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Ford 6.9L and 7.3L IDI Diesel Engines

Cheap Diesel Fun

Text By Jason Thompson, Photography by Jason Thompson

For more than a decade, the Ford F-250 and F-350 trucks came with an International indirect-injection V-8 diesel engine. By studying and driving these fossil-like engines of the past, owners can get a better understanding of the engines we have today. While we are learning, we can also benefit from owning a reliable and simple truck. These budget diesels are great for a teenager’s first vehicle, occasional tow rig, or farm truck. The 6.9L (’83 to ’87) and 7.3L (’88 to ’92) engines International (Navistar) built can be considered true old-school diesels. This means they are mechanically injected so they don’t require any complicated, expensive, or failure-prone electronics. They also never came with problematic emissions equipment such as EGR, DPF, or SCR technologies. Don’t know what regeneration means? That’s OK, this engine was built way before anyone else knew what it meant, either. Another benefit is you’ll never have to pay thousands of dollars for fuel injectors. Instead, if they wear out, you can get a complete set from DPS for $288. Many are drawn to this engine because it’s able to run 100 percent biodiesel. Although it’s cheap and easy, it’s not very sophisticated. The exhaust has a distinct smell, which will create cold stares from strangers and possible rejection of business (if you’re using the truck for work in an H.O.A. neighborhood). For better or worse, here is everything you need to know about Ford IDI diesels.

A. Return lines: If everyone replaced their return lines at the first hint of a problem (or as Mike “Maintenance” McGlothlin says, “Get it before the problem starts.”), 95 percent of peoples’ aggravations would be solved. A great aftermarket solution for rubber lines with multiple failure points would be a steel bolt-on kit like the 5.9L Cummins. Installing an electric fuel pump is also highly recommended.

B. Injection pump: The injection pump is the heart of old-school diesels. This compact unit is kind of like the distributor on a spark-ignition engine, but instead of sending a spark to the cylinder, it sends a metered charge of pressurized fuel at the right time. The pump itself is geardriven and has a pin so it can only be bolted to the engine one way. When the pump is out of the engine, the gear stays in its correct place and will not move since it does not have enough room to jump a gear in the housing. The static timing marks will get the engine running, but it’ll need to be timed to function. We got this injection pump from Diesel Performance Specialists (DPS); it retails for $450. Not bad if you consider this single pump does the job of all the parts in an HEUI or common-rail injection system, including the computer and sensors.

C. Glow Plugs: The glow plugs should be replaced as a set while you’re replacing the fuel return lines. If you hear a clicking sound at startup, that’s the glow plugs not warming up. Initial startup time will increase and put wear on the engine. Unplug the wiring harness while checking it for cracks. Then use a test light and put it to the tip of the plug while it’s still in the engine. The ones that don’t light up are the ones that are bad.

D. Later is Better: If you have a choice, select the newest-model Ford IDI you can find, with the ’93 to ’94 years being best. You’ll get a better glow plug controller (D), serpentine belt system, and the turbo engine comes with stronger connecting rods. The 7.3L is desired more than the 6.9L because it has larger, ½-inch head bolts instead of 7⁄16-inch versions. Although, the 6.9L has thicker cylinder walls, so maybe a hybrid is in order?

To set the timing, clean the damper and the magnetic pickup holder. Then install the magnetic pickup line connected to the SPX Kent-Moore J33300-A timing machine. This measures the engine’s rpm. We used the top skinny holder next to the damper. Then sand the number 4 injection line to bare metal and install the clamp. The cylinder numbers are marked on the intake manifold runners. The odd-numbered cylinders are on the left, the even ones are on the right. The low-number cylinders are toward the front. The wire has a ground and connects the machine to the clamp. This registers when the injection pump fires. Put the transmission in Park and rev the engine up to 2,000 rpm. An initial run will usually come up retarded, and it’ll sound like a big-block gas engine. If so, advance the engine by turning the pump counterclockwise (looking at it from the front bumper or turning the wrench toward the passenger fender). Do the timing change without the engine running and then test again. The reading should say 9.6 degree before top dead center (BTDC). The electrical connection closest to the firewall on the Stanadyne DB2 pump controls the timing advance and needs to be unplugged when timing the engine. The electrical connection closest to the radiator is the fuel shutoff. The firing order is written on the valve cover: 1,2,7,3,4,5,6, and 8.

By Jason Thompson
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