1991 Ford Mustang LX 5.0: Difference between revisions
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== ECM == | == ECM == | ||
===KOEO Test=== | ===KOEO Test=== | ||
Key On Engine Off Test. Using The Check-Engine Light this Mustang will allow you to use a jump wire and count the check-engine light in the dash. The jump wire (I’d use spades on each end) would connect the STI (test input) with #2 pin on the connector. | Key On Engine Off Test. Checking codes is one of the most important diagnostic procedures that you can do on your own for your Mustang. | ||
Using The Check-Engine Light this Mustang will allow you to use a jump wire and count the check-engine light in the dash. The jump wire (I’d use spades on each end) would connect the STI (test input) with #2 pin on the connector. | |||
The fox Mustang’s EEC IV computer has two connectors for self-testing and located on the driver-side firewall. The large connector contains the self test output (STO) and ground (SIG RTN). The small pigtail is the self test input (STI). | The fox Mustang’s EEC IV computer has two connectors for self-testing and located on the driver-side firewall. The large connector contains the self test output (STO) and ground (SIG RTN). The small pigtail is the self test input (STI). | ||
Revision as of 19:16, 6 August 2025
ECM
KOEO Test
Key On Engine Off Test. Checking codes is one of the most important diagnostic procedures that you can do on your own for your Mustang.
Using The Check-Engine Light this Mustang will allow you to use a jump wire and count the check-engine light in the dash. The jump wire (I’d use spades on each end) would connect the STI (test input) with #2 pin on the connector.
The fox Mustang’s EEC IV computer has two connectors for self-testing and located on the driver-side firewall. The large connector contains the self test output (STO) and ground (SIG RTN). The small pigtail is the self test input (STI).
Engine Stalling or Misfiring Erratic engine behavior may also indicate a bad or failing ECM. A faulty computer may cause the vehicle to intermittently stall or misfire. The symptoms might come and go.
Mustangs VIP Connector Location
located behind the driver side strut tower
- Use a paperclip or 3-inch wire with spade terminals to jumper the STI (Self-Test Input) to the SIG RTN (Signal Return) pin on the diagnostic connector.
- Turn the ignition to the ON position (engine off) to run the Key On Engine Off (KOEO) test.
- Observe the Check Engine Light (CEL) flashes or use an analog voltmeter to read the codes by counting needle sweeps.
- Record the trouble codes and compare them to a Ford OBD-I code list (available online or in a service manual) to identify ECM-related issues.
- Optionally, perform a Key On Engine Running (KOER) test after warming the engine to check dynamic performance and a Cylinder Balance Test to detect misfires.