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May 2015 Top Diesel Tech Questions

You’ve got questions? We’ve got answers!

Jason Sands
Apr 25, 2015
Photographers: Jason Sands
Welcome to Top Tech Questions. One of our favorite forms of reader communication is tech questions. Our Top Tech section is a place where you ask what’s on your mind, and we answer. Send us an email at dieselpowertech@enthusiastnetwork.com and ask away!
Bogging Duramax
Question: I have an ’03 Duramax with 42,000 miles, and I want to get a little better mileage and more power without risking the reliability of the truck. I put an AFE air cleaner and 4-inch downpipe-back exhaust on it, but those didn’t seem to do much in the way of response off the line, which is mainly what I’m looking for. When starting out, there’s a scary amount of lag before the truck gets going, which isn’t good if another vehicle is coming!
Hans Lange
via email
Photo 2/4   |   A diesel engine’s fueling is one of the main contributing factors in how quickly the turbocharger spools up. While adding fuel can help turbo spooling, it only works up to a point. Adding too much fuel will not only create a lot of black smoke, it can actually “flood out” the turbo and cause it to spool even later in the rpm band.
Answer: Improving the airflow of your engine is usually a good start. But in your case, it’s likely the fueling that you need to address. Trucks equipped with turbodiesel engines usually experience a decent amount of turbo lag—even those with the newer variable-geometry turbos. While driving newer rigs, we often found ourselves needing to use the brake-boost technique (build turbo boost pressure while holding the truck still with the brakes) in order to make quick turns without getting run over by Los Angeles traffic. When you see a diesel that blows out a puff of black smoke when rolling on the throttle, often that extra fuel is added to increase the rate the turbo comes to life and makes boost. In factory form, LB7 Duramax-powered GMs have very little fuel off idle, and a good bit of rail pressure and duration can be added to spool the turbo quicker yet not produce much black smoke. Any type of basic tuner such as those available from Edge, Banks, or PPE can add enough fuel and timing to make the truck responsive, even if you just drive around on a “Tow” tune.
If you want to step it up a notch, you can always try EFILive. It’s a tuning tool that allows an end user to access the engine’s computer via a laptop and change parameters like fueling duration, timing, rail pressure, and other engine functions that affect the rate at which a turbo spools up. These custom tunes will allow you to set the fueling as high as you wish in order to get as much response as possible. Keep in mind that adding too much fuel not only creates smoke, it also slows spooling rather than helping it.
While off-idle power will never be instant on a turbodiesel, performance tuning (especially on ’05-and-up Duramax trucks with variable-geometry turbos) goes a long way to reduce the time it takes for the turbo to spool up and for the engine to make some power.
Death-Wobble Dodge
Question: I have an ’11 Ram 3500 4x4 with 71,000 miles on it. The truck has an aftermarket 600-pound front bumper from Bodyguard Bumpers, a leveling kit on the front suspension, and dual front steering stabilizers from BDS. Recently, I have been experiencing the Dodge “death wobble” with it at highway speeds, at about 60 to 70 mph. The only way to stop the shaking and not lose control is to slow down to less than 38 mph. I’ve had the tires balanced and an alignment done, and everybody tells me the front end is tight, but I still experience this when the left front wheel hits a deep pothole or bump first. Should I be looking to upgrade the front suspension? Is it the heavier bumper that’s causing it? I don’t want to change the ride height or install a lift kit, but there has to be a solution. Any advice on this would be great. I need to fix this because I do a lot of highway driving for work.
Paul Barnes
via email
Photo 3/4   |   Chasing down death wobble can be a chore, and if the truck’s suspension is neglected or worn out, most likely there are many issues in the front end that can cause the steering and suspension oscillation.
Answer: We’ve experienced “death wobble” firsthand and can definitely say it lives up to its nickname. A lot of suspension techs prefer to call it “uncontrolled front suspension oscillation,” which sounds more correct but might not make a good headline for the evening news. Either way, what you’re describing occurs when one side of a live-axle suspension gets either compressed or unloaded and the front suspension is sent into a horrifying back-and-forth motion, which can often cause a driver to lose control of the vehicle completely.
The good news is “death wobble” is something that’s fixable. However, the bad news, in many cases, is that it’s hard to diagnose. Our first step would be to check the tires. Over-inflated tires or tires that are starting to separate may look visibly fine but can definitely be a contributing factor to a dancing front end. Try rotating the tires or, if they have a good amount of miles already on them, just replace them. While you’re checking out the tires, it’s probably a good idea to also do an alignment—especially if the truck is equipped with aftermarket suspension parts. Since you’ve already done this, the next thing we’d check is the factory track bar, ball joints, and bushings in the suspension. Even at 71,000 miles, worn bushings or a loose track bar can cause the death wobble you’re describing, which is then probably exacerbated by the large bumper on the truck.
If the tires, track bar, ball joints, and bushings all appear to be in good shape, our next step would be to move on to the steering box to see if the box itself is loose. Remember, any slop whatsoever in the front suspension can cause death wobble, even if it starts with the steering box. If the steering box is OK, move on to the rest of the suspension: the drag link, tie-rod ends, and even the wheel bearings. Finally, if death wobble still presents itself, we’d look into upgrading the track bar and adding a steering box brace to keep everything rigid right from the start.
In the case of our Ford 7.3L-equipped truck, it took replacing most of the front suspension to get it fixed, but since the rig’s main use was off-roading, nearly everything was worn, used, or abused anyway.
Fummins Questions
Question: I am gathering components for a Fummins build. My powerplant of choice is a 5.9L 24-valve Cummins, because I already have a donor truck. I fully intend to do a P-pump conversion for its simplicity and durability. My donor truck has an NV5600 manual transmission, which I plan on keeping behind the engine in this conversion. My goal is to build a reliable tow rig with good fuel economy. I would like the engine to make in the range of 400 hp. My questions are many, but I will start with these: What are your recommendations for pump, delivery valves, injector line sizes, and turbos? How about the clutch? I can see a “Hot Street” pump filling my needs, but I’m ignorant about the rest.
Kevin Walters
via email
Photo 4/4   |   Cummins-powered Fords have become quite popular over the years, with conversions ranging from stock engines in stock trucks to 1,000hp monsters. A good source for random conversion parts is
Answer: For many folks, a Cummins engine in a Ford body and chassis makes an unbeatable diesel combination, which is why these swaps are so popular. Before you get carried away with your hybrid project, however, we’d suggest thinking about sticking with the VP44 pump. Even a stock engine with a healthy tuner will make more than 300 hp at the wheels and, when properly maintained, VP44s can last for hundreds of thousands of miles. However, we’re not here to argue that the P-pump isn’t the better choice; it will provide more fuel and rpm capability and should be more reliable than the VP44. For the swap itself, you’ll need to find a core pump (or buy a rebuilt one), a 12-valve front cover and gear case, a pump gear, custom injection lines, and assorted pump hardware such as the throttle linkage and shutoff solenoid. If everything is new, you’re looking at quite an expensive proposition ($3,000 or more), which leads many people to collect parts and pieces for a P-pump swap over time, wherever they can find them.
If you go through with the P-pump swap, the next thing to tackle would be reaching your horsepower goal. Honestly, even at the rear wheels, 400 hp isn’t that hard for a P-pumped truck, especially since your 24-valve will have better airflow than a 12-valve Cummins. Your parts combination will depend on the type of pump you’re able to find, as 160hp, 180hp, and 215hp engines all had different pumps. For a 160hp pump (which is common and one of the cheapest to buy), a set of 5x14 or similarly sized injectors, 0.024 delivery valves, 3,000-rpm governor springs, a Mack Rack Plug, around 18 to 20 degrees of timing, and sliding the fuel plate (or taking it out) ought to put you close to the 400hp mark, even with a factory HY35 turbocharger. With a 180hp pump, you could probably get away with smaller injectors, and we’ve seen a truck with a 215hp pump make 386 hp right out of the box with just timing and sliding the fuel plate. While it may be tempting to just try and find a 215hp pump, either the 160hp or 180hp pumps can support power levels of more than 700 hp with additional modifications and turbocharger upgrades.
One area where you’re ahead of the game is with the NV5600 manual transmission. The electronically controlled 47RE automatics that came in VP44-equipped Dodges aren’t easy to mate with Ford’s wiring or control, and hydraulically controlled 47RH Overdrive tail sections are getting harder and harder to find. So, in this case, all you really need is a clutch. If you plan to stay around 400 hp, an aftermarket single-disc clutch from a company like Valair or South Bend Clutch will do nicely, and it will drive just like a stock unit. Stepping up to a dual-disc clutch means a power-handling capability of 500, 600, or even 700 hp, but it comes at the price of a lot higher pedal pressure and jerky engagement, especially while backing up. Whether or not you’re willing to live with this mostly depends on your ability to deal with a vehicle that drives different than stock.
We don’t mean to rain on your parade as a final note but, as you’re building your truck, check the code on the block. If it is a “053” block, we’d suggest finding a new donor engine, as those castings are more prone to cracking than other blocks. They crack all the way across the side and are difficult to fix, and that often requires sourcing a new engine block. Other than that, good luck with the project, and make sure to send pictures!



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