This article originally appeared in
Big Rig Owner
January 1, 2015
By Bruce Mallinson
“My truck smokes!” Many times during the week, I will answer the phone and hear this statement. Before I can help you, I will first need to know what kind of truck and engine you have, when it smokes, and what color the smoke is. Once I know all that, I can help. There are four kinds of smoke: white, blue, black and black just when you shift. Usually, it is the last one. If you are seeing black smoke when shifting, you are shifting at too low of an RPM or your right foot is too heavy on the throttle when the turbo boost is below 8 psi. Let’s look at this issue first, then go over the other types of smoke later in this column
It takes 8 psi of boost to turn black smoke into clear, and if your fuel system is responsive and you push too hard on the throttle, the engine will produce black smoke until the turbo boost gets to 8 psi. Eight is the magic number, and you should know when your engine has developed 8 psi of boost by the sound of the engine and the turbo. Also, you should have a small spot mirror on the top of your driver’s side mirror bracket looking up at your stack. With one eye on the spot mirror and one eye on the turbo boost gauge, accelerate slowly. Once you get to 8 psi, give her more fuel, just don’t mash on the throttle, roll into it gently. This one change in your driving habits should decrease your amount of black smoke you see when accelerating or shifting.
Back in the days of the mechanical engines, there were aneroid valves that did not work very well so they were removed. Then, in late 1977, Cummins put the aneroid valve into the AFC fuel pump. It had some problems for a couple years, then the engineers at Cummins got them working perfect, but they were a little on the light side for fuel. We figured out how to make the adjustment so you still had response when starting out and when you shifted a gear with only a slight puff of smoke. If you were easy on the pedal, there was no smoke.
Then came the electronic engines. The engineers at the engine companies knew it took 8 psi of boost to make the stack smoke clear, however some of their calibrations were too restrictive on the fuel and it took as high as 14 psi of boost to allow the engine to have fuel so you, the driver, could pick up the load and go. When the ECM will not give the engine fuel, the driver keeps pushing on the throttle until something finally happens. This is very hard on the driveline and the drive tires, and the end result is a lazy truck that is very annoying to drive and hard on fuel. Once you get used to driving this type of engine, which takes a heavy foot, you have to re-train yourself to be gentle on the throttle again once the ECM is set properly. The spot mirror looking at your stack and the turbo boost gauge on your dash will help you get back to driving properly (with a light foot).
If your engine is responsive and makes the black smoke when starting out or shifting and you ask an ECM programmer to take that out, the engine will lose some of its response. That is okay, and that is how we prefer to set up an engine, but you still have to do your part, which is to be gentle on the throttle. After all, it’s your driveline, fuel and drive tires you will be saving! Truck stop ECM tuners are NOT setting the ECM properly, which is why they are working in the parking lot (like the lizards used to) and not in a shop. If your truck produces black smoke while pulling a hill, that is an entirely different issue.
If your engine is producing 10, 15, 20 or even 25 pounds of turbo boost under a steady pull and there is black smoke coming out of the stack, then the overhead needs to be set, the charge air cooler or air intake system has a leak, or the injectors are worn out. Black smoke under a steady pull is different than black smoke when starting out or shifting. If your truck is making blue smoke it either has bad valve guides, a bad turbo, or a worn-out engine altogether (if that is the case, it might be time for a rebuild). If you are seeing white smoke, the bottom O-ring on the injector could be cut, burned or shaved, or an injector tip might be cracked, which allows un-atomized fuel to get into the combustion chamber. We can help you correct these issues.
Let’s switch gears to injector and valve settings. Back in the days of the mechanical engines, the valves and injectors had to be set at least once a year, or about every 100,000 miles. With the electronic engines, the mileage can be extended to 200,000 miles. If you run really extended oil drains, you might want to have yours checked every 150,000 miles – as the bushings in the rocker arm and shafts wear out, the valve and injector adjustments will go out of spec sooner. We recently had an Acert Cat in for an overhead setting – it had been 600,000 miles since the last setting – and we found a broken actuator housing caused by loose valves (see photo above).
The price of this part was $879. Save your injectors, valves and money by making it a regular practice to get your overhead set every 200,000 miles. And, always ask the mechanic how far out of adjustment it was – if only .001, you can do the next adjustment at 250,000 miles.
The better your preventative maintenance, the longer your truck will stay running in like-new condition. The next time you call me about your truck smoking, please be ready to tell me exactly what type of smoke you have – this will help me to better diagnose your problem and let me know that you read this article! If you have any questions, I can be reached at Pittsburgh Power by calling (724) 360-4080 or via e-mail at firstname.lastname@example.org.
Many of the articles compiled here where written by Bruce Mallinson. Attribution to other contributors is given in the specific articles.