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I own a 1991 9kt with 105 K and a Jak Stoll chip that experiences what I would describe as a hard to severe miss under a heavy load/boost (12 to 15 lbs)once the engine is fully warmed. It also experiences a similar, less severe miss under moderate load/boost (8 to 10 lbs) when the engine's temperature is above the blue mark, but not fully warmed. It occurs more often when the throttle is applied abruptly under modest boost. The miss almost feels like a backfire when it occurs under heavy load/boost and is severe in my opinion. I have experienced miss from plugs and a bad DI cassette and this is very different.
Car's history:
I have checked/replaced the following components: Plugs, DI cassette, BPC valve, hooter valve, temperature sensor and fuel filter. I also replaced all of the vacuum hoses. I recently replaced the fuel pump with a unit that I was told was good with 70k. however, I have not tested the fuel pressure from either the current or the prior unit. The plugs have hot spots on the ceramic insulator, but otherwise are normal in color. The gap is se a bit below 1.0.
I replaced the head gasket and had the head replaned, checked for cracks and the valves were serviced and the seals replaced. At the time I replaced the head gasket, I found that the block and head had more pitting than I hoped to find. The pitting didn't appear to be too close to the cylinders to cause me to look for another block, so I did a very modest patch job with JB weld and reassembled the engine.
There was evidence that the gasket had been bad for a while before I replaced it. The cooling system had a great deal of crud within in spite of service records that documented regular service fo the cooling system. Also, the owner had complained of coolant loss, but the shop checked the car an found no visible leaks. Go figure!
Anyway, the head gasket is leaking again. As it did before, it leaks compression into the cooling system. Bubbles are visible in the tank and cooland is visible around the head gasket. The engine runs very quietly, smoothly and strong other than the hard miss, of course.
My question:
Could the hard miss that I experienced be caused by the compression leak in the head gasket? It occurred immediately after I replaced the gasket, but I didn't drive the car enough before I replaced the gasket to know if it had this issue prior to my efforts.
I would like to replace the HG ASAP, but I am reluctant to replace the gasket until I know the cause of the hard miss, since I believe that it may have been a contributing or causal factor to the gasket failing after the initial replacement.
My apologies for the length of this letter, but I tried to cover the history of the car and address what I have done in terms of the usual steps to diagnose a miss under boost.
I really like this car and the body is rust free, but I need some guidance. It is my fourth 1991 9kt and I don't want to give up.
Thanks,
Dan
posted by 98.212.79...
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