Misfire on cold start
- Thread starter mcbutler
- Start date
Have you moved away from the theory of a leaking injector? Or hoping it's something cheaper? :wink:mcbutler said:
I suppose if it stays in No.6 you'll know it's more likely to be the injector.
Could also try warming the engine up, turning it off, resetting the code and starting up again before the injector has time to leak?
The annoying thing is that all the coils are brand new Bosch and so are the plugs. All done around 300 miles ago! I am hoping a coil has just come loose or not clipped on properly. Check out my optimism lolZforbes said:mcbutler said:
Rule out the cheapest options and work your way back
Whilst you're in there you may as well do the plug as well
Nope only what you get on a cold day but it smells very rich until the cold start sequence finishes - so is the injector leaking excessive fuel or is the ignition failing so the fuel isn’t burned!Pondrew said:
Thing that bugs me is why only for 40 seconds. Let’s see what tomorrow brings, if I get time.
mcbutler said:The annoying thing is that all the coils are brand new Bosch and so are the plugs. All done around 300 miles ago! I am hoping a coil has just come loose or not clipped on properly. Check out my optimism lolZforbes said:mcbutler said:
Rule out the cheapest options and work your way back
Whilst you're in there you may as well do the plug as well
Fingers crossed, 300 miles isn't proof enough to me they are reliable and the only reason I questioned plugs and coils before the injectors. Single cylinder misfire should rule out other potentials like airflow meter, lambda sensor or air / vac leaks
Fair point - I am going to remove the cover and check plug and coil today, I am hoping that maybe I didnt push the coil on hard enough. Failing that I will swap number 6 coil/plug with number 1 and see what happens.Zforbes said:mcbutler said:The annoying thing is that all the coils are brand new Bosch and so are the plugs. All done around 300 miles ago! I am hoping a coil has just come loose or not clipped on properly. Check out my optimism lolZforbes said:Rule out the cheapest options and work your way back
Whilst you're in there you may as well do the plug as well
Fingers crossed, 300 miles isn't proof enough to me they are reliable and the only reason I questioned plugs and coils before the injectors. Single cylinder misfire should rule out other potentials like airflow meter, lambda sensor or air / vac leaks
Might start it for a moment before I do that, leave it 5 min and see if I have a wet plug in number 6
If it's starting bad after a night parked up then that would imply if it's the injector that the plug is still wet in the morning.mcbutler said:
No real need to start it up first. Whip the plug out straight away and see if it's wet.
If it is, dry it off (a lighter works!) and put it back in. Then start up and see what happens.
If diagnosing a leaking injector you need to understand that the injectors typically only leak when fuel pressure is present.
Upon unlocking the car the electronic in-tank fuel pump will pressurise the fuel rail to 72.5PSI. When the engine starts running the high pressure fuel pump will begin to turn and the DME will then modulate the rail pressure.
If you haven't disabled cold start in the engine tune then the DME will ask the high pressure pump to pressurise the rail at 2000PSI for the first 45 seconds of operation and the it will step down back to 700PSI for normal operation. In normal driving the rail pressure will be around 700PSI but once you start loading the engine up it will run around 1500-2000PSI again.
Injectors won't continuously leak as the line pressure falls after you turn the car off. They might not leak at 72.5PSI or only slightly but at 2000PSI they could be leaking like a fountain.
You can verify all this by looking at live engine data with MHD. If you unlock the car and see the fuel pressure reading 72PSI but it quickly drops down then you know there's a leak. If it stays high you are fine at low pressure. If the fuel pressure on startup is violently oscillating the the pump could be weak. If the pressure stays high then the pump is OK and you then need to consider the lambda readings on each bank. If 1 bank is reading a crazy rich value like 10:1 then you know that bank has a leaking injector.
Upon unlocking the car the electronic in-tank fuel pump will pressurise the fuel rail to 72.5PSI. When the engine starts running the high pressure fuel pump will begin to turn and the DME will then modulate the rail pressure.
If you haven't disabled cold start in the engine tune then the DME will ask the high pressure pump to pressurise the rail at 2000PSI for the first 45 seconds of operation and the it will step down back to 700PSI for normal operation. In normal driving the rail pressure will be around 700PSI but once you start loading the engine up it will run around 1500-2000PSI again.
Injectors won't continuously leak as the line pressure falls after you turn the car off. They might not leak at 72.5PSI or only slightly but at 2000PSI they could be leaking like a fountain.
You can verify all this by looking at live engine data with MHD. If you unlock the car and see the fuel pressure reading 72PSI but it quickly drops down then you know there's a leak. If it stays high you are fine at low pressure. If the fuel pressure on startup is violently oscillating the the pump could be weak. If the pressure stays high then the pump is OK and you then need to consider the lambda readings on each bank. If 1 bank is reading a crazy rich value like 10:1 then you know that bank has a leaking injector.
Progress report
So this morning with the car cold I removed plug and coils from 6 - the misfiring cylinder the plug looked dry but stank of fuel and was very dirty for only 300 miles. However saying that I let the car sit on Rickover yesterday for a hour while I was working on the interior.
I then removed plug and coil from number 1, plug smelt ok, dark but not as bad as 1 and a clean spot on one side, presume this is where the injector spray hits it.
I swapped plugs and coils around and the misfire was still present but a lot less noisy etc than before.
I have photos I will add later for you all to see.
Looks like scarlet might get a new set of index 12 - thanks Warranty Direct - fingers crossed.
So this morning with the car cold I removed plug and coils from 6 - the misfiring cylinder the plug looked dry but stank of fuel and was very dirty for only 300 miles. However saying that I let the car sit on Rickover yesterday for a hour while I was working on the interior.
I then removed plug and coil from number 1, plug smelt ok, dark but not as bad as 1 and a clean spot on one side, presume this is where the injector spray hits it.
I swapped plugs and coils around and the misfire was still present but a lot less noisy etc than before.
I have photos I will add later for you all to see.
Looks like scarlet might get a new set of index 12 - thanks Warranty Direct - fingers crossed.
mcbutler said:
Yes, fairly easy.
You can customise the data channels that it records but by default it will record everything you are interested in.
Just go to the Mon. menu then press the text that says "Data Logging" and if connected to the car it should display some basic data in the gauge view. These gauges are only live displays, you can set them up however you like but the important thing for you is to record the data so you can review after. You just need to press the green button at the top labelled "start logging" to begin recording the data, then press the button again to stop the logging when you are done.
I would suggest just pressing the ignition button without a foot on the brake to bring on accessory power then connect MHD and begin logging before starting the engine. Let it record until the idle smooths out a bit then upload the csv file here.
Just a Z4 specific note on the logging: The low pressure fuel sensor reading will show 0 as the Z4 doesn't have one. This isn't a problem as we can just observer the rail pressure instead for this test.
Jeez! If you told me that was a 50k plug I would have believed you!
Me thinks you may have found your issue.
However, bear in mind that if the plug isn't sparking for some reason then it will still end up covered in unburnt fuel.
That can be checked by running it up to warm today then checking again tomorrow to see which plug is sooty, and which cylinder is showing the misfire.
Bear in mind my diagnosis methods are very old-fashioned.
[ref]R.E92[/ref]'s methods are far more scientific and probably suit the car better.
Me thinks you may have found your issue.
However, bear in mind that if the plug isn't sparking for some reason then it will still end up covered in unburnt fuel.
That can be checked by running it up to warm today then checking again tomorrow to see which plug is sooty, and which cylinder is showing the misfire.
Bear in mind my diagnosis methods are very old-fashioned.
[ref]R.E92[/ref]'s methods are far more scientific and probably suit the car better.
