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FORD DIESEL SHORTCOMINGS, FROM ’94.5 TO PRESENT

It’s true that all engines have their unique sets of issues. Every powerplant that’s ever been produced ends up with problem areas that are exclusive to that specific design. Still, other failures aren’t engine-specific (e.g., emissions components) and exist across the entire spectrum, regardless of brand. Add in a little wear, tear, and age and you start to see not only an ever-expanding list of part failures, but failures that were rare just five years ago now becoming commonplace.

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CAMSHAFT POSITION SENSOR If the venerable 7.3L Power Stroke had one Achilles heel, it’s this vital little sensor: the camshaft position sensor (PN F7TZ-12K073-B). Failure of the camshaft position sensor will lead to a nostart condition without warning, and it’s typically diagnosed when the engine cranks but the tachometer needle doesn’t move. Thanks to updated versions of the sensor being released over the years, failures are much less frequent than they used to be. Still, most 7.3L owners keep a spare in the glovebox or toolbox for good measure.

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BURNT UVCH HARNESSES A poor connection at the under-valve cover harness (UVCH) plugs can lead to overheating and melting of the plastic. It’s typical for the connector to burn up around the outer edges, as is the case on the ’94.5-97 UVCH connector shown here. Eventually, the engine would be down a cylinder, and down two cylinders if the opposite edge was in the same kind of shape.

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LEAKING UP-PIPES Blown up-pipes are very common on the 7.3L Power Stroke. From the factory, crush donut gaskets (one per side) are used to seal each up-pipe to the exhaust collector (the cast Y assembly that attaches to the turbo). Throughout their service life, the up-pipes expand and contract thousands of times, and the gaskets eventually begin to leak. The impending result of the exhaust leak is a loss in performance, decreased fuel economy, elevated EGT, and soot coating the rear of the engine, firewall, and transmission.

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AGED WIRING After enduring between 15 to 23 years’ worth of vibration (depending on which 7.3L model year you’re looking at), facing a wiring gremlin or two is always a possibility. Once the wire loom, tape, and/or insulation is eroded enough and an exposed wire makes contact with anything metallic, you’ll be facing a ground-out issue. Depending on which wire is affected, the truck will throw and store various codes or see a (sometimes intermittent) miss with the engine running.

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DEAD GLOW PLUGS Out of all Power Stroke engines produced, glow plug problems were most rampant on the 7.3L. Anytime after 80,000 miles failure is possible, although it’s not unheard of to get 150,000 miles out of them. In our experience, the glow plug relay will bite the dust before any glow plug will. Running a periodic ohms test is the easiest way to give the glow plugs a quick checkup.

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PCM FAILURES As the 7.3L continues to age, powertrain control module (PCM) failure is becoming more and more prevalent. When the internal circuits within the PCM burn up, there is no going back or an easy, quickfix repair. We’ll note that a bad ground or a short somewhere in the engine’s wiring harness is often misdiagnosed as PCM failure. As a general rule of thumb, if all fuses check out OK (especially the PCM relay) and a sufficient scan tool is unable to communicate with the PCM, it is likely fried.

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PLUGGED OIL COOLER Of the myriad problems that plagued the 6.0L Power Stroke, the oil cooler sits at the top of the list. Casting sand from the block, solid deposits left behind from running a non-compatible coolant, or a combination of the ladder becomes lodged in the ultra-tight coolant passageways within the stackedplate heat exchanger. As coolant is no longer able to flow freely through the oil cooler the oil becomes superheated. In addition to the harm caused by sending 250+ degree oil through the injectors, highpressure oil pump, turbocharger, and rotating assembly, the oil cooler is also responsible for 90 percent of all EGR cooler failures (more on this in the “Failed EGR Coolers” section).

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FAILED EGR COOLERS Most industry experts would agree that the biggest headache with the 6.0L engine lies in its exhaust gas recirculation system: specifically, the EGR cooler. While the circular tube EGR cooler used on ’03 engines proved more reliable (right), eventually all of them will plug up from soot, carbon, and oil vapor deposits. However, nine times out of ten a plugged oil cooler— which is no longer supplying coolant to the EGR cooler to drop the exhaust gas temperature passing through it—will cause the assembly to rupture (oftentimes along the welds). When this happens, coolant can flow into the intake and/ or exhaust, potentially leading to a blown head gasket.

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DAMAGED INLET STRAINER Finding a torn screen on the factory high-pressure oil pump inlet strainer that sits below the oil cooler is typical. Its fine mesh screen isn’t robust enough to handle larger debris being forced through it via pressure. If debris makes it past this point, its next stop is the high-pressure oil pump, followed by the injection pressure regulator (IPR). As you can imagine, repairs can rack up in a hurry once this screen fails to do its job.

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STUCK EGR VALVE In as few as 20,000 miles, a 6.0L’s EGR valve can be in this condition. EGR valve issues are most common on engines that see a lot of idle time or those that are rarely driven hard. Once the carbon and soot buildup reaches critical mass, the valve will either stick at or near the closed position (P0401 CEL), or remain in the near open position (prompting a P0402). Unbeknownst to a lot of 6.0L owners, Ford recommends the EGR valve be cleaned on a regular basis as part of a routine maintenance regimen.

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STRETCHED HEAD BOLTS Along with what many consider to be a lack of head-to-block fasteners (four head bolts per cylinder vs. six on comparable engines), the 6.0L Power Stroke’s employment of torque-to-yield head bolts allow them to stretch under extreme cylinder pressure. The result is what the 6.0L is most notorious for: blown head gaskets. When the inevitable blown head gasket scenario unfolds, more than 90 percent of all 6.0L owners opt for Automotive Racing Product (ARP) head studs when everything goes back together (PN 250-4202). Throughout the last decade, and because nearly 2 million 6.0L Power Strokes were produced, head studs for the 6.0L Power Stroke have been one of ARP’s bestselling products.

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BLOWN HEAD GASKETS Here you can see what happens when a head lifts and compression is allowed to slip past the head gasket. Once this occurred, the engine’s cooling system was pressurized, culminating in coolant purging at the degas bottle cap. This particular truck’s cylinder heads received a resurface, new Ford head gaskets, and the aforementioned ARP head studs when it went back together.

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UNRELIABLE HPOPS Whether it ingests something the oil cooler sends its way or comes apart on its own, the highpressure oil pumps in all model year 6.0L Power Strokes seem to fail prematurely. According to DieselSite, even the housings on the early pumps (right) were questionable, reason enough for the company to produce its own billet housing, high-volume version for ’03 to ’04.5 engines. When the factory pumps give up the ghost, there is often no warning.

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RAMPANT INJECTOR FAILURE Injector issues are extremely widespread on the 6.0L engine, with lack of maintenance, contaminated oil, and lack of fuel pressure contributing to most failures. A key mechanical weak point in the injectors rests in the spool valve (what allows high-pressure oil into the injector), which can become scored by debris present in contaminated oil and lead to a sticking spool valve. We would advise to always observe a 5,000-mile oil change interval, and make sure you are seeing at least 45 psi or more fuel supply pressure as measured at the fuel pressure regulator (and look into the “blue spring” upgrade if you’re not seeing adequate pressure and the lift pump checks out, PN 3C3Z-9T517-AG). Improperly torqued injector hold-downs and damaged O-rings are other common causes of injector issues.

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STC FITTING The most common cause of a no-start situation with a warm engine on ’05-07 Super Duty trucks is this fitting. The snap-to-connect (STC) fitting links the high-pressure oil branch tubes to the high-pressure oil pump. As the branch tubes give and flex during normal engine operation, the two-piece fitting’s seal eventually wears out. This leads to a slight leak in high-pressure oil pressure, where warm (thinner) oil makes it past the seal and cold oil (higher viscosity) doesn’t— hence the reason the truck starts when cold, but won’t re-fire once warm.

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STICTION When the aforementioned spool valve in the injectors is unable to open and close as precisely and effectively as it needs to (usually due to carbon buildup), injector stiction is occurring. Symptoms of stiction include hard starts, excessive smoke at low oil temperature, and rough idle until warm. Oil additives such as Hot Shot’s Secret, Rev-X, and Archoil AR9100 have been known to clean up (and even re-coat) the spool valve, as well as other internal areas within the injector, and bring it back into sound working order. However, while these products have been known to cure stiction issues, they aren’t a permanent solution if excessive damage has already been done to the spool valve bore.

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STUCK VGT 6.0L trucks that idle a lot or aren’t driven (and driven hard) on a regular basis are prone to falling victim to “sticking” turbo issues. Within the exhaust side of the 6.0L’s variable geometry turbocharger exists moveable vanes which are mechanically activated via a unison ring. Steady state driving or sitting allows rust and carbon buildup to bind or seize the unison ring in place, making it so the vanes can’t vary exhaust flow. If the vanes remain in the near-closed position, low-rpm response will be good but top end will be non-existent. If the vanes stick in the near-open position, low-rpm response will be lethargic and the truck will really only be drivable at higher engine speeds. A typical R&R of the VGT turbo takes about three hours at a reputable independent shop.

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FICM FAILURE This one’s a bit tricky. As the batteries become weaker and weaker on a 6.0L Power Stroke, the fuel injection control module (FICM) slowly dies. As it sees less and less voltage supplied by the batteries, the internal drivers within the FICM are being damaged. And, because the FICM is in charge of sending a precise 48-volt signal to the injector solenoids (telling them when to fire), the result is decreased performance, fuel economy, and drivability. A FICM in its death throes will be extremely noticeable in the form of a truck that will barely start, produces excessive smoke, idles rough and stumbles until warm. A voltage reading of 45 to 48 volts during key-on, cranking over, and idling the engine is within spec according to Ford. Below that and it’s worth looking into a new “driver” side FICM half shell or an aftermarket unit.

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HIGH PRESSURE OIL LEAKS High-pressure oil leaks run amok in the 6.0L Power Stroke, all of which can result in a nostart situation on a warm engine. The standpipes shown allow high-pressure oil to pass from the high-pressure oil pump, through the branch tubes, to the oil rails. The O-rings on the unit pictured on the right (the ’04.5-07 version) are known to fail. Surging injection control pressure (ICP), hard starts, and a general lack of performance are typical symptoms of one of these O-rings checking out.

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DIESEL PARTICULATE FILTER A whole host of the 6.4L Power Stroke’s biggest problems stem from its emissions control systems. At the top of the list is the diesel particulate filter (DPF). The DPF’s job is to capture soot (particulate matter) produced by the engine and store it until it can be burned off during an “active regeneration” process. As you can imagine, this device is guaranteed to fill up and fail at some point, and it carries a hefty replacement cost. Being the first diesel engine in the pickup segment that Navistar and Ford had to equip with a diesel particulate filter system didn’t come without growing pains, either. Many 6.4L owners reported DPFs that leaked straight from the factory.

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CRACKED UP-PIPES The 6.4L is somewhat similar to the 7.3L in that leaking up-pipes are fairly common. However, the 6.4L’s up-pipes don’t feature crush donuts; they instead crack at the bellows (i.e., expansion joints). A lack of “give” in the OEM pipes combined with the engine rocking back and forth proves to be the primary culprit behind this failure, and it’s not uncommon for a leaking up-pipe to occur inside of 100,000 miles. When an up-pipe cracks, it’s usually followed by a hissing exhaust note, a loss of power, and a transmission and firewall coated in soot.

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RADIATOR LEAKS Leaking radiators plagued the entire production run of the 6.4L Power Stroke. The factory units are notorious for separating at the seams, specifically where the aluminum core mates with the plastic end tanks, which is prone to springing a coolant leak. Although it’s rumored that the updated version of the 6.4L radiator is more durable, the jury is still out on how long they last.

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OIL DILUTION Revisiting the emissions system-related failures brings us to the 6.4L’s ability to make oil. During the engine’s active regeneration cycle, additional fuel is introduced on the exhaust stroke and is then used to incinerate the accumulated soot in the diesel particulate filter. Along with hurting fuel economy, active regeneration also washes the cylinder down with fuel, some of which inevitably makes it into the crankcase. It’s not uncommon for the 6.4L to gain a gallon of oil (diesel fuel-diluted oil) between oil change intervals.

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HPFP WIRING ISSUE A poor performance or no-start situation that triggers a P0003, P0004, or P0091 code on an early 6.4L Power Stroke (built before August 20, 2007) often means the volume control circuit for the Siemens K16 VDO high-pressure fuel pump is grounding out. Due to the inherent vibrations of the engine, the wires within the high-pressure fuel pump’s cover gasket make contact with the block. Eventually, a hole will be worn through the insulation and the bare wire is exposed. While the fix itself is fairly simple (PN 8C3Z-9G805-A), the high-pressure fuel pump is enclosed at the rear of the engine, under the turbochargers. It’s a labor-intensive fix that prompts many shops to pull the cab.

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CRACKED BLOCK This one is really only observed in the aftermarket, where enthusiasts add head studs to the engine. Unfortunately, iron material is pretty thin around the head fastener bores in the center, top of the 6.4L block (shown). Over-tightening the head studs that reside in these bores is the best educated guess as to the cause of cracked block scenarios. Stopping in the 190 ft-lb spec range (vs. 200+) has helped quell the cracked block epidemic in recent years, but it’s always a risk you take when playing with one of these engines.

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RUST IN THE FUEL SYSTEM The combination of a poor water separator design and a lack of maintenance can spell disaster in a hurry for the 6.4L Power Stroke’s high-pressure common-rail fuel system. Once fuel coagulation occurs in the collection bowl, water is allowed to pass through it and make its way into the fuel system. When water is present in the fuel system it reacts with the metal to form rust. The rust can eventually take out the high-pressure fuel pump, which in turn can send shrapnel through the injectors, which return contaminated fuel back to the fuel tank, effectively trashing the entire fuel system (a cost of $6,000 to $7,500). In cases where debris causes an injector to stick open, catastrophic engine failure is often the result. In these all-out engine failures, it’s not unheard of for the repair bill to top $15,000 or more, which forces many owners to simply walk away from the truck.

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BLOWN TURBOCHARGERS While the 6.7L Power Stroke has been remarkably reliable to date, ’11-14 engines were equipped with the Garrett GT32 SST turbocharger that was known for its overspeeding issues. With dual 46mm compressor wheels and a 64mm turbine, the GT32 helped the 6.7L engine produce massive torque right off idle, but it was dangerously restrictive up top. It didn’t matter that these chargers were wastegated either, as they could easily be spun too fast with nothing more than a programmer in the mix. A popular upgrade these days is to fit an ’11-14 engine with the GT37-based turbo found on ’15 to present powerplants.

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FAILED EGT SENSORS Exhaust gas temperature (EGT) sensor failure is extremely common on the 6.7L Power Stroke—and four of them exist in the factory exhaust system. When an EGT sensor quits working, the PCM thinks the DPF is seeing too much heat, a P2033 code is thrown, and the engine shuts down (or at the very least, only allows the engine to idle). EGT sensor failure is so frequent that at one point in 2014 there was a nationwide backorder on them. Depending on how often they see elevated temperature, some EGT sensors fail inside of 10,000 miles. Our advice would be to keep a spare EGT sensor in the glove box just in case (PN AC3Z-5J213-B).

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LEAKING RADIATORS Like the 6.4L Power Stroke, radiator leak issues are prevalent on the 6.7L as well, although it seems to be to a lesser degree. However, both the 6.7L’s primary and secondary radiators are known to spring leaks (remember, the 6.7L requires a traditional cooling system for the engine as well as a second cooling circuit for the water-to-air intercooler, EGR system, and transmission). It’s become enough of a problem that Mishimoto took the initiative to produce aluminum versions of both radiators for ’11-16 Ford owners (Mishimoto’s primary radiators are shown).

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THE SAME OLD SONG We’ve seen EGR cooler and valve failures on low-mile trucks (primarily on early engine models) that see extended idle time, but the average lifespan seems to be 70,000 to 90,000 miles before it’s time for EGR cooler replacement. As with any EGR-equipped diesel engine, it’s in the very nature of these components to eventually fail, given the environment they’re forced to live and operate in.

Be they mechanical, electronic, or emissions-related, no engine is without its weak points. This is why we’ve composed a comprehensive list of the key problems associated with the best-selling diesel engine in the truck segment: Power Stroke. From the 7.3L’s relatively minor quirks to the 6.0L’s extensive rap sheet, and the 6.4L’s mild-to-catastrophic setbacks to the trials and tribulations facing the current 6.7L, we’ve got you covered. On ’94.5 to present Blue Ovals, the following issues will be the most common foes you’ll face with your truck. DW