2005 Corsa C Misfire

Hi, I am currently looking at a Corsa C 1.2 Twin port. The vehicle starts and runs fine for about 20 seconds then the eng man light starts to flash and the engine misfires.
Fault codes stored are P0300 Random / Multiple misfire, P0301 Misfire Cylinder 1 and P0304 Misfire Cylinder 4. Switch the ignition off, restart the vehicle and it runs fine again for about 20 seconds then the fault reoccurs.

On my initial look, I attached a vacuum gauge to the inlet manifold which displayed good vacuum with a steady needle so the engine mechanically seems good.

I decided to look at the ignition primary voltage and current and injector voltage and current, it was obvious that their was no command form the ECU or current for injectors 1 + 4, then I remembered that the ECU can turn these off when a misfire is detected . Ignition off then restart the engine all 4 injector command and current are visible, engine seems to run fine, no misfire that I can notice then injectors 1 + 4 are turned off and a misfire is obvious. It looks like the ECU is detecting a misfire then turning off the injectors for the relevant cylinders.

On returning to the vehicle the following day looking again at ignition primary their were 2 and sometimes 3 saturation events for each cycle. This looked very odd to me, zooming in on the first event I noticed a very brief high spark line voltage, I removed the plugs, they were worn out so I replaced them and the spark line voltage lowered but still had more that one saturation period. After quite a while this did return back to one event.

I am wondering if the captures show a fault to a more experienced eye, if anyone can explain what is happening in the captures and may be suggest some further tests to try get to the bottom of this fault. I was considering looking at fuel quality next before doing too much more, thank you for your time, kind regards, Andy
(Looks like some of my files are too big to upload)

Captures 1 and 2 the sample rate is too low.

Capture 3, Nice sample rate. What coil are you connected to? I suspect if you hooked onto the secondary (extension leads) you may spot a fault. Also add primary 2/3 (Don't know this engine so a bit of guess work involved).

FF

Hi FF, thanks for the reply. Sorry about the sample rate, something else I will have to brush up on... the coil is the cassette type, on top of the plugs, 6 wires. I hooked up to pin 6, I think it is cylinder no 4, primary voltage. What i found strange is why the coil attempts to fire twice on all the cylinders at various times and if this was a symptom or a fault. I will take a look at secondary ignition with the extension leads, off work now until Friday, so I'll get the captures and report back, thanks again for the reply, Andy

What i found strange is why the coil attempts to fire twice on all the cylinders at various times and if this was a symptom or a fault.

Not looked at captures but they do multi-strike, from what i have seen scoping them.

Not looked at captures but they do multi-strike, from what i have seen scoping them.

Have a look. It's not the multi strike X2. It's the initial kick - ignition is something I still have to get to grips with. I am suspecting if a secondary lead is used to obtain secondary the initial kick will differ. It's more of a hunch.

OP

Any previous work before you started looking ?

Do you have COP extension leads ? You will probably have to use some small cable ties on the boots to hold firm.

Capture a few frames of secondaries before & after the injectors get shut down @ 1µs sample interval, i have a sneaky suspicion or 2 on this ...............

The vehicle has had no previous work. I know it well, been parked up waiting for a body repair, flat battery, jump stated a couple of time.
I do have the COP extension leads, I will get the captures you suggest and post them for you to view. Off work until Friday, will get them up asap, thank you for the interest, Andy.

I will get the captures you suggest and post them for you to view

Check sample rate is as requested in properties, not what you asked for in the tool bar.


FF

Hi, went to the vehicle today, started ok, fault still present as before. Pulled it into the workshop, decided to remove the plugs from the ECU to check everything looked visually ok. Refitted the connectors, started the vehicle, the fault has now gone. Tried wiggling the connectors and wires to recreate the fault but is all ok. Road tested and all ok. I have had one of the connectors off while this fault has been present already. Today I removed and refitted the other and the fault disappeared before I had chance to get any secondary ignition captures. It must have been a poor connection in this plug, thank you for your time and interest, Kind regards, Andy

You have to be happy with that.

Are you still able to get the capture even though the vehicle is fixed. If that's not a problem.

FF