Hi guys,
I have a big trouble with Fiat Grande Punto 2011.It's a 1.3 multijet diesel engine with Magneti Marelli 6F3 ECM.The problem is hard starting and irregular idle and turning off occasionally at idle.There is no dtc codes read out with factory scanner.
The cause is that ECM doesn't see engine rpm correctly so it turn off injectors at idle occasionally or it has trouble to start engine while cranking.In one moment,in engine pids,RPM is 190-250 and at another moment it's a 0 and vice verse,while engine is cranked.At idling "RPM pid" on scanner drops occasionally to 0 rpm and goes back to 800 rpm in just one second.Sometimes it's enough to turn off engine sometimes it's not.RPM needle on instrument panel also have same behavior.
ECM,CKP and CMP sensors were replaced with known good parts.Wiring from CKP sensor to ECM was also replaced.
I have scoped CKP and CMP signal at ECM connector and I don't see any anomaly at all !? I have a reference known good CKPvs CMP waveform from a car that doesn't have any problems and it's a very similar to my car that has a problem.Look at it by your self.
Because we were desperate,we try one more thing.We put another same car,side by side with faulty one.Then,we connect wiring from CKP sensor in faulty car to the ECM in reference car with unplugged CMP sensors on both cars.While we cranked faulty car we monitored RPM "pid" with scanner on reference car and it has same problem (rpm "pid" rapidly goes from 0 to 190-280 and vice verse).When we reconnect back reference CKP sensor to reference ECM on reference car (factory condition) with disconnected CMP sensor,there is no fault (rpm "pid" is constant at around 250 rpm).
Obviously there is a problem with CKP signal on faulty car with no regard to CMP signal or CKP vs CMP synchronicity but I can't see it with scope!!! WTF???
Hello.
Remove glow plugs and check again if the engine speed drop to 0 RPM when starter is engaged.Maybe ECU is sensitive to the crankshaft signal amplitude.
Best regards
victor2k wrote:Hello.
Remove glow plugs and check again if the engine speed drop to 0 RPM when starter is engaged.Maybe ECU is sensitive to the crankshaft signal amplitude.
Best regards