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My brothers 84' 900t 8v is in tip top shape mechanically...unfortunately the body is another story.
I swapped in an 83' motor w/a new cylinder head & recent Erikkson tranny already bolted on (only $200! :) a few years ago, well seven actually - where does the time go?! Everything was perfect up until last year, or the year before...anyway whenever it was, the engine started knocking before the boost needle got 3/4 up the orange (it used to pull hard to the red). The car still runs great & pulls reasonably hard, but then rattattatt. The knock sensor/APC does NOT cut to reduce the boost. High octane gas helps, but the car used to run fine on regular. We've checked the timing & it's spot on...so we retarded it a little, then a little more - this helped some. The distributor vac. diaphragm is good. The over boost switch has been disconnected/bypassed since before I put the motor in, so that's not it either. I guess there could be some carbon build up, but I kind of doubt it.
I found some info on the Townsend site a while ago regarding an 84' turbo specific CIS engine speed relay (85-78-346 superseded to 85-99-433) which limits detonation at engine speeds over 3800 rpm by locking the Lambda pulse ratio at 75%.
However, the knocking occurs at ANY rpm under 'brisk' acceleration, but not all the time - once in a while the car pulls like "Herbie" :) - though it's been a while since I've driven the car.
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Now here's a twist! - "Fix my Saab.com" makes reference an MSD ignition upgrade Jeff did on his 89' turbo (along w/a lot of other performance mods) that allowed him to use an 84' 900t 8v distributor vacuum diaphragm, because it didn't retard the timing as much as a 16v vac. diaphragm would under boost. So following this logic...could I do the opposite & install a 16v vac diaphragm on the 8v distributor to retard the timing more - thus eliminating (fingers crossed) the pre-ignition?
My 8v CIS knowledge is fleeting & I've purged a lot of it to make room in my head for the newer 16v LH systems...about all I can do w/the old beast now is stick a 3mm allen key into the fuel distributor & twist it until the o2 sensor swings properly.
Thanks for reading & all opinions count.
posted by 68.99.169...
, Tue, 29 May 2007 15:35:33
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