Sidetracked: problems on a Rover 827

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Sidetracked: problems on a Rover 827

Postby ed800uk » Fri Jul 21, 2006 10:52 am

I have a problem on a 1994 Honda 2.7 V6 engined Rover 827.

Its emissions exceed the limits. I strongly suspect injector problems but the scope traces didn't look too bad. As a routine I put the scope on the ignition -- although I never really understand what I was looking at -- I never seem to get those nice plots that you see in the library.

Attached is what I see on the ignition. They're so strange that I started another thread using a car that has no fault, to try to understand the waveforms, and the MI074 HT probe.

These traces are from free-running because I had trouble triggering. Due to the slow timebase and limited storage in the cheap scope there is gross aliasing in the display. But now that I have inverted the secondary on Ch2, you can see enough of the ignition event to identify it.

Fig.10 shows three cylinders firing.

Fig.10a is a zoom on the middle event of Fig.10. You can see some of the characteristics. But how to explain the intial dip of Ch2 to about -4.5kV during the current build-up stage of the primary in Ch1?

Fig.10b show the same parade but zoomed out to show the full extent of the "wandering" zero-line of the Ch2.

Apart from the emissions problem the car drives well.

As well as the attachments, the images will shortly be available at:
http://www.netcareltd.plus.com/R827/

Grateful for any help,
Ed
Attachments
10&10a&10b.pdf
PDF file of the three figures.
(28.34 KiB) Downloaded 478 times
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Postby Guest » Fri Jul 21, 2006 1:42 pm

Hi ed, not much help to you but I have not seen that before. R U sure the car drives OK. Does it idle OK?
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Secondary

Postby Autonerdz » Sat Jul 22, 2006 3:44 pm

Hi Ed,

The wandering of the secondary is normal. I have seen that on many applications and different equipment. It's worse on DIS systems but also occurs on distributor systems, especially what there is a sudden rise in KV demands.

I can see by your captures that the scope you are using is not sampling very well. I have attached an example of a 1994 Mustang 5.0 HO application showing the MAF output and secondary on a snap accel. This is a psd file. I would have attached it but the size limitation prevented that. You can get it here:

http://www.autonerdz.com/downloads/tar2.psd

You can open and examine it with the PicoScope automotive demo software if you don't have The full version.

Zoom in and see all the detail. You can see the lag before the gulp of air reaches the cylinders, then the lean condition in the combustion chamber in the spark line. Then you can see when the control system catches up and adds the fuel. You can see the KV demand curve rise with the increased compression and leanness and spark near TDC then fall later as the RPM rises and the advance kicks in lowering the KV demand as spark occurs with more fuel in a lower compression environment farther from TDC. Also note the combustion turbulence.

Not likely you would be able to duplicate this capture with any other automotive scope. The samples are about 3 microseconds apart. on both channels. The detail is astounding. I have a series of these from a record session, but I picked this one out because it shows the wandering you refer to.
Tom Roberts
(The Picotologist)
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Postby ed800uk » Thu Jul 27, 2006 11:44 am

Apologies to Guest and Autonerdz for delay; I've been away much of the last few days. Thanks for replies.

I've only had my new Pico Sope for a little while and not yet had time to repeat the tests with the great hardware and SUPERB software.

The 87 page manual (!) hasn't yet sunk in, so I've only scratched the surface with the software so it will take me a while to study Autonerdz' example. I will examine it carefully as you suggest, as soon as I get the hang of how to do it.

Best regards,
Ed
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Postby ed800uk » Wed Aug 09, 2006 1:37 pm

Autonerdz,

Thanks again for your trace, very educational.

I think I have now duplicated it for my car, but it's a bit different having a MAP sensor fuelling instead of MAF.

[pdf and trace attached]

There seem to be so many irregularities in the HT signal. Hopefully I am homing on the cause of the problem. I will upload later a trace showing injector dwell during the throttle snap.

EDIT: Ben, actually I had uploaded the files to a server, but forgot to say, sorry:

http://www.netcareltd.plus.com/R827/


Best regards,
Ed
Attachments
2006_08_08_030 ChA-HT ChB-MAP.psd
(358.28 KiB) Downloaded 459 times
HT-MAP.pdf
HT ignition and MAP sensor
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