testing pressure transducers

[Toby_Goodmk]

Gremlins are coming out in force over the winter let me tell you!!

Common sense tells me that if I have a three wire 0-5v pressure transducer that if I have 12v and good ground that at 45psi of pressure off my fuel rail that I should see over 2 volts.

I have back probed the sensor, I have 12v. I have a good ground. When I back probe the signal wire....nadda.....

Here is what is crazy... The other sensor I have measuring oil pressure is showing the conditions....I mean..come on...two at the same time?

Am I running the correct diagnosis on the pressure transducers????

 

[Boost231]

Is it a 12v sensor or a 5 volt?

Is this a 0 to 100 sensor or?

 

[BobbyBuick]

if it is a 0-5 v sensor then you cant put 12v to it only 5v from hot to ground.you need to get your hot from a 5v source .you may have burnt up the transducer

 

[Toby_Goodmk]

hey Bob, its the one you sold me last year for my PL. But now I am using FAST tapping the feed off the EGR.

 

[BobbyBuick]

That is a 5 volt unit can't put 12 volts to it just like a map sensor

 

[pacecarta]

also note
the cheaper ebay sensors are 5v input sensor and have a .5-4.5 output signal
the more expensive SSI sensors like the ones in the casper xfi plug and play logging kit are usually 12v input sensors and read 1v - 5v output
a 5v 100psi sensor at 50psi will be at center of its output range and should read 2.5v , a 12v SSI 100psi sensor should read 3v at 50psi . you'll need to adjust the analog sensor setup in the fast depending on what sensor you have. the values to enter to read the raw voltage and formula to get the sensor gain and offset values can be found in the XFI "help/ index /23.0 auxiliary analog sensor setup.


i would have thought they should have made the connector slightly different to avoid issues with accidentally swapping a 5v power input sensor where a 12v power input should be but no such luck , they both use the same connector

 

[RANDALL]

Was searching TB trying to solve sensor issues and found this thread. I am having the same issues as Toby was having. Does this mean a 5V sensor can be used with 12V feed as long as XFI-C-COM oil and fuel pressures are calibrated properly or do I need 12V sensors? If I applied 12V to a 5V sensor I may have hurt the sensors?

 

[GNVenom]

If you apply 12v to a 5v sensor, end of game. It's junk.

The 5v sensors generally swing from 0.5v. to 4.5v full scale, 5v being zero PSI
The 12v sensors swing from 1v. to 5v. full scale, 1v being zero PSI.

And then to complicate things, there's the "GAUGE" curve, or the "ATMOSPHERIC" curve. As in "PSIA or PSIG". The Gage curve takes into account atmospheric pressure, using a 15PSI offset. The other does not.

 

[bison]

If using SSI media sensors be sure to look at the specifications if you're not sure. If the sensor part number ends in 4.5v-000-000 then the sensor requires a 5v input. As John stated it's game over if you hit it with 12v. If the sensor ends in 5v-000-000 it's a 12v sensor. 5v input sensor requires 5v + or - .5v input. 12v input requires 8-30v input. The value on the sensor 5v-000-000 is the highest value the sensor will output 0-100psi 5v being 100psi. Not the voltage required to make the sensor operate! I use these sensors all the time. I've never had a problem with them.


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[RANDALL]

John, Bison,

Thanks for the help. Much clearer now. I must have C-Com set up issues.

 

[pacecarta]

also note that now since some are changing over to 2.05 there is separate sensor setting for fuel (aux1) and oil (aux2) which are now dedicated to the system ( can reconfiged or turned off but you need to set it up)
for the ecu to correctly make changes based on the sensors those sensors now also need to be programmed for the ecu to know their value and its not under auxillary sensor setup ... goto VIEW> system configuration> sensor calibration> fuel pressure sensor calibration (and also oil sensor below it) and program the sensor there
those system settings affect what you see from the sensors when you look at fuel and oil pressure on an edash not the auxillary sensor setup
when logging be aware there are also different channels for the aux setup fuel pressure and the system configed values for that fuel sensor .. one will be based on whatever you labeled the sensor in the auxilliary analog sensor setup
for example "Fuel Pressure" is the default name for Aux1 analog setup value and "Fuel Press(PSI)" near bottom of the Dashboard list is the value based on the system config fuel pressure sensor setting

with 2.05 you can also now see on the dashboard the fuel and oil pressure sensor raw voltage (near bottom of dashboard list)

 

[Chuck Leeper]

What I have for the 2 sensors, 0/100, and 0/200, 5 v.
0-100
0 = .5V
25 = 1.5
50 = 2.5
75 = 3.5
100 = 4.5

0-200
0 = .5
50 = 1.5
100 = 2.5
150 = 3.5
200 = 4.5

 

[RANDALL]

Calibrated fuel pressure to 5V = 100 psi, 0.5V = 0 psi. Dash is showing 22 psi (1.5V raw) with engine off, about 65psi (3.5V raw) with engine running, mechanical gauge shows ~44 psi running. Set gain and offset according to Fast formulas, check of formula/math = should be reading 43.9 psi on dash, but reading about 20 psi high. If I set 0 psi to about 2.2V psi reads close to mechanical gage psi. Should 2.2V = 0 psi?

pacarta,
Thanks, that was a great help.

Chuck,
Thanks. Have conversions for 12V sensor?

 

[Chuck Leeper]

Chuck,
Thanks. Have conversions for 12V sensor?

Sorry, I don't. Mine are all 5's on the Dominator set up.

 

[pacecarta]

what you just posted .5v = 0 and 5v =100 cant be correct
your sensor range is either .5 - 4.5 with a 5v input sensor or with 12v input sensor its 1v-5v

 

[RANDALL]

what you just posted .5v = 0 and 5v =100 cant be correct
your sensor range is either .5 - 4.5 with a 5v input sensor or with 12v input sensor its 1v-5v

Understood. Have 12V sensor and tried 1V = 0 psi, went above and below 1V to try and effect some change I could make sense of. With 1V = 0 psi dash was reading about 20 psi high compared to mechanical gauge. The only way I was able to get dash to equal mechanical gauge was 2.2V = 0 psi.

 

[bison]

what you just posted .5v = 0 and 5v =100 cant be correct
your sensor range is either .5 - 4.5 with a 5v input sensor or with 12v input sensor its 1v-5v

He may have absolute sensors.


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[turbo nasty]

Understood. Have 12V sensor and tried 1V = 0 psi, went above and below 1V to try and effect some change I could make sense of. With 1V = 0 psi dash was reading about 20 psi high compared to mechanical gauge. The only way I was able to get dash to equal mechanical gauge was 2.2V = 0 psi.

FWIW on my XFI 2ish volts...Thats around where mine is at to read where the analog for both fuel and oil psi logging

 

[bison]

FWIW on my XFI 2ish volts...Thats around where mine is at to read where the analog for both fuel and oil psi logging

What sensors?


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[RANDALL]

He may have absolute sensors.

Great point, and you are correct, SSI PN (P51-100-A-B-P-5V-000-000) measures absolute pressure. So if I take dash pressure (absolute) and -14.7 (gage) that gets me to dash = 50.3 psi (closer to 44psi mech gauge is reading.

FWIW on my XFI 2ish volts...Thats around where mine is at to read where the analog for both fuel and oil psi logging

Interesting, thanks for the reply.

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Any opinion on experience, which have you deferred to, mech gage or sensor as being most accurate? I would imagine gauge would be +/- 5% worst case. Need to figure out how gage vs absolute correlates to XFI gain/offset. Fast told me that their sensors are absolute as well, but, could not offer any advice on what to do with gain/offset tables to correct other than what turbo nasty and I have done. Surprising that Fast tech was unaware of similar issues (?) but was approving of turbo nasty and I did.

Anyone have similar issues/experience and find a different solution?