Poofy Goof Rant-O-Matic

I have a 1991 subaru loyale. it's only a couple hundred miles away from 200,000, and has become my "bucket" workhorse vehicle. as it has aged, various problems have cropped up, mostly electrical, but one long term problem that's been getting worse has been the engine timing. it had been pinging under load, which I offset by using 89 and 92 octane gas in it, but under load even 89 octane had started to ping, and with gas prices close to 3.50/gallon for the 92, I've been investigating the feasability of getting it to run on cheaper 87.

the timing had been advanced slightly years ago, (likely unchanged since the 100,000 tune-up,) and by retarding it, I got all pinging to dissapear, but now the engine runs a little hotter than it previously did, and economy has gone down from 25mpg to 20mpg. I'm not overly concerned about the temperature, as the engine used to run quite a bit hotter before the radiator was replaced. however, I am concerned about economy.

enter the Intellitronix Air/Fuel Gauge: http://www.jetlink.net/~okayfine/su/airfuel.html

the subaru ECU is already wired for a single-wire O2 sensor, so it seems it would be rather straightforward to wire in an air/fuel gauge. this would let me advance the timing based on unburned fuel, instead of listening for pinging. it would also give me some economy indications.

while I'm wiring about the engine, I could add a light for the ping detector, to make sure it's working correctly, as well as getting visual indication of pinging.

all to be done in my copious free spare time, of course!

update, 2008-03-19

after going in for its 200,000 mile overhaul which involved fixing a coolant leak, and replacing various gaskets, seals, sensors, and filters, the "subaru of the apocalypse" now runs fine on 87 octane without any engine grumblings or MPG loss. under heavy throttle I still get a little bit of smoke, but the necessary ring job to fix the cause would cost more than the car is worth at this point. ("fair" blue book value is ~$900. hooray.)