Ever had a pre-CAN Ford with a miss you could feel, but it had no code set? There is help in finding this problem if you know what to look for in Global OBD2's Mode $06.
First, Mode $06 is a listing of the individual tests and results the ECM uses in running the non-continuous monitors. Even though the misfire monitor is continuous, Ford thought having access to the individual tests for this monitor would be beneficial to techs, so they included it in their Mode $06 data.
The misfire monitor is a twofold monitor that checks for variations in the CKP signal to detect a miss. The first part is the percentage of misfires detected over a 200-revolution period and looks for catalyst-damaging misfires. The second part is the percentage of misfires detected over a 1,000-revolution period, looking for emissions-related misfires. These misfires are referred to as Type A and Type B, respectively.
EMISSIONS-related misfires are generally in the range of 1 to 3 percent at all engine speeds and are a two-trip code. The misfire must either be detected in the first 1,000 revolutions at start up or on four different 1,000-revolution checks while running.
CATALYST-damaging misfires are anywhere from 4 percent to 30 percent and depends on RPM and load under which the misfire occurs. If a Type A misfire is detected, the MIL will flash and a code will be set on the first trip. Last, because there are minor variances in the manufacture of the teeth on the crank reluctor, the ECM must first learn this variance before the misfire monitor will run. This is done during three 60-to-40 mph decelerations with no brake applied.
If KAM is cleared by a scan tool or by disconnecting the battery for longer than 10 minutes, this profile will have to be relearned to enable the monitor.
Mode $06 on most scan tools will look something like this:
TID $53 CID $01 MEASURED 420 MINIMUM 0 MAXIMUM 20,992 "PASSED"
The values shown are in "computer speak" and have to be converted to a number you can understand. For most of Ford's misfire tests, you multiply by 0.0015 and the result is a percentage. For example, if we translate the example above, we get:
TID $53 CID $01 MEASURED 0.6% MINIMUM 0 MAXIMUM 31.4% "PASSED"
In other words, out of the total number of times the plug fired, a misfire was detected on 0.6 percent of them. This is below the 1 to 3 percent Type B "threshold" and certainly below the Type A threshold, so the test passed. The maximum tells us that the test level used to pass this test was based on the Type A threshold and was done at or near idle due to the high percentage "Pass" level.
Back to the opening question. If you know what the tests are, you can use them to find the cylinders that are misfiring, even when there is no code stored or pending. You also can use them to verify the repair, as long as the same conditions are present as when the misfire occurred. The following is a listing and description of the Ford Mode $06 misfire tests. Multiply these values by 0.0015 to convert to percentages.
TID $50: Total misfire rate in percent as compared to emissions threshold in percent.
This test is "active" and when checked KOEO, the measured value will always show "0." However, if you access this test with the engine running, you will get a number if there are any misfires occurring. Test results are updated every 1,000 revolutions.
TID $53 (TID $51 ON EARLY OBD2 FORDS): Cylinder-specific misfire rates in percent and the threshold value used for test "pass or fail."
Probably the most commonly used Mode $06 test, this will list up to 10 separate CDs. These CIDs correspond to the individual cylinders, with those not used showing inferred test results. For example, only the first six tests will be accurate for a six-cylinder engine.
This test updates whenever a higher misfire rate is detected and will usually "freeze" if a code is set or pending. It is useful in identifying the cylinder or cylinder(s) that are contributing to the misfire problem and by how much.
TID $54: Highest catalyst damaging misfire rate calculated and threshold used.
Because the Type A threshold value varies from roughly 30 percent at idle to as low as 4 percent under high rpm and load conditions, the threshold value shown here may help in identifying the conditions under which the misfire occurred. If a code is set, compare this to freeze frame data. But keep in mind, freeze frame is logged when the code is set and in the case of a misfire, this isn't the same as the instant the miss occurred.
TID $55: Highest emissions-related misfire rate calculated and threshold used. Same as TID $54, but based on lower Type B threshold of 1 to 3 percent.
TID $56: Cylinder events tested and number needed to complete monitor.
These test values do not need to be converted. They are simply total counts. The threshold value is the number of cylinders times 500 – 500 "sparks" for each cylinder for every 1,000 engine revolutions.
This is also an "active" test and will show "0" measured if checked KOEO. However, if you look at it KOER, you will get a count. Typically, this measured value will be close to the threshold value and indicates the monitor is working.
It is possible for the misfire monitor status to show "complete" and not be working. Check this test for a "passed" status to make sure the profile has been learned.
Now that you're armed, check out Mode $06 on your next Ford. You may cure that nagging miss a lot easier.
