Hello,
        Im working on a vehicle with an engine miss.I have the basic 4423 picoscope kit and was wondering is there a way with the included equpiment to find which cylinder has the miss.Its a six cylinder vehicle and all the spark associated equipment has been replaced  and the miss is still present , its pointing to something to do with fuel/injectors.Want to know how to find the cylinder at fault.I dont have a pressure/vacuum sensor to plug into the picoscope.

Thanks Brett

brettless02 wrote on Jun 11^th, 2010 at 2:33am:

Hello,         Im working on a vehicle with an engine miss.I have the basic 4423 picoscope kit and was wondering is there a way with the included equpiment to find which cylinder has the miss.Its a six cylinder vehicle and all the spark associated equipment has been replaced  and the miss is still present , its pointing to something to do with fuel/injectors.Want to know how to find the cylinder at fault.I dont have a pressure/vacuum sensor to plug into the picoscope. Thanks Brett

Hi Brett. I would at least request from you Year, Make, Model, Engine size(with engine code) and other info to help put me where you are at in your testing so far.

Why was the ignition parts replaced? Testing or parts shotgun?

What gives you an impression of something pointing to the fuel/injectors?

Spence

Yes, please post make, model, year and engine size.
DTC's if any and what testing has been done.
Captures would be nice too  :)

If you don't know how to post a capture, someone here will help you if you ask.

Hello,
        The car is a VX Commodore in Australia.Its a V6 wasted spark system similar to the Buick motor in USA.If you rev the engine from idle you can hear the miss in the exhaust and when driven with slight open throttle you can also feel it miss.I have checked the plugs and leads and all appeared ok.To make absolutely sure that they were not  the problem i replaced the spark plugs and leads but problem still there.I have also replaced the coils and DFI module from a know good working unit and the miss is still present.Today i removed the plenum chamber and checked the injectors for operation and all appear to be spraying ok.I have also checked the crank and cam angle sensors and they too appear ok.Also checked EST and EST bypass as there was a fault present for bypass circuit but this appears to be an old fault.Checked its operation with scope and looks ok.Was thinking if the bypass was taking control of spark timing it may not have been advanced enough,also i get a backfire through air cleaner on revving and that is intermittent.Was thing it had a blocked injector causing a lean mixture but doesnt appear to be the case.

Cheers Brett

brettless02 wrote on Jun 12^th, 2010 at 2:59am:

Hello,         The car is a VX Commodore in Australia.Its a V6 wasted spark system similar to the Buick motor in USA.If you rev the engine from idle you can hear the miss in the exhaust and when driven with slight open throttle you can also feel it miss.I have checked the plugs and leads and all appeared ok.To make absolutely sure that they were not  the problem i replaced the spark plugs and leads but problem still there.I have also replaced the coils and DFI module from a know good working unit and the miss is still present.Today i removed the plenum chamber and checked the injectors for operation and all appear to be spraying ok.I have also checked the crank and cam angle sensors and they too appear ok.Also checked EST and EST bypass as there was a fault present for bypass circuit but this appears to be an old fault.Checked its operation with scope and looks ok.Was thinking if the bypass was taking control of spark timing it may not have been advanced enough,also i get a backfire through air cleaner on revving and that is intermittent.Was thing it had a blocked injector causing a lean mixture but doesnt appear to be the case. Cheers Brett

You are still not quite giving me the info needed so I can do a little research on my end so I can give you good info back to try and help you... If you look back at my first post on this thread as well as Todd's you'll see we asked for.

Have you done a compression test or better yet do you have an amp clamp so you can do a relative compression test?

Does this use a MAF, MAP or both?

Do you have a scan tool to get data for this?

I'll stop there until I see the results.

Spence

Hi Brett,

before you start replacing any parts under the bonnet, it is best to start with a good look at all the basics.
The 3.8 litre ecotec engine runs the Delco waste spark system.

The KV voltage and spark line can be observed on each cylinder, but the best starting point is with a compression test.You need to check the condition of the engine in the first place.

Go to supa cheap autos or Repco & grab a compression tester.

Brad

Hi Brett

Before you pull the plugs to do your compression test. Why not use your scope to do a relative compression test. Using your amp clamp and ignition pickup to help identify the low cylinder if any.

Is this motor running just on petrol or is it a dual fuel system?

Andy

Brettles02,

Could you clarify about the misfire is it a complete cylinder misfire that can be felt at idle or one that only takes place in certain conditions?

If it is a dead hole you could do a low tech cylinder kill.  There is some risk involved both to equipment and person.  The process is to use a back probe inserted into one ignition cable at a time.  Then using a jumper lead ground the cylinder.

IF NOT DONE RIGHT IT WILL SHOCK YOU.  IF NOT DONE RIGHT IT COULD DAMAGE EQUIPMENT. So be careful if you try it.

The idea is with a cylinder not contributing there will be no engine speed drop on the bad cylinder.  The problem is if it is a partial misfire it will not work as well especially if the miss is not at idle.

Have you replaced any GM fuel pumps with in tank pressure sensor?
If you have you have a low cost pulse sensor for the exhaust you can build yourself.  That is of course additional equipment you would need to fabricate.

The technique with the least effort would be to observe secondary ignition.  Based oh the post I am assuming you do not have a DIS adapter such as the Mixmaster or the Ferret.  You should have at 2 or four KV probes that came with your scope.  Connect the two probes to the two coil towers and duplicate the symptom.  Do this two times if you have 4 probes or 3 times if you only have two.

So you will be connecting to 1/4, 2/5, 3/6 if that is similar to a Buick V6.

I am posting a link to a video I uploaded on Google video some time ago.  It was from a Ford, although it should give you an example of what the set up is.  I also used Pico Diagnostics.  I did not mention that because there is not a good way to determine the cylinder that is missing through Pico diagnostics. at this time.  The video clip I posted had a broken spark plug, I suspect from a head gasket leak.

Here is the video:

http://video.google.com/videoplay?docid=2358961231410204381&q=automotive+testing+movie%22%3Ehttp://video.google.com/videoplay?docid=2358961231410204381&q=automotive+testing+movie#

Once you record you files with the misfire present post the psd files here and we will try to help further.

Good luck

Sam

Hello all,
            Thanks for all your help but i have fixed this problem.I did do all the suggested items prior Eg.compression test with a compression tester and a relative compression test with the picoscope,also did a cylinder balance test which did show up some low values.I will post those results and a photo of the plenum chamber.Basically i bridged the fuel pump and fired each injector individually and found there to be no great issues with them and looked to be good,spraying ok.I was told be a friend that has heard of issues of dirty throttle body and plenum and by cleaning it the problem disappeared.I have done this and the problem has gone and car running fine.What i did notice was the middle two cylinders were cleaner than the rest and the hole where the PCV fumes come back was close to these cylinders.The PCV was cleaned with Carby cleaner along with the throttle body.I put it back together and problem solved.A couple of thoughts was either sucking air near these 2 cylinders and resealing has fixed it,by cleaning a possible sticky PCV,or i have been told the dirty plenum courses air tubulance,but after cleanibg it all out away it went.

Thanks For your help i will post some of the results i got and plenum photo.

Cheers Brett ;)

Hello,
        Here is the pics of the plenum chamber

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looking at the picture it doesnt look too bad for an egr engine? what was the fuel trims at idle?

Here are the compression and cylinder balance test results

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Hi Brandonb,
                  I dont have a scan tool to check for fuel trims at idle.

Cheers Brett

Question for ya...  Was the miss only at idle? In other words did the miss go away when you reved the engine to 2000 to 2500?

Spence

brettless02 wrote on Jun 13^th, 2010 at 2:27am:

Here are the compression and cylinder balance test results

I could not open either of these files. Is anyone else having the same problem?

Brett,

you'll find the problem was a hose under the throttle body.
I can't remember if it is the PCV valve hose, it probably is. If the vehicle is still with you,pull the hose off at one end and see if the poor running condition is repeated.
If the engine ever suffers a backfire, it will blow this hose off.

What format are saving you captures in ?
I couldn't open them either.

Brad

Brad H wrote on Jun 13^th, 2010 at 5:20am:

Brett, you'll find the problem was a hose under the throttle body. I can't remember if it is the PCV valve hose, it probably is. If the vehicle is still with you,pull the hose off at one end and see if the poor running condition is repeated. If the engine ever suffers a backfire, it will blow this hose off. What format are saving you captures in ? I couldn't open them either. Brad

These  are pico diagnostic files showing cylinder balance and compression.

Mick

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Hi Spence,
                At idle it seemed ok it was only when you quickly revved it you could notice it ,then on the road  under light load with slight acceleration or going up a slight climb you could also notice it.Also when i uploaded the files i too couldnt open them,what i did was open pico diagnostics program and load the file from where it was saved on computer when you uploaded to and i was able to get it to work that way.The file was uploaded to a temp file when you clicked on one of the 2 pddata files.Use Load from the file tab in that software to view.

Mick wrote on Jun 13^th, 2010 at 5:38am:

Brad H wrote on Jun 13th, 2010 at 5:20am: Brett, you'll find the problem was a hose under the throttle body. I can't remember if it is the PCV valve hose, it probably is. If the vehicle is still with you,pull the hose off at one end and see if the poor running condition is repeated. If the engine ever suffers a backfire, it will blow this hose off. What format are saving you captures in ? I couldn't open them either. Brad These  are pico diagnostic files showing cylinder balance. Mick

Hence the pddata instead of the psdata? I'm checking my version now...

Spence

brettless02 wrote on Jun 13^th, 2010 at 5:43am:

Hi Spence,                 At idle it seemed ok it was only when you quickly revved it you could notice it ,then on the road  under light load with slight acceleration or going up a slight climb you could also notice it.

Hi Brett and thanks for answering my question. If you knew this during the opening post I feel you should of mention it.

Thanks again

Spence

Here ya go

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Hi Brad,
           There is a hose on the inlet manifold that goes to the throttle body and another smaller hose going from the throttle body to the purge valve from memory.The PCV is located under the plenum chamber and no hose directly connects to it.In the plenum chamber pics you can see where the PVC hole is in between the 2 middle cylinders.Thats where the blow by gases come in.All hoses did appear to be connected properly before removal.

Cheers Brett

Yeah Mick,

older version of pico on the pc I was trying to open Brett's post on.

:-[

Brad

Brad H wrote on Jun 13^th, 2010 at 4:39pm:

Yeah Mick, older version of pico on the pc I was trying to open Brett's post on. :-[ Brad

Same here, all fixed now...   8-)