Fuel readout question

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Fuel readout question

July 26, 2009, 11:41:41 AM

I was drivng the other night and my fuel gauge went from reading 19 to C 5. Has this happened to anyone else. It's an 87 XR-7 with full digi gauges.

Fuel readout question

Reply #1 – July 29, 2009, 01:20:28 AM

hexadecimal code is being displayed,,, which easily converts to binary but who cares bout that stuff.

Tach/Multi guage diagnostic

all codes are Hexadecimal format and can range from 00 to FF (binary 0000 to 11111111)or (decimal 0 - 128) . While active in the various modes, they can be used as a "wiggle test" to check for shorts and intermittant circuits. Anyway,, display will be in hex format.

hold the guages button in and turn the ign key to RUN
Advance through the tests by pressing the guages button.
A steady Tone and 8 bars lit is a passing test
No tone with 24 bars lit is a fail

To enter the Fuel computer self test
Press and hold the Select button atleast 5 or so seconds until the test display appears then advance thru the tests by pressing on Select over again.

Fuel readout question

Reply #2 – July 29, 2009, 11:45:45 AM

What else can you do in there? My fuel readout displayed CO when I last filled up.

Does it time out to exit, or do you just turn the key off?

Fuel readout question

Reply #3 – July 29, 2009, 12:38:05 PM

My digi fuel gauge also reads CO sometimes. I will have to try JCassity's test procedure.
Please let me know if you find out what causes this.

Fuel readout question

Reply #4 – July 30, 2009, 07:55:36 PM

all i've figured out so far is that my car failed every test

Fuel readout question

Reply #5 – July 31, 2009, 02:51:36 AM

then check the resistance on the fuel sending unit.

Fuel sending unit info
87 Evtm page 127 or 129 shows
Empty - high resistance - 60 to 86 ohms
Full - low resistance - 8 to 12 ohms

87 shop manual 33-20-1 shows
Empty-low resistance-22.5ohms
Full-high resistance - 146 ohms

Fuel readout question

Reply #6 – August 01, 2009, 12:21:46 PM

new sending unit fixed the problem, thanks jc

Fuel readout question

Reply #7 – August 02, 2009, 10:39:38 AM

glad it was'nt the fuel computer,

the sending unit is pretty easy to fix though, the wiper arm is exposed to the coil that changes the voltage.