Hey guys, here's what I've been up to lately.
(sorry for the crap pics and video -- I've lost my camera so I'm using a cell phone)
I've always been bothered by the idea that in most cars you really don't have a way of knowing how clogged any of your filters are. So I decided to do something about it.
I've been working on creating a differential pressure sensor setup so that I can measure the pressure drop across my fuel filters. Its based on a motorolla differential pressure sensor:
I soldered up a little board consisting of a power supply and an op-amp in order to boost the output of the pressure sensor so that it can drive a gauge:
to plumb this sensor into my fuel system, I assembled two brass 'tee' fittings. I used 5/16" barbed fittings for the fuel line fittings, and used an 1/8"
barb for the pressure sensor line. thus, I'm 'tapping' the fuel lines before and after the fuel pre-filter, so that I can I measure the pressure drop across it.
The fuel line I'm using is 1/4" tygon F-4040-A from mcmaster-carr. Tygon is a transparent tubing which is resistant to fuels (its the only clear fuel line I know of). The 1/4" tubing stretches to fit over the 5/16" barbed fittings as well as the mercedes fittings and makes a good seal without the need for hose clamps (I'm not using any hose clamps on my entire fuel system).
I housed the electronics in a disposable tupperware container.
here's a crappy cellphone video of the setup with the engine running (note: the sound in these videos is completely corrupted):
http://www.youtube.com/watch?v=ZEmNuHfVL18
here's a video of the gauge:
http://www.youtube.com/watch?v=Ksm4L9hBoPs
the needle really bounces around like crazy. the fuel pressure must be varying wildly as the lift pump goes through its pumping cycle each revolution.
I haven't printed up a custom gauge backplate, so I translate the voltage readout on the gauge (averaging about 1.5 volts) into a pressure using the datasheet. The output is linear, and a full 5 volt output would translate to 1.5 psi, so 1.5 volts translates to about 0.45 psi.
I'll try swapping out a fresh fuel filter and see if that makes any difference on the pressure drop.
after that I'll plumb in a second sensor to measure the drop across the main fuel filter, as well as a third absolute (rather than differential) sensor past the main fuel filter to measure the total pressure drop of the fuel system.