pico first look sensor waveform

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pico first look sensor waveform

Postby Crikeskank » Wed Feb 08, 2017 9:59 pm

I have a renault scenic 1.6 with an annoying fault of intermittent power.
No fault codes,only fuel trims awry LtFT 14% positive with short term from -20 to +20.
I have just tracked down a used pico first look sensor and a 3223 pico scope capturing this waveform.
any body see anything amiss with an experienced eye
The engine was fully hot at idle

cheers
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Re: pico first look sensor waveform

Postby STC » Wed Feb 08, 2017 10:47 pm

In the absence of + or - 20/25 STFT you would not have any LTFT

First and foremost, force it rich and then lean. Verify that that the O2 is good.

No profit / advantage in shooting the messenger.

EVAP - MAF - ECT - Unmeasured Air ..... ..... ..... .....
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Re: pico first look sensor waveform

Postby EAAD » Thu Feb 09, 2017 11:44 pm

Crikeskank wrote:I have a renault scenic 1.6 with an annoying fault of intermittent power.
No fault codes,only fuel trims awry LtFT 14% positive with short term from -20 to +20.
I have just tracked down a used pico first look sensor and a 3223 pico scope capturing this waveform.
any body see anything amiss with an experienced eye
The engine was fully hot at idle

cheers


Hello

I assume that you have used the FLS in the exhaust tailpipe to capture the psdata file? It is a pulse sensor rather than a pressure transducer of which the pulses appear unremarkable, I note that there is nothing to sync from but no matter as all pulses appear relatively even, nothing of note

Self quote
other than tickover seems very low???

Edit: I didn't move my cursors from 720deg to 360deg, sorry but not particularly relevant given the above paragraph.

You describing intermittent power? but the capture was at idle.

You are on the right track by LT & STFT.

As has already been said in the post above start with test on the lambda sensors, that will give you more information/evidence and then think upstream, what would make this happen?

Also
What kind of intermittent power, revs load etc (does it run ok cold for instance)......year, mileage and any other info or tests carried out, engine code etc?

all the best
Last edited by EAAD on Fri Feb 10, 2017 4:54 pm, edited 2 times in total.
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Re: pico first look sensor waveform

Postby STC » Fri Feb 10, 2017 8:20 am

I have just tracked down a used pico first look sensor and a 3223


Good tools to have on board, the FLS has shown you that you have smooth running, equal contribution from all four cylinders, albeit with massive fuel adjustments made by the ECU.

It is adding an additional 20% in the short term and 14% in the longer term, it has detected a Lean Condition, which is absolutely brilliant as far as the Catalyst, Emissions and Smooth Running are concerned but it is trying to mask the fault and symptoms, not so good from a diagnostic point of view.

No fault codes

What scanner ?? And how often are you hitting the Clear Codes button ??

The upshot is that without those FT adjustments it would be running Lean.

Assuming your O2 is functioning correctly - That is your starting point !

ScannerDanner (Youtube) is big on fuel trims.

NB - I have measured idle at 770 RPM from your capture, you can compare that to the Specs for it.
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