Misfire diagnosis on Opel Astra P2

Ok guys. Im starting a new topic on an not so old discusion to start again from zero as the problem somewhat changed, and update a few things. If you want to fully know the background here there is a not so old topic:

www.scannerdanner.com/forum/post-your-re...e-on-opel-astra.html

There was some rambling from my side in that topic so now i ll try to keep it simple:

Car: 2008 Opel Astra 2.0L 8 valve - Wasted Spark ignition - Engine has about 60K miles on it, completely stock.

Main problem:

Misfire can be heard from the exhaust. Engine is a bit shaky at idle, attached video of the sound of the engine at constant 2K Rpm.



Also idles rough and very shaky, engine speed at idle is consistent and on the spot (800 rpm)

Must read other symptoms of problems:

Random misfires that seem to happen in every cylinder
Car reeks of fuel when started cold until warms up
Little bit hesitation under soft load, good reaction on heavy load.
Long trim always between 1 and 3. Short trims can go down to -11 when engine is cold.
Sparkplugs a bit on the black side, specially number 2 but i dont discard a failing valve seal the culprit on that particular cylinder.
It gets better with the car warmed up
At some point the car throw a P304 code, and was running very rough, after some cleaning of the throtle body and doing plugs, wires and coil it got a bit better but still runs rough

Very imporntant: What I already did and tested

Already did coil, wires and plugs, tested two types of plugs, one grade colder than stock and one grade hotter. Hotter plugs than stock seem to work bettter.
Compression is good and consistent in all cylinders. Also done cylinder leakeage test with vey good results.
Already did injector cleaning and testing for flow and leakage. No leakage, consistent flow on all of them.

I have just received a hantek 1008 oscilloscope that i can use to pull data you think may help. Also have a datalogger for the ecu. But didnt see nothing odd there apart from the O2 sensor working mostly in the 70-700 mv range and short trims leaning always on the negative, can provide logs if wanted.

To start diagnosing im attaching some secondary ignition screenshots I was able to take but im still trying to learn how to use the oscilloscope.

Thanks in advance for any help.

Tell the VIN or the engine-code please.

For sure, you have very low ignition-voltage on Cylinder 4. Now is the question why. I want to take a look into the schematic of this ignition System. for this, i Need the above informations..

BR from Switzerland
Matthias

Thank you Matthias for your reply.

Engine code es X20SE. But wont help you since this is a GM Brasil car, (im from South America) and schematics are very hard to find. I have a copy of the schematics im attaching the ignition system for you.

Can someone please tell me if that jump during the spark line is normal or maybe a problem also there?

This oscillation on Cylinder 1 after the big Impulse reminds me of a short circuit. Have you scoped the Inputs for both coils too? this whould be my next step.

I didnt test for primary ignition. Dont know exactly how tbh. I just got the oscilloscope yesterday and im trying to learn as fast as possible how to use it.

Definitely agree with kostelectronics, #4 is a problem. If that waveform is repeatable during the misfire, then I think you've found your issue.

I usually see that secondary waveform when there's a secondary short to ground, with no arc taking place. Coolant in the plug tube, blown head gasket, water on a plug wire, like that. I know you've replaced the ignition system already, just noting where I usually see that waveform.

Yes it looks like the HT voltage has found an easier route to ground --- new ignition casette required

Im back guys.

Still getting to grips with the oscilloscope now I m attaching pics of a probe in the O2 sensor just to see if you guys spot something and more important. Primary ignition on ground of the coil that controls 1 and 4 and secondary of cyl 4. I have recorded the waveform but mostly look like what is shown below. I realized I recorded the channels inverted (i guess?) when it was too late.

Pics are bigger if you click on them

Just because and it was easy to do: O2 sensor wave at idle.

If more detail are needed I can provide a video of the recording of the wave or the file to reproduce it.

I really thank you guys for the hand. The dealers in my country are useless. And the rest of technicians still think carburetors are the way to go. (we have a very low standard on the automotive industry over here, no emissions control, and most cars on the road have at least 10 years or are "new" chinese death traps)

SERIOUSLY: I took the car to 2 differente shops, both said that it was running odly but i shouldnt be worried, that if it was too hard to solve I should wait for it to completely broke down so it would be easier to figure out what was wrong.... :S

Just for the laughs: Here base model chevy cruze 1.4 turbo? 35K dollars. Base camaro? 98K. Gallon of gas/petrol? 8 dollars. Average net income? 500 dollars. Sad but true.

At this point, i would take a different way.
Take the car to a gas exhaust test. Record the data when engine is misfiring and let us know. Check for HC levels in cooling system with the coolant hot enough to read vapors but not hurting you.
Is the PCM able to control injection or ignition pulse width individually?
Are you sure misfire is now at all cylinders? or it's just because you are seing now all spark plugs black?

You are saying you have a good reaction at heavy load, which means you are taking PCM to an open loop and pushing ignition system and fuel system to their maximun power. Can you notice a lack of power at heavy load and misfire is still there but you didn't notice because of engine speed? If can't i would change focus to fuel system.

According to book cylinder #1 is ok for me, cylinder #2 has a plug wire shorted and cylinder#4 spark is jumping to ground.

That's the reason i would perform an emission test.

Hi, i cant feel hesitation or lack of power at full load open loop as you say. I cant feel it maybe because of engine speed or maybe because isnt there at all. But the exhaust and acceleration feels smooth when I go WOT or highway driving.

Unfortunately not even performance shops have gas analyzers here, let alone any regular shop. Emissions are not regulated nor controled, and no one figured out yet that gas analysis is a usefull tool to diagnose a car. Go figure. Third world issues.

Is not an orthodox method but you are going to use your nose.

I had hard start issues with a carburetor car which i converted to mpfi. The car is 1300cc and injection system was programmed for a 1150cc.

In order to give a little bit more fuel to the engine, i simulated a cold ECT sensor (by adding a resistor in series). I recommend the same only for test because you can change the coolant fan fire temp.

When i putted a big resistor (let say 7kohms i could feel unburned fuel

If you have a lean condition (not shown by scanner) you can add fuel and check for misfire.

If you are not sure misfire is present at WOT, you are going to need a climb ability test (if misfire is present you are going to feel a fart for sure). If not, i would say you only have problems when PCM is in closed loop.

Guys, any comment on that primary ignition waveform?

Hi, There is another quick check you can perform to increase fuel in injectors.

In fuel return (after pressure regulator) you can strangle a little bit the hose in order to increase fuel pressure. That is, when engine misfiring, increase fuel in combustion chambers and discard if you have misfire due to a lean condition.