Advice on waveform

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Advice on waveform

Postby onboardtech333 » Sat May 25, 2013 5:47 pm

I am just looking for another set of eyes to give their opinion on this wps waveform that I took from a cylinder on a
2002 Chevrolet Camaro SS 5.7l. Vehicle has a steady misfire on this cylinder and all primary and secondary ignition components have been replaced.
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running compression cyl 4.psdata
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Re: Advice on waveform

Postby Robski » Sat May 25, 2013 8:36 pm

A quick look to me says the Exh cam timing is advanced & Inlet is retarded (maybe??).BUT manifold vac looks to be around 20-21 InHg.

What did you think ?

Is it VVT ?

I would expect that whole bank to miss though.

Can you capture a known good from the other bank ? (if it's a 'V' engine(??) sorry not clued up on American cars))

EDIT: I looked at buffer #7 .
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Re: Advice on waveform

Postby Valhalla » Sat May 25, 2013 10:24 pm

Is this the Chevy LS1 engine? If so, it looks like it would be an easy swap to move the injectors over on this cylinder and its adjacent cylinder. Have you done this yet, just to see that the misfire stays with the cylinder you have measured in the Pico trace?

I put a 1kHz low pass filter on your trace, just to make it easier to see whatever the WPS transducer was saying. The manifold pressures on both sides of the cylinder look pretty healthy. The valve durations look a bit short; I think that the LS1 engines available this side of the pond have inlet and exhaust durations of 200degrees apiece, with hydraulic tappets and roller followers. If all else failed (all the easy fixes, like fuel injector checking, and scoping the secondary currents near the plug), then it might be worth checking valve lifter gear for wear on this cylinder.

I have a RangeRover 3.5l V8 that I have given up trying to diagnose the intake/exhaust profiles from the WPS; it just gets to the point where a spare engine is quicker, once you know you have to strip down the whole unit! :roll:
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Re: Advice on waveform

Postby Fat Freddy » Sun May 26, 2013 7:29 am

As previously mentioned. A capture from the other bank.

You really want it's companion cylinder (#7 on an LS1?) plus have the crank signal on both to compare with.

An ignition capture on cyl 4 with the crank sensor, sample rate of 1us and a bit of time on the screen may help.

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Re: Advice on waveform

Postby onboardtech333 » Sun May 26, 2013 4:42 pm

This is from Cylinder 1 running compression which is the opposite bank. The companion cylinder on this LS2 is Cylinder 3. The injectors have been swapped from 2 to 4 and all around at this point. I should add that I am a novice scope user just getting my feet wet with some of these waveforms.
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running compression cyl 1.psdata
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Re: Advice on waveform

Postby Robski » Sun May 26, 2013 5:20 pm

as FF suggests take the opposite cylinder & compare to see if you have this ?
Running comp_exh pocket notch_1.jpg


This is a comparison of a known good (different vehicle).......
Running comp_known good_exh pockets_1.jpg


Exhaust valve seating issue ?? however i don't see the compression peaks dropping.
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Re: Advice on waveform

Postby Valhalla » Sun May 26, 2013 10:49 pm

Overlaying cylinders 1 and 4 for a single cycle, there doesn't seem to be anything between them. Down to the subtle oscillations into the manifolds, both compare well. So unless the companion cylinder shows something dramatically affected by the faulty cylinder, then the problem is not going to be showed by a compression trace like these.

If you have swapped over the injectors, then the next thing to rule out is the harness supply to the injectors, so might be worth digging-out a couple of attenuators and back-probing the voltages into the injectors of the dodgy cylinder and its companion. A running trace of the two injector supplies back-to-back ought to rule out an injector drive issue.

If nothing else, I reckon you have pretty-well eliminated the base compressions with your traces.
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Re: Advice on waveform

Postby onboardtech333 » Wed May 29, 2013 12:09 am

Terrible response time only due to a holiday here in the US. I no longer have a transducer hose thanks to the wonderful engineers that decided to put the companion cylinder four inches from the frame. However I went back to spark and injector drivers. I can clearly see an issue with the secondary in cylinder 4. I will also provide a shot of the secondary for its companion (cyl #3). I had believed it to be because the exhaust valve might be hanging open slightly. As I said earlier though, I am still a novice scope user. Am I wrong in thinking it could cause this type of disturbance? Again all secondary and coils have been replaced as far as 6 cylinders. There is no access to cylinders 6 and 8 without removal of motor mounts and wiper cowl. Since this vehicle has 13,000 miles on it the customer would like to opt out on that venture for now,( I just do what they ask :roll: ). I appreciate all the advice given thus far. Injector drops are all identical as a last second thought.
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CamaroCyl4.psdata
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Re: Advice on waveform

Postby onboardtech333 » Wed May 29, 2013 12:13 am

And the injector current ramp
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cyilnder 4 current.psdata
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Re: Advice on waveform

Postby KimAndersen » Wed May 29, 2013 10:09 am

Hi

Do you know what ignition system there are installed on your car ?

The reason I'm asking is that i know that some GM cars are using a system called "Compression Sense Ignition (CSI)".

If this is the case you has to use a different strategy to diagnose these ignition systems.

Regards
Kim
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