my car doesn't have user adjustable ignition timing. the ignition hall effect sensor is run off the flex plate on the bell housing. theres nothing to adjust since the flex plate isn't adjustable, and the sensor fits in a hole in the bell housing, i cannot rotate it to advance or retard the timing. the only way to adjust the timing via conventional means is by using a drb-3 scan tool, these cost about 4000 usd, which is more than my entire car is worth. that option is going to be alwalys and forever out of the question.
so i had an idea, since the cars computer advances the timing based on input sensor signals, i should perhaps modify one of those to increase timing. i looked up my factory service manual and it turns out the map sensor is what is primarily used to advance or retard ignition timing. other sensors are the coolant temp, air temp, a/c, tps etc. the map sensor has most control however.
since the computer advances timing under high vacuum and retards it under low vacuum, i figured that i should lower the map sensor output voltage a little bit. im sure you have all seen instructions on how to use a voltage mod on a map sensor.
http://www.angelfire.com/my/fan/MAP_adjuster.html
i had seen this and decided that i could use his method to adjust my ignition timing but i wanted to do it an easier way that did not have adjust ability. i wont need constant adjust ability for timing. so i plugged in a autotap data logger i have and went for a cruise to record the ignition timing at various rpm and throttle inputs. when i got home i started working on my mod. i cut the output wire of the map sensor and installed a 4 amp diode in series with the wire. this dropped the map sensor output voltage by .55V across the entire range of the sensor. for example, if the sensor was outputting 4.6V at zero vacuum (as if the throttle was wide open) then it would now output 4.05v.
if the sensor was outputting 1.8v at idle, it was now outputting 1.25v at idle.
this had the effect of increasing my ignition timing by about 4 degrees across the board except at idle. idle it stayed at 10btdc. but anything higher than idle speed and my timing is advanced a few degrees compared to stock. i tried adding a second diode in series with the first one, but the car didn't run very good and i think i could hear pinging. messing with timing and fuel economy isn't worth engine damage, so i backed off to 1 diode and the pinging went away. my engine ran normally again as well. side effect of this diode is that my engine seems to be running leaner during a warm up from a cold start. hey that sounds good to me.
wonder what other sensors i can mess with.
csrmel 
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