Video: Alliant Power 6.4L Power Stroke Diagnostic Guide

Every time you turn the key in the ignition, one thing should happen – the engine should fire up. When you’re driving your 6.4-liter Power Stroke, you depend on that engine to do its job and get you where you need to go. Without that assurance, you’re basically an owner of a four-ton bummer. Hearing the engine run rough or have a hard start means something is wrong, but thankfully, the experts at Alliant Power have some tips on what to do.

Alliant Power’s Matt Heacox walks us through the procedure done on a 2008 Ford F-250 with the 6.4-liter Power Stroke. It starts with a proper test drive of the vehicle, where he listens for problems and gets on the throttle to test responsiveness. He confirms that the engine is not operating properly. He then begins the diagnostic process by opening the hood and looking for anything that appears out of order.

Matt does inspections in the engine bay to start off.

In rapid order, Matt goes through several areas that require closer inspection. He checks the engine bay for plumbing leaks and electrical fraying. He then checks the fluid levels, observing the levels of oil, coolant, and transmission fluid. On the oil level, he wipes and re-tests the dipstick, but leaves out an inch of slack, which will test to see if the oil is overfilled; if it was, it would likely indicate fuel seeping into the crankcase. Thankfully, that’s not the case here.

Matt checks for leaks in the intake and exhaust, then checks to see if clean fuel is reaching the engine.

Underneath the truck, Matt checks for leaks in the exhaust system (as well as any general leaks) and finds none. He returns to the engine bay and reviews the intake and its air restriction gauge, finding everything in order. Inside the cabin, he turns the key to see if the fuel level has changed, or if the water or fuel light have illuminated. All good there, so it’s back to the engine bay to see if the secondary fuel filter shows any signs of contamination. It too gets a clean pass.

The next part to look at is the fuel system, specifically the fuel supply pump. Matt checks for leaks in the lines, and then uses a specialized gauge to determine if the fuel supply pressure is at the proper level. He then checks for fuel supply inlet restriction at the HFCM, making sure it reads between 0-6 inches of mercury. Afterwards, Matt uses an OBD-II scanner to look for DTCs, and runs key-on-engine-off tests before turning the engine on with a data logger connected. The data logger reads out performance of the cylinders to assist in the diagnostic process.

Matt continues the process. His evaluations run deeper than visual inspections now, involving the OBD-II port and key-on-engine-off or key-on-engine-running tests.

Now at Step 9, Matt performs key-on-engine-running and glow plug tests. He notes that a cylinder misfire may or may not throw a code. Moving along, he verifies to see if the PCM is calibrated. Satisfied that it is, he moves to the power balance test, which identifies that Cylinder 3 is firing slowly. Whether it’s the piston, a valve, or the injector’s fault, only a compression test will reveal, which it does – it’s a faulty injector causing all the trouble.

On Step 11, a power balance test reveals the #3 cylinder is running more slowly than the other cylinders. That narrows down where the problem must be. After a relative compression test shows all cylinders are equal, Matt can make an educated guess – the injector must be the issue.

“There’s no one thing that can cause hard starting,” said Alliant Power’s Bert Bonilla. “Bad sensors, shorted sensors, battery voltage, until you actually get into it, you won’t know. With all of these electronics, the cause could be anything, so narrowing it down through a process like this is essential.”

Matt points out the dirty inlet connection on the faulty injector, which might explain why it started failing. He replaces the injector with a new, remanufactured injector sold by Alliant Power.

Confident that he’s narrowed down all of the possibilities, Matt begins deconstructing the engine bay to get to the injectors. It involves removing the air filter, crankcase filter, glow plug control module, injector harness, and valve cover. With the injectors visible, Matt locates the #3 injector and removes it. He inspects the injector visually and sees possible contamination in the inlet connection.

Replacing the injector is quite simple, and is done using PN AP64900, a remanufactured 6.4-liter Power Stroke injector offered by Alliant Power. It installs into the injector hole and clips back into the electrical connector. Then, the parts go back in reverse order – valve cover, injector harness, glow plug control module, crankcase filter, and finally, the air filter.

At the conclusion, Matt points out the good sense in changing the filters for the fuel and engine oil. The reason is that the faulty injector would have shortened the lifespan of these filters, so they may be on their way out faster than expected. He returns to the cabin and starts the engine, noting that longer-than-normal cranking, as well as residual rough running of the engine for up to 40 miles, is actually normal here because air enters the fuel system when replacing an injector and is only displaced by running the engine.

Back from the road test, Matt runs another on-demand and power balance test. He boxes up the faulty injector, just like any customer would to make good on the core credit.

This concludes the Alliant Power diagnostic guide, showcasing all of the steps necessary to do it right. The truck is back up and running happily, and with the right tools, it’s something you can do too. Find out more on truck care and Alliant Power’s parts catalog by visiting the company’s website.

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About the author

David Chick

David Chick comes to us ready for adventure. With passions that span clean and fast Corvettes all the way to down and dirty off-road vehicles (just ask him about his dream Jurassic Park Explorer), David's eclectic tastes lend well to his multiple automotive writing passions.
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