Carboned intake valves and intake pulses

I had a GDI Commodore (V6 GM alloytec) in today with p0300 code. It's a well known fault around here that this can be caused by carboned up intake valves. Removing the plenum and cleaning them cured this one too.
My question to the forum is, assuming the misfire comes from leaking valve seats, is it possible to see any form of uneven pulses in the intake? I scoped the MAP but it was completely flatline. I've read people talk about first look sensors but have no experience at all with them. Is this what I should be looking at? Any input genuinely appreciated.

I've heard the same thing, as far as using the FirstLook sensor. Can't remember where I saw them, exactly, but I have seen captures from carboned-up GDI engines, and they pretty well spell out the problem once you know what to look for. Takes some getting used to, as well as a good timing overlay for your captures.

Andy MacFadyen has posted about more affordable versions of the FirstLook, and I've been very tempted to get one. The name brand sensor goes for around $400 last time I looked, a bit too steep for me.

I've also had luck scoping the MAP sensor, using AC coupling. I usually use it to find valve adjustment issues on Honda's, but the same principle applies. The only problem is the location of the MAP sensor on the intake, as it needs to be as centrally located as possible.

I've also had luck scoping the MAP sensor, using AC coupling. I usually use it to find valve adjustment issues on Honda's, but the same principle applies

I'd like to see this process if you maybe felt like starting a thread... :whistle:

Sure! I'll see if I can get a hold of a lab rat for testing, since my Scion doesn't have a MAP sensor

Simulating the leaking intake valve will be tough, maybe we'd have to settle for a loosened spark plug?

You don't have to go nuts, I figured you had some captures saved in "Tyler's Super Library Of Awesome Waveforms and Data PID Captures"

Thanks for the replies boys. Please don't go overboard Tyler. A loose plug won't have the same result as its not really effecting the intake is it?!
I didn't even think about ac coupling. This job was one of those ones where you know what's wrong and you're expected to just fix it. I thought I'd just quickly throw the scope on it and see what it looks like before I rip into it.
One reason in particular I'm questioning the process is the same cars we're starting to see injectors failing mechanically to the point of jamming open and flooding the car. In the back of my mind I'm thinking it'll get to the point one day where I do a carbon clean and miss a failing injector. I need to get my head around some sort of routine or procedure to diagnose gdi systems. Maybe it's just me. I'm pretty confident diagnosing blocked port injection injectors but still pretty green on gdi.
The more I learn off guys like you two and Paul the more I realise i don't know. Lol

Pull up a tool box and I will tell a war story;
40 years back the bitter sweet pleasure of owning and occaisionally racing a Lotus with the old Lotus-Ford Twincam engine and because of this I looked afer a couple more. Outside of the USA these engines had twin Weber 40DCOE carbs so like a motorcycle each cylinder had one barrel directly feeding each cylinder with no plenum or balance tube. In those days we used to synchronise the the carb butterflys by ear using a sethoscope held at a sweet spot in the carbeurettor trumpets.
It was really easy to bend a valve on these engines but listening to the inlets a inlet valve that wasn't sealing would make a very distinctive plop-plop sound.

Was yours the post in the old forum that had talk of using a 5V battery from a drone? I forgot that there'd been a post about making a pressure transducer.

I love old war stories.

Noah wrote: You don't have to go nuts, I figured you had some captures saved in "Tyler's Super Library Of Awesome Waveforms and Data PID Captures"

Haha no intake stuff, sorry, mostly because I've started using the in-cylinder transducer more often.

Matt, yeah the plug wouldn't be a great simulation, but I think it would produce some kind of change in the intake? Because that cylinder is no longer producing the same amount of vacuum? Maybe I'm thinking of it wrong.

Talking about procedural stuff, did your Commodore come with an injector balance scan tool test? The newer GM GDI engines (including the High Feature engines, as we know them) I've seen all come with an automated balance test, which I've been playing with when I can. I can post some scan data captures of a test if you want.

Honestly hadn't noticed. I was focusing on misfire data but we all know that can be misleading and limited in its use. I'll definitely have to have more of a poke around next time we get one in. I've seen and played with the ford one but thought it was unique to ford.

Yes true with the lower vacuum created with a loose plug. Totally missed that. I was thinking more of any positive pulses back into the intake through the leaking valves.

Totally up to you man. Do you run SO gear? You know if it's in functional tests?

With the AC coupling, that removes the DC part of the signal doesn't it? So then you can really focus on the slight variations in the signal? Sorry for the noob question.