What does “blow the carbon out” really do?
Occasionally, I will see a car in front of me, floor it (gas pedal), and when they do puffs of black smoke, come out the back of the car as the car hits full throttle. What gives?
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The black smoke means your fuel mix is too rich, aka there’s not enough air to burn all the fuel. In newer cars and trucks this means that something is broken or dirty in the engine.
White-ish smoke at full throttle usually means either the vehicle is using more fuel than air during the combustion cycle (in a petrol engine) and what you’re seeing is excess fuel that has been heated, but not fully consumed.
The right “settings” on spark plugs and air/fuel ratios (usually set via software these days) helps alleviate this.
Some sports cars or cars that have been modified after purchase will intentionally run “rich”, meaning there is a certain level of waste (smoke you’re seeing) that is accepted. The general reason for this is a safety measure for the engine. When changes are made to increase power and torque in a car, if the aforementioned air/fuel ratio swings the other way (when there is more air than fuel), it can do thermal damage to the engine (and beyond).
However, black smoke can also be a sign of other issues. Sometimes oil leaks in various places can cause oil to enter the combustion chamber(s). Then the smoke is coming from oil burning (or more precisely, not burning up all the way). In all but very small cases, oil should not be entering the area where petrol and air are burning.
“Blowing the carbon out” would mean to run the engine up to its highest state of tune (usually high/peak RPMs for a somewhat sustained period of time (15-120 seconds depending on context and capabilities). Someone smarter than me will have to explain whether there is any real benefit to this in modern fuel management systems.
Hope that makes sense.
I recently had this done because my check engine light came on. The dealer said come back in 2 weeks and for $199 we’ll tell you what the light means.
I went to Midas, it was my catalytic converter sensors. They did a fuel injection cleaner, told me to put higher octane gas in the car and put in some STP and drive it 100 miles. For $99, they fixed the problem in 2 hours instead of making me wait 2 weeks to find out what the problem was.
It actually took 140 miles, the check engine light went off, I passed my inspection, and I am good to go for another year. FO Ford dealer.
It’s burning oil, either because it’s a diesel engine or the driver has floored it so often that the engine is worn.
Back in the days of carburetors you could get a build-up of carbon inside the combustion chamber, which if bad enough could lead to poor running. I used to warm up the engine, pull the plugs and squirt in a little RedEx. Leave that to soak in for a while, then go for a ride, trailing white smoke behind me for around 30 minutes.
It definitely ran better afterwards.
These days manufacturers are under pressure to use as little fuel as possible and the days of carbs are long gone. The advice to “blow out the carbon” will only apply to classic cars.
I believe in this context it means to blow the carbon residue buildup, most common in diesel engines.
Driving short distances and not giving it enough revs doesn’t bring the temperature up enough for that carbon to dissolve and so it builds up, diesel is a bit oily and unlike gasoline so it has much more carbon buildup.
Blowing it out now and than mean’s basically going on a highway and driving for some amount of time in like 3000-3500 or maybe even 4000 rpm so that the engine and rest of the exhaust and intake system can reach temperatures high enough to dissolve that buildup and shoot it trough exhaust cleaning the engine in the process.
There are reasons why an engine might produce smoke; other answers here have covered those. But from your description, I imagine you are seeing more of a dark brown “smoke” when someone floors the accelerator and makes the engine run faster than normal as they speed away, even in a car in perfect working order. It both is and isn’t quite smoke in the usual sense of the word, it’s sort of a bit like secondhand smoke: particulate matter that resulted from combustion, but did not escape out to the atmosphere because it got trapped in the crevices and glass-fibre packing of the muffler or stuck to the inside walls of the exhaust pipes. When the engine revs up to a high speed, there’s a greater volume of exhaust flowing through the exhaust system, and at a higher speed. This blows some of that accumulated particulate matter out of the packing and off the pipe walls, and it leaves the tailpipe as a fine dark-brown dust, which looks like a cloud of smoke.
Ahhhh the Italian tune up. With fuel injected motored, the gasoline is either injecteddirectly into the combustion chamber, direct injection, or it is mixed with the intake air,
Carbon builds up on your valves of your intake manifold. The valves are just that, little spring loaded valves thay when open allow air to enter the combustion chamber. Well, above the valves is a crank system called the cambers, most motors have dual cambers, these campers have metal lobes built into the that when rotated, push down on the valves opening them. Anyway, this assembly is covered amd sealed by the valve cover and gasket. This is the top of the bottom you see when looking at your car, where you pour in the oil and draw the dip stick from.
One side has the valves for the intake, while the other controls the valves for the exhaust. Gases from the combustion chamber will invariably leak through the valves and build up in under the valve cover. For this, a blow back hose connect from the valve cover and hooks back into the air intake, to be recombusted and exhausted. This blow back has a mixture of gas, air, oil vapors, and water moisture.
Well, some kf this blow back ends up on the intake valves as carbon deposits. Left untreated, the efficiency of the intake valves decreases, meaning the engine must work harder to supply the same power, aka lower gas efficiency, plus less zip when hitting the accelerator.
The older air fuel injectors would spray gas into the air intake. Gas is a natural solvent meaning it will break down and clean oils, greases, and carbon deposits. The older fuel injected engines would have much less carbon build ups on the valves. The new direct fuel injected engines when new are more efficient and a better system, but because the gas is injected into the combustion chamber and not the air intake, the gas never has a chance to clean the valves. Hence a service should be performed to manually clean them every once in a while.
Back to the older air injection fuel injectors and the heart of your question. In slow city traffic, stop and go, short trips where the care doesn’t have a chance to warm up, etc. The older engines would be prone to carbon build up too. The term Italian tune up is exactly the same thing as the term blow the carbon off. Italian racers were stereotypically fast drivers who proffered the gas pedal over the brake. Like wise, blowing. The carbon off just means driving the car hard for a little bit, getting out on the free way and accelerating to 80mph as quickly as possible, hitting the hills and keeping the rims up for a little while. This forces more gas vapors in those older engines to be injected, effectively cleaning the carbon build up that occired from slower day to day city driving. It actually works in those older vehicles, to an extent at least. Better fuel economy, and power performance and be felt after
‘Blow the carbon out’ is also known as ‘The Italian Tune-up’. Basically red line the engine for an extended period to get it to maximum heat and pressures to burn off/blow out any deposits that built up.
This is different from what you’re seeing when a car ‘floors it’. During the latter, you’re seeing incomplete combustion. Basically, the engine is dumping more fuel into the engine than can be fully consumed until all the components, like a turbo catch up. Diesel engines are particularly bad for this.
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