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Discussion Starter · #1 ·
Hi all,

Hoping you guys can help out a roadster builder who is installing a LS3 into his [email protected] replica, seeing as you have the LS power over here.

I am running the GMPP stand alone ECU that can be connected to the standard LS3 oil pressure sensor. There is a pin out from the ECU wiring bulkhead connector that could then go to the F5R gauge. The query is to whether this will scale right with the factory five gauges?

I guess real question is, is the signal output from the GM sensor the same signal as what the gauge is expecting? I do know the output is 32*sensor voltage - 16 = psig.

The GM also give some conflicting advice about whether or not the ECU will fail to function without the oil pressure signal. Some places it says to make sure its connected, other sections say the ECU does not require it. Do you guys have any feedback on this?

Many thanks
 

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I've read concerns about this, but never had a conclusive answer. From my
experience, the oil pressure sensor does not disable the engine running
capability.

Don't quote me just yet; I'll check it out, and respond.

As for the guage, you can always use a resistor to calibrate the needle position
once you get a point of reference. Best is to use a trusted mechanical
gauge to calibrate/check the electrical signal.
 

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The GM oil pressure sender is only good for the signal to the ECU. You can not use it to operate the gauge...and you also can't use the FFR sender to send a signal to the ECU. The dash gauge works off of 12v. The ECU sends a 5v signal to the GM sensor....they are not compatable.
 

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Discussion Starter · #4 ·
Thanks for the responses guys.

I look forward to some confirmation as to whethr the ECU is happy not to receive the oil press signal meaning I can just use the F5 sensor in its place.
 

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Hmmm...Voltage divider. Why wont this work to bring the voltage into range?

Low power, 1/4 watt (maybe 1/2 watt) resistors?

---+ 12V
-
-
-
----xxx(var.)xxx +5V
-
-
v (ground)

Just to clarify, are we discussing the Autometer 4327?
 

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Discussion Starter · #7 ·
Actually I have the F5R vintage look gauges, I think they are from speedhut? But your logic seems reasonable.

And thanks for help Steve - it does make me feel happier to delete the LS3 sensor.
 

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Discussion Starter · #10 ·
Thanks.
I do have to admit this is a bit over my head, but it looks impressive.
I had a look at the vintage gauges, however I do not see any part numbers or any marks on them at all.
 

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Tim,

Do you own, or have access to an Ohm Meter (or multi-meter)?

I`m not getting much in the way of technical info on your gauges.

All we really need to know is the DC resistance of the input terminal to
ground.

PM your home e-mail/phone number so we can firm this up quick.

If anyone else has the same gauges, feel free to post the resistance reading.
We'll need them to determine the proper resistor values. I will also post
the results here for anyone else wanting to convert their gauges.
 

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Discussion Starter · #13 ·
Hi,
I put my multimeter on the input and ground to the gauge but it gave no reading, ie open circuit. Not sure if this was the right answer.

PS - For work I will be out of country for 2 weeks (off to Mali!) so I will be radio silent till then.

Thanks again.
 

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Attached is about what a gauge looks like, even from point S to GND, it takes about 2 volt and 20 ma for full scale, also it is none linear while the sender output is linear with .5V offset and 1V for each 32 psi.

For normal operations it take about 80 to 100 ma to set the gauge to full scale.

so not easy to do if you want accuracy over all range and only if the sender can drive 20 ma load without any issues which my guess is was not design to do.

I have made devices for my car and is does this conversion also for me, but so busy right now have not done much last 6 months.

Mostafa

Text Line Parallel Diagram
 

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Thanks for that little schematic.

I'm measuring 85.5 ohms on my Autometer oil gauge.

The question marks on the diagram don't make me feel too warm, and fuzzy,
but once Tim returns we can have him retest the resistance of his gauge.

With that info, the resistor calibration should be fairly close.

I will also check the response of the meter movement vs. voltage input
to get a sense of linearity.
 

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I think the point here is the GTM oil and water gauges are not high impedance, and it take lot of current to drive one per designed ( 80 to 100 ma), the least current ( highest impedance) is GND to S, even this will draw 20 ma, also if use this way the reaction is very slow, since only one coil is biased.

the coil resistance is about 300 ohm, the 20 ohm in often not even there so zero, the the 300? will depend on the gauge and sender type, this may be 120 to few hundred.

Mostafa
 

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Mostafa,

Check out the YouTube video I linked a few posts prior.

The meter movement is fairly quick even with the voltage divider present.

This is because we are simply presenting a "ratio" of sorts. The gauge
will receive the proper operating voltage, and therefore the current through the
gauge can be tailored by the values used in the divider circuit.

I was able to get close in the video; although not perfect, with more
calcuations, and the oil sender factored (using a potentiometer), I'm
pretty certain this will work.

If not absolute values, at least a very close representation of pressure
in the oil system.

I'll try to get a more complete circuit built, and tested by the start of
next week, and post another video.
 

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It does not change what I have said, same picture, from gnd to S, it takes about 20+ ma ( 85 ohm) and about 2 volts for full scale! he does no say much about resistors size and current through them.

Again not sure if one can draw 20 ma from the sender without affecting the sender, generally amps may be good to 5 ma or so. also scaling is an issue if you want it to be accurate to full scale.

Mostafa
 
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