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Varn 04-05-2011 05:29 PM

What kind of FE instrumentation for Pre-OBD2 Diesel
Any suggestions on fuel economy gauge for my 1986 VW turbo diesel?

If you haven't noticed from my car choice; it has to be cheap.

I have thought about using a linear variable resistor and wiring it to an electric meter. Since the fuel is used directly by the position of the foot feed (and the rpm) I might have a relative way of improving my mileage.

Backtobasics 04-05-2011 05:38 PM

What about some kind of crank trigger and magnetic pickup device to give you an "rpm" so to speak. It may not give a total and accurate RPM, but I would think it could be hooked to a gauge of some sort to give you feedback, even if the gauge says you are turning 8000 rpm at idle and 10,000 rpm at speed?

bestclimb 04-06-2011 12:12 AM

w terminal on your alternator gives a pulsed signal for RPM.

Boost guage.

EGT guage (peak EGT is best performance mixture) Lean (less throttle) of that gives better MPG.

loulan 02-05-2012 08:57 PM

sorry, i cannt help you, and i want to know th answer.

skyking 03-05-2012 10:34 AM

I am up against this problem as well. My truck has no instrumentation in line on the fuel. I'd need to have two flow devices, on for fuel in and one for return. It is cost prohibitive for me.

Varn 03-05-2012 10:50 AM

Yeah really not much to do unless we want to develop a fuel usage gauge where we could see GPH and then work backward to get MPG.

What I have done is to pull the start lever out. It seems to give better fuel mileage.

rmay635703 03-05-2012 01:15 PM

I am in the same boat on My 89/82 6.2 diesel, without GPH, no way to get instant FE.

I think something needs to exist for GPH.

bestclimb 03-05-2012 01:29 PM

vern if you are pulling the lever out for and it is making a mileage difference you may think about adjusting the injector timing.

my understanding of the VW injection system is that while pressure to the injector is over x value a spring allows the injector to open.

in the pump if a pressure measuring device "knew" when the injector was opening and closing by sensing the pressure in the line (vw uses a variable stroke injector pump) longer stroke means higher flow rate and longer duration with the injector open. that information could be fed to an MPguino.

What we would have then is frequency and duration which is handled well by MPGuino, unfortunately duration and volume of fuel is probably not linear, but that could likely be solved with software.

AndrzejM 03-06-2012 04:33 AM

I just thought that diesel injestion timing may be "measured" by a microphone attached to the injector. Since it'a a fully mechanical unit it should be pretty easy with an oscilloscope to find the point and timing for actual injection. As I remember diesel (old type) injectors are set up for constant fuel pressure, so what's changing is time. If you could actually measure the time of injection you can actually find an amount of injected fuel. Combining that with some kind of vehicle speed sensor will give you a full MPG. I think it can be done pretty easily. I could try to do that but don't have access to any old diesel engine and what worst I don't have oscilloscope to find characteristic points of the measured sound.

oil pan 4 03-09-2012 04:45 PM

Mechanical diesels normally use a lumosity probe adaptor that goes in a glow plug hole to detect combustion. The lumosity adaptors are typically used drive a standard gasoline timing light.
I have one and its so nice, not having to guess at your timing.

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