False Crank Sensor Triggering

Discuss which Sensors work best with these ECUs and share how you are using inputs and outputs
Rob Stevens
Posts: 1247
Joined: Thu Jul 28, 2011 4:10 am
ECU Model: S100 Pro
Distributor: None-Coil On Plug :)

Re: False Crank Sensor Triggering

Post by Rob Stevens »

The earth from the ecu should go directly to the battery, nowhere else, can you confirm this.

Also the sensor ground should not be grounded anywhere, this can be checked by removing the ecu and checking to see if there is no contently between plug pin 28/29 and the vehicle ground/battery -ve.
Alex DTA
Posts: 1622
Joined: Fri Feb 28, 2014 1:03 pm
ECU Model: S40 Pro
Distributor: DTA
Firmware Version: 79

Re: False Crank Sensor Triggering

Post by Alex DTA »

As Rob says, this is now a simple earth issue.

The ECU loom should have one earth only. Ideally it should be on the battery, but mine's actually on the cylinder head, and that causes no issues.

All the sensors must be earthed to the sensor ground circuit on the ECU, not to the chassis or power ground anywhere else.
Alex DTA
Posts: 1622
Joined: Fri Feb 28, 2014 1:03 pm
ECU Model: S40 Pro
Distributor: DTA
Firmware Version: 79

Re: False Crank Sensor Triggering

Post by Alex DTA »

Another thought - is there any earth running off the earth in the crank sensor wiring?
Rob Stevens
Posts: 1247
Joined: Thu Jul 28, 2011 4:10 am
ECU Model: S100 Pro
Distributor: None-Coil On Plug :)

Re: False Crank Sensor Triggering

Post by Rob Stevens »

Alex that will be picked up if the chap undertakes the test I outlined above. But I suspect an inadvertent grounding of the sensor ground may well be the issue.
alistai_Westy
Posts: 16
Joined: Sat Sep 12, 2015 10:17 am
ECU Model: S40 Pro
Firmware Version: 79.0

Re: False Crank Sensor Triggering

Post by alistai_Westy »

Ok,

Thanks for your help guys, much appreciated.

Had a bit of time to experiment.

I have moved the ECU earth from the chassis to the engine. The problem is still evident.

All sensors are earthed to the ECU board and not the chassis. There are no other electrical loads connected to the ECU harness other than a Wide band Lambda. Disconnecting the Wide Band has no effect.

I have removed the ECU multi connector and checked for continuity between pins 28/29 to engine while all sensors are connected. No continuity found.

I mentioned earlier that I had put a capacitor 2200 pico or micro Farad (cant remember which) across the alternator +ve output and the alternator case. This has the effect of stopping the "total teeth before sync" in Engine Diagnostics Starting Information. However it doesn't stop an "Attempted Start" event when I turn on an electrical load eg Lights, hazards etc.

If I disconnect the Capacitor the "total teeth before sync" in Engine Diagnostics Starting Information begins to count however the “Attempted Start” when I turn on the lights, hazards etc does not happen.

Maybe this is not the route cause but I thought I would pass it on.

Does anyone live near Swadlincote, South Derbyshire? Want to come over and take the mick out of my poor electrical skills?
Rob Stevens
Posts: 1247
Joined: Thu Jul 28, 2011 4:10 am
ECU Model: S100 Pro
Distributor: None-Coil On Plug :)

Re: False Crank Sensor Triggering

Post by Rob Stevens »

? Oh, I assume you have a big fat earth lead from the battery to the same place that the ecu earth is now connected.

Try disconnecting the Alternator to see if the problems go away?
alistai_Westy
Posts: 16
Joined: Sat Sep 12, 2015 10:17 am
ECU Model: S40 Pro
Firmware Version: 79.0

Re: False Crank Sensor Triggering

Post by alistai_Westy »

Hi Rob,

My wiring set up is attached.

When I disconnect the alternator exciter coil the total teeth before sync" in Engine Diagnostics Starting Information stops counting however when I turn on an electrical load the problem is still evident.

Cheers

Al
Attachments
Wiring Diagram_Westy.xlsx
(10.77 KiB) Downloaded 375 times
alistai_Westy
Posts: 16
Joined: Sat Sep 12, 2015 10:17 am
ECU Model: S40 Pro
Firmware Version: 79.0

Re: False Crank Sensor Triggering

Post by alistai_Westy »

Hi,

I've had time to do so more work but to no positive affect.

I have tried connecting the -ve ECU lead direct to the battery and ensured that all car-side loom earth's are in good shape.

I removed the alternator from the engine and it had no affect on the problem.

I have tried adding more thick earth cables between battery and cylinder head, chassis and all combinations with no affect.

Sparrow:

When you tested my ECU does your bench test simulate my failure scenario? I assume your bench test only tests ECU wiring inputs and outputs without switching external loads with significant current draw, e.g. hazards, lights etc?
Is there a history of this very odd scenario. Do you have an explanation to why the engine runs fine with this scenario?

Cheers

Alistair
Alex DTA
Posts: 1622
Joined: Fri Feb 28, 2014 1:03 pm
ECU Model: S40 Pro
Distributor: DTA
Firmware Version: 79

Re: False Crank Sensor Triggering

Post by Alex DTA »

alistai_Westy wrote:Sparrow:

When you tested my ECU does your bench test simulate my failure scenario? I assume your bench test only tests ECU wiring inputs and outputs without switching external loads with significant current draw, e.g. hazards, lights etc?
Is there a history of this very odd scenario. Do you have an explanation to why the engine runs fine with this scenario?

Cheers

Alistair
No, we wouldn't test for this scenario, as it's a wiring issue, so not something we could replicate.

It runs fine for one of two reasons:
Either the noise is of a much lower magnitude than the engine signals, or the noise is not present when the engine is running.

I'm running out of ideas now.
What else is earthed to the engine block?
alistai_Westy
Posts: 16
Joined: Sat Sep 12, 2015 10:17 am
ECU Model: S40 Pro
Firmware Version: 79.0

Re: False Crank Sensor Triggering

Post by alistai_Westy »

Ok,

In terms of earthing to the engine. A Water temperature sender that is wired to a in car dashboard VDO water temp gauge. I have just disconnected this and the problem remains.

In essence I now have only the ECU powered up, with all inputs and outputs disconnected except the crank sensor. Flick the hazard lights on and the injectors play a ryhymical tune in time with the flashers.

Ive now run out of ideas. Ive had this car for 14 months and this issue has been there since day one.

Cheers

Al
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