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.
Regeneration During City Driving?
Question: I am curious to know how the newer delivery trucks and larger commercial trucks handle prolonged idling, short trips, and lots of low-speed driving when it comes to their regeneration cycles. Do they have similar exhaust diesel particulate filters (DPF) and sensors? It seems to me that within a short time they would need some long interstate driving to keep things clean.
Dave Beck
Brownsburg, Illinois
| New Ford and GM trucks can be forced to go into regeneration mode while parked by using a scan tool. This can be very helpful when the vehicle sees a majority of city driving.
Answer: Delivery trucks, shuttle buses, and diesel trucks that see extended idling times do have special needs. Within a short amount of time (300 to 400 miles), these trucks will need to see an elevated exhaust gas temperature to clean the DPF. If that cannot occur, a forced, or stationary, regeneration cycle is in order to clean out the DPF. To operate properly, the exhaust going through the DPF needs to be at least 900 degrees for an extended period of time. If this never happens, the vehicle will soon have a plugged-up DPF, and performance will greatly suffer.
So when the driver of a larger commercial vehicle notices the DPF is full (usually there will be a warning light), he can pull over and flip a switch that will manually force a regeneration cycle to clean out the DPF. If this isn’t possible because the driver is stuck in traffic, late to a pickup, or something of the like, then larger trucks will feature a limp mode that allows the driver to continue at a lowered power output. Finally, many large fleets will buy DPF-cleaning hardware and just take care of the heat-induced cleaning at a facility rather than using fuel to perform the task.
Tuner, Programmer, or Nothing?
Question: I recently started my own company transporting vehicles in an enclosed 36-foot Featherlite trailer. I also bought an ’09 Duramax 3500 dualie. I have traveled 90,000 miles since March 2010 and need to obtain better fuel economy since the truck is only averaging 11 mpg towing at 65 mph. A little more torque and horsepower would also be nice. The other very important issue is I don’t want to set my engine or transmission up for failure. The Duramax is my bread and butter.
Scott Johnson
Spring Branch, Texas
| If you plan on driving hundreds of thousands of miles in a short amount of time, a tuner or programmer that maximizes fuel economy can be worth its weight in gold. A 3- to 4-mpg bump over 200,000 miles of driving is approximately a $10,000 savings!
Answer: We get this question more than any other, and it is always a tough one to answer, because we never know the most important aspect of vehicle operation: the driving style of the owner! We’ve seen people trash the transmission in rigs that still had temporary plates on them by trying to do minute-long burnouts and donuts. If you’re going to hammer on your rig, expect it to show you where its weakest link is. If you drive your vehicle in a sensible way, let it warm up to operating temperature before applying full throttle, and are good with maintenance, then it’s probably safe to install an aftermarket programmer on the truck, even if you are using it for a business that demands ultimate reliability, like car hauling.
In all reality, however, even a chipped truck would probably only get 1 to 3 mpg better than what you’re already achieving, as 11 mpg at that speed and weight is pretty good. Running more timing will help with mileage, but it will also put more heat into the pistons, so be careful when the engine is cold or when traveling full-bore up hills. Just because you have an extra 60 to 80 hp doesn’t mean you should use it for extended periods of time without major upgrades. To keep things reliable, we’d use the extra power for passing and other short-duration activities.
GMC Starting Blues
Question: Not long after I turned 16, I was handed down an ’86 GMC with a 6.2L diesel and four-speed automatic transmission, originally purchased by my grandfather. After replacing the water pump, I began driving it almost daily, but it would struggle to start. The glow plugs would stay on for five seconds when the engine was cold, and not at all if it was remotely warm. I replaced the glow plugs, checked the relay and temperature sensor, and installed a high torque starter with only minimal improvements.
| Glow plugs lead a very hard life, as you can see by the burn marks on this unit from a 7.3L Power Stroke.
I then hot-wired the system, which allowed me to manually control the glow plugs. It began to start better, but once the temperature dropped below 50 degrees, it absolutely refused to start, making me park it for the winter. Do you have any idea what else I could check or do to fix my starting problem?
Brandon Pomedli
Englefeld, Saskatchewan, Canada
Answer: Perhaps some of the biggest advancements in diesels come in terms of their ability to start in cold weather. The older engines, such as the 6.2L GM diesels, may start with a lot more difficulty than newer versions, but firing in 50 degree weather shouldn’t be an issue—even for the older trucks. First, we’d look back at the glow plug system and make sure you have a quality set of glow plugs, such as AC-Delco 60Gs or Bosch Duraterm glow plugs. If your glow plugs aren’t working like they should, that could be the cause of your hard-starting issue. There’s also the possibility that air is getting in the fuel system somewhere, or you’re starving for fuel. We’d check the lift pump to make sure it has pressure, and the filter and all fuel lines for leaks. As a general rule, diesels don’t like starting when it’s cold out, and an insufficient fuel supply just makes things worse. An air-free fuel system and quality glow plugs should cure your starting woes, as long as your injectors and injection pump are in reasonably good shape. You made no mention of how many miles there are on the engine, but worn injectors and worn piston rings often show up first when trying to start a cold engine.
