Fault codes
The cosworth ecu has fairly basic fault diagnostic features built into its software which will detect an obvious out of range input and then output the relevant fault code from the diagnostic pin and try and keep the engine running if possible by substituting the faulty input with a typical value. Obviously a fault with the crank sensor, being the main engine position input to the ecu, will result in a non running engine. The phase sensor is also critical as the engine has no idea which of the crank pulses is TDC without it. This will also result in a non running engine on a level 1 or 6 ecu, but the level 8 will try and guess the engine phase by looking at battery volts for each 90' crank pulse and if it can detect a pattern of increasing / decreasing volts every 90' in relation to the increasing load on the starter motor on the compression stroke then it will try and run the engine. The MAP, ECT, ACT and TPS sensor inputs will only show an error if they are totally open circuit or closed circuit. A sensor can be a long way from its correct output and the ecu will continue to believe it to be a valid input which can result in a mixture which is way too rich, or lean, resulting in poor running or a melted engine. The ECT and ACT sensors, when faulty, are just substituted with those of a warm engine (40'C for ECT and 15'C for ACT). A MAP sensor fault on a level 1 or 6 will result in a non running engine but the level 8 will try and create a useable value by calculating engine airflow from the throttle opening and engine rpm. On the level 8 ecu a knock sensor fault is determined by an engine which appears to be not creating enough background noise pickup and an oxygen sensor fault is determined if it does not swap between high/low voltages at all / regularly enough when it should be doing. If the engine is running and a sensor fails then the ecu will go into a limp home mode and limit maximum boost pressure to the base level of 0.3 bar by keeping the amal valve closed. The 3 door cosworth running the level 1 ecu will also bring on a engine fault light.
By linking pin 8 of the ecu to ground the ecu will output any fault codes from pin 27.(These pins are also brought up to a connector in the dash next to the ecu on the cosworth for ease of access). There is a five second delay after power on for the ecu to settle but then, if everything is ok, the output pin will just be pulsing rapidly at about 4Hz. If there are any faults present then the rapid pulsing will be interrupted by low frequency flash codes which can be seen on an analogue meter or a lamp. Note - If pin 8 is not connected to ground then the fault pin will pulse at 4Hz normally and stay low when a fault is present. The fault code is a two digit number with the first digit being displayed as a one second on/off pulse for each count, then a two second pause before the second digit is displayed, again as a one second on/off pulse for each count. The rapid flashing will then repeat for a few seconds before repeating the same fault code or displaying the next one if more than one is present.
Level 1 & 6
1.1 = Crank sensor fault - check sensor, wiring, air gap
1.2 = Phase sensor fault - check sensor, wiring, air gap
1.3 = Crank/Phase sensor pulse pattern fault - check sensors, wiring, air gaps, pick up lugs / concentricity, distributor position
2.1 = ACT short circuit - check sensor, wiring
2.2 = ACT open circuit- check sensor, wiring
2.3 = ECT short circuit- check sensor, wiring
3.1 = ECT open circuit - check sensor, wiring
3.2 = MAP short circuit - check sensor, wiring
3.3 = MAP open circuit - check sensor, wiring
Level 8
1.1 = Crank sensor fault - check sensor, wiring, air gap
1.2 = Phase sensor fault - check sensor, wiring, air gap
1.3 = Crank/Phase sensor pulse pattern fault - check sensors, wiring, air gaps, pick up lugs / concentricity, distributor position
2.1 = ACT short or open circuit - check sensor, wiring
2.2 = Knock sensor fault - check sensor, wiring
2.3 = ECT short or open circuit - check sensor, wiring
3.1 = Oxygen sensor fault - check sensor, wiring, mixture, air leaks
3.2 = MAP short or open circuit - check sensor, wiring
3.3 = TPS short or open circuit - check sensor, wiring
The 1.3 fault will be displayed on its own without a 1.1 or 1.2 fault if ever the engine is creating some crank and phase pulses but the pulses coming into the ecu do not follow the expected pattern as shown below. This could be caused by one of the four lugs on the crank pulley being damaged or the distributor not being set to the correct position causing the crank and phase pulses to overlap. Any difference in height of the lugs may also cause an error when the engine is cranking at low rpm causing it to miss one but see the others.
Level 8 closed loop test mode
The level 8 ecu also has the ability to display the closed loop running conditions through the fault light by toggling the input line in the correct sequence. This is best enabled by replacing the ground link with a switch.