# How do coal rollers control when their vehicle spews black smoke and when it does not? **URL:** \ **Category:** Factual Questions\ **Created:** [July 14, 2021, 10:09pm UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512 "2021-07-14T22:09:37Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [July 14, 2021, 10:09pm UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512/1 "2021-07-14T22:09:37Z")
There are people who - intentionally or not - have vehicles that spew out thick clouds of black smoke. Sometimes they purposefully release the black smoke to harass protesters or someone they don’t like. But - how do they control it specifically? I’ve been behind some of these vehicles, and they didn’t spew smoke **all** the time, not, for instance, every time the driver pressed the gas pedal. What is the combination of pedals (or other things) they do to belch smoke on command? ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [July 14, 2021, 10:22pm UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512/2 "2021-07-14T22:22:51Z")
They install a switch that causes the engine to run extremely fuel rich. Most of the fuel goes unburnt and ends up as particulates in the exhaust. There are various means of implementing the switch, but most of them involve lying to the ECU in some way. At least one device plugs into the OBD-II port (a diagnostic port available on all vehicles) and sends commands. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [July 15, 2021, 5:25pm UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512/3 "2021-07-15T17:25:28Z")
This is specifically an issue with diesel engines that tend to produce a lot of particulates, especially if the diesel particulate filter is removed; running the engine fuel risk produces a large mass of diesel particulate matter (DPM) that are the characteristic of “coal rolling”. Note that DPM emissions are classified as a IARC Group 1 carcinogen linked to lung and bladder cancers as well as general emphysema, COPD, asthma, and cardiac disease. Other Group 1 substances include asbestos, hexavalent chromium compounds, polychlorinated biphenyls, and cadmium, all substances you wouldn’t want to be inhaling or ingesting. Stranger ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [July 15, 2021, 9:37pm UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512/4 "2021-07-15T21:37:53Z")
> [@Dr.Strangelove](#): > > There are various means of implementing the switch, but most of them involve lying to the ECU in some way. It starts with a “DPF delete” kit, which allows the user to remove the diesel particulate filter in the exhaust system. These have been commercially available for some time, championed largely by truck owners who don’t like the exhaust restriction, power loss, and maintenance that results from having that filter in place. Modifying emissions components like this is illegal, and the EPA has been working hard to get these things off the market. The DPF delete kit by itself is not enough to roll coal. AIUI, the “lie” told to the ECU that makes the magic happen has to do with manifold pressure: if you convince the ECU that the engine is at high turbo boost, then it’ll inject all the fuel you ask it to when you step on the accelerator. If the boost isn’t actually that high, then you’ll end up with a rich mixture and make black smoke. I expect you’d need to spoof the manifold pressure sensor, _and_ also do something to limit the boost - either open the wastegate, or disable the variable geometry feature (if it’s present on the turbocharger in question). ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [July 15, 2021, 9:45pm UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512/5 "2021-07-15T21:45:30Z")
It goes to show that coal rollers are not merely opportunistic assholes. They’re people who have spent time and hundreds or thousands of dollars to modify their vehicles. It’s premeditated assault. ---
**Author:** ![Ranch\_Dip](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranch_dip/32/5238_2.png) [@Ranch\_Dip](https://boards.straightdope.com/u/Ranch_Dip)\ **Post date:** [July 15, 2021, 10:00pm UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512/6 "2021-07-15T22:00:00Z")
> [@Dr.Strangelove](#): > > They’re people who have spent time and hundreds or thousands of dollars to modify their vehicles. The ones I have seen have the dual overhead pipes. ---
**Author:** ![Spiderman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spiderman/32/230_2.png) [@Spiderman](https://boards.straightdope.com/u/Spiderman)\ **Post date:** [July 16, 2021, 1:32am UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512/7 "2021-07-16T01:32:07Z")
> [@Ranch\_Dip](#): > > The ones I have seen have the dual overhead pipes. I’ve seen plenty in the normal location; however, they’re _always_ oversized pipes - 2-3x the diameter of a standard exhaust pipe. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [July 16, 2021, 3:40am UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512/8 "2021-07-16T03:40:06Z")
Given that the modifications are illegal and substantial and that coal rolling is used offensively, it’s surprising that the perps aren’t charged very quickly. I would have thought their plates would be reported by the first victim. ---
**Author:** ![jjakucyk](https://avatars.discourse-cdn.com/v4/letter/j/3d9bf3/32.png) [@jjakucyk](https://boards.straightdope.com/u/jjakucyk)\ **Post date:** [July 16, 2021, 1:29pm UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512/9 "2021-07-16T13:29:26Z")
Being in a vehicle nullifies many consequences, whether explicitly or implicitly. When a dangerous action is normalized by society, and driving a vehicle absolutely qualifies, it’s operating heavy machinery after all, it is no longer deemed dangerous by the law. Thus many behaviors that would get you quickly arrested if you were doing it as a pedestrian on the sidewalk are brushed off if you’re driving a vehicle. Coal rolling is assault, so is swerving towards cyclists, or passing too closely, even accelerating too quickly. But there’s a “no touch no crime” mentality from police when it comes to vehicular threats, even though assault, by definition, does not require contact. Very much a double-standard. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [July 16, 2021, 1:33pm UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512/10 "2021-07-16T13:33:56Z")
Understood but I would have thought that reporting someone coal rolling to those responsible for vehicle emission standards would result in action. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [July 19, 2021, 5:01pm UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512/11 "2021-07-19T17:01:31Z")
States don’t usually check individual vehicle emissions unless they have a problem meeting NAAQS: > **[National Ambient Air Quality Standards](https://en.wikipedia.org/wiki/National_Ambient_Air_Quality_Standards)** > > The U.S. National Ambient Air Quality Standards (NAAQS, pronounced /ˈnæks/ naks) are limits on atmospheric concentration of six pollutants that cause smog, acid rain, and other health hazards. Established by the United States Environmental Protection Agency (EPA) under authority of the Clean Air Act (42 U.S.C. 7401 et seq.), NAAQS is applied for outdoor air throughout the country. > The six criteria air pollutants (CAP), or criteria pollutants, for which limits are set in the NAAQS are ozone (O3),... If a state or region is found to be in violation of EPA-mandated NAAQS, then they’re required to develop a SIP: > **[Basic Information about Air Quality SIPs | US EPA](https://www.epa.gov/air-quality-implementation-plans/basic-information-about-air-quality-sips)** > > This page provides basic information on a State Implementation Plan. A SIP is a state’s plan for achieving NAAQS compliance and often targets privately owned vehicles, either with an annual smog check requirement, or (as Denver does) a drive-by roadside emissions check. > [@How does this drive-by emissions test work? (Northern Virginia)](https://boards.straightdope.com/t/how-does-this-drive-by-emissions-test-work-northern-virginia/845513/15): > > The typical location is a highway on-ramp where you are accelerating, i.e. you’re making a significant amount of power (and therefore a useful amount of exhaust). The measurement is optical: the system is sending a light beam across the roadway, roughly through the region where your car will be spewing exhaust, and a receiver on the far side of the road measures the attenuation of specific wavelengths of the beam by the components of your exhaust. The higher the concentration of criteria pol… If a state is in NAAQS compliance, then they often aren’t equipped to do emissions checks. As noted upthread though, the EPA is targeting bigger fish, with some success: > **[EPA says Windham dealership tampered with truck emissions controls](https://www.pressherald.com/2021/07/16/epa-says-windham-dealership-tampered-with-truck-emissions-controls/)** > > The federal agency is seeking a $168,700 fine for the alleged violations of the Clean Air Act. > **[Clean Air Act Vehicle and Engine Enforcement Case Resolutions | US EPA](https://www.epa.gov/enforcement/clean-air-act-vehicle-and-engine-enforcement-case-resolutions)** > > The Clean Air Act requires new engines and equipment sold or distributed in the United States to be certified to meet EPA-established emissions requirements to protect public health and the environment from air pollution. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [July 19, 2021, 5:39pm UTC](https://boards.straightdope.com/t/how-do-coal-rollers-control-when-their-vehicle-spews-black-smoke-and-when-it-does-not/946512/12 "2021-07-19T17:39:28Z")
Like who? The EPA doesn’t really have any law enforcement capabilities toward personal vehicles. As noted above they are _seeking a fine_ for the Windham dealership for making alterations to some trucks, but they can’t levee a fine against personal vehicles on a one by one basis. No manpower or enforcement capabilities. Large areas in the US have no vehicle inspections at all. My area in Oregon does not. In the 20 years that I have had my muscle car the Dept of Motor Vehicles has never even seen the car. I just go on line to apply for new registration tags, get them in the mail, and put them on myself. They have no idea of the modifications I may have made.