Injector Interrupt For Enhanced Diagnostics
INJECTOR INTERRUPT FOR ENHANCED DIAGNOSTICSDiagnose Rough Idle Only
This test will help diagnose weak cylinders/injectors by allowing the diagnostic tool operator to interrupt injectors individually. This is carried out by using the diagnostic tool to interrupt the injector output to the engine cylinder that corresponds to the number on the injector parameter identification (PID).
A performance diagnostic sheet should be completed before using this tool. High injection control pressure (ICP) after the completion of the high idle test (test 12 on the performance diagnostics sheet to indicate oil aeration) low fuel pressure, the dual-mass flywheel, and high crankcase pressure are just a few of the possibilities that can cause a rough idle. After completing the performance diagnostic sheet, if there is no direction given for corrective action and rough idle is present, use the enhanced diagnostic ability of the Injector Interrupt.
Start the engine and monitor the engine oil temperature (EOT) PID. The EOT is to be maintained within -15°C (5°F) during the test. The test must be carried out while the rough idle is occurring. Record the mass fuel desired (MFDES) reading before interrupting any injectors; this will be the baseline for the rest of the test. The MFDES reading will not steady and will fluctuate rapidly. Take a five second snapshot of the PID information and record the high and low MFDES readings on the Injector Interrupt Tool Enhanced diagnostics sheet, using only MFDES numbers that have appeared at lease two times during the recording. After recording a baseline, interrupt each injector individually and repeat the given steps to obtain the high and low readings while each injector is interrupted. These numbers should be recorded on the lnjector Interrupt Tool Enhanced diagnostic sheet.
The enhanced diagnostic sheet is intended to be photocopied and then completed for each vehicle that is tested. A completed performance diagnostic sheet and enhanced diagnostic sheet must accompany any returned warranty parts and cores.
The example illustrates the use of a diagnostic tool to monitor the MFDES, as described.
Complete the enhanced diagnostic graph to illustrate the difference between cylinders and help identify weak cylinders/injectors. To start this process, derive the average for each of the MFDES readings by adding the high and low numbers together and dividing by two. For example, cylinder number 5 has a reading of 10.5-10.9. Therefore, the equation would be: 10.5 + 10.9 = 21.4 divided by 2 = 10.7 (if needed, round the number up to the nearest tenth). Record this number on the enhanced diagnostic sheet for the appropriate cylinder. Now, subtract his number from the average MFDES recorded for the baseline. For example, cylinder No.5 has an average MFDES of 10.7 and if the baseline MFDES was 10.1, the equation would be: 10.7-10.1 = 0.6. Therefore, 0.6 would be the deviation from the baseline. Carry out these calculations for all cylinder readings.
Average all of the deviations to get the cutoff number. For example, add the following numbers: 0.7 + 0.7 + 0.7 + 0.1 + 0.6 + 0.3 + 0.6 + 0.6 = 4.3. Divide the sum by eight and round to the nearest tenth: 4.3 ÷ 8 = 0.5375 ~ 0.5. Therefore, 0.5 would be the cutoff line for weak cylinders/injectors. By using this test, cylinders No.4 and 6 have been identified as being weak.
Carry out a relative compression test using a diagnostic tool or check compression with a mechanical gauge on the weak cylinders and one or two of the strong contributing cylinders. Compare the weak cylinder readings against the strong contributing cylinders to verify that the power cylinder is mechanically sound. If the compression readings are within 20% of each other, the power cylinders can be considered good.
After injector replacement, test drive the vehicle for at least 20 miles and confirm that the rough idle concern has been corrected, do not retest.
If a rough idle persists, the test should be carried out again After all of the tests are carried out, all DTCs should be cleared before returning the vehicle to the customer.
