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.
½-Ton Half-Truths
Question: I keep hearing over and over again that ½-ton diesels are supposed to come to market, yet none have shown up. What’s the big deal, and why is it taking so long?
George Jones
Mesa, Arizona
| We keep hearing ½-ton noises from Ram trucks, and we wouldn’t be surprised if a diesel-equipped Ram 1500 comes to be in the next couple of years.
Answer: Like you, we’ve been waiting for the ½-ton diesel trucks to come along for some time now and have even been convinced to report on them a few times. There are many reasons why we haven’t seen these trucks show up yet, from pricing to emissions.
A heavy-duty diesel vehicle has a big advantage in towing, reliability under high load, and efficiently moving its heft. Most people use their ¾-ton trucks to tow, or as all-around work vehicles. Although ½-ton truck owners tow small loads occasionally, most just use their trucks to jaunt around town. With diesel engine options currently at a $7,000 premium, the manufacturers aren’t convinced the public is ready to spend that type of money if they don’t need to.
Another large wrench in small diesel trucks coming to market is emissions regulations. Until technology catches up with federal mandates, manufacturers are stuck using expensive after-treatments and exhaust catalysts to meet emissions standards, which means even more money. In addition to these measures, the diesel fuel economy advantage is also cut short of what it could be due to EGR, particulate filters, and engine computer strategies designed to limit NOx.
So in summation, there are still roadblocks for ½-ton diesels, but if the Jetta TDI is any indication, there is a market for diesels in smaller, lightweight vehicles—it’s just going to take a manufacturer to step up to the plate and do it.
The Real Story Behind IFS?
Question: I have a friend who says independent front suspensions have no business on a fullsize truck and that I should avoid buying a GMC or Chevy with the 6.6L Duramax because of the fact that it has IFS. Is he right, or do those trucks hold up pretty well?
Jonathan Moon
Orlando, Florida
| Even the abuse of off-roading is no problem for GM diesels, as long as proper upgrades are made to the suspension and steering system as wheel and tire size is increased.
Answer: Especially with the off-road crowd, who favor solid axles, independent front suspension has gotten a pretty bad rap over the years, but there are pros and cons of each setup. The theory goes that IFS is much weaker than a traditional solid-axle, and that since there are many more wear points, it is more costly to maintain. While this was true of older independent fronts, the front suspension on the new Duramax-powered trucks is actually very good.
In stock form, we’ve done repeated boosted launches in four-wheel drive, without as much as a hint of a problem. We also did some pretty aggressive off-roading in last year’s Truck of the Year test, and we could find no weak point in the GMC’s front end. So from the factory, it’s clear the IFS is one stout piece of hardware.
However, it should be noted that the stock suspension was never designed for the type of lifts or tire sizes many people put on their trucks. When it comes to lifts, huge tires, or sled pulling, the front end needs some help, in the form of tie-rod sleeves and steering braces, the likes of which can be ordered from places like Pacific Performance Engineering (PPE). If your rig is rolling on big tires or lifted, these are a must-have—without them you can break or bend a tie rod.
Regardless of whether you have stock suspension on your stock truck, or a modified suspension on your modified truck, we wouldn’t shy away from a GM product because of its front suspension design—they are very reliable.
New Injectors and a Drop in Mileage
Question: I have an ’03 Dodge with the 5.9L Cummins with 258,000 miles on it. Recently, all my injectors were replaced, and I was told all six of them were bad. Before, I was averaging 22.4 mpg city/highway and could get almost 17 mpg while towing. Now, with the new injectors, I am lucky to get 17.5 mpg as an average. Is there any reason the mileage would drop this much, and how can I get some of it back?
George Woodbury
Lillington, North Carolina
| We’ve heard outrageous 25- to 30-mpg claims by Dodge owners (especially manual transmission owners, for some reason), but if by some chance your Dodge is getting crazy mileage, you might have to look into replacing an engine soon.
Answer: This is a common issue with the newer Dodges, and there can be a few reasons why there will be a mileage drop with the replacement injectors. For starters, 17 mpg while pulling a trailer and 22.4 mpg around town is absolutely excellent—almost unheard-of type of fuel economy figures—while the 17.5 mpg you’re getting right now seems to be about normal. So the real question is, what was going on to make the mileage so good before, that isn’t happening now. For starters, when injectors go bad, it can throw off the overhead display. What happens is that initially, folks do a test and find out that the truck’s dash display more or less matches the hand-calculated fuel economy figures. As the injectors start going out, the mileage will be way off, but the truck owners will still go off the electronic settings.
If the mileage has been hand-calculated, there is still a reason why it can be way off. When the injectors fail, they will start leaking extra fuel during injection events. Since the newer Cummins common-rails have a pretty decent-sized pilot injection event, extra fuel at that moment will add a lot of timing to the overall injection event. More timing will also add power, meaning less fuel (throttle) is required to get the same amount of work done. The downside to this is that more fuel earlier also puts more heat in the piston, and it can result in a melted piston, especially while towing with bad injectors. While the mileage might be awesome, it ultimately isn’t worth the repair bill.
To get some of the mileage back, you’ll need to add the timing the bad injectors were effectively giving you. While you probably won’t see the numbers you did before, your pistons will be much safer. Many programmers such as the H&S, Banks, and MADS Smarty have timing added to their tunes, which should give you a safe fuel economy increase with your new injectors.
