Pictures of my inlet ports....

[ArthurPE]

way to be, demeaning...nice
I knew there would be one of 'those guys', a bit surprised it was you...

I don't believe the scenario you postulate could possibly occur if what you are implying the deposits cause the misfire...what mechanism would cause it? other than 'it is the deposits' or 'everybody knows they do'...

in these engines cold misfires usually are a result of over fueling when starting cold...the mixture is too rich to fire...a couple of cycles, the cylinder is warmed a bit and evacuated...cold fuel shot into a cold cylinder with poor air mixing characteristics, ie, DI, not shot into the airstream...
in addition plug selection has some bearing: it's hard to find a plug that will fire fine cold, at 800 rpm, with fuel squirted on it, and then function well when hot at 8000 rpm...it's a compromise, running rough when warming up is preferable to an 8000 rpm full load malfunction...

since your 'scenario' can't occur, it can't really be 'answered'...a hypothetical must at least be within the realm of possibilities...or a logical arguement, not one that asks one to suspend the laws of physics or 'reality'...

answer: nothing, deposits are not related to the misfires...
I'm betting that's not what you wanted to hear...

not sure what you mean by knock detection is used to control Pme?
if you mean torque control advances timing until the onset of detonation (knock gets louder or out of time) then backs off, I'm not sure that is accurate...some kind of adaptive control, beyond the factory set limits...

a map selects the timing value (based on several parameters, rpm, throttle, temp, load, etc.) usually an optimsitic/idealized value...if this value is too high, knock (mild) will be detected and timing reset, knock is a secondary control variable, a safety, not a primary variable...one way tuners eek out power is by adjusting the map, ie, add a bit more timing...hence the requirement for higher grade fuel at times...they are basically minimizing the safety margin the mfgr built into the system...

mixture control as trimmed by the O2 sensors has as much to do with power (mixture ratio) as timing...can't seperate them...

save your 'back patting' for yourself...not sure why you feel compelled to insult a bunch of guys who have done nothing to you, heck, that you don't even know...

Not to disrupt the cerebral back-patting, but how about we look at something else besides airflow for a moment.

We can even make it hypothetical, so that it doesn't get dismissed with a simple "well, that will simply never happen".

Lets say a DI engine is suffering from misfires upon cold start up. There are no misfires during normal operation. Sometimes the total misfire count is only 8-10 in the first 30 seconds after startup (below the threshold for a CEL), but sometimes its 40-50, or even as high as 200-300 misfires, in which case the CEL/MIL will flash, but then go off.

Then the valves are cleaned.

Misfires are logged for the next 15 cold starts. Not a single misfire occurs. Another significant change is noted in the ignition timing. The average level of retardation has dropped, so after the valve cleaning, the actual timing is closer to the target, or set point.

Question - what does a clean set of valves have to do with less cold start misfires and less retardation in a DI engine with closed-loop knock control?

Added info - closed-loop knock control is used to achieve peak cylinder pressure (and torque) with a variety of fuel grades in addition to detecting detonation (knock).

I'll save the back-patting until someone gives a good effort at answering a direct question, hypothetical or not. If there are no takers...well,that's OK too.

[ArthurPE]

on a side note we are confusing/melding 3 different conditions into a common phenomena
detonation: starts with normal ignition by the plug, followed by abnormal propogation, can be mitigated, controlled
pre-ignition: charge ignited by a source other than the plug, usually catastrophic if not abated
mis-fire: failure to ignite, like a bad plug/coil, can be sporadic/random

3 different things with different causes (although some overlap)

so which do deposits cause?
under what operating conditions?
and by what mechanism?

[2manytoys]

I'm with silverRS4. The question is why? Why does carbon electronically limit the engine through timing. Why is after 6000rpm. I mean forget actual dyno peak numbers, why is it flat at around 6000rpm then after the clean it's not (again, please forget the actual power out numbers). It's greater than 2% because as many have said, you can feel the difference.

I've now had my entire manifold replaced, so it's not flaps (it wasn't at the start either, the flaps only happened recently). I do know that the timing is being pulled back now though.

Something is common, be it to a handful of people I don't know, that when carbon is cleaned the power curve is normal. Obviously those that still have the punch at 6000rpm don't suffer the problem, I understand that 100%, but those that don't get it, yes, I'm sure they have carbon.

Haven't many great discoveries been by accidently dropping something into the beaker so to speak

Any takers?

[SR71]

I'll have a stab at it...although its purely an opinion derived from my own reading...

That said it all makes sense in my mind.

In Fuel Stratified Injection (FSI) engines, stratification of the inlet charge is critical to enabling the concept, although the engine isn't in lean burn mode at WOT. That said, the intake manifold flaps will be closed on start up, which is what we're talking about.

The funtion of the inlet manifold flaps is to induce tumble in the airflow. Tumble is critical to ensuring the rich fuel air mixture is concentrated in the vicinity of the plug by the time the compression stroke is coming to an end and is subsequently ignited. (The process of ensuring this to be the case is almost the opposite of what you'd prefer for port-injected engines where valve and intake aerodynamnics are optimised to ensure homogenous mixtures throughout the cylinder.)

Intake geometry and piston bowl geometry are critical to assisting this process, as is a clean path through the torus created by the valve opening, although as the literature will show, it isn't so much the intake stroke aerodynamics that is affected, but the compression stroke aerodynamics, where everything is "squished".

So on the assumption that Audi designed their FSI V8 with no deposits anywhere near it, my guess is that it is the occlusions in the intake/on the valve itself, that screw with the intake aerodynamics. This effect is magnified at low piston velocities once the compression stroke commences - that is what the piston design is for and the head geometry cannot counter the effect - which then results in less than optimal mixtures being present at the spark plug resulting in....misfires.

This continues until the initial transients die down and residual heat starts to assist the process?

So I'd agree with Art when he says

in these engines cold misfires usually are a result of over fueling when starting cold...the mixture is too rich to fire...a couple of cycles, the cylinder is warmed a bit and evacuated...cold fuel shot into a cold cylinder with poor air mixing characteristics, ie, DI, not shot into the airstream...

but the question is "Why?"

How did I do?

[Sims]

save your 'back patting' for yourself...not sure why you feel compelled to insult a bunch of guys who have done nothing to you, heck, that you don't even know...

Did SilverRS4 insult anyone?

Is Art frequently compelled to insult a bunch of guys who have done nothing to him, heck, that he don't even know...

The fair minded people on this forum can decide, and recognise that reigning in Art's attacks can only be for the good of the forum.

[P_G]

I'll have a stab at it...although its purely an opinion derived from my own reading...

That said it all makes sense in my mind.

In Fuel Stratified Injection (FSI) engines, stratification of the inlet charge is critical to enabling the concept, although the engine isn't in lean burn mode at WOT. That said, the intake manifold flaps will be closed on start up, which is what we're talking about.

The funtion of the inlet manifold flaps is to induce tumble in the airflow. Tumble is critical to ensuring the rich fuel air mixture is concentrated in the vicinity of the plug by the time the compression stroke is coming to an end and is subsequently ignited. (The process of ensuring this to be the case is almost the opposite of what you'd prefer for port-injected engines where valve and intake aerodynamnics are optimised to ensure homogenous mixtures throughout the cylinder.)

Intake geometry and piston bowl geometry are critical to assisting this process, as is a clean path through the torus created by the valve opening, although as the literature will show, it isn't so much the intake stroke aerodynamics that is affected, but the compression stroke aerodynamics, where everything is "squished".

So on the assumption that Audi designed their FSI V8 with no deposits anywhere near it, my guess is that it is the occlusions in the intake/on the valve itself, that screw with the intake aerodynamics. This effect is magnified at low piston velocities once the compression stroke commences - that is what the piston design is for and the head geometry cannot counter the effect - which then results in less than optimal mixtures being present at the spark plug resulting in....misfires.

This continues until the initial transients die down and residual heat starts to assist the process?

So I'd agree with Art when he says

in these engines cold misfires usually are a result of over fueling when starting cold...the mixture is too rich to fire...a couple of cycles, the cylinder is warmed a bit and evacuated...cold fuel shot into a cold cylinder with poor air mixing characteristics, ie, DI, not shot into the airstream...

but the question is "Why?"

How did I do?

Pat on the back for that man, sounds plausible but don't have the answer to your 'why'?

[Sims]

..

How did I do?

Pat on the back for that man, sounds plausible..

Absolutely, all SR71's posts have great balance.

[SR71]

P_G,

The "Why?" in my post was referring to why Art's observation might be the case.

My suggestion is my proposed answer to SilverRS4's question but also the explanation for Art's observation which I quoted.

Just to clarify.

[P_G]

P_G,

The "Why?" in my post was referring to why Art's observation might be the case.

My suggestion is my proposed answer to SilverRS4's question but also the explanation for Art's observation which I quoted.

Just to clarify.

That's how I had read it, can't answer why Art's observation may be the case or if what you proposed is actually the case.

[2manytoys]

Interestingly my pinging comes mostly from light throttle. The intake runner flaps would be closed...go SR71, that sounds ok to me

[ArthurPE]

a lot of good information, 'pats' for all!!!
I agree, deposits may make a bad situation worse when cold starting, but once warmed and running, especially under load, the effects diminish to the point of inconsequential
another good point SR71 made, the intake does not have as much to do with mixture swirling as the piston shape and movement...

one issue with this engine that it is a DI (optimized for injection right before TDC) but it operates in a homogeneous mode (fuel injected on the intake stroke vs compression stroke)

none of this would mitigate deposits, which in my opinion are caused by the valve seals seepage, nor would they offset the 1-2% power loss from extreme cases of deposits...

the SAE has a paper out on this very issue (actually all about DI engines) but a chapt on intake valve deposits...I'm gonna try to get my paws on it...

still, is the engine?
detonating, common and expected, but easily controlled
pre-igniting: bad, very bad
or mis-firing

let's remember, this is a high compression 12.5:1 engine, unheard of 10 years ago (race car domain) run on variable quality street gas...

it's an optimized system of compromises, not a perfect system

[ArthurPE]

Interestingly my pinging comes mostly from light throttle. The intake runner flaps would be closed...go SR71, that sounds ok to me

this may be the engine 'lugging', ie, load>output...
???

[2manytoys]

I'm not sure. When it first starting pinging it was random. By the end you could recreate it by very lightly (while moving) touch the throttle. It would ping for a split second.

I know it's been talked about before, but once the carbon was cleaned the pinging stopped. Believe me I tried to get it to ping, I didn't want a car that kept pinging. Now, about 5000km after the first clean, the pinging is coming back (it's random at the moment).

[pippyrips]

SR-71 for Prime Minister

That said, he's got so much time on his hands at the moment i would have expected him to have solved this ages ago

[pad125]

Without wishing to go off topic (and you can PM me with the answer Arthur if you wish) but coming from a 2-stroke tuning background, can you explain the difference between pre-ignition and detonation. All I know is that if you had one or the other on a 2-stroke you’d be lucky to get 200yrds before the engine ripped itself another asrehole, shat itself all over the track and left your wallet in tatters. Thanks