Idle Speed - Service Procedures
84ford16Article No. 84-7-13
IDLE - (4.9L) LIGHT TRUCK IDLE CONCERN DIAGNOSIS
LIGHT TRUCKS 1984 E, F AND BRONCO
Numerous claims are being submitted by dealers concerning the 4.9L idle speed control system. Often, these claims are not diagnosed using the correct procedures concerning high or low idles, and are not catalogued correctly. If the service procedures resulted in incorrect carburetor adjustments, further performance complications can be introduced by the misadjustment while leaving the original cause of the concern unresolved.
The following documentation outlines the correct procedures for diagnosing idle out of spec concerns. FAILURE TO PERFORM THESE PROCEDURES OR IGNORING THEM IN ORDER TO EXECUTE A QUICK ADJUSTMENT WILL RESULT IN IMPROPER VEHICLE OPERATION. Any improper adjustment or other modification to the idle speed control system can cause the EEC-IV control system to malfunction resulting in degraded starting performance, fuel economy or driveability.
1. For 1984, the correct warm idle speeds for all 4.9L vehicles are (refer to decal for details):
a. 650 RPM (manuals)
b. 600 RPM (automatics in drive)
c. 750 RPM (automatics in neutral)
FIGURE 12:
If the idle speed is out of specification by more than +/- 50 RPM, an adjustment as outlined in this procedure may be required. UNDER NO CIRCUMSTANCES SHOULD THE CURB IDLE BE ADJUSTED MANUALLY BY TURNING THE MAX AIRFLOW EXTENSION SCREW
(Reference: Figure 12) ON THE THROTTLE LEVER OF THE CARBURETOR. NEITHER SHOULD THE ANTIDIESEL SCREW BE ADJUSTED TO COMPENSATE FOR A LOW IDLE.
A. Check for a binding throttle or check to see if the throttle is trapped on the fast idle cam. Sometimes the throttle cable bracket requires bending in order to ensure correct throttle position at idle. If a binding condition exists, service as necessary.
B. The kickdown screw is used to adjust the cold fast idle. It is pre-set at the factory and should not require any adjustment. Adjustment procedures are
outlined in the 1984 Car/Truck Shop Manual (Volume H Section 4-81). The kickdown setting is 1600 RPM (1450 RPM for engines with less than 100 miles), as shown on the decal.
C. The max air flow extension screw is pre-set at the factory and should not require any adjustment. Adjustment procedures are outlined in the 1984 Car/Truck Shop Manual (Volume H Section 4-81). The 1984 maximum extension setting is 1550 RPM, as shown on the decal (1400 RPM for engines with less than 100 miles).
D. The anti-diesel screw is pre-set at the factory and should never be used to adjust for a low out of specification curb idle. If this screw was used to compensate for a low curb idle, it can be set back to its correct setting as follows:
1. Warm vehicle to normal operating temperature.
2. Air conditioning off.
FIGURE 13:
3. Shut engine off and remove air cleaner (plug open vacuum hose). In the engine compartment, locate the self-test connector and self-test input (STI) connector. These two connectors are located next to each other (Figure 13).
4. Connect a jumper wire between the STI connector and the signal return pin on the self-test connector.
5. Turn the ignition key to the run position. DO NOT START ENGINE.
6. The ISC plunger will retract. Wait about ten (10) seconds.
7. Shut off the key.
8. Remove the jumper wire.
9. At this point, the idle speed motor should be retracted allowing the throttle to rest against the anti-diesel screw. Unplug the ISC electrical connection. If the idle speed motor is not retracted, refer to the 4.9L Quick Test, Section 22 of the 1984 Car/Truck Shop Manual, Volume H.
10. Start engine and verify that anti-diesel setting is below 550 RPM in neutral.
11. If it is higher than 550 RPM, remove tamperproof cap and reset to 500 RPM.
12. Install a new tamperproof cap (Part No. E3PZ- 9C984-A) and reconnect the idle speed motor electrical connection. Whenever the idle speed motor is replaced, it will be necessary to readjust the Maximum Extension setting for the idle speed motor as outlined in the 1984 Car/Truck Shop Manual (Volume H Section 4-81)
If the curb idle speed is still out of specification, then the following EEC diagnostic procedures should be followed:
1. Run the Quick Test with the STAR Tester and record the codes. Refer to the 1984 Car/Truck Shop Manual (Volume H Section 22).
2. Follow the correct Pinpoint Test as indicated by the results of the Quick Test. Pinpoint tests are located in the 1984 Car/Truck Shop Manual (Volume H Section 25).
If a rough idle condition exists, and the curb idle is as specified, perform the following diagnostic procedure in sequence until the concern is resolved:
1. Run QUICK test with the STAR Tester and verify a PASS Code 11.
2. Propane the engine as outlined in the 1984 Car/Truck Shop Manual (Volume H Section 4-133).
3. If the propane gain is within specification (10-90 RPM) then set the mixture screw to the low side of the specification to improve the idle quality.
4. If the rough idle condition still exists, run Step 7.0 (Diagnostics by Symptom) of the Quick Test.
NOTE: DO NOT BY ANY MEANS ARTIFICIALLY INCREASE THE IDLE RPM ON THE ANTI-DIESEL SCREW. This will override the idle speed motor and cause erroneous calculations within the EEC system. This, in turn, could cause other concerns to arise, including intermittent operation in the failure mode.
Other items relevent to the 4.9L truck engine diagnostics include:
A. Electrical connectors which are not pushed all the way in create intermittent concerns. Check the electrical connections at the idle speed motor and the EEC IV power relay (located near the processor under the dash).
B. Sometimes the pins in the electrical connector attaching the power relay are not locked in all of the way. They may get pushed out of the connector when the relay is installed.
C. On 1984 4.9L trucks equipped with the EEC IV system and automatic transmission, the following items may be observed:
1. When the engine is throttled in neutral, the speed may remain at about 1000 to 1300 RPM for about 10 to 20 seconds, and then return to 750 RPM.
2. As long as the engine drops to 600 RPM in drive, then the system is operating correctly and the momentary speed condition described in Step 1 is considered normal.
D. Low engine coolant level can result in out of specification curb idles due to unusual or abnormal ECT (engine coolant temperature) sensor readings. It is important that the correct coolant level be maintained on all 1984 4.9L trucks.
E. The Cruise Control chain should not be adjusted so tight that it impedes idle speed motor control of the throttle at idle.
F. Check the part number on the power relay (It should be E47E-12A646-AA). The power relay is located under the instrument panel near the processor. Some 4.9L vehicles may have been built with the wrong power relay.
G. NOTE: The majority of idle speed control concerns can usually be traced to the following components:
^ Idle Speed Motor
^ EEC IV Processor
^ ECT Sensor
^ Power Relay (located under the instrument panel near the processor).
OTHER APPLICABLE ARTICLES: None
WARRANTY STATUS: "INFORMATION ONLY"