More Carbon Build-Up Problems
Extracted from July August 2014 - Australian Workshop Manager, Technically Speaking Article by Maurice Donovan Products referenced in this article;
Our customer was complaining of excessive fuel consumption in his V6 Kia Carnival. As we worked through our intensive list of possibilities that may cause this issue, (I am happy to email anyone this list should you like a copy) we came to the primary and secondary ignition integrity checks that are on our list.
So out comes my Pico lab scope. As this car has a built-in igniter in the coils, it is not possible to check the primary side of the ignition system, but we can check the secondary. We only had access to the 3 outside coils and plugs as the other 3 are hidden under the intake manifold on the firewall side of the engine.
The first cylinder that was checked had a good secondary pattern, so we moved to the next cylinder and we discovered a short burn time. We only had .77 ms (millisecond). We should have had at least 1.3 ms or longer at idle. So we swapped plugs and coils from the good cylinder to the bad cylinder expecting the problem to transfer. Often short burn times can be a result of a bad plug or coil. The problem did not transfer.
The length of the spark burn time is directly affected by the amount of secondary coil voltage available. The amount of voltage required to overcome secondary circuit resistance and create the spark and the amount of voltage remaining to sustain the spark (in relation to the conditions within the combustion chamber).
Factors that have direct effect on Spark Burn Time Duration include;
- Coil output (energy) Secondary circuit resistance
- Air/Fuel charge quality and quantity
- Secondary short circuits that cause the spark energy to be shunted elsewhere
- Low primary circuit current
So, by swapping the coil and plug we have ruled out Coil output, secondary shorts (at least in the coil or spark plug) low primary current (we had a steady 12v into the coil, the primary transistor is tricked from the PCM and is built in the coil). That leaves Air/ Fuel charge quality and quantity.
There is one more variable that will affect the burn time of the secondary, and one we needed to check. We already knew we had good cranking compression, but did we have good running compression? Low compression can also cause a short burn time.
So we used my pressure transducer and hooked it to our Snap- On Modis lab scope. Running compression is usually half the cranking compression, and the running compression was good, but the whole compression wave pattern looked very messy. We then checked the good cylinder and it looked clean.
We had previously checked fuel trims and O2 readings which were good. We know if we have a short burn line due to fuel mixture quantity it will be because it is lean. A rich mixture will increase the spark burn time. So if we had a lean condition we would see more fuel being added, but this was clearly not happening. The other strange thing was it was only one cylinder (that is of the 3 front cylinders, we could not access the rear 3 cylinders) that had a short burning duration.
We were a little confused, but wondered if a build-up of carbon in the combustion chamber could be affecting the fuel ratio in this cylinder. During the combustion process, carbon will accumulate on hot components within the combustion chamber with an exceptionally grainy composure, making it extremely porous and a natural absorbent of additional raw or unreacted hydrocarbons. Heavily carboned valves become a very effective fuel sponge, absorbing greater and greater quantities of raw hydrocarbons before they open. This effectively causes a lean air/fuel charge to be drawn into the chamber.
We decided to carry out an intake system service. My preference is to us a BG206J, which is a very powerful de-carboning chemical that will soften the carbon and dissolve it into harmless particles that will safely burn off as it goes through into the combustion chamber and out the exhaust. The last thing you want is for hard pieces of carbon to flake off and cause damage to the engine.
BG products use a special apparatus that is used with compressed air into the dispense canister that safely atomises the BG206J chemical into a very fine mist that is safely drawn into the combustion chamber as the engine is idling. This product has proven to me to be very effective in the cleaning off carbon.
Any carbon that has not been completely cleaned by the BG206J is now softened and is later cleaned out by a very powerful fuel treatment I use (BG208J) that is poured into the fuel tank. This is slowly disbursed through the normal fuel going through the engine and continues to clean the injectors and the combustion chamber as the chemical goes through the fuel system. After this treatment we hooked up our Pico lab scope to the secondary coil of the bad cylinder, and the results were astonishing, we now had increased my burn time from .77 ms to 1.3 ms. I was very surprised.
We then decided to recheck the running compression on this cylinder and the results were even more surprising as we had the perfect compression waveform pattern. No longer was it messy to look at.
Sometimes we waste hours chasing a fix and often leave the simplest treatments to last. I have been using BG products for a long time with enormous success in improving driveability and fuel consumption issues. But until now I had never had such powerful evidence as to how much carbon affects the secondary burn time and how powerful the use of a good brand carbon cleaning treatment is.
I plan to experiment further with my findings and see how other vehicles can improve after intake services.
- Maurice Donovan