r34/c34 factory boost sensor best results?

[Dan_J]

hey all

so s1 c34 stagea non neo running r34 neo ecu.
i'm not running an o2 sensor and tuning VE maps for better cruise fuel economy so i'm trying to factor all the boost sensor problems that would come up, including hacks that would negatively affect fuel economy

initially disabled boost sensor in DTC with no dtc codes
now it's been recommended( plus visibly recommended in the new software update) by matt to turn on boost sensor DTC as there might be timing/ lean out fluctuations.

another option recommended by matt is just splice into the tps signal if you dont even have a factory boost sensor on hand ( which is my case), i see this being a problem for fuel economy if the ecu is seeing boost due to tps movement yet your just on cruise.

would running a 5v 2bar boost sensor that one would use for data logging and just play with the nistune min/max volt setting work out better ?
with a quick search i cant seem to find a 5v 0-30psi boost sensor that would work most are -15- 50 psi to 0-100psi or even 4-100 psi which would be a bit hard to scale i figure
https://au.element14.com/w/c/semiconduc ... 4.97v|5.5v

can anyone also recommend a 5v boost sensor that would suit ?

thanks guys

[Matt]

Seems like your best best is just run with boost sensor disabled completely (DTC and set min/max) and then just tune the TP scales upto 132 (the TP cut on decel drops from > 132 back to 132)

Other option is get a used boost sensor from ebay etc, but they are around $50-$100AUD range I've seen. They run 0-18psi, so 2 bar is too high unfortunately

[Dan_J]

hey matt.
thanks for the reply

now i'm just thinking out the box and dont have any real knowledge on these types of sensors, however considering anyone that runs over 18psi will have trouble with the factory boost sensor that is limited to 18psi at 5100mv, wouldn't a 30psi 5v sensor work just the same just 5100mv at 30psi?

i assume dropping the max volt load cut setting in nistune to just above same percent of boost running would work perfect for over boost protection as intended by nissan ( eg 75% of 30 = 22.5 psi 75% of 5100 = 3825 mv) , albeit ve maps might need to be altered to suit, as far i understand ve maps also reference boost settings to enrich under boost.

i'd rather just try a 5v 2bar sensor if you have one to recommend?
i'm not even sure if the s1 stagea came with a boost sensor as it basically runs a s2 r33 engine so should be a stuff around to get a factory r34 sensor to work so same effort to wire a aftermarket 5v data logger type

[Matt]

I'm not sure how it would work. You would need to adjust the scaling to match the new bar range, if that is possible. Never looked into it honestly. Above 18psi we set max volts to ignore it

[Dan_J]

can anyone confirm that pin 104 is for the neo ecu boost sensor signal wire ?

[Matt]

Pin 47 is the turbo pressure sensor input (boost sensor)

[Dan_J]

thanks matt

pin 47 is blank on my S1 stagea ecu harness plug, so will unpin 104 into 47 to connect up the MPX4250 boost sensor, if it doesn't work out well can go to the trouble of finding and hacking off the boost sensor pigtail off a r34 turbo harness and splice it in.

best 5v source i could find was on the tps with ignition on car not running, was static at 5v as i was opening the th/b, i figure i wont get power draw using that source?
also do i need ecu ground or just chassis?

just to confirm;
-Vout- i wont need ?
+Vout- 0-5v reading going to pin 47
Vsupply- +5v off tps power source or other stable +5v found in engine bay

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[Matt]

This is what you need:

Pin 43 - sensor ground (GND)
Pin 47 - Boost sensor input (INPUT)
Pin 48 - TPS/boost sensor power (5V)

[polemite]

now i'm just thinking out the box and dont have any real knowledge on these types of sensors, however considering anyone that runs over 18psi will have trouble with the factory boost sensor that is limited to 18psi at 5100mv, wouldn't a 30psi 5v sensor work just the same just 5100mv at 30psi?

if the sensor's input reference voltage is 5v (5000mv), and 18psi = 5000mv, then that is full scale deflection.

if nistune could read a higher reference voltage, like let's say 6v, / 6000mv, and the oem sensor could handle a 6v input, you could get better resolution, but you'd still be maxed out at 18psi.

a 30psi @ 5v sensor would give you greater range, but less resolution. a 30psi @ 12v sensor would give you lots of range, and lots of resolution.

hope that helps explain the sensor operation a bit.

[Matt]

On top of this, I could not locate table which scales boost 0-18psi to how it is used with the throttle enrich (VE) indexes

What I did find was a combination of TPS and the boost lookup value. Given most boost sensors are linear output, it may just be a constant multiplier adjustment parameter, rather than a table

http://nistune.com/docs/Nistune%20NEO%2 ... Tuning.pdf