Adjustable MAP Sensor
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Transcript of Adjustable MAP Sensor
1/11/12 Adjustable MAP sensor
1/9jeep-xj.info/HowtoMAPsensor.htm
Adjustable MAP sensor
The MAP sensor ( Manifold Absolute Pressure ) has a 5 volt input and then reduces this
voltage according to throttle opening, altitude etc and sends the signal to the ECU. So by
supplying a higher or lower voltage, the return signal is varied by the same amount. This
can be used to fine tune the air fuel ratio at throttle openings over 80% and before the
engine is up to temperature. This can be an aid in getting better fuel economy under those
conditions but I have also used it to stop engine pinging after fitting a stroker engine for
a customer. Many stock engines also do this when running lower octane fuels. So what I
did was follow Dino's write up and take 12 volts and run in through a potentiometer and a
voltage regulator so I could adjust the input voltage to anything I wanted. If you supply a
higher voltage, the effect is that the injectors stay open longer so it is richer and vice a
versa. You can however only tune from 80% throttle opening to wide open throttle when
the ECU is in open loop mode. This is because below that the ECU will keep it as close as
it can to lambda 1 or stoichiometric which is 14.7 parts O2 to 1 part fuel. At WOT
throttle though it ignores the o2 sensor and relies on the map sensor to set the length of
time the injector is open. The other time is when you are running cold before the
thermostat has fully opened where the O2 sensor is not read either before it goes into
closed loop mode. This is a big reason not to run a lower temp thermostat as the ECU will
be waiting for it to reach operating temp but it never gets there if a lower one is used
effectively keeping the ECU in open loop mode where is does not read the o2 sensor.
Part list needed below which can be bought from Radio Shack, or here in Australia, Dick
Smith or Jaycar:
Multi-turn (15) Cermet Potentiometer 1000 ohm
LM317T Adjustable Voltage Regulator
220 ohm metal film resistor
Mini Terminal Strip
Heat sink for Regulator
SPDT toggle switch
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You start with the regulator by bending the two pins outwards and then down so it can be
inserted into the terminal strip. I had to extend them by just soldering on some wire cut
from the resistor. It is then placed into the terminal block No. 2, 3 & 4. Only No.4 should
be screwed down at this point and the other two when the resistor is added.
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The potentiometer is added using only the last two pins into No. 1 & 2. The resistor is
added to No. 2 & 3.
Time to add it to the box you wish to keep it in. I just used a small one sold at the
electronic store. I used a rivet from the other side to hold the heat sink to the regulator
and keeps the hold thing in place too. You will see also in the next shot the toggle switch
has also been put in place. The grey wire at No.1 goes to earth on the firewall. The purple
wire in No.3 runs the modified voltage to the switch. No.4 has the 12v input.
1/11/12 Adjustable MAP sensor
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You can see here how the purple wire from above has been terminated at the switch. The
second purple wire to the centre of the switch is the return voltage be in modified or
stock voltage depending on the switches position. The dirty white wire on the last switch
position is the original 5v that supplied the MAP sensor.
Here above you can see how the stock purple wire with a white stripe has been cut that
1/11/12 Adjustable MAP sensor
5/9jeep-xj.info/HowtoMAPsensor.htm
went to the MAP sensor. This is the original 5v supply. The end coming from the harness
gets the white wire soldered to it and goes to one side of the switch. The other end going
to the MAP sensor has the purple wire from the middle of the switch soldered to it with
either the modified or stock voltage suppling the MAP sensor depending on the switches
position.
I found a good 12v source right next to the ECU and washer filler at a plug that was not
being used. This is the diagnostic port and is ignition only which is what you want and
already fused. The box I mounted next to the bonnet hinge to keep it away from heat and
water.
1/11/12 Adjustable MAP sensor
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You can see above how it fits neatly there. Now for the tuning part. I had it easier than
most due to the fact that a good mate of mine Peter from FMA car and truck repairs lent
me his wide band exhaust gas analyser so I could test the voltage I needed to run a full
throttle. The picture shows what the ECU has it set at idle. I set mine at around 12.7 at
WOT which is considered safe and not wasting fuel or having it too lean to burn valves
etc. If you don't have a meter you could get very close just adjusting until pinging is just
heard and then richening it back up a bit more or vice a versa if trying to get rid of
pinging in the first place. Below will give you an idea of different settings.
A/F
RATIODESCRIPTION
6-9 EXTREMELY RICH: Black smoke and low power.
10-11VERY RICH: Some supercharged engines run in this range at full power as a
means of controlling detonation.
12-13 RICH: Best power A/F: Un-supercharged WOT.
14-15CHEMICALLY IDEAL: At 14.6 the A/F is at the theoretical ideal ratio with no
excess fuel or oxygen after combustion. Good A/F for part throttle cruise and
1/11/12 Adjustable MAP sensor
7/9jeep-xj.info/HowtoMAPsensor.htm
light to moderate acceleration.
16-17LEAN: Best economy A/F ratio. Borderline for part throttle drivability (worse
than borderline if EGR is used).
18-19 VERY LEAN: Usual lean limit (Driveability).
If you do not have one you can read the voltage from the O2 sensor to give you a rough
idea of the best setting. It will need you to have a nice long hill that you can hold it at
WOT to get some the voltages needed. It will fluctuate a lot so be prepared for it and it
is best to have some one read it for you. Remember you must have the engine up to full
temperature so that the ECU is in closed loop mode and reading the O2 sensor and that is
at the right temperature too.
These charts above will give you some idea of what to shoot for. All you have to do is
connect a wire long enough from the O2 plug to your digital multimeter inside where your
passenger can read it while testing. Just make sure that that wire never touches ground as
it will damage the sensor. The negative lead of the multimeter goes to ground so you can
read the voltage changes. You will find 4 wires on the O2 sensor. Two are for the heater +
& - and the other two are ground for the sensor and output to the ECU. The grounds will
be easy to measure and the two positives will have one at 12v for the heater and the other
will be at .450 volts when the engine is cold and in open loop mode will running. The chart
below shows a typical three wire sensor which uses the exhaust as the other ground.
1/11/12 Adjustable MAP sensor
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�
After reasoning operational temperature, the reading will begin to start changing from
near 0v to 1v. If this happens all is as it should. It should vary quickly and if not change
your sensor. If you do not get a change by the time your thermostat has opened, then
there is a problem and could be you are running too cold a one so it is staying in open loop
mode. The range is as follows: 3mV being the leanest, 1V being the richest. Part throttle
does not matter so much as the ECU always keeps it somewhere in this range depending
several on variables and inputs from other systems sensors. At Wide open throttle the
MOST desirable voltage should be somewhere between .850mV an .900mV Make
adjustments accordingly to reach the desired settings. Remember, the lower the voltage
the leaner, the higher the voltage the richer.
To give you some ideas of what to run here is mine and some others that have this setup
and what modifications that will influence the voltage:
Voltage Modifications Owner
4.25
Ford 24 lb injectors, 62mm T/B and spacer, Headers with
2.5" system, Ported head, 9.25:1 compression, JET stage 2
PCM, FIPK
Dr.
Dyno
4.65
2000 intake & injectors, T/B spacer, Adjustable fuel
pressure regulator at 47 psi, Headers with 2.5" system and
Bored 60mm T/B
Gojeep
5.15
Ford 24 lb injectors, 4.6L stroker, 65mm T/B and spacer,
Headers with 2.5" system, Ported head, 9.25:1 compression,
Crane 260/272, JET stage 2 PCM, FIPK
Dr.
Dyno
6.00
Ford 24 lb injectors, 4.6L Titan stroker, 60mm T/B,
Headers with 2.25" system, 9.25:1 compression, .420 lift
Clevite cam, Stock air box and filter, 1995 XJ with stock
39 psi fuel pressure. Engine only 200 miles old and stillGojeep
1/11/12 Adjustable MAP sensor
9/9jeep-xj.info/HowtoMAPsensor.htm
breaking in. Solved pinging problem.
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