Why does your diesel engine smoke under load?

Answer 1

A conventional diesel engine will smoke excessively under load in situations whereby the engine rpm are too low for the throttle position ie, your throttle is opened too far and the revs are too low for the load the engine is expected to move- This is sometimes called "overfuelling". It basically means there is too much diesel being injected in relation to too little air being induced into the engine, in the same way that when you pour too much charcoal onto your barbeque fire it smokes because you are smothering it and there is not enough air. The amount of air that is induced into your engine is proportional to the engine rpm on most diesels like old landrovers, so don't change gear too early, or lug your engine. You will notice if you look in your side rearview mirror that when you go up a steep hill it may smoke excessively if you step on the gas pedal too much, but you will also notice that beyond a point you will get no corresponding increase in power, in other words you are just pouring fuel into the engine which is not even being burnt properly, and you are just wasting fuel and carboning up your engine. Some modern diesels overcome this problem by electronics. The gas pedal position is measured in conjunction with the air intake pressure and engine rpm and if you floor the pedal with the revs being too low, the computer will to some extent override your decision to prevent wasteful and incomplete burning of fuel.- This "drive by wire" system has its dissadvantages, imagine if a rat eats your wiring loom or there is a bad connection, you could have no throttle. the conventional system is better if you monitor the amount of overfuelling as you drive and tap off a bit when the smoke gets excessive.