became standard in 1987. During this same timeframe, the F-350 came standard with the D50 TTB up until 1985. In February of that year, the Dana 60 solid axle became standard front fare on all F-350 models and remained the standard for years to come.
Axle ratios were limited to 3.54: and 4.10:1 and transmission options were the Borg Warner T-19 four speed and Ford’s own corporate C-6 automatic. It’s interesting to note that the 4.10:1 equipped trucks had a 14,000 pound gross combined vehicle weight (GCVW) while the 3.54:1 equipped trucks were limited to 13,000 pounds for the manual; and 12,000 pounds for the automatic. All 4X4 models came with the Borg Warner 1345 transfer case.
1987 was a transition year for Ford diesel trucks. They went through a complete styling change which resulted in the eighth generation of F series trucks. New aerodynamic front sheet metal that included flush headlights and wrap around turn signals were part of the new design. They also came with a completely new interior. They were roomier with a new dash design incorporating easier to read gauges and a larger glove box. Trim levels and colors, both interior and exterior, remained virtually unchanged with the base models receiving vinyl as standard and all others getting cloth in variations on the grey, red, blue, and tan previously offered. The very rare green color interior from the former generation was dropped as an option. The only major chassis upgrade for the new model was the addition of rear anti-lock brakes (RABS) as standard equipment. Ford was the first truck to provide this feature. Interestingly enough, missing from the new makeover were any changes to the diesel powertrain lineup. Several years earlier, Caterpillar had put out a press release stating they were developing a new diesel engine to replace the 6.9 when Navistar’s contract with Ford was up. This would not come to fruition as 1988 would see Navistar still providing Ford with diesel engines, although they would be an upgraded version.
And so the reign of the 6.9 liter IDI comes to an end with the 1987 model year. Exact production numbers could not be provided by either Navistar or Ford. However, Navistar reports that it sold more than 300,000 6.9’s to Ford Motor Company.
Enter 1988 and the completion of a totally new truck with the introduction of Navistar’s new 7.3 liter IDI diesel engine. Although not revolutionary, there are many improvements that accompanied the introduction of the new engine.
The 7.3 now used select fit pistons at the manufacturer. The pistons were stamped with A, B, C, and D and had to coincide with the letter stamped at the base of the cylinder bore. Replacement pistons were stamped with an S. New plateau honing procedures accompanied the select fit pistons for better ring seating and engine break-in. Also the lower rear corner coolant passages at the head mating surface were blocked to coincide with plugged coolant passages on the heads. This was an effort to reduce coolant seepage during cold start and warm-up.
Most of the changes were made to the heads, making them not interchangeable between the 6.9 and 7.3. The precombustion chamber volume was increased to 20.42 cubic cm for emissions certification. Even though the pre-cup chamber inserts are physically interchangeable, the throat was re-designed and an “88” stamped on the 7.3’s to distinguish them. The glow plugs were now off-center and the injection nozzles retracted .060” for emissions. The injector lines were also now .060” shorter to coincide with the injector retraction. However, this is negligible and the injector lines are still interchangeable between the two engines. The new 7.3 valve stem shields are larger to reduce emissions and both intake and exhaust shields are now color coded, though they are interchangeable. Also the 7.3 exhaust valve metallurgy has been changed, increasing the nickel, chrome, and silver content while reducing the manganese content. This makes the 7.3 valves usable in a 6.9, but not the other way around. The gasket cutouts between cylinders were eliminated to prevent cosmetic corrosion and improved viton oil drain back seals were added to the gaskets. The 7.3 also used a new embossed front cover to aid in gasket sealing and eliminate water pump replacement due to seepage.
Specifications for the 7.3 are as follows.
Max HP 185 @ 3300 RPM
Max torque 338 ft/lb @ 1800 RPM
Cylinder bore 4.11”
Displacement 7.3 liters or 444 cubic inches
Comp ratio 21.5:1
Top deck thickness .560”
Oil drain back holes 7/16”
Cylinder head bolts ˝” -13 UNC 6” long
Head bolt washers .134” thick
Head bolt torque 100ft/lbs new or used
Head gasket fire ring ID 4.22”
Glow plugs off center in pre-cup
Pre-combustion chamber volume 20.42 cubic cm
Injector Pump Stanadyne DB2 High altitude 1809045C91
Low altitude 1809121C91
Notice the stroke is unchanged, only bore was increased. The increase in bore diameter resulted in thinner walled cylinder liners. This would prove in years to come that the 7.3 would become susceptible to cavitation if proper preventative maintenance practices were not followed. A definition of cavitation and the associated preventative measures can be researched elsewhere on the internet since it is too lengthy a topic to delve into here.
1988 also brought about the introduction of the ZF 5 speed manual transmission. This new transmission with an overdrive 5th gear was a welcome improvement, significantly reducing engine RPM at highway speeds. A new automatic transmission would not be realized until the 1989 model year.
Two significant events happened in 1989 which affected Ford diesel trucks. The entrance by the last of the “Big Three” into the light truck diesel market by Dodge and its Cummins engine option had some negative effect on Ford truck sales. However, Dodge trucks had been plagued for years with quality issues, either true or perceived. Even with the addition of the Cummins 5.9 liter 6BT diesel engine to the Dodge lineup, they were still only able to capture approximately 1/3 of Ford’s hold on the diesel market. GM wasn’t much of a player at this point. Ford was still the leader in US truck sales.
The other significant change for that model year was the introduction of the E4OD electronic 4 speed automatic transmission. Like the addition of the 5 speed manual the year before, this new-to-diesels automatic was what automatic transmission customers wanted for highway travel. This was the first time a drivetrain “computer” would be associated with an IDI equipped Ford in it’s now 6 year history. The transmission proved to be somewhat temperamental and if not meticulously maintained was not always reliable.
The only other noteworthy change for the remainder of this generation of Ford diesel came in 1991 with the addition of automatic locking front hubs on 4X4 models. Manual locking hubs became optional equipment.
With the 1992 model year came the introduction of the 9th generation of the Ford F series. Although the cab and bed remained unchanged, the front sheet metal became even more aerodynamic with new wrap around headlights and corner markers, new grill, and hood. The interior was again a completely new redesign. Even though the cab was unchanged for ’92, the doors are not necessarily interchangeable between this and the previous generation. Due to the new dash design, the vent windows are different to prevent interference when opening. The doors can physically be interchanged; however, the vent windows may become inoperable. This new sheet metal, with the exception of the center-mounted third brake light in 1994, would prevail until the introduction of the Super Duty for the 1999 model year. Ford produced roughly 500,000 F series trucks in 1992 which rose steadily to nearly 800,000 trucks by 1996, indicating its rising popularity.
An interesting, or frustrating for some, observation is the omission of any visible forward badging indicating the diesel engine on all 1992 models, and on normally aspirated models for 1993 and ’94. The only indicator of the all important diesel engine was a very small, indescript “diesel” badge on the tailgate. This would be remedied in 1993 if the correct engine option were ordered, but more on that later.
For 1993, the Custom model was dropped from the lineup. The XL became the new base model. Now you had a choice between XL and XLT since the Lariat trim package was dropped after the 1991 model. Interior color choices remained red, blue, tan, and grey, although the shades changed every few years and no less than three different cloth material patterns were introduced over the next several years. This makes repair and restoration somewhat confusing. Two new interior options showed up for the 1994 model year: a CD player and the infamous 40/20/40 front seat. A driver’s side airbag was also introduced into the F150’s for this model year, but did not find its way into the HD models.
The biggest improvement and most sought after option for 1993 was the introduction of the first factory turbo option. This option was available for the two remaining years of IDI production and is significant for several reasons. From the very beginning of the 6.9 liter production, a turbocharger was considered, but the normally aspirated engine was already a $2000 option and the addition of the turbo would nearly double that figure. Many believed that the extra amount on the sticker in the mid ‘80’s would put it over the edge price wise. Luckily, companies such as Gale Banks Engineering, Advanced Turbo Systems (ATS), and Hypermax saw this as an opportunity. ATS was chosen as the turbo system provider for the new factory turbo option and Ford/Navistar implemented other engine upgrades to compliment the addition of the turbo. Trucks equipped with this engine option can be identified by the small “Turbo Diesel” emblem under the F250/350 front fender badges.
The additional engine changes are as follows:
Cylinder head gasket heavier ring and armor wrap
Increased wrist pin bore on connecting rods
Larger wrist pin
Anodized piston head
Keystone design top and intermediate piston rings
Increased number of oil passages in oil cooler (30 fin/inch vs. 24 on NA)
Turbo specific flywheel
Turbo specific vibration dampener
Turbo injector pump
Modified injector fuel return line routing
Modified E4OD dipstick
Modified E4OD turbo micro processor
Turbo specific cooling fan clutch
Lower restriction exhaust
Additionally, the truck received a slotted front bumper and an air dam below the radiator. These improvements conservatively raised the power output to 185hp and 360ft/lbs of torque. These numbers are believed to be under-inflated so as not to downplay the mid year introduction of the new diesel engine.
An important point to note is that while the production of the 6.9 liter IDI stopped in 1987, development of replacement parts did not. As improved parts such as new rocker arms and head gasket designs were proven on the 7.3, they were adapted to the 6.9 where applicable.
Exact production numbers for the 7.3 liter IDI could not be found, but the previous 11 years of IDI production paved the way for the introduction of Navistar’s DT444E in mid-year 1994. Dubbed the Powerstroke by Ford Motor Company, this combination did more to put diesel powered trucks in the hands of the general public than any other truck to date. Demand increased so much that the 1 millionth 7.3 liter Powerstroke built was installed in Gary and Monika Wescott’s 1999 “Turtle V” F-550. A demand that saw 540 Powerstrokes being produced per day at the Navistar Indianapolis plant.
We can indirectly thank the venerable IDI for the popularity of diesel powered pick up trucks today.