is there any negative side effect to tapping into a map sensor... like just splicing a wire in to run a gauge off of?

I know it is just a normal 5v signal, like most other sensors... So i would assume you could splice/tap in with no problem... but just wanted to see if anyone had done this, or if there are any problems with it, like skewed readings, or voltage drops.

ummm Vac/Boost gauge....... Could also read in HPT scanner.....



P&P Tuning
420.5whp / 359.8wtq

well thank you for the suggestions... but already am doing all of the above.

i asked this intentionally.

I am running a 2bar map sensor on the car. So the ECU (and likewise HPT) only sees up to 14psi. And i choose to keep it this way for drivability, as i dont want to fake a 2.5 or 3bar.

I DO have a 3bar map sensor, but i do not want to REPLACE the 2bar. the engine is keeping the 2 bar to run the car.

The 3 bar is hooked to my MSD DIS-2 box, to control timing retard in boosted situation. so even above 14psi, i can still retard the timing.

I have a vacuum/boost gauge, so i can see the actual boost pressure with my own eyes, but for logging purposes, hpt and the ecu max out and never show more than 14psi.

It makes it hard to adjust things looking back at the logs above 14psi. I never know if the car was right at 14psi, or if it was 17psi or even 21psi... it isnt like i can take notes while driving and looking at the boost gauge.

So if i can tap into my 3bar sensor... i can use it as a custom input in HPT, and log the results... so the car is still RUNNING off the 2bar with the good resolution... but i still have an accurate pressure reading when looking back at the logs... so i can see if i need a lil more retard at 16psi... or how much time i actually spend between 14psi and max boost, or at what point i hit max pressure... and can better tune for it.

anyone? Come on... it is a simple wiring question... any electrical engineers in here?

will tapping into a 5v sensor wire to add a gauge or logging input effect sensors accuracy at all? like will the added wire create a voltage drop? will the lower resistance of an additional wire spliced in change the readings? etc....

I'm not an engineer, but logic says there would be a voltage drop. You could try it out and read the drop with a meter so see if it actually exists or not.

Basically, you're wanting to be able to read actual boost pressure with HPT?

yes. above and beyond the 14psi max of my 2bar sensor.

I know i cant compensate for the info from the 3bar on the fly (without replacing the 2bar)... but having the data available in the logs and such would allow me to better tune for it above the 2bar map's range.

I figure i have it, and will be using it, so why not make the most of it?

I have a mechanical boost gauge... so i can see the true pressure with my eyeball... but i dont have a photographic (or in this case a videographic) memory to recall what the gauge said when i am looking back at my logs.

when i was supercharged on my 96z24 i ran a EGR delete thing. Basically it tapped into your map sensor wires and the egr plug plugged into the little box deal. It was for a GTP. (when the egr opens, the map sensor senses a change and the car is happy.)

car ran like crap, randomly stalled, idled bad. Ran around for a while like that, thought it was other issues, removed the simulator and was alot better. and yes i had it wired good and correct(only two wires and the car didnt run hooked up one way)

I didnt have anything to read the voltage, all i know it didnt work out like i hoped.


good luck

Admiral Jedi wrote:I'm not an engineer, but logic says there would be a voltage drop. You could try it out and read the drop with a meter so see if it actually exists or not.

Basically, you're wanting to be able to read actual boost pressure with HPT?

I'm not trying to be a dick and contradict you, but if you wire almost anything in parallel there should be no voltage drop. Voltage stays the same. One of the first rules of parallel circiuts. However if you add another resistance in parallel, the total resistance of the circiut will be less than before.

I have no idea if this helps at all, or if you can achieve what you want to do.

ok well we will find out how it works soon... I just did some tests and in the garage... uses a vacuum pump on the map, and had it hooked to the MSD watching its output... tapped the signal wire and hooked it up to a multimeter.. at least going thru the multimeter, it had no effect at all on the msds readings. I cant imagine eio on hpt acting much different that a multimeter.

i will let you all know how it turns out here soon.



If this works, the next step is going to be tapping into the CPS and running that to the MSD as a cam sensor, so i can play with ind. cyl timing.

So long as you are measuring with a high impedance load it would probably be fine.
Multimeter's have very high impedance, thus the sensor does not get loaded down causing a signal loss.

You would also open yourself up to increased noise on the signal line when you tap it and run a wire in/through/around the engine bay.
(probable less of an issue, as its generally a pretty "noisy" environment anyway.


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"forcast for tomorrow... a few sprinkles of genius and a chance of doom"