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Diesel Tech Questions

You've Got Questions? We've Got Answers!

Bruce W. Smith
Apr 11, 2017

Mysterious Vibration

I have an ’05 Chevrolet Silverado 2500HD. It has a BDS 6-inch lift, 17x10 rims, and 35x12.50 tires. My truck has an intermittent vibration between 40 and 50 mph. It has a new Pitman arm, U-joints, dual front stabilizing shocks, tie-rod ends, idler arm, and steering box, and the new tires are balanced and wheels aligned. What else could cause the vibration?
Bill Owen
via email
Photo 2/6   |   Vibrations at certain speeds in lifted four-wheel-drive trucks are caused by many different variables, including worn stub-shaft bearings in the front differential, a bad shock, and an improper angle of the driveshaft. Diagnosing the exact cause typically requires a close inspection of all moving parts while the truck is on a hoist.
There are a lot of parts moving in different directions when your Silverado 2500HD is rolling down the road. Here are some other common causes for vibrations on 4x4s that are a decade old or lifted: cupped or out-of-round tires; worn CV shafts or stub-shaft bearings on the front differential, a worn driveshaft carrier bearing (if your truck’s driveshaft is a two-piece part), an improperly aligned driveshaft, a worn pinion bearing, a bad shock, and toe-out or caster that might be on the low end of their specified tolerances.
Any of these concerns can cause vibration at a certain speed, or when the steering wheel is turned in a specific position at a certain speed. Vibrations are tough to pinpoint. Putting the truck on a rack and checking all the above should help track down the cause of the mystery vibration.

Setup for Compounds

I have a ’97 Ford F-350 and I am considering adding compound turbochargers. My current setup consists of a single BorgWarner S366. Which turbo can I use with the S366 in order to create a decent compound system? I've been trying to do my research, but I haven't had very much luck as far as how to choose the turbos. I was thinking of maybe trying to use a Holset HX-35, but I'm not sure how that would work out.
Dal Hendricks
via email
The BorgWarner S366 can be used in a variety of compound-turbocharger setups depending on your truck’s internal engine modifications, the turbos’ turbine housings, usable rpm, and your target horsepower. One of our contacts in the engineering department of BD Diesel Performance (dieselperformance.com) says, “Pairing the S366 with a BorgWarner S472 SX-E will provide more than enough air for 600 rear-wheel horsepower. Alternatively, using a turbocharger that’s similar to a BorgWarner S257 SX-E with the S366 will improve low-end response while allowing 425-plus horsepower if the correct turbine housings are used.”

Too Much Pressure

I have a 128,000-mile 5.9L Cummins-powered ’07 Dodge 3500 with a G56 six-speed manual transmission and South Bend dual-disc clutch. The stock lift pump isn’t pumping quite enough, so I replaced it with an aftermarket 165-gph air/fuel separation system, following the instructions to the “T” when installing it. The engine started behaving erratically and popping after it reached operating temperature, and it got progressively worse on each trip. I called the lift-pump manufacturer and was told the fuel pressure should be 15 to 17 psi. I checked the pressure and it bottomed out my 30-psi fuel gauge. The new pump wasn’t set correctly by the manufacturer, so I adjusted the pressure down to 16 psi. Could too much fuel pressure kill the CP3 injection pump and injectors, or is there another source of the new problem? If it is the injectors, who makes the best 50 to 100hp injectors that I can replace mine with? What about a replacement CP3? Reliability and quality parts are my greatest concerns.
This truck is a daily driver and sees some pretty heavy towing up to 35,000 pounds gross weight, and I will be tuning it with EFILive. I don’t have a horsepower goal in mind. I just want a reliable, powerful, daily-driven tow rig.
Milton Vick
via email
Photo 3/6   |   Older Dodges with Cummins 5.9L engines can get a nice boost in towing power without sacrificing reliability by running a blueprinted CP3 injection pump and rebuilt Bosch injectors with 50hp tips.
The Cummins technical gurus we spoke with about high fuel pressure say there shouldn’t be any issues with hurting the injectors or the CP3. However, the high rail pressure will over-fuel the engine, potentially hurting it internally if you let the problem go for too long. Fortunately, it sounds like you caught it in time and adjusted those high pressures to an acceptable level and prevented any damage.
For long-term reliability for your towing application, Oregon Fuel Injection’s (oregonfuelinjection.com) Mark Gotchall recommends installing Dynomite Diesel Products’ 50hp nozzle tips on rebuilt Bosch injectors. Since you’re tuning with EFILive, Mark also recommends staying with a stock CP3.
For even more pulling power while staying reliable for daily driving and towing use, Shawn Smalley at Mobile Diesel Service (mobilediesel.co ) recommends Industrial Injection’s PhatShaft Viper 63/80 turbo and R1 100hp injectors. A good tune will top it off nicely, providing strong power with great reliability.
If you do go with that combination, consider upgrading to BD’s Pulseflow exhaust manifold, a Fleece Performance Engineering coolant bypass kit, and an exhaust brake, all of which are great additions for older Cummins-powered Dodge rigs that do a lot of heavy trailer-toting.

Name that Tune

I have two Ford Super Duty trucks for my landscaping business: an ’05 F-350 and an ’08 F-450. What is your recommendation for a tune that will improve both trucks’ fuel economy?
Arturo A Maldonado Ortiz
via Facebook
Photo 4/6   |   Edge Products, Hypertech, and Bully Dog offer ECM calibrations that are designed to help promote better fuel mileage. Our research shows that most of the popular handheld programmers typically improve fuel economy 1 to 3 mpg over that of the stock tune.
We receive “econo-tune” questions on a regular basis from business owners. Just to name a few, companies such as Edge Products, Hypertech, and Bully Dog have tunes they say promote better fuel mileage. Our research shows various programmers typically improve fuel economy 1 to 3 mpg over fuel mileage with stock ECM calibration.
Mike Dunks at Dunks Performance (dunksperformance.com ) also suggests using custom tunes from third-party suppliers that specifically focus on improving fuel economy.
Keep in mind the fact that fuel-economy gains and losses begin with the right foot: Be smooth while driving, avoid excessive speed, and you’ll be surprised by the gain in mpg, tune or no tune. Using a cetane booster with every fill-up may also help improve fuel economy if the diesel you are running in your truck is of poor quality. Keeping the engines well maintained is also going to help on the overall fuel-economy front.

Gas vs. Diesel

I’m looking at Class B camper vans, one of which is a Roadtrek, whose ad touts its 6.0L Vortec EFI V-8 engine. In doing some research, I came across your trucktrend.com/features/1507-nine-best-diesel-engines-for-pickup-trucks/ article, where I noticed the 3.0L EcoDiesel “is as ‘green’ as clean diesels get, and knocks down the best fuel mileage (28 mpg highway) in the fullsize-pickup segment,” Is there any chance the Vortec gets anything close in fuel mileage, or am I insulting your intelligence by even mentioning it in the same breath? Every mechanic I spoke with says diesel is the way to go. Are V-8-diesel-powered trucks in the 20-plus-mpg range? I’m guessing the 5.9L 12-valve Cummins I-6 has six cylinders. In general, one might figure the more cylinders an engine has, the less mpg it makes. Is this true regarding diesels? Most things have advantages and disadvantages. What’s the downside of a diesel engine? Slower acceleration? Anything else of any significance?
David Myers
via email
Photo 5/6   |   Class B diesel-powered, camper-type vans are becoming quite popular among RVers. Today’s turbodiesel engines provide good fuel economy along with other advantages over gas engines.
In a nutshell, diesel fuel produces about 28 percent more power per gallon (higher BTU) than regular unleaded gasoline, which is why turbodiesel engines are more efficient than gasoline-powered engines, all other things being equal.
Advantages: Diesel engines develop considerably more low-end torque than gas engines of similar size, which enables them to move heavy loads easily. Torque is the force that gets a load moving and helps maintain a truck’s momentum when climbing steep grades. If an RV is geared properly, a diesel will usually perform better than a gas engine.
Another benefit of a diesel powerplant, be it in a car, pickup, or RV, is it typically gives the vehicle a higher resale value than its gas-powered counterpart. This means owners usually recoup a portion of their investment in a diesel over a gas engine. Properly maintained diesel engines also last many times longer than a gas engine.
Yes, the EcoDiesel engine in the Ram 1500 is very fuel-friendly when the truck is empty; we’ve seen highway mpg consistently in the high 20s and low 30s on multiple road tests. Load it down, however, and its overall performance isn’t as good as some gas V-8s in the ½-ton class, and when it comes to towing performance, it’s nowhere close to being in the same league as the bigger diesels found in late-model, heavy-duty pickups.
Gasoline V-8-powered trucks such as the 6.2L GM EcoTec3 generally get around 18 to 22 mpg empty and 8 to 10 mpg when towing or hauling a decent load. The newest turbodiesel V-8s (and the Cummins I-6) typically get 18 to 20 mpg empty, 10 to 12 mpg when they are burdened with a load of similar size. Class B vans powered by V-6 diesels will probably get 15 to 18 mpg, depending on the size of the rig and how heavily it’s loaded.
With regard to the question, “which engine configuration gets better mileage?” axle gearing is a big determining factor for the engines that power the Big Three’s heavy-duty trucks, more than displacement or design. It’s not unusual to see 10 percent better fuel economy from all of today’s high-output diesels when running 3.42-ratio gears instead of 3.73s or 3.92s.
Disadvantages include the overall cost of ownership compared to a gas engine. Fuel is more expensive; diesels require more lubricants, filters, and frequent oil changes; they need fuel additives and DEF fluid; and the engines also have considerably higher out-of-warranty repair/maintenance costs compared to gas-powered rigs.

Hot-Blooded GM 6.5L

I have a ’94 Chevrolet Silverado 2500. The truck’s 6.5L diesel engine has plenty of power, but it overheats as soon as it’s loaded down. I have used the military version of this engine with good results. But I understand this commercial version of the engine is prone to overheating. I’m considering installing a replacement engine, possibly a CAT I-6 or a Cummins 5.9L. Do you have any suggestions or recommendations?
Roy Crouse
via email
Photo 6/6   |   Good airflow over a big cooling surface is very effective for keeping water temperatures under control for diesel engines that are prone to running hot. Installing an efficient radiator and electric fans is a lot cheaper than doing a full-on engine swap.
It sounds like your truck’s old 6.5L still has a lot of life left in it. Before ditching it for another engine, have you considered swapping the stock radiator with an aluminum four-core unit and dual electric fans? We used a Flex-a-lite replacement radiator and 284-cfm dual-electric-fan kit on a similar hot-running turbocharged 6.5L and it solved the overheating issue. Good airflow over a big cooling surface is very effective for keeping water temperatures under control—and it’s a lot cheaper than doing a full-on engine swap.
If you want to install a diesel engine, a 5.9L Cummins is a tried-and-true option. Kits and other parts for your truck’s era are readily available from either Auto World Conversions (cumminsdieselrepowers.com) or Diesel Conversion Specialists (dieselconversion.com).
Sean Patterson at DCS says, “We have lots of helpful parts and information for Chevy / GMC trucks from 1973 to 1999. We also have a ‘Kit Builder’ section on our website, which finds kits made up of the most popular parts combinations, including one for the 6.5L GM-to-Cummins swap.”



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