Injector Interrupt For Enhanced Diagnostics

Injector Interrupt for Enhanced Diagnostics

Diagnose Rough Idle Only

This test will help diagnose weak cylinders/injectors by allowing the scan tool operator to interrupt injectors individually. This is performed by using scan tools to interrupt injector output to the engine cylinder that corresponds to the number on the injector PID.

A performance diagnostic sheet should be completed before using this tool. High ICP (Injection Control Pressure) afier the high idle test (test 12 on the performance diagnostics sheet to indicate oil aeration), low fuel pressure, bad 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.

Diagnose Rough Idle (Only)

Start the engine and monitor the EOT the EOT is to be maintained within 5°F during the test. The test must be performed while rough idle is occurring. Record the 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 MEDES readings on the Injector Interrupt Tool Enhanced diagnostics sheet, using only MEDES numbers that have appeared at lease two times during the recording. Afier recording a baseline, interrupt each injector individually and repeat the above steps to obtain the high and low readings while each injector is interrupted. These numbers should be recorded on the Injector 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 following example illustrates the use of a scan tool to monitor the MEDES, as described in the paragraph above.






EOT = 176°F

mg = milligrams

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 MEDES readings by adding the high and low numbers together and dividing by two. For example, cylinder No.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 MEDES recorded for the baseline. For example~ cylinder No.5 has an average MFDES of 10.7 and if the baseline MEDES was 10. 1, the equation would be: 10.7-10.1 = 0.6. Therefore, 0.6 would be the deviation from the baseline. Perform these calculations for all cylinder readings.

In order to get the cutoff number, average all of the deviations. For example, as in the sample we would 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.

The next step is to remove the valve cover and observe the oil exiting the injector spill spout while the engine is at an idle. Less oil exiting the spill spouts in comparison to other injectors indicates that less fuel is being delivered to that cylinder.

Check compression on the weak cylinders and one or two of the strong contributing cylinders. Then 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 performed again. After all tests are run, all DTCs should be cleared before returning the vehicle to the customer.