Diagnostic Aids

Perform this test only when directed by CIRCUIT TEST AA, CIRCUIT TEST AB or CIRCUIT TEST AC. This test is intended to diagnose:

• ISC by-pass air system.
• MAP system.
• ERG system.
• MAF system.

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

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

1) ISC-BPA Check  Try to start engine at part throttle. If engine starts and runs smoothly at part throttle, go to CIRCUIT TEST KE, step 4). If engine does not run as described, go to step 2).

2) Check For RPM Drop  Turn ignition off. Connect a tachometer to engine. Start engine. Disconnect ISC solenoid. If RPM drops or engine stalls, reconnect ISC solenoid and go to step 3). 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 to step 8). Test MAP/BP using Ford Motor Co. MAP/BP tester. Disconnect MAP/BP sensor. Turn ignition off. Connect MAP/BP tester between wiring harness and MAP/BP sensor. See Fig 1 . Connect banana plugs of tester into DVOM. Set DVOM on 20-volt scale. With tester connected, turn ignition on. If Green light is on, go to step 4). 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 location and date of testing. With MAP/BP tester and DVOM connected, turn ignition on. Measure MAP/BP voltage at MAP sensor. If voltage is in within specification for specific altitude, go to step 5). See MAP VOLTAGE OUTPUT  . If voltage is not within specification for specific altitude, replace MAP/BP sensor.

Approximate Elevation (Ft.)	Voltage Output (Volts)
0	1.59
1000	1.56
2000	1.53
3000	1.50
4000	1.47
5000	1.44
6000	1.41
7000	1.39

5) Check Vacuum Lines  Check vacuum lines for correct routing. Refer to VECI decal. Check MAP sensor vacuum line for leaks and blockage. If vacuum lines are okay, go to step 6). If vacuum lines are not okay, repair as necessary. Repeat QUICK TEST  .

6) Check MAP Sensor  Turn ignition off. Disconnect vacuum hose from manifold vacuum source. Install vacuum pump to MAP sensor hose. Apply 18 in. Hg vacuum to MAP sensor. If MAP sensor holds vacuum, release vacuum and remove vacuum pump. Reconnect vacuum hose to MAP sensor, and go to step 7). If MAP sensor does not hold vacuum, replace MAP sensor or hose and rerun QUICK TEST  .

7) Check Vacuum Manifold Source  Turn ignition off. Disconnect MAP sensor vacuum hose from manifold vacuum source. Install vacuum gauge at manifold vacuum source. Start engine and observe vacuum gauge. If manifold vacuum is present, remove vacuum gauge. Reconnect MAP sensor vacuum hose, and go to step 8). 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, go to procedures in CIRCUIT TEST H, step 2). Disconnect and plug vacuum line at EGR valve. Attempt to start engine. If vehicle did not start previously but starts now or if driveability symptoms are eliminated, go to procedures in CIRCUIT TEST DN, step 42) (for vehicles with EVP) or CIRCUIT TEST DL, step 21) (all others). If vehicle could not start previously and still does not start or if vehicle driveability fault is still present, go to step 9).

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