using first look

Ive just started using my first look sensor coupled to pico 3223.
Captured this waveform on a renault scenic 1.6 16v 2001 plate.
Can anybody see anything unusual,the car as varying power

Hey ian! Welcome to the forums.

I grabbed a screenshot of your Pico waveform, for anyone else following along:



This waveform looks OK at first glance. Reasonable amplitude, uniform peaks. But, what we really need is some kind of ignition sync. That'd help us distinguish individual events in the waveform. It'd also enable the use of a software overlay to correlate events to specific cylinders. Here's an example:



Just FYI, I have limited experience with FLS waveforms. :blush: But I do think it's a great testing method if you can decypher the waveforms.

What pressure pulses are you hooked up to ? The exhaust and fuel pulse can look very similar in shape what I call a molar tooth pattern. Any way it looks good and consistant.
What are your symptoms?

Tyler wrote:

It'd also enable the use of a software overlay to correlate events to specific cylinders.

Love that overlay. Wish we still had your post from the old forum. Some great info there

Its the exhaust pulse waveform.
I should have synced with no1,but it was a wet dark night,hopefully the weekend will allow me to take another capture.
No fault codes,symptoms are power coming and going.LTFT is 14 positive and the STFT is all over the place.
It shouts air leak ,but I cant find any using carb cleaner and a smoke machine,fuel pressure and flow rate are ok,no bunged up injectors.
As scanner danner says the car wont get out of its own way,most of the time
I can post a video of the trims.
A quick grab of another part of the buffer,I wonder if this is just spurious what Ive marked?

cheers

ian.broadbent wrote: A quick grab of another part of the buffer,I wonder if this is just spurious what Ive marked?

Possibly? Not trying to harp on the ignition sync, but it's tough to read too much into these waveforms without a reference. At first glance, it looks like all cylinders are contributing in that capture.

Low power... Any chance of a restricted exhaust problem? I've never done an FLS on a plugged exhaust, so I'm not positive how/if it changes the waveform.

unplug the mass air flow if it has one, and drive the vehicle.

No two cylinder firing events are identical so expect minor variations in exhaust pluses.
Without a definite misfire I would be looking for a fault that effects all cylinders equally, MAF, exhaust back pressure, vacuum leak, EGR.

been tied up with work and not had time to put any effort in to this until now.
Got round to trying a relative compression test,straight away noticed the engines cranking being irregular hmm
Cylinders 1 and 2 fine 3 and 4 down to 100 psi,after a while the readings came back to normal.So Im thinking hydraulic lifter issues draining out and not opening valves far enough,explains the power coming and going

ian.broadbent wrote: Got round to trying a relative compression test,straight away noticed the engines cranking being irregular hmm
Cylinders 1 and 2 fine 3 and 4 down to 100 psi,after a while the readings came back to normal.

Interesting! Maybe we were looking at a mechanical issue in your FLS capture... An intake waveform hot and cold might back up your theory about lifter issues.

Heres a capture of vacuum using the first look sensor,when the engine was running like a bag of bolts.
Engine was hot,didnt have time to put a no1 sync on as well clearly somethings a miss

Something but what -- I would only be making a wild guess to suggest the cause, the compression being low on two cylinders then recovering is a puzzle -- hydraulic tappets jacking up when the oil is cold? bore washing? I think I would go for a cylinder leak-down test.