Misfire only at cold start.

[dalmation53]

Just hit 100k. has been doing it for 2 months. have carbon cleaned valves,new spark plugs 2 months ago,new PCV valve Ah version. I start the car in the morning and seems like its misfiring as soon as car starts. So then i decided to get Bosch ignition coils. sometimes it does it somestimes not. as soon as i hit the gas pedal like maybe 300 more rpms the misfire completly stops. only in start up. not while driving or no codes either. live data for misfire recognition all say 0 meaning no misfires. Could it be one Injector?

[dalmation53]

well now it threw codes how the hell do i have all misfires in all cylinders with no carbon,plugs and coils??? but live data shows zero? Screenshot_20200629-231030.jpegScreenshot_20200629-231150.jpeg

[dalmation53]

Oh great no ones knows. or had this issue.

[zizouomar]

Oh great no ones knows. or had this issue.

I have the same thing. It stopped for a while after carbon cleaning and chains, but it came back few weeks later. Everything has been replaced like you.

[SDF1]

I've had that issue since I've owned my car.
New Piston Rings, Short Block, Chain, ETC lol
I think it's the 2nd air pump during cold start for emissions. If you wait 60 seconds for rpm to go down the misfires are gone.
Biggest difference I found was gas I used. Shell V-Power in Canada had 0% ethanol and the misfires were not noticable while some cheap gas was obvious.

Not sure which is the best gas in the US. Still trying them out to see what my car likes best.

[dalmation53]

So you have put new piston rings, a short block and chain and still does it in cold start?

I've had that issue since I've owned my car.
New Piston Rings, Short Block, Chain, ETC lol
I think it's the 2nd air pump during cold start for emissions. If you wait 60 seconds for rpm to go down the misfires are gone.
Biggest difference I found was gas I used. Shell V-Power in Canada had 0% ethanol and the misfires were not noticable while some cheap gas was obvious.

Not sure which is the best gas in the US. Still trying them out to see what my car likes best.

[SDF1]

So you have put new piston rings, a short block and chain and still does it in cold start?

Since I've had the car at 50,000km till now ~175,000km I still have this issue. I'm saying I don't think you can solve it. I've had everything replaced on my end from piston & rings, short block, intake manifold, spark plugs, coil pack, pvc, etc.

[FR_A4]

HPFP?


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[SDF1]

HPFP?


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Never changed.
Also origional fuel filter.

[dalmation53]

Damn i mean is not a big deal but is kind of sad to have an audi doing this in cold starts..did.you change your HPFP by any chance?

Since I've had the car at 50,000km till now ~175,000km I still have this issue. I'm saying I don't think you can solve it. I've had everything replaced on my end from piston & rings, short block, intake manifold, spark plugs, coil pack, pvc, etc.

[SDF1]

Damn i mean is not a big deal but is kind of sad to have an audi doing this in cold starts..did.you change your HPFP by any chance?

Origional HPFP. Never needed to change it or had any codes (yet)

[old guy]

I think it may be because of the cold start protocol used during a cold start to get the cat up to temp faster. When you cold start the ignition angle goes to -20° (after top dead center) and the intake cam goes to full advance. This condition increases the valve overlap and pushes some of the fuel ignition further downstream which serves to heat up the cat faster. It also causes a bit of a lumpy idle. After ~ 30 seconds the ignition angle returns to a few degrees BTDC and the intake cam returns to the normal idle position.

[dalmation53]

Yes it goes away indeed. This did not happen on my B7 or on my fathers b8.5 at all.. only on my A5. and it only happens sometimes. not all the time. is there a solution to that or is that a tunning thing?

I think it may be because of the cold start protocol used during a cold start to get the cat up to temp faster. When you cold start the ignition angle goes to -20° (after top dead center) and the intake cam goes to full advance. This condition increases the valve overlap and pushes some of the fuel ignition further downstream which serves to heat up the cat faster. It also causes a bit of a lumpy idle. After ~ 30 seconds the ignition angle returns to a few degrees BTDC and the intake cam returns to the normal idle position.

[Traptalk]

well now it threw codes how the hell do i have all misfires in all cylinders with no carbon,plugs and coils??? but live data shows zero? Screenshot_20200629-231030.jpegScreenshot_20200629-231150.jpeg

After chasing down misfires in my own car you need to pay attention to what cylinders are misfiring.

If only one cylinder is misfiring it is most likely something mechanical on that one cylinder (ie plug, coil, injector) moving those parts around to other cylinders should move the misfire with it to a different cylinder.

If all 4 cylinders are misfiring then you need to look at what’s common between all cylinders (ie timing, fuel delivery)

For example if your low pressure in tank fuel pump was dying and failing to prime and supply enough pressure to the hpfp than the rail pressure will be low for all 4 cylinders and they should all misfire randomly

The fact that this is on cold start would point me to the lpfp. Almost sounds like the prime is weak and losing pressure when it sits over night or an extended length of time and fuel leaks back into the tank.

Look at your hpfp actual vs request since we can only watch lpfp request (no low pressure fuel sensor). Can also trying to install a fuel gauge between metal hard fuel line and the hpfp and see its flowing

[old guy]

Yes it goes away indeed. This did not happen on my B7 or on my fathers b8.5 at all.. only on my A5. and it only happens sometimes. not all the time. is there a solution to that or is that a tunning thing?

I don't think the cold start protocol is anything you can easily alter. It's part of being able to meet emission standards. But something to consider: When you are running an engine at 20° ATDC I don't think it would take much of a variation in the fueling or ignition to make the fast idle lumpy.

I don't know if this helps but here is what my fuel pressure and advance looked like just now when I cold started my engine.