adjusting the ignition timing via the map sensor. - Fuelly Forums

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Old 10-23-2007, 10:01 PM   #1
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adjusting the ignition timing via the map sensor.

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.
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Old 10-24-2007, 04:29 AM   #2
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The map is used in determining how much fuel to deliver. if it thinks there is less manifold pressure it will deliver less fuel, till it warms up and goes into closed loop mode and the O2 sensor can compensate, then you need something like an efie (unless you have a wideband sensor car, then the diode trick or a simple voltage divider will work too).
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Old 10-24-2007, 06:33 AM   #3
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If you want to adjust timing, you'd be better off altering your coolant temp signal. That won't effect fueling as much as altering map signal will.

Running lean means its possible you could damage your engine, and your also increasing the amount of pollution thrown out as well.
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Old 10-30-2007, 08:33 AM   #4
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skewbe, i already have a diy efie.

daox, ive already done the coolant temp sensor, but for other reasons (leaner startup).
im not concerned about pollution in the slightest. damaging me engine is a pretty big concern, but things seem to be going OK.
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Old 10-30-2007, 08:41 AM   #5
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Do you have a wideband sensor?
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Old 10-30-2007, 10:19 AM   #6
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no, and i know that by not having a wideband i am only slightly better than flying blind, but things seem to be going ok. i take the steps slowly and monitor results (and watch like a hawk for ping).
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Old 10-30-2007, 10:44 AM   #7
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Did you follow my meaning on:
http://www.gassavers.org/showthread.php?t=5372#10
?

How are you monitoring the effects of your diy efie?
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Old 10-30-2007, 12:12 PM   #8
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i understood what you had typed, but my results dont agree with youre theory.

my car has a digital instant fuel economy display, as well as an average fuel economy display. i monitor the results by looking at the fuel economy before and after, and verifying it using the old gallons into miles at the gas pump method. i *^*am*^* getting better fuel economy using the o2 sensor ground mod and map sensor mod. individually the mpg is better, and together it is better than either one of them produce alone.
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Old 11-09-2007, 05:21 PM   #9
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Cool

Relocate the crankshaft position sensor itself, or buy a real piggyback.
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Old 11-09-2007, 10:08 PM   #10
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Since you were on Dinos page, I think he also has the link to Hesco's CKPS sensor relocation bracket that moves its to the crankshaft pulley. That would probably give a more conventional adjustment method.

Besides the MAP on Dodge/Chrysler/Jeep ECUS you've got the
Intake Air Temp
Coolant Temp Sensor
Throttle Position Sensor
Crankshaft Position Sensor
Camshaft Position Sensor
and of course the O2 sensors
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