1997 Ford Ranger Engine running rough

Tiny
ROADBUM
  • MEMBER
  • 1997 FORD RANGER
Engine Performance problem
1997 Ford Ranger 4 cyl Two Wheel Drive 115000 miles

I've noticed my 97 ranger seems to be running rough lately. I've also noticed that when I turn OFF the heater A/C blower switch the engine seems to smooth out, turn the switch back on the truck starts running rough again, although not right away, turn the switch off it smooths out again. I also notice the headlights flicker for a second when I turn that switch. I've been told that it's the alternator, but the one on the engine is only 2 years old. I think it's a short somewhere, and anyway there's been no hard starting of the vehicle or anything of that nature, any ideas?
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Tuesday, December 16th, 2008 AT 6:21 PM

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Tiny
DAVE H
  • EXPERT
GENERAL INSPECTION
Ensure battery posts and cables are clean and tight. Check drive belt tension. Ensure connections at generator, regulator and engine ground are clean and tight. Check fuses and fusible links, replace as necessary.
Check condition of battery to see if battery has the ability to accept and hold a charge. If battery capacity meets requirements, charge battery before proceeding with testing to ensure battery is fully charged.
NO-LOAD TEST
Connect voltmeter positive lead to B+ terminal on generator and negative lead to ground. Start and run engine at 1500 RPM with no electrical load (foot off brake and doors closed). Read voltmeter when voltage stabilizes. This may require waiting a few minutes. Voltage should be 13-15 volts.
If voltage increases to proper level, proceed to LOAD TEST. If voltage increases beyond proper level, proceed to OVERCHARGE CONDITION. If there is no voltage increase, proceed to LOW OR NO CHARGE CONDITION.
Fig. 1: Identifying Generator-Regulator Terminals
Courtesy of FORD MOTOR COMPANY
LOAD TEST
Ensure drive belt is in good condition and properly tightened. Connect charging system load tester in accordance with manufacturer's instructions. Start and run engine at 2000 RPM and apply load until generator output amperage levels off.
Record maximum generator amperage output. See GENERATOR OUTPUT SPECIFICATIONS TABLE for output values. If generator output is within 20 percent of rated output amperage and voltage remains 12.5-14.5 volts, generator output is okay. If generator does not produce rated output, proceed with appropriate testing.
GENERATOR OUTPUT SPECIFICATIONS
ApplicationAmps Rating
Standard95
Optional130

OVERCHARGE CONDITION
If voltmeter indicates high voltage (more than 15.4 volts), turn ignition switch to ON position. Connect negative voltmeter lead to ground. Connect positive voltmeter lead to generator output connection at starter solenoid. Record voltage.
Connect positive voltmeter lead to regulator "A" terminal screw on rear of generator. See Fig. 1 and Fig. 3. If voltage difference between both locations exceeds 0.25 volt, repair high resistance condition in "A" circuit wiring.
If excessive voltage still exists, check ground connections for both generator and regulator. Tighten regulator ground screws to 16-24 INCH lbs. (1.8-2.7 N.M.), And recheck output voltage.
If excessive voltage still exists, connect voltmeter negative lead to ground. Connect positive voltmeter lead first to regulator "A" terminal screw, then to "F" terminal screw. Record readings. Different voltages at each screw head indicates a short in field circuit or a grounded rotor coil. To correct either condition, replace generator.
If same voltage appears at both screw heads, no internal short to ground is indicated. Replace voltage regulator.
LOW OR NO CHARGE CONDITION
Unplug harness connector from regulator at rear of generator. Connect ohmmeter between regulator "A" and "F" terminal screws. See Fig. 1 and Fig. 3. If resistance is not greater than 2.4 ohms, a short in field circuit or a grounded rotor coil is indicated. Replace generator. If resistance is greater than 2.4 ohms, go to next step.
Reconnect regulator wiring plug. Connect negative voltmeter lead to ground. Contact positive voltmeter lead to regulator "A" terminal screw. If voltmeter does not indicate battery voltage, repair open or high resistance in "A" circuit wiring. Perform load test after repairs.
If battery voltage is indicated at "A" terminal screw, ensure ignition switch is in OFF position. Connect positive voltmeter lead to regulator "F" terminal screw. If battery voltage is present, go to step 4). If battery voltage is not present, replace generator.
Turn ignition switch to ON position (engine off). With voltmeter negative lead to ground, contact positive lead of voltmeter to regulator "F" terminal screw. If voltmeter indicates 2 volts or less, go to next step. If voltage is greater than 2 volts, check circuit between "I" terminal and ignition switch. Repair if necessary. See "S" & "I" CIRCUIT TEST. If "I" circuit is okay, replace regulator. Perform LOAD TEST after repair.
Start engine and run at 2000 RPM with headlights on. Measure voltage at "B+" terminal of generator and at generator feed wire at starter relay. If voltage readings differ by more than 0.5 volt, repair high resistance or open in wire between "B+" terminal and junction near starter relay.
If generator still does not charge sufficiently, connect a jumper wire to regulator "F" terminal screw and ground it to rear housing. If output voltage increases to 13-15 volts, replace regulator. If output voltage does not increase to at least 13 volts, replace generator.
"S" & "I" CIRCUIT TEST
Unplug regulator 3-wire harness connector. Connect jumper wire from harness "A" terminal to regulator "A" terminal. See Fig. 1 and Fig. 2. Connect another jumper wire from regulator "F" terminal screw to generator housing.
With engine idling, connect voltmeter negative lead to battery ground terminal. Connect voltmeter positive lead first to "S" terminal and then to "I" terminal of regulator harness connector. See Fig. 2. Voltage at "S" terminal should be about 7 volts and about 14 vo lts at "I" terminal. If "S" terminal and "I" voltages are okay, replace voltage regulator. Repeat LOAD TEST. If "S" and "I" circuit voltages are not as specified, go to next step.
If voltage is present at "S" terminal, but not 6-8 volts, replace generator. If no voltage is present at "S" terminal, disconnect one-wire connector ("S" terminal) on back of generator. See Fig. 1. Check voltage at single "S" terminal. If about 7 volts are present repair "S" circuit wiring. If no voltage is present at single "S" terminal, replace generator.
If no voltage is present at "I" terminal, repair indicator light wiring circuit. Restore wiring connections and repeat LOAD TEST.
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Tuesday, December 16th, 2008 AT 6:35 PM

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