I've been using a 10k ohm potential switch for a few months.
http://www.dieselplace.com/forum/uploads/9C6_switch.jpg
I recently installed an additional 10k ohm inline resistor(Sodered inline on the "B" wire off the MAP).
http://www.dieselplace.com/forum/uploads/713_resistors.jpg
The sensor shows some interesting results. The inline switch by itself only reduces MAP signal by .02 volts
where as the potential switch takes the signal down .23 volts (1.45v to 1.22v)

It seems to be a good combination of resistance as the signal won't drop below 1.22v (full swich) at idle(causing DTC for MAP volts)
and when you increase the volt output of the MAP signal, i.e. you press on th APP switch, the volt signal shows increased resistance( the inline resistor)
I can feel the difference in uphill acceleration, especially below 2000 RPM.


I have recently "bumped" the optical sensor a 1/2mm advanced and my truck now run at 185 deg as long as I don't stay on the fuel too long and
comes back to 185 quick after accelerating or sitting still too long.

I've collapsed two vacuum lines due to increased vacuum and had to reseal the transmission pan which suddenly started spraying fluid during accelerations..
Edited by: quantum mechanic

What does the computer read for boost at idle?

With the switch off and only the inline resisting it reads 100 kPa.
That's 2 kPa less than no resistor reading at 102 kPa.
With the potential switch on it reads 85.7 kPa.

Full acceleration it reads 120+ kPa switched or not.Edited by: quantum mechanic

Ok Calll me stupid but is this a manual controller for your turbo boost ?


or does it do somethinf else

It tricks the PCM into allowing more boost pressure than stock programming allows for.
It lowers the MAP signal (interpreted by the PCM as lower boost)
The computer thinks it's low so it closes the waste gate tighter, making more boost or
with mechanical boost levers it lets you increase the tension without SES light coming on.Edited by: quantum mechanic

Can't you make it read in PSI?


I guess I could go out and hook mine up and switch it to metric but don't feel like it right now. I was just wondering about the reading because mine sets a code if I turn it below -5 psi.


I just put a turbo master on mine and removed the pot and replaced it with fixed resistors. I was running it set at about -4 psi before to get 12 - 13 psi (real boost on the gauge) and would peg the gauge under light throttle.

hey whatnot


what kind do you have and where it come from ?

What kind of what? If you are refering to the scan tool, it is an older OTC 4000E


I got it several years ago real cheap and bought a cartridge to go up to '96 last year off ebay for about $50


I think you can get one on ebay for between $100 and $200.


It can't set the timing but will show pretty much everything in the data stream. (is also nice for clearing codes while driving without stopping the truck)

for some reason it won't switch back to engilsh from metric.
lowest reading was 85.7 kPa full switch and inline resistor.
how much resistance did you have to put in before it read-4?Edited by: quantum mechanic

I just went out and switched mine to metric. I have a little too much resistance on mine and it will get a codes sometimes while idling. (actual manifold pressure goes slightly below zero) It reads 58 kpa which is -6 psi.


How exactly did you wire it? I first tried a 5K (5,000 ohm) pot on mine and I could adjust the voltage but it wouldn't change when the boost went up. I then used a 20K pot and it worked fine.

Here is how I did mine. The center connection on the pot picture is the wiper (connection that changes resistance when the shaft is turned)


http://www.dieselplace.com/forum/uploads/boost_sensor_2.jpg

I don't use the "A" wire from the MAP. I figured out how to wire mine myself and have tried a few ways.
I tap into the "B" wire with the wiper sodered to two posts(the first two) at the end of the wires I spliced in and the fixed resistor sodered between my splice(onthe "B" wire) and the stock wire off the MAP.

Did you say you switched to a fixed resistor?
25 ohm?
Edited by: quantum mechanic

Hey guys


I hate to hi-jack your topic but any chance ya got some pictures for a new guy, sounds like something I'd like to put on my truck. Would any of this be needed on a truck uses a spring loaded wastegate control?


Thanks for your time

It depends.


I assume you have a turbomaster by the spring control. If so, and you want to raise the boost up, the computer will set a code. If you trick the computer as shown above, you can turn the boost up and not get a SES light.

To continue this experiment I put a second fixed 10k ohm resistor.
it doesn't reduce the MAP signal any more than before installation.
The fixed resistors seem to be the better way to go once you get the level of resistance right.
full acceleration was held to a reading of 115 kPa without the pot switch.

in which wire would you put the 20k ohm's of resistiors, Would one 20k be just as good as the 2 10k's?

I don't know the answer to 20k ohm vs. two 10k ohms(havn't tried it).
"B" wire off MAP sensor goes to PCM. A resistor spliced into this wire reduces the MAP sensor signal as read by a scantool or PCM.