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Prior to the head gasket replacement job on my 82 T 8V, the engine's performance was noticably affected. Boost under any condition was out of the question as that would only cause misfiring and a screen of fog to blow out the tailpipe. The initial warm-up was also filled with misfirings and a difficult idle. Right before the gasket replacement I pulled each spark plug for an inspection. As expected, they were a mess, a combination of oil and coolant deposits, plus misreadings from the O2 sensor telling it to burn rich. When I pulled the head, the combustion chamber ceilings and piston crowns were caked thick with both loose and hardened carbon. I'll guess that the hardened carbonizing occured well before I took over ownership of this car and began using premium gas only and doing proper regular maintenance. A reasonable guess considering the seriously ill-kept prior condition plus it's 200K miles.
Cleaning of the combustion ceilings and piston crowns was a combination of kerosene, carb cleaner, various scraping tools, sandpaper and steel wool.
After reassembly and a period of moderate driving to ensure the gasket and head were sound, only then did I begin to test the boost. I was quite surprised at the responsiveness! A huge difference between then and now. And I'm not just talking about the few weeks of driving with a failed gasket prior to the replacement. The acceleration in general and turbo boost are markedly better than ever under all conditions.
Before the head gasket job the car would only perform best after the initial warm-up from a cold start. Then as the engine increased operating temperatures coupled with warm to hot conditions outside, the car would bog down. Forget about boosting beyond base psi before the APC system began operating. Now the car can't seem to get to full boost fast enough! Even at the higher temps! When I accelerate wot through 3rd and 4th gears, as I reach the boost limit (9/10 psi) I can feel the APC system suddenly kick in and drop the intake boost pressure.
I can only guess that the now cleaned combustion chambers is the reason for this dramatic performance change. All those petrol company commercials declaring how their premium gasoline with (enter brand name) additives that "cleans essential combustion chambers of performance robbing deposits" weren't lying after all!
The only problem that remained after the head gasket job was an overly rough start-up idle and a curious accelaration hesitation at low rpms. It felt as if the modulating valve was shuttling between a lean and rich setting. Thinking about it, I thought to check the oxygen sensor. It too was caked with carbon. A relatively new one, even if I cleaned off the exterior shield which protects the sensor itself, I can only guess that the sensor function had also been degraded. The only way to know was to replace it and see if there was a performance difference. I did just that and the improvement was immediate.
Speaking of gasoline additives for cleaning, a friend told me of an easy way to clean the combustion chambers by using the fuel system cleaning product Techron, a Chevron oil company product. He said to saturate the combustion chambers with Techron, by either pouring it in through the spark plug holes or the injection chambers, then turning the engine over a few times with the coil wire disconnected from the distributor. Then let it sit overnight. The final step is to start the car the following morning, increase the rpms after a reasonable warm-up period and watch as the disolved carbon is blown out the exhaust pipe. It'll be very obvious - lots of ugly black smoke.
posted by 205.188.19...
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