Engine - Hard Start/Poor Performance/Fuel Economy
Article No. 86-12-19HARD START/ POOR PERFORMANCE/ FUEL ECONOMY (5.8L AND 7.5L) - EQUIPPED WITH HOLLEY 4180-C CARBURETOR
LIGHT TRUCK 1984-86 E-SERIES, F-SERIES, BRONCO
The subject concerns may be caused by the choke not fully opening due to binding and/or no power to the choke cap.
To diagnose the Holley 4180-C choke system, perform Steps I, II, and III of the following revised procedure (pre-check instructions, freedom of linkage and system integrity check and electric choke functional test). Replace pages 4-133 and 4-134 of the 1986 Emissions Diagnosis Shop Manual with this revised procedure.
OTHER APPLICABLE ARTICLES: None
WARRANTY STATUS: "INFORMATION ONLY"
Choke Adjustment Procedure
5.8L AND 7.5L TRUCK
AUTOMATIC CHOKE SYSTEM - HOLLEY 4180-C 4V (ELECTRIC)
I. Pre-Check Instructions
A. Apply parking brake and block the wheels.
B. Start the engine, bring to normal operating temperature, and turn OFF.
C. Remove the air cleaner assembly and plug the vacuum hose(s) to the air cleaner.
II. Freedom of Linkage and System Integrity Check
A. Verify that all vacuum hoses and solenoid wires are properly connected and intact; correct as required. Check torque of carburetor holddown nuts; retighten to specification, if necessary.*
B. Check all carburetor linkages for freedom of operation as follows:
1. Bring engine to normal operating temperature and manually depress the throttle lever to 1/4 open position, and rotate the choke plate to the closed position. Release the choke plate; the choke plate should rotate smoothly to the open position. If sticking or binding is exhibited, clean/ service/replace/adjust the choke linkage, as required, to restore freedom of choke plate movement.
III. Electric Choke Functional Test
The Holley 4V carburetors for the 7.5L engines use an alternator powered (7.2V nominal) dual pill choke system. The choke power lead is connected to the alternator stator terminal. The Holley 4V carburetor for the 5.8L engine uses a battery powered 12V source from a relay. This relay is located on the left hand top of the dash panel on F-Series vehicles. The relay is located on the left hand grille top (prior to February, 1986) or the right hand grille top (after February, 1986) on E-Series vehicles.
A. Choke Cap Continuity
1. Turn ignition switch OFF.
2. Connect one lead of a test lamp to the positive terminal of the battery and the other lead to the choke cap terminal. If the lamp glows, proceed to Step B.
3. Connect one end of a jumper wire to the choke shroud and the other end to the positive terminal of the battery.
4. The test lamp should glow. If not, connect the jumper wire directly to the choke cap ground. Now if the lamp glows, correct the poor continuity between the choke clamp shroud and the choke cap ground. If the lamp does not glow, replace the choke cap. Refer to the Engine Shop Manual, Group 24 for choke cap removal and installation procedure.
B. Continuity of all circuit components, alternator powered choke (7.5L engines):
1. Connect one lead of a test lamp to the choke cap wire and the other lead to the negative terminal of the battery.
2. Start the engine, the test lamp should indicate continuity. If not, locate and service the open circuit between choke cap to alternator stator terminal. If no open circuit is found, check alternator output and service as required.
* Refer to the Special Specifications Issue TSB Publications.
Choke Adjustment Procedure
C. Continuity of all circuit components, battery powered choke (5.8L engines):
1. Connect one lead of a 12V test lamp to the choke cap wire. Connect the other lead to the negative terminal of the battery or other ground source.
2. Start the engine. The test lamp should glow. If not, locate and service the open circuit, which may be in the wire to the choke relay, from the relay back to the stator feed, or other -9E724- wiring harness connections. If no open circuit is found, check the choke relay for proper function and replace if required.
D. Choke Cap Resistance Test
1. With an ohmmeter, set to lowest range that will indicate 3O-ohms (maximum). Connect one lead of an ohmmeter to choke cap terminal and the other lead to choke cap shroud. Be sure metal-tometal contact is achieved (not metal-oxide film) and false readings are prevented. The ohm reading should be under 30 but never zero. If the ohm reading is outside this range, start the test all over. If this improper reading repeats, the choke cap is defective. The cap should be replaced per Shop Manual, Group 24.
IV. A. Choke Pulldown
1 Remove carburetor from vehicle and cover intake manifold.
2. Place carburetor on a stand which allows access to the pulldown diaphragm vacuum passage on the underside of the throttle body, Figure 1.
3. Mark choke cap and choke housing as indicated on Figure 2. Remove choke cap, gasket, and retainer. Refer to Shop Manual, Group 24 for removal (of the choke cap retainer) instructions.
4. Reinstall choke cap temporarily with a standard choke cap gasket. Line up marks made previously on the cap and housing and rotate cap 90~ counterclockwise from that position. Secure with one screw.
5. With the choke plate in the full closed position, actuate the choke pulldown motor using an outside vacuum source, (17 in.-Hg. minimum) in the diaphragm vacuum passage.
6. Using a drill gauge of the specified size, check the clearance between the lower edge of the choke plate and the air horn wall. NOTE: The gauge should fit in such a manner that it contacts the air horn and choke plate but does not move the plate.
7. If the pulldown dimension is out of specification, carefully remove the diaphragm adjustment screw cap with a small sharp punch or screwdriver, Figure 3.
8. Turn the adjustment screw with a 5/64 inch Allen wrench clockwise to decrease the pulldown set or counterclockwise to increase the pulldown set. NOTE: Maintain a minimum of 17 inches Hg. to the pulldown diaphragm during adjustment. Cycle vacuum from 0 to 17 inches Hg. to verify proper set.
9. Apply RTV sealant to the adjustment screw cavity and check the fast idle cam adjustment.