Astra rough idle

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Re: Astra rough idle

Postby BradCobbs » Sun Feb 15, 2015 7:51 am

Is inducing an air leak not forcing it lean? I've not simply disconnected the MAF, I've blocked and unblocked the breather.
And my Voltage scale has increased.
What are the specifics you'd like to see?
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Re: Astra rough idle

Postby BradCobbs » Mon Feb 16, 2015 4:49 pm

Robski wrote:that's not what I asked for in the slightest, disconnecting the MAF proves nothing much & masks faults.I wanted to see the O2's .

You crack on ! :roll: :?

Hi Robski, managed to get some time on the Astra this afternoon.
Hoping I've captured the waveforms you were looking for, I've managed to clamp the fuel pipe enough to force it lean without completely stalling the engine.
During this period the pre-cat lambda seems to be switching like I would expect, post-cat still at a volt (Cat not up to temp?). S/T FT: -6% ~ -4% roughly.
Once I release the clamp it's straight up to 1V solid on both sensors and my S/T FT is -13%.
Attachments
Astra lambda clamp test.psdata
Idle then slightly clamping pipe.
(4.31 MiB) Downloaded 118 times
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Re: Astra rough idle

Postby Robski » Mon Feb 16, 2015 5:41 pm

So it has the ability to go closed loop.This is what I wanted to know.

Does it do this @ 2500 RPM ?

Have you checked the fuel pressure ? Have you clamped the EVAP ?

To force rich/lean all you need to do is spray a little brake cleaner/propane in the intake & allow extra air in.

If you noticed, the rear O2 dropped leaner as well which says to me that it is actually running rich.

Take a longer capture, 1 buffer @ idle, the next @ 2500 RPM, then back to idle.

I don't like the 'spikes' you're getting on the signals though & it's not like they line up with each other neither !
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Re: Astra rough idle

Postby BradCobbs » Thu Feb 26, 2015 3:37 pm

All sorted now, thanks everyone for their help- it's much appreciated.
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Re: Astra rough idle

Postby Wally » Thu Feb 26, 2015 9:32 pm

It's also much appreciated to know what the fault was or what was done to finally to confirm the fault.

It helps a lot for future diagnosis.

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Re: Astra rough idle

Postby BradCobbs » Sat Feb 28, 2015 12:07 pm

It was a schoolboy error on my behalf, when initially checking the MAF sensor I didn't read the idle voltage and compare to Autodata.
The L/T fuel trim was at -13 and when the new MAF was fitted it was a lower voltage therefore making it run much leaner and eventually brought the L/T fuel trim up to 0.
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Re: Astra rough idle

Postby sigoaprendiendo » Mon Apr 06, 2015 8:32 pm

Hi all

It's weird the scanner didn't show any DTC related to MAF values before the fix. :roll:

So it is good to point out how Pico really helps to pinpoint glitches when the PCM criteria doesn't meet the conditions to set trouble codes. :D

Kind regards
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