Adding a Fuel Pressure Gauge

[mach4]

The trials and tribulations of OM617YOTA in a long but interesting troubleshooting exercise around solving a rough running engine in his Toyota repower project (see 617 weird behavior diagnoses beginning at around post 101 for background) has led me to the conclusion that a fuel pressure gauge can be a very valuable monitoring, early warning and troubleshooting component to a set of engine instruments. I currently have installed a suite of engine monitoring instruments that include TIT (turbine inlet temp), intake temp, oil temp, transmission temp, engine bay temp, boost pressure and vacuum pressure. A thread describing the development of my Arduino based data collection system and bluetooth enabled Android display system is described in the following thread - Engine Instrumentation Project The Android display also provides HUD functionality and navigation capabilities. Here's the current system in use.



I've decided to add Fuel Pressure to the system (as well as Voltage, but that's another subject) and this thread is a documentation of the thinking and the design and the installation of the components.

Since I'm already running boost, vacuum and temp sensors that use a 5v supply, it's trivial to add a three wire pressure transducer that uses the same wiring configuration. It's literally adding one wire to the Arduino to take the pressure signal. The code changes are probably a dozen lines of code on the Arduino and a more complex matter to add gauges and/or digital readouts to the display program.

My current research and thinking points to using the following pressure transducer which should be about $25 or so.



As a 30 psi device this will give me excellent resolution for a nominal 14psi fuel pressure. The device has a less than 1ms response time so there will be very little delay in the signal. Knowing that fuel pressures vary, especially at lower rpms, the plan is to average 10 samples every time a dataset is sent to the display, which means I shouldn't need a pulse modulator as might be required with a manual gauge.

The installation plan is to tap into the supply line to the IP to get actual fuel pressure at the IP. This will be downstream of fuel strainer, primary and secondary filters. Fuel pressures that deviate from normal will be due to a filter problem or a lift pump problem or a pressure relief valve problem and can be easily troubleshot. The pressure transducers are inexpensive enough that I might install a second one on the supply line to the primary filter thus giving absolute confirmation of the need to change the primary filter by showing pressure drop across the filter. (I've got 62k miles on my primary filter and there is currently no way to know when it will need to be changed - other than a drop in performance and potentially a side-of-the-road filter change)

I mocked up a potential mounting method on my spare engine. I drilled and tapped the banjo bolt for a 1/8 NPT fitting. The image shows a capillary tube from an oil pressure gauge installed as might be used with a remote mounting of the pressure transducer. More likely I'll mount the transducer directly, probably using a 90 degree adapter due to clearance to the dipstick.



That's the current thinking....subject to change as research and design continue - all of which will be documented here.