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for the past few weeks i have had the 90 900t laid up due to coolant loss and steam in the exhaust. initially i suspected a shot headgasket so i spent a friday night and saturday changing it out only to find continued, and even increased, coolant loss and steam in the exhaust. with given symptoms only other real possibility was the head. also of note when i initially had the head off, was that combustion chamber #2 was black. despite noting a blacker spark plug in #2 than the others, it never really looked that far off. however, it was obvious that #2 was getting too much fuel. when i looked into the intake manifold, i noted that the #2 injector was the only one that was wet; apparently partially stuck open (at 72# that can be a lot of fuel...). all of a sudden, my problems with tuning made sense. i can remember gradually decreasing the global fueling in my map to compensate for increasing richness of the fuel mixture. i can remember still getting pretty bad gas milage. in essense, i was compensating for the richness of #2 and leaning out the other 3 cylinders. as a result, a couple burnt valves were noted in the other combustion chambers.
so my new head arrived yesterday. i spent this morning pulling the head, getting quicker by the way (only 3 hours to have head on the bench). and just finished getting it back on and timed. i'll finish it up tomorrow.
but when i pulled the head off this morning, i found the smoking gun in the head. cylinder #2 which was the black one (too rich) had a puddle on top of the piston. when i flipped over the head, i noticed a crack between the exhaust and intake valve in the combustion chamber. it must have been covered with gunk the 1st time i head the head off. plus, i assumed the crack would have been in a cylinder that was experiencing more lean conditions than rich conditions.
i'm pretty stoked that the issues i experienced over the past few months all now seem to make sense. cylinders were running uneven. i was adjusting global fueling to compensate, but i was not correcting the problem. so tomorrow, i'll get her going again. i have a new injector, new head with redone valve seats. the car tomorrow should be the champ i originally had going. can't wait to get it on the road again...
posted by 24.60.15...
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