The Misfire monitor diagnostic is based on crankshaft rotation velocity variation. The ECM determines crankshaft rotational velocity using the crankshaft position sensor and camshaft position sensor. When a cylinder misfires the crankshaft slows down momentarily. By monitoring the crankshaft and camshaft position sensor signals, the ECM can calculate when a misfire occurs. For a non-catalyst damaging misfire, the diagnostic will be required to report a misfire present within 1000-3200 engine revolutions. For catalyst damaging misfire, the diagnostic will respond to monitor 200 engine revolutions. Rough roads may cause false misfire detection. The rough road(acceleration)sensor consists of a piezoelectric vibration pick up which detects vertical acceleration of the vehicle. The sensor signal is used by the ECM to determine the degree of vertical movement of the car, for example, on a bumpy road. Since this may also cause uneven engine running, the ECM uses the signal to distinguish the phenomenon from actual misfiring.
If the ECM detects that engine speed variation indicates a misfire sufficient to cause three-way catalyst converter damage or emissions level to exceed standard value, the ECM sets misfire DTC. If the misfire rate is high enough to damage the catalyst, the MIL will flash to alert the vehicle operator. With a more than two cylinder misfire detection, the ECM sets P0300
Item | Detecting Condition | Possible Cause |
DTC Strategy | ● Calculation of engine roughness | ● Faulty spark plugs, high-tension lead, or Ignition coil ● Incorrect valve timing ● Uneven compression ● Air leakage ● Improper Fuel pressure or dirty fuel. ● Blocked/Leaking injectors ● Leakage between cooling system and cylinder |
Enable Conditions | ● 170 < Mass air flow(mg/rev.) < 726 ● 512 < Engine speed(RPM) < 4500 ● 40 < MAF gradient(mg/rev/Seg.) < 400 ● 141 < Throttle gradient(°TPS/sec.) <199 ● Coolant temperature > 20°C (-4℉) if Start temperature < -7°C (19.4℉) ● No rough road ● No relevant failure ● 11V< Battery voltage< 16V ● Fuel cut off not active | |
Threshold Value | ● Misfire detected on 2 or more cylinders | |
MIL On Condition | ● When misfire rate is high enough to damage the catalyst : Immediate ● When emissions level to exceed standard value : 2 Driving Cycles |
Temp.(°C) | Temp.(°F) | Primary ignition coil (Ω) | Secondary ignition coil(kΩ) |
20 | 68 | 0.5~0.6 | 7.5~10.2 |
