Fuel System

The correct fuelling calibration is essential to provide reliable starting and running of the engine while warming up.

ECM - A new tune has been developed to optimize fueling calibration at temperatures below -23°C (-10°F). This should be installed in all vehicles that will be expected to operate in this temperature range. Use the following work procedure to replace the PROM:

1. Remove the ECM from right side closure panel on 1994 MY Defender 90/or under R/F seat on 1995 MY Defender 90, and disconnect the multiple connector.

2. Place the ECM on a grounded anti-static mat. Slip on anti-static wrist cuff and connect spiral jumper lead to the mat. Use longer jumper wire to ground the mat to an electrical conduit or a cold water pipe.

3. Remove four Torx(R) (T20) screws from the ECM and remove bottom half of cover.

4. Remove printed circuit board from case and place on anti-static mat.

5. Locate PROM cover and remove it by grasping with pliers across its width at one end or the other (avoid the center). A rocking motion aids removal. Set cover aside for later use.

6. Using the PROM removal tool, carefully lift the PROM from its socket.

NOTE:
Be careful not to damage Printed Circuit Board or other components. Store PROM in parts retention area with a completed Warranty Parts Tag.





7. Remove the new PROM (PRM3652) from its package and insert it into the socket. Make sure all pins are engaged before pressing PROM fully in socket (figure 1). Snap PROM cover in place. If it doesn't fit. recheck PROM for correct installation.

8. Place Printed Circuit Board in case and reassemble cover. Make sure gasket is in place.

9. Attach multiple connector to the ECM and perform the following checks:

A. Switch on ignition. The fuel pump should run for a short period. Listen for any unusual noises such as injectors operating or relays clicking which would indicate a problem.

B. Observe that the "Check Engine" light comes on and then extinguishes during the bulb check. If not, check the multiple connection and if necessary, replace the ECM.

C. If the vehicle fails steps A or B. recheck the multiple connector pins and socket. If this does not resolve the problem. check that the PROM was installed correctly.

Quality-Check Procedure

Start the engine and observe the following:

1. The "Check Engine" light remains out.

2. Idle speed smoothness is stabilized.

3. Switch on A/C and note idle speed compensation.

4. Rev the engine; no misfire should be noted.

Replace the ECM if the vehicle fails any part of this procedure.

Otherwise:

1. Attach a new label.

2. Install ECM and trim panels.