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Your Diesel Questions Asked and Answered

You’ve Got Questions, We’ve Got Answers

Bruce W. Smith
Apr 17, 2019

Manuals Disappearing

QUESTION: After reading the buyer’s guide in your January 2019 issue, it is disappointing to see Ford and GM not offering manually shifted transmissions anymore. Ram still offers them. My question is: For the new Ram Heavy Duty, why is the standard transmission only available on trucks with the lower-power-output Cummins engine? I always thought a manual transmission was stronger than an automatic.
Todd Urban
via email
Photo 2/7   |   Manual transmissions are almost a thing of the past in diesel trucks, as they aren’t as capable of handling the torque of today’s engines as the new automatics are. There’s also less buyer demand; automatics are easier to drive and require fewer repairs over the length of vehicle ownership.
ANSWER: It’s all a matter of managing the torque being delivered to the differential, which, because of its many computer-operated clutch packs, means an automatic transmission does much better than a standard gearbox (which only has one or two manually operated clutch discs). Manual transmissions were fine a decade ago when diesel torque numbers were less than 600 lb-ft and tow ratings were less than 20,000 pounds. But in this age of torque monsters making 1,000 lb-ft in stock trim and tow ratings exceeding 30,000 pounds, manual transmission longevity is severely challenged, because its harsher delivery of torque puts an enormous strain on the shafts and gears inside a transmission, as well as the clutch disc itself. Warranty concerns, along with a low buyer demand, is why Ford and GM stopped offering manual transmissions in their diesel trucks. Ram was the last holdout. But that is set to become a thing of the past, as power levels continue to rise. As Fiat Chrysler America’s Ram Truck PR representative Nick Cappa, tells us, offering a manual transmission capable of surviving the torque produced by the newest 6.7L High Output Cummins engine “would require a newly developed manual transmission and heavy clutch.” We have not received anything that hints to Ram developing a new manual-shift transmission. Instead, it’s only offered for trucks with the lower-powered Cummins, which is going away once ’19 Heavy Duty trucks hit dealers. Another reason standard shifts are becoming obsolete in heavy-duty pickups is because the majority of today’s car and truck buyers prefer the convenience of an automatic over having to use a clutch to shift. Automatics are easier to drive than a manual. There are also those who like not having the added expense of replacing the clutch multiple times during ownership, which standard-shift diesel owners are all too familiar with.

T3 vs. T4 Mounts

QUESTION: I have an opportunity to purchase a used Speed Steed T4 stainless exhaust manifold for a 5.9L Cummins engine for my ’06 Dodge Ram for a fraction of the price of a new one. What is the difference between the T3 and T4 turbocharger flanges? I understand that my stock T3 turbo won't mount up to this manifold, but I wouldn't be opposed to putting a compatible turbo on if there’s anything to be gained by doing the swap. With the exception of a simple tuner and a few other minor modifications, the engine is pretty much stock. My truck is used primarily to tow a fifth-wheel trailer.
Mike Yates
via email
Photo 3/7   |   Turbocharger mounting flanges and exhaust flow (through the manifold) are key to diesel performance. For example, a T4 mount has an opening that’s more than 20 percent larger than a T3. A bigger opening can provide the exhaust flow that’s necessary to spool larger turbos.
ANSWER: Steed Speed builds its CNC-machined, one-piece manifolds out of 1018 mild steel coated with Techline or an optional ceramic material. Be that as it may, just because you are getting a great deal on the manifold doesn’t mean it’s the correct combination for your rig’s 24-valve Cummins engine. In fact, it might be a poor choice. “He can do that Steed Speed T4 mated to a BorgWarner SX-E 62 turbo, but depending on tuning it will not be as responsive as a stock ’charger,” says Alec Hembury at Industrial Injection Diesel Performance. “If tuning is way off, the truck will not even run as well as it did stock. The correct package for a good tow setup is using EFILive for tuning, along with the Steed Speed T4 manifold, a set of our 62hp injectors, and the SX-E 62 turbo.”
As far the difference between a T3 and T4 mounting flange is concerned, the T3 has a smaller opening than a T4. The T3 flange has an inside opening of 2.50 inches wide by 2.08 inches tall, with a bolt center spacing of 1.75x3.38 inches. A T4 has an opening of 3.04x2.08 inches and flange bolt spacing of 4.42x2.75 inches. Looking at it another way, a T3 flange opening is 5.2 square inches, while a T4’s is 6.32 square inches (21 percent greater). The smaller opening of the T3 flange creates more exhaust velocity, but less volume. That means a turbo mounted on a T3 flange will spool faster than it would when mounted on a T4 flange. The downside is the T3’s restriction in exhaust volume (compared to a T4 flange) means it will not be able to make as much horsepower—all other things being equal.

Rough-Idling Duramax

QUESTION: I purchased a ’13 GMC Sierra 2500HD from an out-of-state seller. It has 130,000 miles on it and looks brand new. The only issue: The previous owner says it had a chaffed injector wiring harness, which he repaired. He also pulled the injectors while doing the repair and had a diesel shop check them. All were fine. The truck runs great out on the road, but the engine idles rough and seems to have a miss. A friend’s scan tool recorded a “P026D” diagnostic trouble code (Injector Mass High Flow). He says it may need new injectors. This is my first diesel and I hope that’s really not the case after putting less than 1,000 miles on it since I purchased it. Injectors cost $2,000!
Bud Jenkins
via email
Photo 4/7   |   The numbers etched in the top of Bosch piezoelectric injectors, like these pulled from a 6.6L Duramax LML engine, are actually data markers that tell the ECM how to adjust an injector’s “on time” to balance it correctly with the other injectors for a smooth idle and optimum engine performance.
ANSWER: The most common cause of a 6.6L Duramax LML engine’s rough idle after having injectors removed/replaced is the ECM not sending the correct voltage signals to each of the injectors. It’s not the ECM’s fault: The person who replaced the injectors is to blame. Here’s why. The Duramax LML uses piezoelectric injectors, which are very sophisticated, and they must have the proper information from the ECM to work properly.
According to Oregon Fuel Injection’s diesel diagnostics page, the injectors function in this manner: “The engine control module provides a high-voltage supply circuit and a high-voltage control circuit for each fuel injector. The injector high-voltage supply circuit and the high-voltage control circuit are both controlled by the ECM. The ECM energizes each fuel injector by grounding the control circuit and supplying each fuel injector with up to 250 volts and 20 amps on the voltage-supply circuit to activate the piezo-type fuel injectors. This is controlled by boost capacitors in the ECM. During the 250-volt boost phase, the capacitor is used to charge the injector piezo stack, allowing injectors to open. The injector is then held open with this high voltage. At the end of the injection event, the ECM closes the injector by discharging the piezo stack.”
Here’s why that explanation is important. Anyone who looks at a Bosch LML injector will notice a string of letters and numbers engraved around the rim where the high-pressure injection line is attached, along with a tiny QR code. Those numbers are not the part number of the injectors: They are the individual injector’s trim code, an ID stamped into the injector when it was built. That ID number is the key to making sure a Duramax LML idles smoothly, because it tells the ECM how to electronically control that specific injector so it can balance the fuel flow to all eight injectors when the engine is idling. If the flow (trim) is out of balance, the engine will idle rough—or even go into “Limp Home” mode if the injector flow balance is bad enough.
“The flow rate of every Bosch diesel injector is tested before leaving the factory,” explains Brian Bailey, a technical guru at Dynomite Diesel Products (dynomitediesel.com). “There can be a wide tolerance in those flow rates from injector to injector, maybe as much as +/- 14 percent of specification because of slight variances in machine tolerances, magnetic forces, or even friction between injector parts. Bosch then assigns an ID number to that injector, according to where its flow rate falls, that tells the ECM how much current to apply to bring that injector within spec. That ID number is called the injector’s ‘trim code.’ There’s a finite number of trim-code IDs for those injectors, and every Duramax LML ECM already has those codes stored when the vehicle leaves the GM assembly line.”
Brian says when injectors are installed, the ECM has to be told: 1) the injector trim code ID, and 2) what cylinder it’s feeding. With that information, the ECM can send the proper “injector on-time” signal to that injector to trim its flow rate up or down so it perfectly matches the specs and balances with the injectors feeding the other cylinders. When the injector flow rates are balanced properly, the truck idles smoothly. When they don’t, the engine idles rough. Brian says the trim codes only apply to idle quality, nothing more.
What often happens when a diesel’s piezoelectric injectors are removed and either reinstalled or replaced altogether is they don’t end up back in the same cylinder from which they were removed—eight injectors might be in eight new locations. The ECM still thinks the original injectors are feeding the same cylinders—so it’s supplying the same electrical signals to the new injectors according to the old injector’s trim codes. Result: Rough idle, poor fuel economy, increased emissions, and possibly an engine stuck in “Limp Home” mode.
So, whenever injectors in an LML are removed, write down the ID code on the injector along with what cylinder it was feeding. If new injectors are installed, write down the Bosch ID code of each new injector—and the cylinder in which it is installed. Then plug those fuel trim codes and cylinder locations into the scan tool so the ECM has all the information it needs to properly balance injector flow across all eight cylinders.

Weak 6.7L Cummins

QUESTION: I’m wondering if anyone else has had any problems like this with their ’16 Ram 2500: My truck’s engine is behaving as if the turbo isn’t spooling up. But not one diagnostic-trouble code has been triggered, and the dealership has checked it multiple times. They even put on a flight recorder and towed my toy hauler up a small grade. Pedal to the floor with the 8,500-pound trailer, it’ll only go 45 mph. The service manager says technicians can’t find anything wrong. The only thing I’ve done to the truck is add an aftermarket air filter. I’m so frustrated, I’m ready to go trade in my diesel for a gasser. Please somebody help.
Tony Turano
via email
ANSWER: Our initial thought is that the turbocharger isn’t making the proper amount of boost. But without a diagnostic-trouble code, tracking down the exact reason requires eliminating the common causes first. Did you just replace the air filter, or did you change the cold-air-intake box along with the filter? If you changed the air-filter housing, is the MAP sensor plugged in correctly? What type of air filter did you change to, dry or oiled? If you are using an oiled air filter, it’s common for some of that oil to foul the MAP sensor, which will then send the ECM bad information that could cause low boost under load. But usually a P0237, P0236, or P0299 DTC will be activated. If you changed the stock airbox, that could be the issue. Is the MAP sensor in the exact location in the air tube that it was prior to changing everything? Ram changed the intake system on its diesel offerings in 2013 to what it calls “Ram Active Air,” which is a dual-inlet air filter box with the ability to vary the source of incoming air. During normal driving conditions, air is drawn in from under the hood. As underhood temperature rises (from pulling long grades or towing in hot, dry weather conditions), the Ram Active Air filter box switches to a version of a cold-air intake, sucking air from directly behind the truck’s big grille. The location of the MAP sensor is critical to this airflow system’s function. Another possible cause for your engine not making the power you are accustomed to is boost pressure being lost somewhere in the piping to/from the charge-air cooler. If there is a small hole in one of the tubes, a flex coupler, or a loose clamp anywhere in that system, boost will bleed off. Such a loss of pressure will result in the engine not making full power. The engine’s inability to build/maintain power under heavy throttle and load can also be affected by a loose clamp on the exhaust side, a damaged up-pipe, or even a plugged DPF or other restriction causing too much backpressure in the exhaust.

Leaky Oil Pan

QUESTION: My ’14 Ford pickup’s 6.7L Power Stroke engine is leaking around the upper oil pan gasket. Should I replace just the gasket or invest in an entirely new oil-pan assembly? I plan on doing the work myself. The truck just passed 210,000 miles.
Mark Leach
via email
Photo 5/7   |   Ford 6.7L Power Stroke engines use two-piece oil pans, which are known to leak. On ’14-to-present models, the lower pan (black) is sealed with silicone and is easy to reseal. However, the massive upper section uses a gasket between it and the block that requires removing the transmission to access the bolts securing the assembly to the engine block.
ANSWER: It’s not going to be an easy repair if the leak is actually coming from the upper “bed pan” instead of from the lower oil pan. Before attacking the oil leak, thoroughly clean the engine top and bottom and then recheck to see exactly where the oil leak is originating. You might even want to consider spending the money for Tracer Products’ Dye-Lite TP3100 diesel engine oil dye at an auto parts store, along with a black light to illuminate the dye so you can easily see where the actual leak is originating. It’s not uncommon for the 6.7L engines to leak oil from around the front corners, where the timing cover meets the upper oil-pan assembly. If the leak is coming from the gasket that seals this assembly with the block, you’ll have to pull the transmission back far enough to remove the flexplate in order to access some of the oil pan bolts. It’s a time-consuming job, and you’ll find that a round-head 3/8-inch flex ratchet with extensions is a big help when you try and do it. When the cast-aluminum upper pan is removed, make sure the mating surface to the block is perfectly flat and not warped, which may require it being checked by a machine shop. If the surface is perfectly flat, there should be no need to replace it. If it shows any signs of warping, then by all means, buy a new one. Either way, you will need to replace the gaskets for the oil cooler and adapter housing and reseal the lower oil pan with the sealant. While the flexplate is off, it’s a good idea to replace the rear main seal. Use the proper tool, of course, so you don’t nick the new seal when it’s installed.

Home of Bad NOx

QUESTION: I bought a one-owner ’11 GMC Sierra 2500HD with 102,000 miles on it. It’s immaculately maintained, but the Check Engine light lit up while on a road trip. A local parts store scanned the ECM and recorded diagnostic-trouble code P2206, which is associated with a bad NOx sensor. The code was cleared, and I will replace the sensors. Are they hard to replace? The auto-parts store says they cost $175 each.
Zeke Quinten
via email
Photo 6/7   |   The two NOx sensors on the ’10-to-’11 6.6L Duramax, each of which is attached to a control module, are easy to replace, and they cost about $175 apiece. Their replacement is also covered under an extended GM warranty (up to 10 years or 120,000 miles).
ANSWER: No, the NOx sensors are not difficult to replace—especially when GM dealers will replace them under warranty. In 2015, GM issued a technical-service bulletin (GM TSB#13386A: “Special Coverage Adjustment”) related to a problem with NOx sensors in the ’10-to-’11 6.6L Duramax. That TSB extended the warranty of the LML NOx sensors to 10 years or 120,000 miles, whichever comes first. The TSB allows 2.3 hours shop labor to scan for the codes and to replace the two sensors—one in the downpipe near the turbocharger outlet and the other in the middle of the diesel particulate filter that’s located under the truck, beneath the front passenger seat. GM’s TSB says: “The nitrous-oxide sensor may fail due to contamination between the terminals in the sensor and the wire interface. The contamination may cause the NOx-sensor signal to become unstable/or oscillate, which may cause a malfunction light to illuminate.”
The TSB also instructs service technicians to pull both NOx sensors out and inspect the date code on the back of each one’s control module. If the first six digits of the date code, located at the bottom of the module, are prior to “120914xxxx” (Sept. 14, 2012), that NOx sensor/module should also be replaced under warranty. This TSB applies to both the U.S. and Canada. If your truck has an early model 6.6L Duramax LML, it might be prudent to have the dealer check the modules even if there have been no codes triggered. As you discovered, the replacements cost about $350 per pair.

Best DEF

QUESTION: What is the best brand of DEF to use? Is the fluid you get at the pump, Ford dealer, or auto-parts store all the same? I want to make sure I treat the 6.7L Power Stroke engine in my ’18 Ford Super Duty right.
Ruben Salazar
via email
Photo 7/7   |   The best DEF to use is the one that has the “API Certified” seal of approval on the container or posted on the DEF dispenser at the filling station. Using DEF that doesn’t meet the strict ISO 22241 DEF production standard should be avoided at all costs.
ANSWER: The best DEF to use is the one that has the American Petroleum Institute seal of approval label on the container or posted on the fueling station’s dispenser. If it has the API certification label, then packaging and brand shouldn’t matter. Buy whatever best fits your budget. If the DEF doesn’t have the API seal, don’t use it.
Here’s the deal: API plays a very important role in ensuring DEF is a mixture of 32.5 percent urea and 67.5 percent deionized water and meets ISO 22241 requirements. Impurities in the mixture can damage a diesel’s catalytic converter, diesel particulate filter, and the sensors in the system that control the application of DEF. API has a voluntary program that tests DEF, and if that brand/maker’s fluid passes, the manufacturer gets to put an “API Certified” label on the containers or at the pump.