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Thread: Digital Dash Fake Oil Pressure Gauge - Sabotaged by Ford

  1. #1
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    Default Digital Dash Fake Oil Pressure Gauge - Sabotaged by Ford

    I think I figured out an additional reason why Ford made the oil pressure gauge "fake". It seems that between the tolerances of even the fat sender and the dashboard that there was no winning.

    Look at tolerances of a typical Wells oil pressure PS4 sender here -> http://www.wellsve.com/showall_ds_oil.php

    0-4 PSI - Open Ckt
    4-8 PSI - 24-36 Ohms
    90 PSI - 8.5-17.5 Ohms

    All over the place. Oh, and you can now see the reason why they call it a sender and a switch, because it becomes open circuit below 4 PSI.

    Now look at what I got for readings when I put a decade box between the sensor wire and ground. It's almost as if the gauge wants to see something between a real sender like the Autometer 2241 and the OEM switch/sender. Here are some numbers and graphs to confuse you:

    Digital Dash Oil Pressure Gauge.JPG


    Bottom line, using the fat sender, mine reads off-scale high due to the sender reading low by 5 ohms (I used air pressure @ ~58 psi and saw 15 ohms, yet it should read ~20 ohms looking at the plot. EXCEPT that if you look at the range of acceptable values for a typical sender unit (PS4), it's probably barely within tolerance :/

    If I add a 10 ohm resistor in series with my sender, it reads "O" cold and falls to "R" when warm.

    Of course if you note in my pic above, the gauge has 5 readings,

    • 1 bar is open circuit (less than 4 PSI)
    • 4 bars is the next level, also known as "R" - this covers all pressures between 4-54 psi (my estimate)
    • 5 bars is "O" 55-79 psi is my estimate
    • 6 bars is "N" or >80 psi (my guess)
    • "8 bars" is an error condition where it sees pressure that's "too high" (<6 ohms) It displays as the 2 highest bars and 2 lowest bars


    It's possible I'm off in my estimated range of pressure of each bar, and it follows the nominal gauge output, or maybe the lower tolerance, but it matters not since there's very little to be learned from a gauge that can't read below ~40 psi.

    Unlike the speedo 85MPH limit fix, it's unlikely that the shared bar gauge could be made to read properly without reprogramming a PROM in there. If anybody has any electrical diagrams of the speedo, or any idea how to fix this problem, I'd love to see it.

    The tolerances are so loose, I wouldn't even dare to recommend a sender and resistance to add in series to get it to use the 3 available bars intelligently. I am considering getting the Autometer 2241 and trying to work with that as it must have a better tolerance than the cheesy OEM "sender/switches"
    Last edited by Cougar5.0; 10-13-2017 at 08:19 PM.
    11.96 @ 118 MPH old 306 KB; 428W coming soon.

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    So, in other words, even with the big sender it's still full of crap.

    I have an Autometer tach on the steering column because the stock digital tach is laughably inaccurate. I really don't want to add a bunch of aftermarket gauges to the car, (I'd love to remove the Autometer tach) because they look tacky, but the stock stuff just sucks.
    '88 Thunderbird LX: 306, Edelbrock Performer heads, Comp 266HR cam, Edelbrock Performer RPM intake, Edelbrock 70mm TB, 76mm C&L MAF, 30lb injectors, 2.5" exhaust, AOD with 2800 PI converter, 8.8 with 3.73 gears, 31 spline Traction-Lok, 31 spline Moser axles, 04 Cobra front arms, Maximum Motorsports extreme duty rear arms, subframes.
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  3. #3
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    Quote Originally Posted by Cougar5.0 View Post

    The tolerances are so loose, I wouldn't even dare to recommend a sender and resistance to add in series to get it to use the 3 available bars intelligently. I am considering getting the Autometer 2241 and trying to work with that as it must have a better tolerance than the cheesy OEM "sender/switches"
    A resistor and the SMALLER sender was Ford's "fix" via a TSB. IIRC the resistor was 22 ohms. It had been done to my car before I purchased it. It did absolutely nothing. I went back to the larger sender and the problem is ALMOST GONE followi g my rewire of the charging system, additional grounds, and upgraded alternator a few years ago. Will still go off at around 20 PSI on a hot day after a long drive at idle. I'm fairly certain to alleviate the issue totally in my car I'd have to replace the entire engine harness. I happen to have a.pristine one. I'm not quite ready to install it yet.....
    -- 05 Mustang GT-Whipplecharged !! -- 87 5.0 Trick Flow Heads & Intake - Custom Cam - Many other goodies...3100Lbs...Low12's! http://www.fquick.com/V8Demon

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    Ive wanted to work on this topic for a while but keep falling prey to the idea that I dont really find it too very important. anything above 8 or 9 psi is ok so....... i just keep putting it off.

    the thing i wanted to "start with" on the digi dash is this....

    I would remove the cluster, undo the rear harness, extract the wires associated to the sender from the dash connector and insulate them. Insert temp wires from the connector where the oil sender was out to open air where i can get to them.
    reconnect the dash.

    aligator clip in a variable resistor to the wire(s) i brought out to me.

    turn key on

    verify the qty of bars lighting up to the ohmic value i am injecting & plot on a chart.

    -next i would demo out my temp setup and then re-install everything like it was in the dash.

    I would then wash / rense and repeat the same process but........ i would install my variable resistor up to the engine bay harness.

    i would verify the qty of bars lighting up to the ohmic value i am injecting & plot on a chart.

    with this process i see the delta between no engine harness and with an engine harness and if or where i may or may not have chassis wiring influences that may or may not be throwing off the digi or analog guage.


    for an analog cluster you depend on the IVR to set the stage for a reference voltage on the Temp, Oil & Volts.
    **acturally and more exact-- you depend on a tiny gray solid conductor from the ignitioin switch which is by length a calibrated resistance to about 8 ohms which then asssists the IVR in making the 5volts reference voltage.

    we gutted my son's amp meter and omitted the shunt monitoring design & such.
    you may not know this but... if you go to tractor supply and purchase the Volt meter for tractors............
    you gut your cars amps guage coil interlals and keep the face, needle & housing.
    you install the tractor supply internals and then bring in hot in run conductor to the guage & give it a near by ground.
    You then mount it back in the cluster but use insulation washers where the metal studs pass through so the studs are not in the electrical game of the cluster.,

    the guage now reads max sweep with car running and a confirmed 13.8v. we moved the needle down a tad so it was not "maxed out" during run.
    Reason was i wanted mason to understand that if ever the needle was max ,, he likely had a regulator going out or a shorted diode, this would generally show a higher voltage on your hand held volt meter and so... when the needle ever got to max, it would cause him to inspect and repair before the problem got out of control.

    Now back to the oil sender............
    for digi clusters... its probably a different approach.

    for analog oil guages, omitting the dependancy of the 8 ohm resistive wire & the IVR and redo this oil guage with 12v internals might allow you to regain controll of the input signaling of the oil sender.

    The idiot light sender has a few moving parts including a spring.
    the sender for the analog guage (especially the larger senders) have a bunch of parts in there many of which move and can be a challenge to calibrate.

    migrating the oil analog guage from 5volts to 12volts is a good move i believe,, it gives you more "volts" to spread out your ohms law in a more calibrated way.

    it also would allow you to start off with a whole new Resistance total on the guage.
    Using an oem regular off the shelf oil sender you could the use air presure on the sender to substitue the PSI force to then manually verify 32 psi is now matching the guage needle as "LOW", then inject 30 psi and so on.
    using your oem off the shelf sender if needed you may find inserting a resistor in series will help your calibration.

    long and short of this is i personally believe the analog guages would benefit more by "**NOT***" using the IVR & the gray ignition switch resistive wire.

  5. #5
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    by the way ,, i have a lot of very tiny resistive resistors if needed,, call for what you need to calibrate 304 772 3411, im willing to assist and since your in full swing of this mod.. its a benefit to the whole board ,, someone like you could certainly solve this.

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    here is the the thread for your review pertaining to the Ammeter retrofit i spoke of above just incase it becomes useful to you or anyone.

    http://www.foxtbirdcougarforums.com/...hlight=ammeter

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    and for the big ass resistor on the back of the cluster,,,

    buy a piece of soap stone.... the type welders use about 3/8'' wide and about 3/16'' thick,, they use them like carpenters pencil.
    use a rat tail file and file in a cavity long ways.
    cut the soap stone to the length of the resistor.
    loosen resistor hold down screws....
    insert soap stone under the resistor and tighten screws.
    the resistor now sits inside the cavity you filed out.

    Now non of those watts are melting your flex print anymore.

  8. #8
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    No worries, I have tons of components here (do electronics for a living), but thanks anyway.

    I also have a spare dash I can take apart and look at in my lab.

    Unfortunate, like you, I have limited time to look into this issue.
    11.96 @ 118 MPH old 306 KB; 428W coming soon.

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