Propane-Assisted Idle - Adjustment
83mitsubishi02SUBJECT:
PROPANE-ASSISTED IDLE ADJUSTMENT
NO. STB-83-14-006
DATE November 1983
MODEL All With Carburetor
INTRODUCTION Idle speed and mixture are usually adjusted using a CO meter. The procedures are covered in Group 14 of the service manuals. However, there may be times when a CO meter is not available. At these times, idle speed and mixture can be adjusted by using the propane-assisted adjustment procedure described in this bulletin.
FIGURE 1:
FIGURE 2:
A. PROPANE-ASSISTED IDLE SPEED SETTING PROCEDURE
1. Be sure the engine is at normal operating temperature; lights, cooling fan and all accessories OFF, transmission in neutral or Park, parking brake ON.
2. For vehicles with Feedback Carburetor System (FBC), do the following:
a. Turn off ignition.
b. Disconnect negative cable terminal from battery for at least five seconds; then re-connect.
c. Disconnect the O2 sensor at the connector. Fig. 2
3. For all vehicles run the engine for five-ten seconds at 2,000-3,000 RPM.
4. Allow engine to idle for two minutes.
5. Check engine curb idle speed and ignition timing Adjust if necessary to values in Table I.
FIGURE 3:
6. Disconnect the air cleaner fresh air duct from the air cleaner. Insert the supply hose from the propane bottle into the air cleaner approximately four inches. Figure 3.
CAUTION
Make sure both valves on the propane bottle are fully closed and the bottle is upright and in a safe position from falling, etc.
7. Open the propane main valve. Slowly open the propane control valve. Note change in idle speed. Fig. 3.
NOTE
Too much propane will reduce idle speed.
8. If idle speed increase is as specified in Table II, shut off the propane, remove propane hose from air cleaner, re-connect air duct, and on FBC vehicles, re-connect the oxygen sensor.
9. If idle speed increase differs more than 25 RPM from the speed increase values in Table II, adjust idle mixture as in Part B below:
B. PROPANE-ASSISTED IDLE MIXTURE SET PROCEDURE
1. Remove mixture adjusting screw (MAS) concealment plug as described in the Service Manual.
2. When performing step 7 in Part A, if engine speed increases, go to step 3 below. If engine speed immediately decreases in step 7, instead of increasing, then do the following:
a. Close the propane main valve.
b. Turn the MAS clockwise until maximum engine speed is reached.
c. Turn the idle speed adjusting screw to get the specified "Propane Idle Speed" shown in Table II.
d. Turn the MAS clockwise to bring the idle speed to "Curb Idle Speed" shown in Table II.
3. Turn off the propane main valve and allow engine speed to stabilize. Slowly adjust MAS to achieve the "Curb Idle Speed" shown in Table II.
4. Repeat step 7 to re-check maximum engine speed. If more than 25 RPM gain is noted above "Propane Idle Speed" shown in Table II, repeat steps 2a-2d above.
5. Turn off the propane valves. Remove the hose from the air cleaner. Re-connect the fresh air duct. On FBC vehicles, re-connect the O2 sensor. On all vehicles, install a new concealment plug to seal the idle mixture adjusting screw (MAS).