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Topic: Fuel Pressure Sensor for Vehicle Application (Read 2 times) previous topic - next topic

Nick_Pyner



the simplest solution (I think) would be to use an analog oil pressure sensor


I hadn't thought to use an automotive oil pressure sender... So something like this perhaps?
http://amzn.com/B00029JXMA

It certainly borders on cheap enough to play around with, but I don't like burning $20s either if someone can tell me that's all I'd be doing :)


Probably too cheap for the job you want to do. Oil pressure senders in cars aren't that accurate, they don't need to be, and are largely there for decoration, which goes some way to explain why most modern cars don't bother with them.

Two questions, though:

1. Are you sure the system doesn't already have a fuel pressure sensor?

I would have thought that, if it was merited, that would be a pretty obvious item in a modern electronic fuel injection system.

2. What would you do with the data once you obtained it?

I had an older injection system and the manual had nearly as much ink in it telling you what you can't do as telling you what you could do. I imagine the situation has only gotten worse in that respect.



permnoob

dude he's on an arduino forum talking about modding his "old" 80s car (my arduino design is getting scrapped for some dedicated ICs and a Raspi going into my 73 VW, but I digress).  Lets not talk about what is sensible or reasonable ok?  I also am finishing a nixie tube dash display....


anyways, a real simple pressure guage to use are the MPX5100s, they take 5v (steal it off the arduino, its regulator will drop the cars 12 to what you need, but will get warm) and will spit out reasonable voltage for your ADC.  Just go thru the choices and pick the right pressure range, I have been using them for low pressure stuff and know they make a 3psi max, 15 psi max, and 100 psi max guages, there may be more inbetween.  However I doubt they are fuel proof, but if you isolate the fuel so only vapor makes it to the sensor, you might make it work.  a length of hose, and vertical placement could let you get by for a while.  the sensor is slightly protected on the inside, and they are only about 16 bucks iirc.  Also you can nab a vacuum guage from the same sensor line, and check MAP or any other fun stuff. I plan on using it to compare fuel pressure to manifold vacuum, as thats how the old VWs enriched under load.

however if you do settle on the perfect sensor, let me know!  thats more money than I want to spend at 90 bucks cause I have a bunch of other sensors going in (accel, cylinder head temp, oil temp, oil pressure) and fuel pressure is just a fun but useless value to know.   I have a analog guage for tune ups, you don't need it while driving, but need is niether here nor there.

permnoob


retrolefty

#13
Feb 02, 2013, 02:46 am Last Edit: Feb 02, 2013, 02:48 am by retrolefty Reason: 1
Quote
However I doubt they are fuel proof, but if you isolate the fuel so only vapor makes it to the sensor, you might make it work.  a length of hose, and vertical placement could let you get by for a while.


That doesn't work. When measuring liquid pressures there must be no vapour pocket anywhere in the sensing lead as liquids are incompressible and will transfer their applied pressure to the sensor element. Vapour is compressible so will not accurately transfer the applied pressure to the sensor. Liquids and gasses cannot be allowed to mix in the sample line to the sensor as it will cause large errors in measurement values.

Pressure sensors designed for 'hostile' liquid service typical have a stainless steel metallic barrier between the sensor pressure element and the 'process' attachment. Then there is an inert liquid packed between the barrier and the sensor element so that there is no trapped vapour space, so the pressure will transfer accurately.

A installation rule for pressure sensors is:

If for air/gas/vapour only service, mount pressure sensor higher then pressure sample take off point so any condensation will self-drain back to into the process being measured.

If for liquid pressure service, mount pressure sensor lower then pressure sample take off point so any trapped gas partials will travel up and back into the process.

Failure to follow either of these 'rules' can lead to inaccurate and unstable pressure readings.

Lefty

js35

#14
Feb 03, 2013, 05:46 pm Last Edit: Feb 03, 2013, 05:48 pm by js35 Reason: 1
http://www.ebay.com/itm/Audi-VW-Seat-Skoda-Fuel-pressure-thrust-sensor-06D906051A-06H906051A-03C906051D-/230843184814?pt=Motors_Car_Truck_Parts_Accessories&hash=item35bf5376ae&vxp=mtr

I have one like this sitting on my tool box:  http://www.ebay.com/itm/GENUINE-Audi-A4-A6-Quattro-Volkswagen-Jetta-Passat-Fuel-Pressure-Thrust-Sensor-/121056224772?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3AAudi&hash=item1c2f836604&vxp=mtr

These will both will meet your requirements, are 0-5v, and will handle well over 4 bar,  check your local audi/vw dealer there is one on every TSI/TFSI(direct injection) engine, and the tech are always throwing these things out.  There is an issue with them causing a check engine light but I feel most are replaced for no reason.  Talk to the techs, a quick explanation of what you are doing and maybe a $20 bill will likely net you one.

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