Chrysler RAM50/D50/Arrow 1979-1993 Repair Guide

High Altitude Compensation System

Print

OPERATION



See Figure 1

This system is only found on the 2.0L and 2.6L engines.

The carburetor meters fuel according to the volumetric flow rate of air and supplies the resultant mixture to the engine. Therefore, even if the carburetor is set for optimum air-fuel rate at low altitude, the mixture becomes too rich at high altitude since the air is less dense at high altitudes.

At high altitude, this high altitude compensation system supplies additional bleed air to the carburetor emulsion well and jet air passage to dilute the fuel, preventing an over-rich air-fuel mixture caused by the drop of air density at high altitudes.

The system also advances the ignition timing by a fixed amount to reduce CO and HC emission and to secure driveability at high altitudes.

At low altitudes, the HAC opens to allow the intake manifold vacuum to escape from the HAC into the atmosphere. Therefore, the vacuum switching valve and HAC's additional bleed air passage remain closed and bleed air is not supplied to the carburetor. At high altitudes, the HAC closes and the intake manifold vacuum is applied to the vacuum switching valve, HAC's additional bleed air passage and distributor. As a result, the vacuum switching valve and HAC's additional bleed air passage are opened to supply bleed air to the carburetor. At the same time, the distributor advances the ignition timing.



Click image to see an enlarged view

Fig. Fig. 1: Diagram of the high-altitude compensation system-2.0L and 2.6L engines

TESTING NON CALIFORNIA MODELS



A vacuum pump capable of producing more than 10 in. Hg (33.8 kPa) of vacuum will be needed to perform this test.

System Inspection

ALTITUDES BELOW 3,900 FT. (1,200M)

See Figures 2, 3 and 4

When disconnecting the vacuum hose, put a mark on the hose so that it may be reconnected to the original position. The engine coolant temperature should be 185-205-F (85-95-C).

  1. Connect a timing light to the engine.
  2.  
  3. Remove the air filter.
  4.  
  5. Disconnect the vacuum hoses (black, red stripe, black) from the carburetor primary emulsion well bleed nipple, secondary emulsion well bleed nipple and the jet air nipple+ug the nipples.
  6.  
  7. Connect a hand vacuum pump to the vacuum hoses, one hose at a time, and check air tightness (the vacuum should NOT leak) while running the engine at idle.
  8.  
  9. Connect the vacuum hoses back to their original positions.
  10.  
  11. Run the engine at idle and check ignition timing. The timing should be 6-10-° BTDC for the 2.0L engines and 5-9-° BTDC for the 2.6L engines.
  12.  
  13. While the engine is idling, disconnect the vacuum hose (yellow stripe) from the HAC and put a finger at the hose end to check that vacuum is felt.
  14.  



Click image to see an enlarged view

Fig. Fig. 2: Nipple locations for the high altitude compensation system



Click image to see an enlarged view

Fig. Fig. 3: Each of these hoses should hold vacuum



Click image to see an enlarged view

Fig. Fig. 4: Disconnect the yellow striped hose from the HAC and check for vacuum

  1. Connect everything back to its original position and remove the timing light.
  2.  

ALTITUDES ABOVE 3900 FT. (1200M)

See Figure 5

When disconnecting the vacuum hose, put a mark on the hose so that it may be reconnected to the original position. The engine coolant temperature should be 185-205-°F (85-95-°C).

  1. Connect a timing light to the engine.
  2.  
  3. Remove the air filter.
  4.  
  5. Disconnect the vacuum hoses (black, red stripe, black) from the carburetor primary emulsion well bleed nipple, secondary emulsion well bleed nipple and the jet air nipple+ug the nipples.
  6.  
  7. Connect a hand vacuum pump to the vacuum hoses, one hose at a time, and check the air tightness (the vacuum SHOULD leak) while running the engine at idle.
  8.  
  9. Connect the vacuum hoses back to their original positions.
  10.  
  11. Run the engine at idle and check ignition timing. The timing should be 13-° BTDC for the 2.0L engines and 12-° BTDC for the 2.6L engines.
  12.  
  13. Connect everything back to its original position and remove the timing light.
  14.  



Click image to see an enlarged view

Fig. Fig. 5: When at an altitude of 3900 ft. (1200m) or higher, two hand vacuum pumps are needed

High Altitude Compensator (HAC)

A vacuum pump capable of producing more than 10 in. Hg (33.8 kPa) of vacuum will be needed to perform this test.

ALTITUDES BELOW 3,900 FT. (1,200M)
  1. Disconnect the vacuum hose (yellow stripe) from the HAC and connect a hand vacuum pump to the HAC nipple.
  2.  
  3. Apply vacuum and check that it leaks and does not hold steady.
  4.  
  5. Disconnect the hand pump and plug the vacuum hose back onto its nipple.
  6.  
  7. Disconnect the vacuum hose (red stripe) from the HAC and connect a hand vacuum pump to the HAC nipple.
  8.  
  9. Check to see that the vacuum holds steady.
  10.  

ALTITUDES BELOW 3,900 FT. (1,200M)
  1. Disconnect the vacuum hose (yellow stripe) from the HAC and connect a hand vacuum pump to the HAC nipple.
  2.  
  3. Apply vacuum and check that it holds steady.
  4.  
  5. Disconnect the vacuum hose (red stripe) from the HAC and connect a second hand vacuum pump to the HAC nipple.
  6.  
  7. Check to see that the vacuum leaks or does not hold steady.
  8.  
  9. Reconnect the vacuum lines to the HAC.
  10.  

Vacuum Switching Valve (VSV) See Figures 6 and 7

A vacuum pump capable of producing more than 10 in. Hg (33.8 kPa) of vacuum will be needed to perform this test.

When disconnecting the vacuum hose, put a mark on the hose so that it may be reconnected to its original position.

  1. Remove the vacuum switching valve.
  2.  
  3. Connect a hand vacuum pump to the black vacuum nipple of the VSV.
  4.  
  5. Apply a vacuum of 15.7 in. Hg (53 kPa) and check air tightness.
  6.  
  7. Blow air lightly in from the carburetor air bleed side nipple. With the applied vacuum at 8 in. Hg (27 kPa) or less, the air should NOT blow through the valve. With the applied vacuum at 9.75 in. Hg (34 kPa) or more, the air should blow through.
  8.  



Click image to see an enlarged view

Fig. Fig. 6: Apply vacuum and check the air tightness of the vacuum switching valve



Click image to see an enlarged view

Fig. Fig. 7: The VSV should react as indicated

Check Valve See Figures 8 and 9

A vacuum pump capable of producing more than 10 in. Hg (33.8 kPa) of vacuum will be needed to perform this test.

When disconnecting the vacuum hose, put a mark on the hose so that it may be reconnected to its original position.

  1. Remove the check valve.
  2.  
  3. Connect a hand vacuum pump to the check valve and check the air tightness. When the pump is attached to the dark blue nipple, the vacuum should leak. With the pump attached to the white nipple, the vacuum should hold steady and not leak.
  4.  
  5. If the component fails either of these tests, it needs to be replaced.
  6.  



Click image to see an enlarged view

Fig. Fig. 8: Attach a hand vacuum pump to the check valve



Click image to see an enlarged view

Fig. Fig. 9: The check valve should operate as indicated

Carburetor Bleed Air Passage

A vacuum pump capable of producing more than 10 in. Hg (33.8 kPa) of vacuum will be needed to perform this test.

  1. Disconnect the vacuum hoses from the air nipple, the primary well bleed nipple, and the secondary well bleed nipple and connect a hand vacuum pump to the nipple.
  2.  
  3. Apply vacuum to each nipple one after the other, to see that the vacuum leaks and does not build up inside the carburetor. Plug the vacuum hoses which are not being currently tested.
  4.  
  5. If vacuum builds up, have the carburetor disassembled and checked.
  6.  

TESTING - CALIFORNIA MODELS



See Figure 5

A vacuum pump capable of producing more than 10 in. Hg (33.8 kPa) of vacuum will be needed to perform this test.

ALTITUDES BELOW 3,900 FT. (1,200M)

When disconnecting the vacuum hose, put a mark on the hose so that it may be reconnected to the original position. The engine coolant temperature should be 185-205-°F (85-95-°C).

  1. Connect a timing light to the engine.
  2.  
  3. Remove the air filter.
  4.  
  5. Disconnect the vacuum hose (black) from the carburetor primary emulsion well bleed nipple and plug the nipple.
  6.  
  7. Connect a hand vacuum pump to the vacuum hose and check to see that the vacuum does NOT leak, while running the engine at idle.
  8.  
  9. Connect the vacuum hose back to its original position.
  10.  
  11. Run the engine at idle and check ignition timing. The timing should be 6-10-° BTDC for the 2.0L engines and 5-9-° BTDC for the 2.6L engines.
  12.  
  13. While the engine is idling, disconnect the vacuum hose (yellow stripe) from the HAC and put a finger at the hose end to check that vacuum is felt.
  14.  
  15. Connect everything back to its original position and remove the timing light.
  16.  

ALTITUDES ABOVE 3,900 FT. (1,200M)

When disconnecting the vacuum hose, put a mark on the hose so that it may be reconnected to the original position. The engine coolant temperature should be 185-205-°F (85-95-°C).

  1. Connect a timing light to the engine.
  2.  
  3. Remove the air filter.
  4.  
  5. Disconnect the vacuum hose (black) from the carburetor primary emulsion well bleed nipple and plug the nipple.
  6.  
  7. Connect a hand vacuum pump to the vacuum hose and check that the vacuum leaks, while running the engine at idle.
  8.  
  9. Connect the vacuum hose back to their original positions.
  10.  
  11. Run the engine at idle and check ignition timing. The timing should be 13-° BTDC for the 2.0L engines and 12-° BTDC for the 2.6L engines.
  12.  
  13. Connect everything back to its original position and remove the timing light.
  14.  

High Altitude Compensator (HAC)

A vacuum pump capable of producing more than 10 in. Hg (33.8 kPa) of vacuum will be needed to perform this test.

ALTITUDES BELOW 3,900 FT. (1,200M)
  1. Disconnect the vacuum hose (white stripe, two nipples side) from the HAC and connect a hand vacuum pump to the HAC nipple.
  2.  
  3. Apply vacuum and check that it leaks and does not hold steady.
  4.  
  5. Disconnect the hand pump and plug the vacuum hose back onto its nipple.
  6.  
  7. Disconnect the vacuum hose (black) from the HAC and connect a hand vacuum pump to the HAC nipple.
  8.  
  9. Check to see that the vacuum holds steady.
  10.  

ALTITUDES ABOVE 3,900 FT. (1,200M)
  1. Disconnect the vacuum hose (white stripe, two nipples side) from the HAC and connect a hand vacuum pump to the HAC nipple.
  2.  
  3. Apply vacuum and check that it holds steady.
  4.  
  5. Disconnect the vacuum hose (black) from the HAC and connect a second hand vacuum pump to the HAC nipple.
  6.  
  7. Check to see that the vacuum leaks or does not hold steady.
  8.  
  9. Reconnect the vacuum lines to the HAC.
  10.  

Vacuum Switching Valve (VSV)

These procedures are the same as the non-California procedures described earlier.

Check Valve

These procedures are the same as the non-California procedures described earlier.

Carburetor Bleed Air Passage

These procedures are the same as the non-California procedures described earlier.

 
label.common.footer.alt.autozoneLogo