Long sync time on crank sensor

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aleksanderk
Posts: 68
Joined: Fri Feb 01, 2019 4:36 pm
ECU Model: S80 Pro
Firmware Version: 6500

Long sync time on crank sensor

Post by aleksanderk »

Hello everybody!
I have a Volvo 740 with a DTA S80. The car has a magnetic crank sensor, and I struggle with long crank time.

At first i thought it was becuse my start fuelling map was not as it should, but after some investigation it seems like the crank sensor uses a lot of time before it syncs with the S80.
The problem is really bad on cold start. I can crank the engine for probably 30 seconds before something happens. Sometimes it gets sync while cranking, but loses it and have to sync again.
On a hot start it usually gets sync within 3-4 seconds and fires right up.

Battery voltage drops to 10V on cold crank. Could this be a part of the problem?
Since the sensor generates a voltage I would think that it would do that regardless of the battery voltage as there are no power feed to the sensor.

DTASwin Oscilloscope looks fine and it detects my flywheel setup wich is 60-2, and a gap tooth factor of 2000.
In general the car runs great, and I don't see a rise in rejected crank pulses when engine is running.

Other info that might be usefull:
Engine runs wasted spark
Is turbocharged
It's a 2.3L inline 4.
850cc siemens deka injectors.
Not sure of the gap between sensor and flywheel as it is in it's original location. Just assumed it is correct since the engine started ok with the original ECU.

Could it be as easy as a "worn out" crank sensor? I don't know the age of the sensor.
SMR
Posts: 137
Joined: Tue Jan 16, 2018 9:38 am
ECU Model: S100 Pro
Distributor: DTA
Location: Aberdeen

Re: Long sync time on crank sensor

Post by SMR »

Does sound like a dying battery, or bad earth strap.
I'm still (successfully) using a 25 year old magnetic sensor on my installation, so not aware that they could wear out.
Rob Stevens
Posts: 1247
Joined: Thu Jul 28, 2011 4:10 am
ECU Model: S100 Pro
Distributor: None-Coil On Plug :)

Re: Long sync time on crank sensor

Post by Rob Stevens »

Cranking speed might be an issue, try an additional battery, or a new sensor and check its gap and that it's not covered in metal bits.
Alex DTA
Posts: 1622
Joined: Fri Feb 28, 2014 1:03 pm
ECU Model: S40 Pro
Distributor: DTA
Firmware Version: 79

Re: Long sync time on crank sensor

Post by Alex DTA »

If it's taking a long time to sync, it's something to do with the crank signal.
Post a crank scope so we can see what the ECU is seeing.
aleksanderk
Posts: 68
Joined: Fri Feb 01, 2019 4:36 pm
ECU Model: S80 Pro
Firmware Version: 6500

Re: Long sync time on crank sensor

Post by aleksanderk »

Sorry for my late reply.
I haven't got around to get a new oscilloscope image, but I have one from when the car started the first time when I got the DTA in the car again this year.
Image

Today I replaced the battery, but that did not help.
I shot a video of my laptop when starting. You can watch it here: https://www.youtube.com/watch?v=Yhmp0vE_TeM
Alex DTA
Posts: 1622
Joined: Fri Feb 28, 2014 1:03 pm
ECU Model: S40 Pro
Distributor: DTA
Firmware Version: 79

Re: Long sync time on crank sensor

Post by Alex DTA »

It's a bit difficult to see on the image, but your crank sensor wires might be reversed. Try swapping the pins at the crank sensor end.

In General Engine Settings, what's the Gap Tooth Factor set to?

Kind regards

Alex
aleksanderk
Posts: 68
Joined: Fri Feb 01, 2019 4:36 pm
ECU Model: S80 Pro
Firmware Version: 6500

Re: Long sync time on crank sensor

Post by aleksanderk »

Alex DTA wrote:It's a bit difficult to see on the image, but your crank sensor wires might be reversed. Try swapping the pins at the crank sensor end.

In General Engine Settings, what's the Gap Tooth Factor set to?

Kind regards

Alex
Gap tooth factor is 2000 as mentionend in the first post :D
I will upload a new scope image as soon as possible.
Will it be helpful to get one from cold engine and one when it's fully warmed?

EDIT: The sensor (A BOSCH 0986280401) is connected like this:
1: signal to pin 12
2 ground to sensor GND pin 21
3 shield I believe I connected to another sensor GND. Should this be floating on the ECU end? It's connected to the sensor on the original pins.
stevieturbo
Posts: 3577
Joined: Tue Aug 02, 2011 12:08 pm
ECU Model: No ECU
Location: Norn Iron

Re: Long sync time on crank sensor

Post by stevieturbo »

A shield should only be connected to ground at one end.

But are you sure it's a shield, and are you sure it is connected to something at the sensor ? And not floating at one end, just continuous to the end ?

@Alex

What on the scope trace suggests polarity may be incorrect ? I know on an actual oscilloscope the trace would show this, but on the DTA scope, what are the visuals on it ?
aleksanderk
Posts: 68
Joined: Fri Feb 01, 2019 4:36 pm
ECU Model: S80 Pro
Firmware Version: 6500

Re: Long sync time on crank sensor

Post by aleksanderk »

stevieturbo wrote:A shield should only be connected to ground at one end.

But are you sure it's a shield, and are you sure it is connected to something at the sensor ? And not floating at one end, just continuous to the end ?

@Alex

What on the scope trace suggests polarity may be incorrect ? I know on an actual oscilloscope the trace would show this, but on the DTA scope, what are the visuals on it ?
I found some info when building the harness that it was a shield. If it's connected at the sensor or not i don't know, just assumed :roll:
Alex DTA
Posts: 1622
Joined: Fri Feb 28, 2014 1:03 pm
ECU Model: S40 Pro
Distributor: DTA
Firmware Version: 79

Re: Long sync time on crank sensor

Post by Alex DTA »

aleksanderk wrote:Gap tooth factor is 2000 as mentionend in the first post :D
Sorry, missed that.
aleksanderk wrote:Will it be helpful to get one from cold engine and one when it's fully warmed?
May as well.
aleksanderk wrote:EDIT: The sensor (A BOSCH 0986280401) is connected like this:
1: signal to pin 12
2 ground to sensor GND pin 21
3 shield I believe I connected to another sensor GND. Should this be floating on the ECU end? It's connected to the sensor on the original pins.
That is wired correctly.

The reason I queried this is there appears to be a small spike at the start of the gap. The tooth prior to the gap is slightly higher than all the others.
This will have the effect of making the gap appear shorter than it really is. Do you have any pictures of the crank trigger disc?
Try reducing the Gap Tooth Factor to 1800, and try again.
If any of the gaps appear green on the crank scope, reduce the Gap Tooth Factor to 1500.

The reason it will start easier when warm is it will crank more quickly.
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