Engine Controls - MIL ON/Trailing Throttle Misfire
No: 19/03/98/NASRef:
Issue: 1
Date: 10/02/98
Pride - Trailing Throttle Misfire Diagnosis
AFFECTED VEHICLE RANGE:
DISCOVERY (LJ) 1996
SITUATION:
When investigating the source of a misfire code on 1996 Discovery models it is very important to pay close attention to the freeze frame data obtained by using TestBook. This information can identify engine parameters which relate to trailing throttle. See the description in the "Symptom Description..." section below.
RESOLUTION:
When trailing throttle misfire is suspected as the cause for MIL illumination, perform the diagnosis and repair outline in this procedure.
PARTS INFORMATION:
PRM9637 PROM 1996 Automatic
PRM9630 PROM 1996 Manual
LRNASTATK Anti-static Mat
WARRANTY CLAIMS:
19.22.96 Time 1.25 hr.
TestBook Codes DTCR and Drive Cycle "C" per Bulletin W96.007
*19.22.03.0X Time 0.05 hr.
*X = Number of cylinder misfiring
18.30.89.26 Time 0.50 hr.
Replace PROM
FAULT CODE: Z
Normal warranty policy and procedures apply
REPAIR PROCEDURE
TESTBOOK
1. Hook up TestBook and follow directions to retrieve fault codes.
2. Complete a DTCR along with freeze frame data and FAX to LRNA.
3. Complete the DPR and FAX to LRNA.
4. Follow basic diagnostic directions as specified by TestBook.
NOTE:
Perform the diagnostic procedures and repairs outlined in the following page for the correction of trailing throttle misfire.
SYMPTOM DESCRIPTION AND REQUIRE ACTION FOR TRAILING THROTTLE MISFIRE
CAUTION:
It must be clearly understood that misfire faults caused by these conditions are extremely rare.
It is far more likely that the problem is related to misfire problems covered in Operation Pride Phases I and II. (TIB 12/03/96/US) However, LRNA knows of several examples of this fault occurring in vehicles whose owners live in locations where these driving conditions are common i.e. a long downhill driveway. Information obtained from the DPR is particularly useful in determining if these conditions exist.
NOTE:
If the freeze frame data shows an engine speed of approximately 2000 rpm and an engine load below 20%, the vehicle might have a trailing throttle misfire.
^ The low engine load figure would suggest that the vehicle is being operated on a long decline with only light throttle being applied.
^ These conditions may cause the misfire detection system to store a fault and illuminate the MIL.
^ These conditions must exist on two consecutive OBD II trips for the MIL to be illuminated.
1. Refer to the attached DTCR for an example or typical conditions which may cause a trailing throttle misfire.
2. Establish the nominal engine load at idle, fully warm:
^ Turn off all engine loads
^ Place the vehicle in Park.
3. Access the "Engine Load" Icon in Real Time Monitoring of the GEMS Diagnostics. This value is normally between 20-26%.
4. If the freeze frame engine load figure stored when the misfire occurred is less than this nominal engine load, it is likely the fault was set under decelerating, trailing throttle conditions.
5. When it has been determined that trailing throttle misfire may have occurred, change the PROM following the instructions below.
REMOVAL
1. Make sure that the ignition key is turned off.
2. Remove washer reservoir and set aside.
3. Remove ECM cover using suitable tool to remove clips.
4. Unplug the ECM connectors and remove ECM.
NOTE:
Ensure that the white anti-backout strips have not fallen out of the connectors.
1. If anti-backout strips have fallen out, replace them in the connectors.
5. Place ECM, red connector side up, on grounded anti-static mat. Be sure to wear grounding wrist band.
6. Remove five Torx screws (t20) from cover, and remove cover.
NOTE:
Circuit board is easily damaged. Do not pry covers off using screwdrivers or the like.
7. Remove 8 Torx screws holding circuit board.
8. Fold circuit board over onto mat, exposing chips (Figure 1).
9. Using suitable pliers, carefully remove blue and green PROM covers (Figure 2).
10. Remove the exposed PROMs with PROM puller supplied with anti-static mat.
INSTALLATION
CAUTION:
Make sure that the notch on PROM is in line with the notch on the PROM socket. PROM notch will be oriented towards the red connector.
1. Carefully install new PROMs, noting that one PROM has 28 pins and the other 32 pins.
2. Check for bent pins before replacing PROM covers.
3. Position circuit board and fasten with screws.
4. Install outer cover.
5. Fasten with screws removed earlier and torque to 2.25-2.82 Nm (20-25 lbf.in.).
6. Apply the provided self-adhesive update label on the side of the ECM to signify that the update has been performed.
7. Reconnect the wire harnesses.
8. Install ECM, protective cover and washer reservoir.
9. Start vehicle and reset adaptions. Perform Drive cycle "C" as defined in Service Bulletin W97-007.