After removing the cylinder head on my B230 turbo engine
I noticed huge amount of carbon build up on cyl 4 only.
Almost entire combustion chamber was filled with it.
Other cylinders were not bad.
What could have caused this ? Should I change the brand
of fuel I'm using ?

I would guess bad/partially clogged injector. The gas is being injected in the right amounts, but not properly atomized with the right spray pattern for optimum combustion. If the head is off, might as well send them all out to be tested and cleaned. http://www.theinjectorperfector.net/
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Gary Gilliam Sumerduck VA, '94 940 na Regina 150k, '86 240 180k

My first thoughts would be a bad or gummed up oil control ring in that one cylinder. I've seen gummed up rings that had good compression and the vehicle ran fine it simply burned up the oil. In two weeks time the car would use up at least two quarts of oil and the remaining oil would be badly burned and discolored. The inside of the valve cover was covered in carboned up crud. Mind you this was on an engine with about 300K on it but the owner had changed the oil like religion every 3K and used castrol GTX from day one. I know as I did darn near every one of those oil changes. From one oil change to the next it went from spotlessly clean under the valve cover to an absolute sludge bucket. As a last ditch effort I ran two cans of engine flush through it. Change the oil and filter, install one can of motor flush and repeat in 1K. Initially the results were not that good but over a period of a few months the car has quit using oil and is good to go again. Without an engine tear down it is hard to really say what was going on there but I would theorized that the oil control rings were gummed up and causing the problem.
If you have the head off of it you may want to soak the rings down with something to penetrate and dissolve anything like that. Another source for the problem could very well be a leaking valve seal, allowing oil to get into that cylinder. Whatever the cause is it is obviously localized to that cylinder alone.
As far as changing your fuel goes I would run Chevron and be done with it. IF you chose to run something else then I would dump a bottle of techron in it on a regular basis. You need something to keep the injectors clean and you need to change the oil regularly, every 3K.
Why did you pull the head? Are you just going to stuff a head gasket in it or are you going to have a valve job done while it is out. At the very least I would have it hot tanked and stuff in some new valve seals. You will need to get all of the carbon off of the back sides of those valves. We used to have a unit that would blast that stuff off using walnut shells while the head was still on the car. It really worked well for cars that started and stalled in the morning.

Good Luck, Mark

The inside of the valve cover was covered in carboned up crud. Mind you this was on an engine with about 300K on it but the owner had changed the oil like religion every 3K and used castrol GTX from day one. I know as I did darn near every one of those oil changes. From one oil change to the next it went from spotlessly clean under the valve cover to an absolute sludge bucket.

I'd have expected this engine to be quite clean--despite the high mileage. Do you know what types of driving was done on this car; IE short trips to work or lots of highway etc?
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Norm Cook Vancouver BC; 1989 745T 204,000KM

This guy happens to be a copier salesman in the L.A./Orange County area. He does a fair amount of freeway driving but depending upon the time of day you are trying to do that it can be stop and go driving. I'd have to say it was a mixed bag though with about as much of one kind of driving as the other. His engine was spotlessly clean too and I had done a head gasket on it within a year of it turning into a sludge bucket. So when I say it went from spotless to sludge bucket I really mean it.

Mark

I have noticed large carbon build ups on plugs from bad turbo hoses. I don't mean to insinuate that your hoses are bad, only that a large carbon build up occurs very suddenly from a rich running situation. If you are getting this on only one cylinder and not all as occurs in a bad hose situation, I would suggest inspecting the ignition system on the one cylinder that is effected. It must be that you are not getting adequate spark in that cylinder and hence it is running rich. This could come from a problem in the ignition system or perhaps a faulty (or fouled) plug.

I will watch with interest to see if you get more responses.

I would not think it is the fuel as that would affect all cylinders. It could be in the plug wires, plugs, cap or rotor - possibly the injector. A compression check would probably be the first order of business. If that is pretty even across the cylinders (ck faq's for the procedure)then it has to be in one or more of the other areas.

On some distributors there is a hall sensor that can cause runnning probs - but that is probably not it.

Be blessed in your quest!
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'89 764 (110K), '94 940T (180K) , '92 745T (totaled 2-10-05 RIP)