User Manual

Table Of Contents

UT108/109 OPERATING MANUAL

6.Fuel System Testing

It is necessary to add more accurate engine fuel control to a low injection automobile.

Since 1980, the automotive manufacturing industry has used electronically-controlled

carburetor and fuel injection so as to achieve lower fuel injection.

(1) GM (General Motor): Testing the dwell of the C-3 mixed-control solenoid: Place the

solenoid in a cylinder, monitoring the ratio between the air and the fuel, which should

generally be 14.7 to 1 between the air and the fuel so as to reduce the injection of

surplus fuel. The testing is used to see if the solenoid is installed right in the position

and the dwell of the meter can also indirectly used for the testing.

[1] Start the engine of the automobile to achieve a rotation speed of 3000 RPM.

So far as a GM automobile is concerned, set the rotary switch to the DWELL and

select 6CYL.

[2] When the automobile is operating in a short fuel state or in a long fuel state, the

dwell of the meter should be displayed between 10° and 50°.

(2) Fuel Injector Resistance Testing (see gure 21)

The testing method is similar to that of the resistance of an ignition coil.

[1] Cut the electric link off the injector. (Refer to the servicing handbooks of various

kinds of automotive manuals for the detailed position.)

[2] Connect the red and black test lead probes to the two ends of the injector. The