Diagnostic Aids

Perform this test only when directed by TEST A or TEST AA.

This test is intended to diagnose the following components or systems:

• ISC by-pass air system
• MAP system
• EGR system
• MAF system

To prevent replacing good components, be aware that the following non-EEC-IV areas may be at fault:

• Faulty power or ground connections
• Ignition system (distributor cap, rotor, wires, coil and plugs)
• Basic mechanical engine components (cam timing, compression, etc.)

1) ISC-BPA Check  Attempt to start engine at part throttle. If engine starts and runs smoothly at part throttle, go to TEST KE, step 4). If engine does not function as described, go to step 3).

2) Check For RPM Drop  Turn ignition off. Connect a tachometer. Start engine and disconnect ISC solenoid. If RPM drops or engine stalls, reconnect ISC solenoid and go to next step. If RPM does not drop, go to step 4).

3) Power To MAP/BP Sensor  If vehicle is not equipped with a MAP/BP sensor, go directly to step 8). Use Ford Motor Co. MAP/BP tester for this test. If Green light is on, VREF circuit voltage is okay. If Red light (or no light) is on, VREF circuit voltage is either too low or too high. Turn ignition off and disconnect MAP/BP sensor from vehicle harness. Connect MAP/BP tester between vehicle harness and MAP/BP sensor. Connect banana plugs of tester into DVOM, and set DVOM on 20-volt scale. With tester connected, turn ignition on. If Green light is on, go to next step. If light is not on, repair open in VREF circuit and remove MAP/BP tester. Reconnect components and retest symptom.

4) MAP/BP Tester Output Reading  Measure several known good MAP/BP sensors to obtain average voltage for specific location and date of testing. With MAP/BP tester and DVOM connected, turn ignition on and measure MAP/BP SIG voltage at MAP sensor. If voltage is in within specification for the specific altitude, go to step 8) (vehicles with MA sensors), or go to next step (all others). See MAP VOLTAGE OUTPUT  . If voltage is not within specification for the specific altitude, replace MAP/BP sensor.

Fig 1: MAP/BP Tester & Circuit

5) Check Vacuum Lines  Check vacuum lines for correct routing. Refer to VECI decal. Check MAP sensor vacuum line for leaks or blockage. If vacuum lines are okay, go to next step. If vacuum lines are not okay, repair as necessary. Rerun QUICK TEST.

6) Check MAP Sensor  Turn ignition off and wait 10 seconds. Disconnect vacuum line from MAP sensor. Install vacuum pump to MAP sensor. Apply 18 in. Hg vacuum to MAP sensor. If MAP sensor holds vacuum, release vacuum and remove vacuum pump. Reconnect vacuum line to MAP sensor and go to next step. If MAP sensor does not hold vacuum, replace MAP sensor. Reconnect vacuum line and rerun QUICK TEST.

7) Check Vacuum Manifold Source  Turn ignition off. Disconnect MAP sensor vacuum hose from manifold vacuum "T" fitting, and install vacuum gauge in its place. Start engine and observe vacuum gauge. If manifold vacuum is present, remove vacuum gauge; reconnect MAP sensor vacuum hose and go to next step. If vacuum is not present, remove obstruction; reconnect all components and rerun QUICK TEST.

8) Check EGR Vacuum  If vehicle is not equipped with EGR system hardware, go directly to TEST H, step 2). Step 8) and step 9) attempt to determine if EGR system is the cause of driveability symptom or no-start condition. Disconnect and plug vacuum line at EGR valve. Attempt to start engine. If vehicle could not start previously and still does not start, or if vehicle driveability fault is still present, go to next step. If vehicle did not start previously but starts now, or if driveability symptoms are eliminated, go to TEST DN, step 42) (vehicles with EVP), or go to TEST DL, step 21) (all others).

9) Check EGR Valve  Inspect EGR valve for leaks. If valve is fully closed, go to TEST H, step 2). If EGR valve is leaking or is not fully seated, replace or repair valve.