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It's a sensor that reads vacuum pressure from the #2 intake port. It's the hose you have to unhook to sync your carbs. It then transmits a signal to the ignition computer. The ignition uses the signal to determine supplemental ignition advance, if any.
I have what's called an ignition advance circuit that fits between the CDI and pressure sensor. I can set it to stock, 3* or 5* advance. It basically fools the ignition on thinking there's more vacuum than there really is. You notice better acceleration when whacking open the throttle in 3rd or 4th gear...especially between 2500 - 4500 rpms. Here's more info on the subject if you're interested. This mod is better than tboost IMHO.
http://vboost.users1.50megs.com/advance.htm
Mark
#1098
I have what's called an ignition advance circuit that fits between the CDI and pressure sensor. I can set it to stock, 3* or 5* advance. It basically fools the ignition on thinking there's more vacuum than there really is. You notice better acceleration when whacking open the throttle in 3rd or 4th gear...especially between 2500 - 4500 rpms. Here's more info on the subject if you're interested. This mod is better than tboost IMHO.
http://vboost.users1.50megs.com/advance.htm
Mark
#1098
Cool, is there a place to buy this like what you have?
Yeah, vmaxbitz.com is putting it back into production. Jon P. gave me his last one to test out and I like it! Otherwise, that link shows how to make your own.
Mark
#1098
Mark
#1098
hubeerjw
Well-Known Member
I'm bringing this thread back to life as I am starting to worry about my timing with the turbo. From the link above : http://vboost.users1.50megs.com/advance.htm
It states this:
The pressure sensor used on the Vmax is connected with three leads, (ignition battery, ignitor ground and an ignitor sense lead), and a vacuum port which is connected to the intake manifold of cylinder two. Once battery is applied an average sensor will emit 2.0 - 2.3 volts to the ignitor, (key on but without the engine running). An idling Vmax will generally pull anywhere from 170 to 230mm Hg and this will yield approximately 1.7 to 1.6 volts output.
It is important to note that as a greater vacuum is presented to the sensor the output voltage drops and as pressure increases, (less vacuum), the voltage emitted by the sensor increases ... ultimately increasing to the 2.2 volt, (average), range and reflecting normal atmosphere, (no vacuum at all). As a positive pressure is presented to the sensor the output voltage will continue to rise up to a maximum of 4.9 volts. As explained in the Vmax Service Manual, this sensor will respond to pressure variances of -600 to +600mm Hg, (26.6 inches of mercury).
So if I hook up a line with my boost pressure to this unit, I should be able to see a max output of 4.9 volts if enough pressur/boost is applied? Now it says that the sensor will respind to pressure cariances of up to +600mm Hg and that equates to 11.6 lbs/in^2. My question is should I try to make a jumper that always puts out 2.2 volts or will the ignition actually retard the timing if it sees 4.9 volts? Basically I am looking for the most retard I can have. And maybe the easiest thing to do is to attach a hose from my intake (that will have boost) and run it that way. Any thoughts?
Jeff
It states this:
The pressure sensor used on the Vmax is connected with three leads, (ignition battery, ignitor ground and an ignitor sense lead), and a vacuum port which is connected to the intake manifold of cylinder two. Once battery is applied an average sensor will emit 2.0 - 2.3 volts to the ignitor, (key on but without the engine running). An idling Vmax will generally pull anywhere from 170 to 230mm Hg and this will yield approximately 1.7 to 1.6 volts output.
It is important to note that as a greater vacuum is presented to the sensor the output voltage drops and as pressure increases, (less vacuum), the voltage emitted by the sensor increases ... ultimately increasing to the 2.2 volt, (average), range and reflecting normal atmosphere, (no vacuum at all). As a positive pressure is presented to the sensor the output voltage will continue to rise up to a maximum of 4.9 volts. As explained in the Vmax Service Manual, this sensor will respond to pressure variances of -600 to +600mm Hg, (26.6 inches of mercury).
So if I hook up a line with my boost pressure to this unit, I should be able to see a max output of 4.9 volts if enough pressur/boost is applied? Now it says that the sensor will respind to pressure cariances of up to +600mm Hg and that equates to 11.6 lbs/in^2. My question is should I try to make a jumper that always puts out 2.2 volts or will the ignition actually retard the timing if it sees 4.9 volts? Basically I am looking for the most retard I can have. And maybe the easiest thing to do is to attach a hose from my intake (that will have boost) and run it that way. Any thoughts?
Jeff
Birdoprey
Well-Known Member
Jeff,
The timming will not "retard" with full voltage, it just adds less if any. Basically, if their is high vaccum the voltage is lessened and the TCI adds timming TO THE BASE TIMMING MAP(as a supplement to it). Under load(low or no vaccum) the voltage is raised and the TCI adds LESS timming TO THE BASE TIMMING MAP. I'm gonna assume that with NO VACCUM at all(and corresponding highest voltage) that the TCI will just use the BASE TIMMING MAP as-is and NOT ADD ANYTHING TO IT. I don't believe it will actually pull(retard) timming from the base map. I could be wrong though.
Leaving the vaccum line off the MAP sensor will keep the TCI from adding any "Xtra" or supplemental timming to the BASE MAP.
YOU DEFINATELY DO NOT WANT to make a jumper that puts out only 2.2 volts as this will ask the TCI for full supplemental advance. Maybe one that puts out 4.9 volts, but i "believe" you will get the same results from simply leaving the vaccum line off of it.
Something of interest though: you mention that the map sensor will respond to positive pressure??? Can you pressurize the sensor and measure its output? I wonder if it will show higher voltage than it does if the vaccum line is not attatched(no pressure)? Should be easy to check. If it were me, i would do this and then do what ever gave me the highest voltage. If both are the same, just leave the hose off. If pressure gets you a higher voltage, i would make a jumper that would provide this all the time.
Then i might slot the ignition pickup and retard the static timming 4 or so deg.
At least as a safe start to your turbo project.
The timming will not "retard" with full voltage, it just adds less if any. Basically, if their is high vaccum the voltage is lessened and the TCI adds timming TO THE BASE TIMMING MAP(as a supplement to it). Under load(low or no vaccum) the voltage is raised and the TCI adds LESS timming TO THE BASE TIMMING MAP. I'm gonna assume that with NO VACCUM at all(and corresponding highest voltage) that the TCI will just use the BASE TIMMING MAP as-is and NOT ADD ANYTHING TO IT. I don't believe it will actually pull(retard) timming from the base map. I could be wrong though.
Leaving the vaccum line off the MAP sensor will keep the TCI from adding any "Xtra" or supplemental timming to the BASE MAP.
YOU DEFINATELY DO NOT WANT to make a jumper that puts out only 2.2 volts as this will ask the TCI for full supplemental advance. Maybe one that puts out 4.9 volts, but i "believe" you will get the same results from simply leaving the vaccum line off of it.
Something of interest though: you mention that the map sensor will respond to positive pressure??? Can you pressurize the sensor and measure its output? I wonder if it will show higher voltage than it does if the vaccum line is not attatched(no pressure)? Should be easy to check. If it were me, i would do this and then do what ever gave me the highest voltage. If both are the same, just leave the hose off. If pressure gets you a higher voltage, i would make a jumper that would provide this all the time.
Then i might slot the ignition pickup and retard the static timming 4 or so deg.
At least as a safe start to your turbo project.
Mitchell
Well-Known Member
I gotta hand it to you Jeff. You are one determined SOB:worthy: I definitely cant help you with your issue. BUT, I do wish you the best of luck and hope to see that turbo bitch fly by me sometime this summer
unk:
hubeerjw
Well-Known Member
Unfortunately, my pressure sensor from my drag bike is junk, and I don't really want to spend $$ for something I won't really use. I could play around with the one off my 02 I guess.
Thanks,
Jeff
Thanks,
Jeff
Birdoprey
Well-Known Member
I would at least test the 02 unit on the bike as mentioned above. Then just make a jumper providing the max voltage that you see.
This will just keep the supplemental advance at bay, BUT you will still be running with the same timming that any V-max does at WOT. You will still wanna figure a way to pull some timming from that. How much should be based on the amount of boost you plan to run AND the type of fuel.
This will just keep the supplemental advance at bay, BUT you will still be running with the same timming that any V-max does at WOT. You will still wanna figure a way to pull some timming from that. How much should be based on the amount of boost you plan to run AND the type of fuel.
Birdoprey
Well-Known Member
Just found that the TCI will not add any additional advance to the base timming map if the map sensors output exceeds 2.1v, so there is no point in having it do so.
So, though the sensor can raise voltage to as much as 4.9VDC, The TCI does nothing more once its over 2.1VDC.
Here is a break down:
From 2.1V and above the TCI applies the fixed base advance curve above 1500rpm
From 2.0-2.1V the TCI adds PARTIAL supplemental advance on top of the fixed base advance curve above 1500rpm
From less than 2.0V the TCI adds MAXIMUM supplemental advance on top of the fixed base advance curve above 1500rpm
Below 1500rpm, the TCI applies the fixed base advance curve ONLY, regardless of the MAP sensor signal
The amount of additional advance the TCI will add will vary, but may be as high as 10 degrees at 9000rpm(for a total advance of 43 degrees(fixed AND supplemental))
So, though the sensor can raise voltage to as much as 4.9VDC, The TCI does nothing more once its over 2.1VDC.
Here is a break down:
From 2.1V and above the TCI applies the fixed base advance curve above 1500rpm
From 2.0-2.1V the TCI adds PARTIAL supplemental advance on top of the fixed base advance curve above 1500rpm
From less than 2.0V the TCI adds MAXIMUM supplemental advance on top of the fixed base advance curve above 1500rpm
Below 1500rpm, the TCI applies the fixed base advance curve ONLY, regardless of the MAP sensor signal
The amount of additional advance the TCI will add will vary, but may be as high as 10 degrees at 9000rpm(for a total advance of 43 degrees(fixed AND supplemental))
hubeerjw
Well-Known Member
U da MAN!!!!
Thanks, that is exactly what I needed to know!
Jeff
Thanks, that is exactly what I needed to know!
Jeff
RagingMain
Well-Known Member
Jeff, I found this out the hard way.
You can just unplug the wires off the vacuum sensor as well. With NO voltage input at all there is no advance either:bang head::bang head:
Gotta go plug mine back in
You can just unplug the wires off the vacuum sensor as well. With NO voltage input at all there is no advance either:bang head::bang head:
Gotta go plug mine back in
RagingMain
Well-Known Member
Hey White Bread
I read through this and dont see where you can select between 3* or 5*. If I am missing I apologize in advance, could you please point it out to me. All this beautiful warm sunshine in So Cal has blinded me.
Cheers
RagingMain
Well-Known Member
Oh yeah one more thing.
For those of you, Jeff, that have tried to test the output voltage of the map sensor, the tech manual is wrong!!! Imagine that.
If you look at the picture where to put the 12v it has you hook it up to the wrong prongs. Page 7-30 of the tech manual shows where the +/- power is "supposed" to be applied. Look at the actual plug and you will see where the red/white wire plugs to the sensor. The red/white wire is the power wire and the top prong (black/yellow) is the ground. Hook it up between these two, NOT the two it shows in the picture.
Plus just because it is reading the proper output voltage doesnt mean it is working. I hooked up a mini vacuum pump for bleeding brakes to the vacuum sensor port and drew a vacuum and guess what my voltage did not drop with an increase in vacuum.
Cheers
For those of you, Jeff, that have tried to test the output voltage of the map sensor, the tech manual is wrong!!! Imagine that.
If you look at the picture where to put the 12v it has you hook it up to the wrong prongs. Page 7-30 of the tech manual shows where the +/- power is "supposed" to be applied. Look at the actual plug and you will see where the red/white wire plugs to the sensor. The red/white wire is the power wire and the top prong (black/yellow) is the ground. Hook it up between these two, NOT the two it shows in the picture.
Plus just because it is reading the proper output voltage doesnt mean it is working. I hooked up a mini vacuum pump for bleeding brakes to the vacuum sensor port and drew a vacuum and guess what my voltage did not drop with an increase in vacuum.
Cheers
No, the switcheable kind I have is a different circuit from vmaxbitz.com. The amount of advance in the circuit in that article is fixed.
RagingMain
Well-Known Member
So............
where is the circuit drawing for the switchable one?????
Inquiring minds want to know :eusa_dance:
Cheers
I don't have that. Jon Pullara sells them and doubt he would give the schematic.
I have tested my pressure sensor per manual and I get a reading of .63vdc. I thought it was bad and bought another used one off ebay and advertised as good. I tetsed it once I got it and read the same voltage at .64vdc. The manual says it should be 2.0vdc at 68 deg. Is it possible I have 2 bad sensors or am I possibly missing something here? :confused2:
