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There is well less than 1 msec of burn time on all these blowup samples. If I had the car here I would probably current ramp the coil to cover my bases but my gut tells me it's a cylinder turbulance issue. Notice how the burn starts and uses the available fuel then restarts over and over. The avaialable fuel in these cylinders does not look like it is distrubuted or atomized evenly rather it is in uneven pockets causing the burn to start and stop over and over. Could be caused by an EGR open when it shouldn't be causing the intake air to tumble in an abnormal fashion.I guess you could call it lean in a sense but a classic lean pattern (a fairly smooth upward sweep) looks nothing like this. Of course talk is cheap and I've been wrong before but that's my 2 cents worth.  As far as what is wrong with the car we'll have to wait and see what Kevin says.

During a snap throttle test, I would expect to see the firing line higher. It appears as though there is not enough energy left to maintain spark duration (firing time). #1 shows a definate roll off of reserve energy. Look at the burn time on #3 in the paraded pattern. Lack of complete combustion there! Looks like others are lacking as well. #2 might be a suspect for carbon tracking or leaking boot. The misfire during that capture points towards #3 to me to be the worst. And it appears as though there are other cyl's not contributing like they should.

I'll go with low coil output and carbon or boot tracking.

G'Day Guys,

First up ... Good to see Tom initiate this 'diagnostic game' and the great participation by forum members so far. This is 'what it's all about' and I'm sure each and everyone of us will benefit somewhere along the line.
Not only Pico capture techniques, captures interpretation but also diagnostic methodology could also be discussed during the 'diagnostic game'

For the purpose of keeping things relatively simple, let's use the capture and the vehicle it was obtained from, as a sort of 'general guideline' if you like, to the Pico useage, screen capture interpretation and possible diagnostic strategies in this particular instance.

As with any diagnostics, something should be known about the vehicle symptom or symptoms and the vehicle ignition, fuel and air systems.
This particular vehicle is of our local production/consumption, but I'm sure many of you can relate to it with ease.

THE SYMPTOM : service R/O was written thus - " runs roughish and lacks power "
mmmm ... front desk needs some educating me thinks!    

Vehicle general info:
300,000km on speedo
In line 6cyl - firing order 153624
external modular coil
optical ignition - cranksensor 120° and 1° signals
multiport injection - current controlled injectors
2 x fuel pumps ( intank pre pump, external pressure pump )
Bosch Hot Wire Air Mass sensor
3 wire heated O² sensor
No EGR system
No data stream - DTC's only available

I approached this firstly by confirming the symptom before attempting diagnostics/analysis.

Confirmation of the symptom proved out.
Bad multiple mis-fires and poor performance.

A check of DTC's showed 1 stored - 14 (speed sensor )

I chose to connect the Pico and sample the tailpipe emissions with the 5 gas analyser with the thought that the two could support my initial 'confirmation of the symptom' as a possible fuel related issue.

I chose Kv parade to give me an overall view of all the cylinders and the 'effect' of the symptom.

As most of you have ascertained, the capture is showing a ' leanness' issue during combustion and it pertains to all cylinders.

The capture shows the effect but not the cause.
What would you do next?

With regards to the cylinder Kv's in the capture .. Tom has quite rightly noted that the initial higher Kv normally seen with 'lean' during a snap throttle was missed because of my scope settings.

What could/should I have done during initial scope setup before the snap Kv throttle test?

Would using the ' Save On Trigger ' scope function have caught the event?

Would you have approached the symptom with a different diagnostic/analysis strategy?

I won't provide the answer to the 'effect' of the fuelling issue just yet, but, the 'cause' was multi - layered  

Cheers!
Kevin

Hi All,

Those that identified with a carboning or restriction of cylinder breathing are on track. However,
at this stage I still needed to identify totally the lack of HC during combustion.

A current ramp of the fuel pumps provided yet another clue. The pre-pump waveform exhibited a poor commutators/brush signature while the main pump signature showed an expected 5amp, good speed and reasonable signature. The pre-pump is the fuel volume to the main pump so now I knew I had a fuel volume issue as well.

The Bosch Hot Wire Air Mass meter relys on PCM controlled 'self cleaning' and uses the speed sensor in the controlled hotwire burn off process after ignition shut down.

Looking at the waveform signature of the air mass signal output during snap throttle, showed a woeful signature and initial voltage rise. Not to hard to get to see the condition of the sensing element on this model and I confirmed a dirty sensing element.

Re-connection of the speed sensor connector and confirmation of PCM control of burn off was verified.

Whilst I did not mention O² sensor operation and fuel control earlier, the system was in control albeit rather poorly.

So ... I had a 'domino theory' diagnostic and effected repairs had to be done accordingly.
Intake valve restriction was my last stumbling block. With a high miler vehicle such as this one the client opted for an upper cylinder de-carbon service.

After the repairs, the vehicle operation and engine running during all modes ( cold start, warm up, operating temp. idle etc. ) was great and not a sign of mis-fire. The dramatic engine power output improvement would more than satisfy the vehicle owner.

Whether this scenario will be effective for some time? I don't think so. Carbon build up occurs for a reason. Valve guide and seal wear? You bet!!

Now ... how about some answers outlined in my previous post!

Add to the question list ... can engine speed ( rpm ) be calculated from the screen capture?

Cheers!
Kevin

Hi Guys,

Nice captures, similar to captures I've seen on a Ford Ranger pickup with a 3 liter V6.

would you agree with the following

the captures you have shown at idle do show a nice spark-line indicating normal combustion and spark duration, because the mix is right. ( pressure and volume adequate for the occasion )

the waves as shown during snap throttle start out with a good mix and turn in to a lack off conductive HC, likely due to a fuel delivery problem, that is likely caused by a lack of volume from the fuel-pump ( volume tested at the return line, since a weak pump working against a pressure regulator will be flushed out )
of-course restricted injectors would play a part here as well, but the low volume needs to be corrected first.

the sawtooth pattern has also shown up when there is excessive exhaust back pressure so the cylinders are not fully charged up with a pure combustible mix of fuel and air.

Hi Tom and Kevin

If you take the coil turn on time between each event (with out cursors) I measure 8 Ms, if you multiply this by number of cylinder which is 6 you get 48.Then divide 60000 by 48 you get 1250rpm That's approx but if Tom gives us some cursor up the exact rpm will be found.

Kevin What portion of the snap test is that image from Ie. tps state.  

Kevin,
       I have been using Pico for a research project where I have found it necessary to use it to calculate rpm from the waveforms I collect that display one complete combustion cycle for all cylinders. I think what you are forgetting is that for every rpm of the crankshaft there are 2 rpms of the camshaft which is what you are looking at when you measure an ignition reference from #1 combustion stroke to #1 combustion stroke again. Therefore it is necessary to divide 120,000 by the time in msec this takes to calculate crankshaft rpm. I have found that the Pico is extremely accurate for this. Here is an example of a COP Chrysler with #3 coil disconnected to induce a misfire. The rpm was 720 RPM. Hope this helps www.members.aol.com/bgoode007/rpm