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Your Diesel Questions Asked and Answered

You’ve Got Questions, We’ve Got Answers

Bruce W. Smith
Dec 18, 2018

7.3L Misfire

QUESTION: I love my ’01 Ford F-350 and have stayed on top of maintaining it since day one, including changing the oil every 3,500 miles. It currently has more than 256,000 miles on the odometer. The engine has a misfire (after it reaches operating temperature) and is hard to restart. I’ve also noticed a loss of power if I try to give more than half-throttle. A local diesel technician I spoke with says such symptoms typically point to a bad “Huey” pump, since I had the injectors replaced around 205,000 miles. Is he correct?
Name withheld
via the Internet
Photo 2/6   |   The HEUI pump delivers oil through the injection pressure regulator that controls the high-pressure oil pump’s outlet pressure to the injectors, which is between 500 psi and 3,000 psi, depending on throttle and load demand. If the multitude of O-rings inside the pump start failing, then it can’t supply the needed pressure to fire the injectors properly under load—especially when the oil is hot. The result is loss of power or misfiring when the engine is at operating temperature.
ANSWER: From the symptoms you share, in all likelihood, yes. Mat Johnson, a diesel technician at Mobile Diesel Service in Oakland, Oregon, says replacing the HEUI (hydraulically activated electronically-controlled unit injector) pump, also known as the HPOP (high-pressure oil pump), is common for high-mileage 7.3L Power Stroke engines. It’s also used by the Navistar T444E and DT466E, which are variants of the Power Stroke found in medium-duty International trucks of that era. The HEUI diesel injection system was developed as a collaborative effort between Caterpillar and Navistar in the early 1990s and debuted in the 7.3L Power Stroke engines in the ’94½ Ford F-350. The pump delivers oil through the injection-pressure regulator that controls the HPOP’s outlet pressure to the injectors, which is between 500 psi and 3,000 psi, depending on throttle and load demand. If the O-rings inside the pump start failing, then it can’t supply the needed pressure to fire the injectors properly under load—especially when the oil is hot. A bad HEUI pump will also cause hard starting issues when the engine (oil) is warm. A diesel shop will test the HEUI pump pressures as well as check the injectors to make sure fuel isn’t leaking past the external O-rings. If the HPOP is bad, rebuilt OEM-specific versions cost between $400 and $600.

Metal in Fuel System

Question: I received some bad news from a technician at the shop where my ’04 GM pickup is being serviced. There is metal in the fuel system from a CP3 injection pump going bad. The technician says the repair is going to cost between $6,000 and $7,000. Is this something I can fix on my own? I have only had the truck for a couple of years. The shop replaced the rusted fuel tank and the injectors when I bought it.
Ben K
via email
ANSWER: Did the technicians diagnosing your truck scan for diagnostic trouble codes? Did you see them pull the fuel filter? Is that where they found the metal bits? Does the truck have an aftermarket lift pump? We think you should be a bit suspicious of the diagnosis, because the CP3 doesn’t grenade and send metal through the fuel system like the CP4 on ’11-to-present Duramax engines does. A CP3 just stops supplying fuel pressure. Then there’s the concerning issue of the “rusty” fuel tank and need to replace it, which is odd because the stock fuel tank is plastic and can’t rust. Get a second opinion: Find another shop and have specialists do their own diagnostics before opening up your wallet for such a repair bill.

Wander Wonder

QUESTION: I replaced the wheel bearings, upper and lower ball joints, inner and outer tie rods, Pitman and idler arms, and had the alignment done on my ’10 GMC Sierra 2500HD in an attempt to fix its wandering and sloppy steering. It’s better, but the steering wheel still has play in it. There’s still some pull to the right, and it requires more input than I prefer in order to keep the truck on the straight and narrow. I was wondering if there is an adjustment mechanism to recalibrate the steering box? I didn't think the box would be the culprit, but it’s the only thing I didn’t touch. My truck has just a little more than 183,000 miles on it. It’s mildly lifted, running 35-inch tires.
Rusty Wilcox
via the Internet
Photo 3/6   |   A little wear here leads to a little movement there, and eventually, play in the steering system makes a big difference in how a truck tracks on the road. One of the major contributors to sloppy steering in older, high-mileage diesels is the steering box. Replacement with a high-quality gearbox will do wonders to cure wander.
ANSWER: We recommend reading “Setting Things Straight” (trucktrend.com) in which we detail curing several of those steering ills you are chasing with the installation of Cognito Motorsports upgrades. As you know, there are tremendous forces at work in the steering system, trying to keep everything up front on the straight path, especially on lifted rigs fitted with larger tires. A little wear here leads to movement there, and eventually, play in the steering system makes a big difference in how a truck tracks on the road. While you’ve addressed most of the potential wear points that contribute to issues, the one that is probably the biggest contributor to sloppy steering on older GM HDs is the steering box. It’s not adjustable—at least not in the area that wears: the ball bearings in the worm-and-piston assembly. One of the best gearbox replacements on the market is the one offered by RedHead. The company’s steering boxes are fitted with oversized bearings to account for wear, the housing is machined for needle bearings, and the sector shaft is trued on a lathe. This is a good upgrade for all high-mileage, sloppy-steering GM, Dodge/Ram, or Ford heavy-duty trucks.

Oil Life Monitor

QUESTION: I traded in a ’15 Ford F-150 for an ’18 F-250 with a 6.7L Power Stroke engine. I synched my iPhone X to the FordPass app to download the engine’s health report and see oil-life percentage and other details. My question is: How accurate is the oil-life percentage data associated with having the oil changed? The report shows 19 percent and there’s 8,100 miles on my truck. Most of those miles are from towing a 35-foot Coachmen that weighs around 10,000 pounds. The owner’s manual basically says to change the oil every 10,000 miles. So Ford didn’t subtract much for my towing.
Keith Black
via email
ANSWER: Ford claims the “intelligent” Oil Life Monitor takes into account conditions defined as “severe duty,” which include trailer towing, and as the owner’s manual states: “Change the engine oil and filter as indicated by the information display, and perform the services listed in the scheduled maintenance chart.” Ironically, the maintenance section also lists several types of “severe service” uses that require oil changes every 7,000 to 7,500 miles and using SAE 5W-40 API CJ-4. Our recommendation for any 6.7L Power Stroke is to change the oil/filter earlier than later, and not to rely on the oil-life percentage indicated on the engine’s health report. Ford’s intelligent Oil Life Monitor doesn’t physically sample the engine’s oil to determine how much it is broken down or contaminated, nor do any of the other vehicle manufacturers. All are calculations based on inputs from sensors that monitor throttle position, engine run time, EGR, oil and coolant temperatures, engine rpm, and so forth. A diesel’s longevity is predicated on two things: clean fuel and clean oil. We can’t stress that enough. If you want to rely on the cool app, set the Ford Pass Oil Minder to trigger at 7,500 miles—or when there’s 25 percent “oil life” as you currently have it set up. Some Ford insiders we talked with about this suggest changing fluids and filters in the engine (and transmission) twice as often as is stated in the owner’s manual. To really know the “life” of an engine’s oil, start an oil analysis program by sending an oil sample to an independent test laboratory at every other oil change, so analysts can determine if the oil-change frequency needs to be reduced or extended based on how the truck is used.

4BT Ranger Swap

QUESTION: I just inherited a four-wheel-drive ’01 Ford Ranger with a five-speed manual transmission. The 3.0L V-6 engine is done, but everything else is in surprisingly nice shape. Since I have no money invested in the truck, I’d like to drop in a 3.9L Cummins I-4 (4BT) diesel engine and use it as my daily driver. Should I start with a frame-cut 4BT and use its transmission, or can I use the one that’s already in this truck?
Chip Hansen
via email
Photo 4/6   |   Old Ford Rangers are becoming popular homes for 3.9L Cummins 4BT engines that powered delivery vans in the ’80s and ’90s. The little diesels are inexpensive, the adapters to mate the Ford five-speed manual are easy to find, and the swap seems to appeal to those looking for daily drivers with good fuel economy. Meeting emissions for vehicle registration purposes may be another story in many states.
ANSWER: Our 4BT experts say you’re better off sourcing an engine that already has the Ford adapter plate and flywheel so you can use the original M5R2-OD transmission that’s in your Ranger, or step up to a Ford ZF5 (S5-42) five-speed manual that was used behind the small-block V-8 powerplants. The latter are a dime a dozen, so they should be easy to find for a good price If you can’t locate an engine that’s already set up with the Ford bellhousing, good sources for finding the adapters are Diesel Conversion Specialists (dieselconversion.com), Diesel Adapters (dieseladapters.com), or Jeff Daniels Jeep Customizing (jdtruckcustomizing.com). If you don’t plan on doing a lot of hot-rodding with the Cummins, either transmission should be fine for a daily driver. Ranger conversions are becoming more and more popular, so you shouldn’t have much trouble finding information on Cummins and 4BT forums.


QUESTION: I need to address the axle gearing for my restored ’97 Dodge Ram. The truck has 4.10 gears and the 5.9L engine turns 2,400 rpm at 65 mph. The truck has a 4-inch lift and 315/75R16 tires. It occasionally tows a 30-foot travel trailer, but I think the rpm is too high. Would it be beneficial to have the axle gears swapped to 3.73 or 3.55?
B. Keaton
via the Internet
ANSWER: Most Dodge Rams of your truck’s vintage were equipped from the factory with 235/70R16 tires, which measure 29 inches tall. The engine should turn about 2,300 rpm at 65 mph with stock-height tires. Using one of the many tire/gear-ratio calculators found on the Internet, the 34½-inch-tall 315/75R16 puts your actual speed at 80 mph when the engine rpm is 2,400—and only 1,950 rpm at 65 mph. We suspect you haven’t had the speedometer recalibrated since you changed to the taller tires. We always recommend using a GPS to verify a truck’s speed after tire or gearing changes, then having the speedometer gear assembly in the NV4500 transmission re-geared so the speedometer reads accurately. The engine turning 1,900 rpm at 65 mph is good for towing a trailer like yours because the 12-valve’s peak torque comes at 1,600 rpm while the peak horsepower is achieved at 2,600 rpm. Cruising rpm between the horsepower and torque peaks gives the best drivability. We suggest you stick with the 4.10 gears that are currently in the truck. But, if for some reason you still want to lower the cruise rpm, the 3.73 gearset is the “tallest” you want to use because dropping to 3.55 will make your truck too sluggish with a trailer on the hitch.

Winter Tires, Again

Question: I am looking for a set of winter tires for a ’13 GM diesel pickup, and I’m considering the Falken Wildpeak A/T3W. Some of the reviews I’ve read online say they are great on packed snow and ice, which is where I’ll be doing a lot of my driving for the next few winters. Research shows that Falken uses a different compound on the LT version, which worries me a little about its winter performance. I’ve also looked at the Wrangler Ultra Terrains offered by Discount Tire. Any suggestions regarding possible alternatives?
Chris P.
via email
Photo 5/6   |   Dedicated snow tires have special compounds in the rubber to help keep the tread blocks flexible in subfreezing temperatures. They also have special tiny slits in the tread called “sipes” that hold the snow in the tread to maximize traction. The more snow that stays on the tire, the better the traction on plowed- or packed-snow surfaces.
ANSWER: The rubber compound in LT versions of the Falken Wildpeak A/T3W all-terrains don’t have silica, which is one of the key ingredients that gives dedicated winter tires better traction, because the silica-infused rubber compound is what keeps the tread more flexible in subfreezing temperatures. However, if you aren’t towing or hauling heavy loads during the winter, there’s no need to buy the higher-load-capacity LT tires. Non-LT tires are just fine for most pickups, and they provide a softer, more pleasant ride. Keep in mind, the most important aspect of driving on snow/ice road conditions is maintaining vehicle control. Traction on hard-packed snow requires the tread blocks to stay in contact with the snow—and for the snow to remain in the “sipes” (tiny slits) on the tread blocks. The smaller the gaps between tread blocks and the greater the number of sipes—along with tread compounds designed to keep the tread blocks soft and flexible in subfreezing temperatures—the better the grip. (The best traction is snow packing on snow.) So the A/T3W LT tires wouldn’t provide the same level of traction as the non-LTs, even though both appear to have the Rubber Manufacturers Association’s Three Peak Mountain Snow Flake (3PMSF) symbol. Note: The RMA 3PMSF symbol only means the tire passes the minimum requirements for such testing. Members of the Four Wheeler Network staff have participated in hands-on snow-tire testing over the years, in ½-tons, 4x4s, and ¾-ton diesels at the Center for Driving Sciences’ 0.9-mile road course, which uses part of the 77-acre Bridgestone Winter Driving School (winterdrive.com; 800.WHY.SKID) facility just outside Steamboat Springs, Colorado. (Check out “Diggin’ Snow” at fourwheeler.com). The consensus of such extensive tests is conventional traction/mud tires are the worst performers on packed snow roads, while all-terrains are slightly better than factory street treads, and dedicated snow tires, such as Goodyear Ultra Grip ICE WRTs, Nokian Hakkapeliittas, Bridgestone Blizzak W965s, WS-80s, DM-V2s, or Firestone Winterforce LTs. “From a tire-design perspective, snow traction is more pattern-oriented; whereas, ice traction is more tread-compound-oriented,” says Mark Kuykendall, Bridgestone’s light-truck engineering manager. “The typical all-season/M&S-type tire design uses a harder tread compound to give more mileage [better tread wear] and fuel economy. From a compound standpoint, that is the wrong direction for ice. The key factor to a good snow/ice tire is finding a rubber compound that adapts to the road surface and retains that flexibility overall going into lower, colder conditions.” That’s why purpose-built snow tires, which are designed to maximize grip in subfreezing conditions on frozen surfaces, have such a huge performance and safety advantage over their warm weather counterparts. If you are serious about maximizing traction and vehicle control while driving in winter conditions, run a dedicated snow/ice tire. They may not look sexy, but they do the job better than any other tire.

Cracked Impeller

QUESTION: My dad’s ’05 Ford Super Duty’s 6.0L Power Stroke engine has overheating issues. It pukes water out of the reservoir and antifreeze drips from the driver-side cylinder head. I called our local Ford dealer and described the problem, and the service person responded by saying a head gasket has “failed” and we’d need the engine rebuilt to the tune of $11,000. My dad is devastated and says he’ll park it until he can figure out what to do. Is this a common problem for these trucks? It only has 131,000 miles and has been babied since he bought it.
Photo 6/6   |   A common issue with Ford 6.0L and 6.4L engines (and other diesels) using plastic water-pump impellers is the impellers cracking from heat and flexing. When this happens, the water pump can’t supply the needed coolant flow, and the engine experiences overheating issues and coolant leaks. The latter can be misdiagnosed as symptoms of a blown head gasket.
ANSWER: Just because there’s coolant leaking and the engine is overheating doesn’t necessarily mean a head gasket failed—although head gasket failure is a common, and well-documented issue with the 6.0L and 6.4L Power Strokes. Determining where the problem lies demands a thorough, hands-on inspection by a good diesel technician. Coolant leaks can be the result of the degas bottle cracking at the seam between the top and bottom. Overfilling the degas bottle is one of the coolant issues that causes the bottles to fail (Ford revised the fill level decal on the stock degas bottles, so the new fill mark is 5/8 inch below where it was originally located). Another item good mechanics always check is the heater-control valve, which can fail and start leaking coolant down the passenger side of the block, but it can also make its way to the driver side and appear to be coming from the cylinder head. Another well-known culprit of overheating and coolant issues in diesels is a loose or cracked water-pump impeller, which is quite common in pumps that use plastic impellers. The impellers are prone to failure from the effects of heat cycling and flex under heavy coolant flow loads. When an impeller cracks, it can’t circulate the coolant effectively, resulting in high engine temperatures. Kenneth Tripp at Tripp Trucks passes on this experience with bad water pumps: “Years back, I drove a 6.4L-powered Ford that had abnormally high oil temperature. When I drove it starting with a cold engine, I found the oil temperature climbed at a faster rate than coolant does, and it would keep climbing. I had one of my technicians pull the water pump and report back. He didn't ‘see’ anything wrong with it. I told him to grab the impeller and the pulley and see if the impeller turned. Sure enough, it would spin on the shaft. We replaced the water pump, and the truck’s cooling problem was fixed.” Kenneth says although the OEM water pump appeared to be fine, it wasn't moving coolant at the rate needed, leading to the overheating condition and subsequent expansion in the cooling system that caused coolant pressure to throw coolant from the degas bottle. (This is why head gaskets must be tested below full operating temperature.) When it comes to water-pump replacement on 6.0L and 6.4L engines in trucks used for towing, Mobile Diesel Service recommends having the stock water pump and fan clutch upgraded to a Bullet Proof Diesel coolant kit. Its kit includes an aluminum impeller in place of the plastic piece, a high-end water-pump bearing assembly, along with a premium seal in a CNC-machined billet-aluminum housing. The aluminum impeller is both stiffer and stronger than the plastic piece and therefore less likely to flex under heavy loads. A mechanical fan clutch and fan clutch adapter allow you to install a non-electric fan clutch to further improve cooling.