Originally Posted by jsinher3

did you ever open up the gauge cluster? t

Originally Posted by Helms 1988 Civic CRX Shop Manual, page 23-92

Gauge Test

NOTE: Refer to page 23-84 for wiring description of the fuel gauge circuit.

1. Remove the security compartment (see section 20), then remove the maintenance access cover.

2. Disconnect the 2-P connector from the fuel gauge sending unit.

3. Connect the voltmeter positive prove to the A (YEL/WHT) terminal and the negative probe to the B (BLK) terminal, then turn the ignition switch ON. There should be battery voltage.

* If battery voltage, go to step 4.

* If the voltage is not as specified, check for:
- Blown No. 1 (10A) fuse in the dash fuse box.
- An open in the YEL, YEL/WHT or BLK wire.
- Poor ground (G511 or G561).

4. Turn the ignition switch OFF. Attach a jumper wire between the A (YEL/WHT) and B (BLK) terminals.

Turn the ignition switch ON.

Check that the pointer of the fuel gauge starts moving toward "F" mark.

CAUTION: Turn the ignition switch OFF before the pointer reaches "F" mark on the gauge dial. Failure to turn the ignition switch OFF before the pointer reaches the "F" mark may cause damage to the fuel gauge.

NOTE: The fuel gauge is a bobbin (cross coil) type, hence the fuel level is continuously indicated even when the ignition switch is OFF, and the pointer moves more slowly than that of a bimetal type.

* If the pointer of the fuel gauge does not swing at all, replace the gauge.

* Inspect the fuel gauge sending unit if the gauge is OK.

Originally Posted by Helms 1988 Civic CRX Shop Manual, page 23-83

Description

Bobbin Type (Cross Coil Type) Gauge:

* A bobbin type gauge is an electromagnetic instrument in which two intersecting coils are wound around the permanent magnet rotor. By varying the resistance of the unit to vary the current which flows through the col, the magnetic force which energizes the coil will vary, causing the rotor (pointer) to operate. A sliding resistance is employed in the fuel gauge just as in a bimetal type gauge, and a thermistor is used in the temperature gauge.

* The rotor of the fuel gauge is immersed in damper oil and its center of gravity lies roughly along the rotating shaft, hence the fuel gauge level is indicated even when the ignition switch is OFF.

* The coolant temperature gauge is a center point stable small indicating angle type which indicates the temperature of the coolant between about 85°C (185°F) and 100°C (212°F).

Originally Posted by Helms 1988 Civic CRX Shop Manual, page 23-93

Sending Unit Test/Replacement

WARNING Do not smoke while working on fuel system. Keep open flame away from work area.

1. Remove the security compartment (see section 20), then remove the maintenance access cover.

2. Check that the ignition switch OFF, then disconnect the 2-P connector from the fuel gauge sending unit.

3. Remove the fuel gauge sending unit. (FUEL SENDER WRENCH: 07920-SB20000)

4. Measure the resistance between the A and B terminals at E (EMPTY), 1/2 (HALF FULL) and F (FULL) by removing the float.

Float Position: E
Resistance (Ω): 105-110

Float Position: 1/2
Resistance (Ω): 25.5-39.5

Float Position: F
Resistance (Ω): 2-5

(NOFX: The following is information taken from images in the Helms, but I'm not scanning and posting them here because (1) laziness and (2) eventually the pics might die anyway.)

Si and Std models:

Measured from the base of the fuel sending unit mount:
Middle of float position at F: 45 mm (1.8 in.)
Middle of float position at 1/2: 93 mm (3.7 in.)
Middle of float position at E: 144.5 mm (5.7 in.)

HF model:

Measured from the base of the fuel sending unit mount:
Middle of float position at F: 54 mm (2.1 in.)
Middle of float position at 1/2: 97.9 mm (3.9 in.)
Middle of float position at E: 144.4 mm (5.7 in.)

5. If unable to obtain the above readings, replace the fuel gauge sending unit.