Marquis L4-140 2.3L VIN A 1-bbl (1986)
Carburetors, Fuel Charging Assemblies and Throttle Bodies
4-87
Idle Mixture Setting Procedures
IDLE FUEL MIXTURE-PROPANE ENRICHMENT METHOD
2.0L TRUCK UNDER 8600 GVW w/YFA-IV
NOTE:
This procedure is for 2.0L Truck engines only, it is not for trucks over 8500 GVW. Propane specifications are not listed for these applications.
If CO and HC are not within specification, perform appropriate electrical diagnostic procedure, Section 15.
I.
Vehicle Preparation
A.
Apply the parking brake and block the wheels.
B.
Connect an analog tachometer, Rotunda 059-000010 or an equivalent analog tachometer.
C.
Disconnect the flexible fresh air tube from the air cleaner duct or adaptor. Using propane enrichment Tool T75L-9600-A or equivalent, insert
the tool hose approximately 3/4 of the way into the duct or fresh air tube. If necessary, secure the hose with tape.
D.
Disconnect and plug the hose at the air bypass valve.
E.
Disconnect and plug the hose between the purge valve and the spacer at the purge valve.
F.
When the above Steps have been completed, proceed to Section II.
II. Propane Enrichment Method (Except as Noted)
NOTE:
Leave all vacuum signal hoses attached to the air cleaner assembly when relocating the assembly to perform carburetor adjustments. The air
cleaner assembly must be in place, however, when measuring engine speeds.
CAUTION: Prolonged engine idling can result in catalyst overheating and excessive underbody temperatures.
A.
Verify engine timing is set to specification - reset if necessary, Section 15.
B.
Verify that the curb idle speed is being controlled to specification. Then, electrically disconnect idle speed control (ISC) motor from wiring
harness.
C.
Place A/C-heat selector in the Off position and verify that lamps are Off.
NOTE:
Remove PCV valve from grommet, locate the crankcase closure hose and disconnect at the air cleaner end (allowing the PCV valve and
closure hose to vent to underhood air during idle fuel mixture check).
D.
With the transmission in Neutral, run the engine at approximately 2500 rpm for 15 seconds before each mixture check. If check is not completed
within 60 seconds, repeat this cleanout Step.
1986
4-88
Carburetors, Fuel Charging Assemblies and Throttle Bodies
Idle Mixture Setting Procedures
E.
With the engine idling at normal operating temperature gradually open the propane tool valve and watch for engine speed gain, on the tachometer.
When the engine speed reaches a maximum and then begins to drop off, note the amount of speed gain. (Propane cartridge must be in vertical
position).
NOTE:
If the engine speed will not drop off check the propane cartridge gas supply. If necessary repeat Steps D & E with a new propane
cartridge gas supply.
F.
Compare measured speed gain to specified speed gain.*
1.
If the measured speed gain is within specification, proceed to Step H.
NOTE:
The carburetor assembly is equipped with a tamper-resistant idle adjustment feature, the carburetor must be removed from the
vehicle. Refer to Shop Manual, Group 24 for removal of the above feature.
NOTE:
If it is determined that idle fuel mixture adjustment will be necessary, adjust the mixture according to the reset rpm specification.
