Alfa Romeo - Crank Error non start

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Alfa Romeo - Crank Error non start

Postby FioranoCars » Thu May 14, 2015 3:27 pm

I was asked to take a quick look at a non-starting Alfa Romeo GT 2.0, the error code related to the Crank sensor, and having replaced that and no change, I was dragged in to give some insight (or not!).

The crank signal is quite strange, in that at the same point of each rotation the amplitude reduces significantly!

The enclosed trace shows from initial crank to splutter and end crank (cranking the whole time - the engine never catches).

Page 7 gives the issue at a glance, with 2 waveforms showing similar issues, but have done 3-4 traces all the same, all with the issue in the same position of the crank rotation. I did check battery voltage on 1 tace and that was not affected during this drop off (although not the engine ECU 5v output)

Alfa Romeo_GT_Petrol_Crank sensor.psdata
(656.18 KiB) Downloaded 118 times


My thoughts are:
1. possible warped flywheel
2. worn teeth on flywheel at the potion where the drop occurs
3. cracked flywheel
4. Loose flywheel
5. possible dual mass flywheel issue - but this car does not have one!
sadly my blinkered view might be missing something!

Their client is not willing to go forwards without some certainty, my suggestion was a flywheel replacement, but clearly there could be some other explanation I am missing!

Any thoughts or alternative theories?

thanks
Richard
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Re: Alfa Romeo - Crank Error non start

Postby Dejan » Thu May 14, 2015 6:08 pm

Hy,
disable spark or fuel and repeat same test just to be sure that is a mechanical problem.I have seen similar ckp waveforms when igniton timing was off but if it repeats with disabled fuel or spark that is not problem in your case.

After that make sure that cranking speed is constant without rapid slowdowns.If that is ok then it is definitely mechanical problem with flywheel for ckp sensor.If you need to know exact cause then crankcase should be removed...

That is the way I would do it in your situation...

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Re: Alfa Romeo - Crank Error non start

Postby Dejan » Thu May 14, 2015 7:27 pm

Forget disabling fuel or ignition,disconnecting ckp sensor is easer and better way...
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Re: Alfa Romeo - Crank Error non start

Postby tode » Thu May 14, 2015 8:25 pm

I think that if you disassemble the starter you can see if the flywheel is loose, if you have a camera with a sensor, if you take away the speed sensor and you look in the hole after about 90 to 100 degrees after the reference mark can be observed the damage on the flywheel. The defect is too repetitive to be a casual affair, must correspond to a body in motion, to me more doubt is the noise that is generated in the sine wave signal (occurs not only where the signal is attenuated), but could come from the starter motor running.
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Re: Alfa Romeo - Crank Error non start

Postby 4d » Thu May 14, 2015 10:16 pm

My next step would be to remove the gearbox for further investigation.

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Re: Alfa Romeo - Crank Error non start

Postby FioranoCars » Fri May 15, 2015 12:02 pm

For those casual browsers not wanting to download a file, here is the waveform ...
crank.png


The area of concern is at about 40ms and just before 120ms, but as has been said the whole waveform has attenuation.

Has anyone every encountered something like this before?

Thanks
Richard
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Re: Alfa Romeo - Crank Error non start

Postby Dejan » Sat May 16, 2015 11:34 am

FioranoCars wrote:
Has anyone every encountered something like this before?

Thanks
Richard


Yes,like I said the cause was bad ignition timing or damaged rotafonic wheel for CKP sensor.Several ideas are already written how to check that...

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Re: Alfa Romeo - Crank Error non start

Postby FioranoCars » Fri Jun 05, 2015 11:19 am

Well, just for closure for the curious ... I was passing the workshop where this car has been sat, and they finally had authority to strip the engine.

It turns out the crank sensor picks up on a "pressed on" toothed ring onto the crank itself inside the engine, rather than the flywheel. Hence why unable to diagnose further without stripping, access via the starter motor would not achieve anything.

This toothed ring has indeed warped, or been subject to previous mischief, as the engine looks like it has been apart recently. It appears to be only held in place by the interference fit, although I did not see any key-way or pins, it may have utilised some beyond the area I was able to view briefly.

As there was no loose metal objects or anything that could "foul" the ring, the only plausible thing I can think of would be excess heat causing it to buckle and warp, or back to prior bad workmanship. As the car came in as a non-runner and the owner being at best vague about the failure, there's not much more to say.

I did take a couple of photo's but looking at them, they don't really show clearly the issue, so posting some pictures of oily engine parts is rather pointless as we've all seen them before!

thanks
Richard
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