Technician Handbook 874 Engine Control Systems II Engine Misfire Diagnosis To monitor misfires, the ECM uses both the Crankshaft Position (CKP) sensor and the Camshaft Position (CMP) sensor The Crankshaft Position (CKP) sensor is used to measure variations in the crankshaft rotation speed On the power stroke, the crankshaft accelerates If the cylinder misfires, the crankshaft decelerates The Camshaft Position (CMP) sensor is used to identify specific misfiring cylinders When the engine misfires, high concentrations of hydrocarbons (HC) enter the exhaust gas High HC concentration levels can cause increased exhaust emission levels High concentrations of HC can also cause increases in the Three-Way Catalytic Converter (TWC) temperature, which may cause damage to the TWC To prevent this increase in emissions and to limit the possibility of TWC thermal damage, the ECM monitors the misfire rate The misfire monitor is designed to detect increases in emissions caused by cylinder misfires, not to reduce driveability concerns Misfires are counted when the crankshaft rotation speed variations exceed predetermined thresholds When the temperature of the TWC reaches the point of thermal degradation, the ECM blinks the MIL If the misfire exceeds the threshold levels, and could cause emission deterioration, the ECM illuminates the MIL and sets a DTC The engine misfire monitor is a continuous monitor NOTE Technical Training The catalyst temperature is calculated by the ECM based on driving conditions and percentage of misfire 45 Technician Handbook 874 Engine Control Systems II 46 Technical Training Technician Handbook 874 Engine Control Systems II Misfire Monitor Types A and B Misfire Monitor Type A There are two types of misfire monitors: Type A and B •  A type A misfire is one that is severe enough to damage the catalytic converter •  The ECM will blink the MIL if the misfire will result in catalyst temperatures of 1832 degrees F (1000 degrees C) or more •  The ECM will blink the MIL on the first trip that the malfunction is detected but the MIL will not illuminate steady (DTC Stored) until conditions are met on the 2nd trip •  The Misfire Monitor Type A duration is based on 200 crankshaft revolutions Misfire Monitor Type B •  The type B or otherwise known as an emission deterioration misfire is less severe than the type A •  A type B misfire will not damage the catalytic converter •  The ECM will turn the MIL ON after two consecutive trips that the malfunction is detected •  The Misfire Monitor Type B duration is based on 1000 crankshaft revolutions Technical Training 47 Technician Handbook 874 Engine Control Systems II Ignition Counter The ignition counter (Ignition parameter) represents the number of ignition events, as reported to the TIS Techstream, that have occurred during the current ignition cycle The ignition cycle is 1000 revolutions for most 1998 and earlier vehicles, and 200 revolutions for most 1999 and later vehicles 1998 and Earlier Models The TIS Techstream will display the ignition counter recycling at different rates based on the number of cylinders Each cylinder in a four-stroke engine will fire 500 times in 1000 revolutions Therefore, four-cylinder engines will produce 2000 ignition counts in 1000 revolutions, six-cylinder engines will produce 3000 ignition counts in 1000 revolutions, and eight-cylinder engines will produce 4000 ignition counts in 1000 revolutions 1999 and Later Models 48 The TIS Techstream will display the ignition counter recycling at different rates based on the number of cylinders Each cylinder in a four-stroke engine will fire 100 times in 200 revolutions Therefore, four-cylinder engines will produce 400 ignition counts in 200 revolutions, six-cylinder engines will produce 600 ignition counts in 200 revolutions, and eight-cylinder engines will produce 800 ignition counts in 200 revolutions Technical Training Technician Handbook 874 Engine Control Systems II Misfire Data List The Misfire Data List provides selected information related to cylinder misfire The Misfire Data Lists from OBD II and CAN OBD II vehicles will be different Ignition The Ignition parameter represents the ignition counter and indicates how many ignition events (all cylinders) have occurred in the current 200 revolution cycle (1999 and later vehicles) When the ignition counter is cycling, the misfire monitor is operating and reporting to the TIS Techstream Cylinder # Misfire Rate The Cylinder # Misfire Rate parameter indicates how many times (0–100) the cylinder has misfired during the current ignition counter cycle A value above indicates a misfiring cylinder For six- and eight- cylinder engines, the ECM may not set specific misfiring cylinder DTC(s) at high engine RPM and may only set DTC P0300 in this condition Diagnose the cylinder(s) with the highest Cylinder # Misfire Rate first Misfire Margin (CAN OBD II vehicles) The Misfire Margin parameter indicates the percentage chance that a misfire will NOT occur A negative percentage indicates a misfire is occurring A high positive percentage indicates a low chance for a misfire to occur under the current conditions Cat OT MF F/C Technical Training Catalyst OT MF F/C stands for Catalyst Over Temperature Misfire Fuel Cut History and individual cylinder parameter will be turned ON when a Type A misfire is present and fuel injector(s) has been shut down 49 Technician Handbook 874 Engine Control Systems II Misfire Detection Misfire detection due to a catalyst over temperature [Data list → Cylinder # Misfire Count] The misfire ratio is evaluated every 200 engine revolutions, and a DTC is detected when a misfire has taken place three times at or above the threshold misfire ratio that causes a thermal deterioration in the catalyst (Two trip detection logic) While a misfire is taking place under these conditions, the MIL blinks, regardless of the number of trips On some engines, the MIL will continue to blink after the catalyst over temperature conditions have passed On the next key cycle, the MIL will not blink until over temperature conditions occur in the catalytic converter Misfire detection for a deteriorated level of emissions [Data list → All Cylinder Misfire Count] The misfire ratio is evaluated every 1,000 engine revolutions, and a DTC is detected when a misfire has occurred at or above the threshold misfire ratio for a judgment of emission deterioration (Two trip detection logic) If this condition happens on the second consecutive trip, the MIL is turned ON 50 Technical Training Technician Handbook 874 Engine Control Systems II Misfire Monitor The Misfire Monitor counts the number of misfires for all cylinders, individual cylinders, and tracks average misfires from previous trips The ECM counts misfires and is available under misfire test details MISFIRE RATE – total misfire count for all cylinders MISFIRE RATE – number of misfire counts for cylinder Each count represents a cylinder misfire KOEO the test details provides the number of misfires from the last trip This is reset to zero after the engine has started After the engine is started the previous misfire counts are averaged and stored in the Misfire Monitor as EWMA Misfire EWMA stands for Exponentially Weighted Moving Average (EWMA) Misfire which represents the average number of counts for all cylinders as well as individual cylinder misfires This value represents 10% of the last trip’s misfires plus 90% of the average of the previous trips Exponentially Weighted Moving Average (EWMA) Misfire Formula 0.1 x (current counts) + 0.9 x (previous average) EWMA MISFIRE – total average for all cylinders EWMA MISFIRE – average for cylinder The cylinder and misfire count can be useful for the following situations Technical Training 1.  A customer reports the check engine lights was flashing, but now it does not flash There is no DTC and the MIL is off The EWMA can report which cylinder(s) had the misfire 2.  The vehicle has P0300 DTC Which cylinder had the most misfires 3.  The vehicle has a P0300 and multiple misfire DTCs Again, which cylinder had the highest misfire counts 51 Technician Handbook 874 Engine Control Systems II Duplicating Misfires All Cylinders Misfire Count displays the total number of misfires for all cylinders The available range is from to 255 misfire counts This counter line resets to zero every 1000 crankshaft revolutions Misfire RPM and Misfire Load populate when misfire criteria is met on the first trip Parameters will not update on the second trip but Freeze Frame Data will be saved for the Current DTC This information can be very useful in determining vehicle operating conditions while misfires were taking place To duplicate an engine misfire, use the Misfire RPM and Misfire Load values from the Engine Live Misfire data list Reference the Freeze Frame data to duplicate engine operating conditions, such as calculated load, coolant temperature, etc., at the time the DTC set Unfortunately, Misfire Load is displayed in g/rev (grams per revolution) and is derived from the MAF signal To convert g/rev to gm/sec follow the procedure below: 1.  Divide Misfire RPM by 60 sec to get Revolutions per Second 2.  Multiply Revolutions per Seconds by Misfire Load (g/rev) to get grams per second (g/sec) •  Example: Misfire RPM shows 2275 RPM and Misfire Load shows 0.28 g/rev 2275rpm/60=38Hz; 38Hz * 0.28g/rev=10.64 g/sec The misfire was detected at 2275 RPM with a MAF Sensor signal of 10.64 g/sec 52 Technical Training Technician Handbook 874 Engine Control Systems II Misfire Margin Misfire Margin is the difference between the predicted change in crankshaft rotation speed represented electronically by NE signal to the actual change in the NE signal The Misfire Margin will move towards the negative region when misfires are detected If it is under 30% there is a chance misfire is occurring If it is in the negative zone, misfire is occurring This parameter is useful for it will change as the chance of a misfire increases When trying to duplicate the misfire conditions, the misfire margin percentage will decrease as the engine nears or experiences cylinder misfire Technical Training 53 Technician Handbook 874 Engine Control Systems II Single Cylinder Misfire Diagnosis Use the following steps to diagnose a single cylinder misfire (examples based on DTC P0302): 1.  Duplicate the misfire using Engine Live and Freeze Frame data 2.  Compare the spark plug firing tip of the misfiring cylinder to spark plug firing tips from cylinders with no misfires present 3.  Swap the igniter from the misfiring cylinder to a different cylinder with no misfires present (swap the igniter with cylinder # 4) 4.  Swap the spark plug from the misfiring cylinder to a separate different cylinder with no misfires present (swap the spark plug with cylinder # 6) 5.  If the misfire moves to a cylinder with a swapped component, replace the component (e.g if cylinder # begins to misfire, replace the igniter, etc.) 6.  If the misfire stays with the original cylinder, check the cylinder compression pressure and fuel delivery NOTE 54 The diagnostic procedure outlined here is for training purposes only and may not be effective for every issue Always refer to Service Bulletins (SB) and Repair Manuals (RM) for information on specific vehicles and issues Technical Training Technician Handbook 874 Engine Control Systems II Compression Test Proper cylinder compression pressure verifies the misfire is not related to mechanical components When performing a cylinder compression pressure test, fuel injection and ignition must be turned OFF The procedure to turn OFF the fuel injection and ignition, as well as check the compression, varies with vehicle model Always refer to the vehicle Repair Manual for the proper cylinder compression pressure test procedure and pressure specifications Active Test Technical Training Performing a Cylinder Compression active test (some 2005 and later model vehicles) will turn OFF fuel injection and ignition so that a compression pressure test can be performed While this active test may be available, the Repair Manual cylinder compression pressure inspection procedure may not utilize it The fastest way to find out if a Cylinder Compression active test can be performed on a specific vehicle is to check the active tests available within the ECM using the Techstream by clicking Active Test from the Engine Live main menu Performing this active test, if available, will allow a cylinder compression pressure test to be performed without disconnecting all fuel injector connectors and/or removing the EFI fuse or circuit opening relay 55 Technician Handbook 874 Engine Control Systems II Cylinder Speed Data List Some 2006 and later model vehicles will display the speed of each cylinder During a Cylinder Compression active test with all spark plugs installed, if a single cylinder is rotating faster than other cylinders, this may indicate a mechanical issue with that cylinder In the illustration, the spark plug was removed from cylinder number and a Cylinder Compression active test was performed NOTE 56 It may be necessary to crank the engine for up to 20 seconds before accurate Engine Speed of Cyl # readings populate Technical Training Technician Handbook 874 Engine Control Systems II Multiple Cylinder Misfire Diagnosis Misfires can be the result of other system malfunctions If other system DTC(s) are present, diagnose those DTC(s) / systems first If multiple cylinder misfires are present, check for commonalities between cylinders Some commonalities include fuel, mechanical issues, inputs, and outputs Fuel Mechanical Broken or misadjusted valve train components, incorrect valve timing and carbon buildup are some possible mechanical issues that may cause multiple cylinder misfires Inputs Some inputs that may cause multiple cylinder misfires include the crankshaft position sensor, camshaft position sensor, engine coolant temperature sensor, intake air temperature sensor, A/F and/or O2 sensors, and the MAF sensor Outputs Technical Training Improper fuel pressure, restricted injectors, restrictions in the fuel line, incorrect fuel such as E-85 or diesel, or water in the fuel are all possible fuel issues that may cause multiple cylinder misfires Some outputs that may cause multiple cylinder misfires include fuel trim and valve timing (VVT-i) NOTE Rough roads, oversized wheels, etc may also cause multiple cylinder misfires It is very important to talk to the customer and understand the actual driving conditions when the misfire DTC(s) occurred NOTE If several cylinders are misfiring, drive the system rich (+25) with an Injector Volume or A/F Control active test If the misfiring cylinders stop misfiring, this may indicate restricted injectors for these cylinders NOTE If all cylinders but one on a single bank are misfiring, check fuel trims If the fuel trims for the misfiring bank are in the double-digit negatives, perform an Injector Volume active test and drive the system rich (+25%) If the misfiring cylinders stop misfiring, this may indicate a leaking injector in the cylinder that was not misfiring The cylinder with the leaking injector may actually start to misfire with the injection volume commanded rich (+25%) This may apply to single cylinder misfires on four-cylinder engines with two banks 57 Technician Handbook 874 Engine Control Systems II IGF Fail-Safe There are different fail-safe modes depending on the type of ignition system, cylinder displacement, and model year The following is a general summary •  If there is no IGF signal on engines before 1998 model year, the ECM will enter fuel fail-safe and turn off all the fuel injectors •  Beginning with the 1998 model year, for V-6 and V-8 engines equipped with direct ignition system with integrated ignition coil/igniter (1 ignition coil/igniter per cylinder), the engine will still run without the IGF signal, but the MIL will be ON •  Beginning with the 2001 model year on ignition coil/igniter per cylinder engines, the ECM fail-safe will turn off the fuel injector if there is no IGF signal for that cylinder and if engine conditions (such as load and temperature) are sufficient to damage the catalytic converter If the IGF signal returns to normal while the engine is running, the injector may remain off until the next engine start NOTE 58 Some vehicles will disable specific cylinder fuel injectors if a misfire is detected Always clear DTCs and confirm injector operation Technical Training Technician Handbook 874 Engine Control Systems II Technical Training 59 Technician Handbook 874 Engine Control Systems II 60 Technical Training ... Technical Training Technician Handbook 874 Engine Control Systems II Technical Training 59 Technician Handbook 874 Engine Control Systems II 60 Technical Training ...Technician Handbook 874 Engine Control Systems II 46 Technical Training Technician Handbook 874 Engine Control Systems II Misfire Monitor Types A and B Misfire Monitor... be necessary to crank the engine for up to 20 seconds before accurate Engine Speed of Cyl # readings populate Technical Training Technician Handbook 874 Engine Control Systems II Multiple Cylinder