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Topic: 86 5.0 digital dash fuel sender (Read 1378 times) previous topic - next topic

86 5.0 digital dash fuel sender

OK, have had issues with the fuel gauge reading on the 86 'Bird, reads all kinds of random things including the dreaded "CO". And I have rad lots of stuff here and on other forums on what to look for or do.

So I went 'Yarding and found a decent sender for test purposes, reads 16 ohms empty/down and 160 ohms full/up, which I think is correct for 86 digital dash cars. Nice movement that cleanly matches the readings, no dead spots. Tank was under a Stang but don't know for sure, but was near an 88 Bird with digital, sooo...

Dropped the 86's tank to get to the wiring and plugged the wiring into the sender. No change on the dash when I move the sender arm, however turning the ignition off and back on will show a change to wherever the sender is positioned last, just won't show change while moving sender with the ignition left on (does not show "trend"). Tried it with an added ground, tried it with the fuel tank balanced and open and the motor running (!), and no change in gauge reading while moving the sender, unless you switch off and back on.

Soooo... I pulled the sender in the tank, and measured it. Reads 13 ohms empty/down and 180 ohms full/up. Has a few dead spots including one at full-full, but should run a gauge for most of the gauges readings. Tried it out of the tank same as the new one. And it does what it always has done, shows baud or continuous readings (no trend).

By the way, once I cgot the sender out of the car, it is a different unit than the one from the yard, oh well...

So here is my question. Is there something in the digital cluster or elsewhere in the car that converts the resistance signal from the sender to a usable signal for the gauge and those go out or don't reset unless restarting the car or something like that?

I have experience on GM senders and you can hook them up to the gauges and run the gauge up and down by manipulating the sender float arm with the key in the run position, motor off. Is the Fox Bird different? Or do I buy an aftermarket fuel gauge and put that in?

Any help is GREATLY appreciated, as I really need to have this solved, one way or another, and the car is currently torn down on my driveway...

Thank you's in advance,
Tom
1986 Tbird Elan 5.0 - fixing small stuff little by little

86 5.0 digital dash fuel sender

Reply #1 –
OK, put the (I think) Mustang sender and buttoned everything up. The gauge still seems to read whatever level the car was at when started and shows no change until stop and restart. The original sender has some damage to the resistance portion of the resistor card, so maybe I can find another or get this one fixed. Any thoughts?

Is there a controller for the gauge in the cluster? Because if I can determine that the gauge is reading fuel level linearly, and cannot get it to somehow match the dash, its getting and aftermarket gauge in a pod.

Thank you for any input, Happy Easter to all,
Tombe locked
1986 Tbird Elan 5.0 - fixing small stuff little by little

86 5.0 digital dash fuel sender

Reply #2 –
Looking at the 86 EVTM, there is no electronic magic outside the electronic cluster.
Also I see no keep alive voltage for the fuel gauge section of the cluster. It has power in RUN or ACCY.
I do see one thing that is unique to the 85 and 86 EVTMs. The power comes through the n/c contacts of the cluster illumination relay.
And worse yet, with the headlights on the power comes from the dimmer control on the headlight switch.
I don't know if this is an error in the diagrams, but it seems strange to have the voltage to an electronic module be variable by the dimmer control.

86 5.0 digital dash fuel sender

Reply #3 –
softtouch,

Thank you for that tid bit, don't know how that would affect the gauge reading, should I try to have a different hot power coming into the cluster and how would I go about doing this? The gauge has been reading incorrectly for a while, but the headlamp switch was just replaced. Could the new switch be sending power differently than the car wants to see it? Switch I used is spec'd for an 86-87 MVII.

This one: http://www.oreillyauto.com/site/c/detail/BWD0/S930.oap?year=1987&make=Lincoln&model=Mark%2BVII&vi=1188402&ck=Search_s930_1188402_3587&keyword=s930

The correct one for the 86 'Bird was not available at all, but is this one:
http://www.oreillyauto.com/site/c/detail/ACD0/F1538/02006.oap?year=1986&make=Ford&model=Thunderbird&vi=1140208&pt=02006&ppt=C0039

Has that huge heatsink on the side.

Could this minor difference in the switches cause the non-update of the level as the sender position is changed?

Thank you,
Tom
1986 Tbird Elan 5.0 - fixing small stuff little by little

86 5.0 digital dash fuel sender

Reply #4 –
Another update, drove the car around for about an hour on Sunday, gauge read 15 gals when I started, shut off and turned on the ignition several times, it never dropped but did go up to 16 gals then back to 15. Drove the car HARD the whole time, so I imagine it was getting less than 15 MPG indicated, drove it for about 20 miles, so I would think I should have seen the gauge drop some as it should have used more than part of a gallon.

Went and filled the tank, watching as I did with the ignition on and saw no change for about 5 gals (stayed at a reading of 15), so switched off and on the igniton, and reading showed 20. Finished filling at about 6 gals, and gauge reads "F" (full) after off and on..

Sooo, gonna have my son drive it a few days and check the reading on the gauge and then fill it in a few days, and we will see what it shows.

Any thoughts on why the gage doesn't show any changes when the ignition is on, but resets to new float position when the ignition is switched off and then on? Could it be related to the change in the headlamp switch and its control of power to the cluster that softtoush was describing above?

Best regards,
Tom
1986 Tbird Elan 5.0 - fixing small stuff little by little

86 5.0 digital dash fuel sender

Reply #5 –
The headlight dimmer control only comes into play when the headlights or parking lights  are on. With the lights off the LCD display should be on full bright. With the lights on, the LCD display brightness is controlled by the dimmer.
So I don't think the headlight switch is causing your problem.
From the how it works write-up:
When the ignition switch is turned from off to RUN or ACCY, the E,½,F and pump symbol will flash for a period of 2 to 4 seconds then stay on.
The electronic speed indicator will read 188 then read 0.
The illuminated bar indicates the level of fuel. The gage requires several minutes to change the reading. This is to reduce the effects of fuel slosh.

I can post the wiring diagrams if you wish.

86 5.0 digital dash fuel sender

Reply #6 –
Quote from: softtouch;386431
The gage requires several minutes to change the reading. This is to reduce the effects of fuel slosh.


 
Ah-hah!! This might be one more piece of the puzzle, would explain why there was no change when I was actuating the sender (too) quickly under the car. Now, I will try to track how the gauge on the dash is reading as my son drives it to and from school this week, we may see how it works, if it works at all. After one day, not too many miles, still "Full". Should see something in the next day or so. Will update what we find.

softtouch,
Thnak you for the offer of the diags, depending on how this little experiment works I may not need them. If this sender gives a close to realistic reading, we're good (and we may have found an acceptable sender for others to use). If not and I end up replacing the dash gauge with an aftermarket unit I will probably need the diags to chase down wires, and then I will get in contact with you.

Thank you for the excellent input,

Tom
1986 Tbird Elan 5.0 - fixing small stuff little by little

86 5.0 digital dash fuel sender

Reply #7 –
Fueled it up tonight for the first time this week, read 16 gal down from 20 gal, took a little over 4 gallons to fill it. Now reads 19 gal, so maybe we have found a solution of sorts.

More to follow...
1986 Tbird Elan 5.0 - fixing small stuff little by little

86 5.0 digital dash fuel sender

Reply #8 –
Couple of updates:

Sender seems to be giving a useable signal, gets down to 14gals and need 5-6 to fill, so that looks right. However, I seem to be the only one that can get it to read correctly.

After hearing about the gage (among other things that happened to him but I couldn't replicate) over and over, I got my son a new used car from a local dealer, has a warranty, so now he can take it there for repairs. As soon as I determine a fair asking price for the Tbird, I will post it for sale on this forum.

Thank you all for your input,
Tom
1986 Tbird Elan 5.0 - fixing small stuff little by little