Suddenly control signals become crazy

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Joined: Fri Aug 08, 2014 1:29 am

Suddenly control signals become crazy

Post by tubal » Tue Aug 19, 2014 2:20 pm

Hi automotive people:

I know my English is quite bad, I'm sorry for that, but my interest in this forum is stronger so I'd like to ask your opinion on the following case:

The car is a Opel Corsa (A) 1.4i, year 1994, engine C14NZ with a single point Multec IEFI fuel system produced by Delco Remy. The symptom is an intermittent fault, then suddenly the engine jerks and usually is stopped. In addition tachometer jerks up while the fault is happening. In this old car tachometer gets signal from ignition circuit.
Firstly I had a look at primary ignition current. I filled myself with patience waiting for occurring the fault. I tried to cause the problem moving connectors, wires, etc, but I wasn't lucky.
All at once I felt the abnormal vibrations and could see in the screen how the signal frequency increased uncontrollably causing a succession of sparks out of time and engine failure. I didn't save this image, however I send you other that reflects the situation perfectly.
esq electico2.JPG
In canal A (blue) we can see the control signal from ECU to ignition module controlling primary work. In canal B (red) is rpm and reference signal from Hall sensor installed in the distributor.
corsa run well.gif
corsa run bad.gif
When fault appears we can note that signal in A becomes fool. It commands to cut primary without control in a rapid succession. Finding out about this case, I discovered not only control primary is fooled, but also control injector. Both signals have the same problem while rpm signal seems good all the time.

I told the car's owner that the fault is in the engine ECU, which is responsible for developing these control signals. He must change ECU.
Are you agree with me? Should I look closely at other parts?

Thanks a lot. Best Regards

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Re: Suddenly control signals become crazy

Post by arjen » Tue Aug 19, 2014 4:41 pm

If cam and crank are oké and reach ecu connector and the power and ground of the ecu is good than I think the problem is inside the ecu. Mabey you can see the problem in live data while moving the ecu connector. Also warming or cooling the ecu can trigger the faults.

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Fat Freddy
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Re: Suddenly control signals become crazy

Post by Fat Freddy » Fri Aug 22, 2014 10:56 am

I would be extremely weary of calling an ECU on that. I've got 'similar' ringing type captures from similar ECU igniter (not Corsa) circuits. Igniter was the fault.


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Re: Suddenly control signals become crazy

Post by hexibot43 » Fri Aug 22, 2014 2:19 pm

I would concur with both the questions and answers given. I would be looking really hard at the hall sensor(rpm), and grounds. Based on the waveform given I don't see how you've taken the hall sensor assembly out of the equation. It looks to me like the ecu is responding to defects in the signal generated from the hall sensor assembly.

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