Welcome to Top Tech Questions. Oftentimes, readers contact us with questions about articles, or to praise us on what a good job we are doing. But our favorite form of reader communication is tech questions. Our Top Tech section is a place where you ask what’s on your mind, and we answer it. Got a trouble code? Wondering how to get your engine to make more power? Send us an email at jason.sands@sorc.com and we’ll do our best to answer it.
Bang for the Buck
Question: I was looking through all the different products in your magazine, and I was wondering if you could tell me which ones offer the most power per dollar spent? I’m looking at buying my first diesel, and I’m trying to get an idea of what works best on these engines.
David James
Dallas, Texas
| Programming devices that add fuel are usually your best bang for the buck as far as performance goes. Some electronics add fuel through increased injector duration while others increase pressure, but pretty much all of them work—and in some trucks this can add more than 200 rwhp.
Answer: That’s a pretty broad question. We’ve done Proven Power Combination articles on various makes and models through the years, but to say one product or another is the best at producing power on all models is virtually impossible. As a general rule, some sort of programmer is a good place to start with newer trucks, while older trucks will usually respond well to larger injectors. Both make power by adding fuel, although that will only work up to a point.
For example, turning a screw on the injection pump of an ’89 to ’93 Dodge can add more than 100 rwhp for free, but the total power will peak at about 300 rwhp due to the stock turbocharger. Adding more fuel to a new 6.4L Ford can add 250 hp or more, because they have such efficient turbos from the factory. So the amount of power you can add by turning the fuel up varies greatly by make and model. Adding fuel also increases smoke, makes the exhaust gas temperature hotter, and can be hard on transmissions and clutches due to the extra power. It’s for this reason that many diesels are built with a packaged set of upgrades rather than just a single part.
I Want My Mpg Question: I have an ’02 Dodge Ram 3500 with the 5.9L Cummins engine and 3.55 axle gears. A couple of years ago, I removed the muffler and installed an aftermarket air filter. At first, the truck picked up mileage, going from 16 mpg to 18.7 mpg. Within a few weeks, the mileage dropped to 12 mpg, and everything I have done to it since then (replaced the injection pump, added a FASS fuel system, Edge Juice programmer, changed the MAP sensor) has only gotten me a few additional miles per gallon. I’d really like to know what happened to my fuel mileage and how I can get it back.
Steve Wisniewski Scotland, Connecticut
| With electronically controlled trucks, rule number one in calculating fuel economy is to ignore the meter in the dash or overhead display. It can be thrown off by wheel, tire, or even programming changes, so always hand-calculate mileage when trying to figure out a potential problem.
Answer: It sounds like you’ve hit most of the usual suspects. There’s a rumor that over-oiling an air filter can contaminate the MAP (manifold absolute pressure) sensor and cause a mileage drop, but we’ve never actually seen this happen. An injection pump that is worn out is another scenario that can cause poor mileage, as the pump won’t be able to advance timing fully, and mileage (and power) will suffer. If you’ve gotten a used pump or a cheap remanufactured pump from a shady source, chances are it could be mostly worn out with some new parts, giving you an injection pump featuring the same problem as the one you just removed.
The first thing we’d do is verify the pump’s injection timing is correct when the engine is idling. Find a diesel shop that has a clip-on timing light that attaches to the injection pump lines. The shop can then mark the engine’s balancer at top dead center and figure out what the engine’s base injection timing is. Anything less than 12 degrees before top dead center at idle would indicate something was amiss. The VP44 pump also advances timing at higher rpm, so once the engine is revved up, it should hit about 25 degrees. As a last resort, you could put everything back to stock (including the airbox) and see if you can hit 16 mpg again, and then redo your modifications one by one.
Cummins-Max
Question: My buddy bought a dirt-cheap ’03 GMC with a blown-up Duramax. He also has an ’04 5.9L Cummins engine that he got a good deal on, and he’s looking to put the two together. We can handle the swap and the welding, but I was looking for information on how to get the wiring to work with the engine change. Any advice for us?
Spencer Wiltbank
Phoenix, Arizona
| Other than injector issues on the earlier LB7 engines, Duramax diesels are usually pretty reliable. Even with high mileage, they’re usually fixed rather than swapped out for a different engine.
Answer: Besides the obvious question of why, we can see how it would be hard to pass up the swap if you already have the parts. Putting a Cummins into a GMC or Chevy with a Duramax diesel isn’t a common choice, but we’ve heard there’s a couple out there. Engine and transmission adapting parts from www.destroked.com will get you part of the way there, but that isn’t necessarily the hard part. To make the combination work, you’ll need to do a bit of wiring, along with replacing the sensors that won’t work in the Cummins engine with ones that send out the same kind of signal (so the computer thinks your truck still has a Duramax in it) or finding adapters for the different thread sizes the engines use. In the end, you may still have to sacrifice things like cruise control. We’ve seen this same type of thing work for swapping transmissions with electronic controls, and while chasing wires can be time consuming, fooling the truck into thinking it is still stock will give you the best reliability, driveability, and performance.
