Engine missing when cold?

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GuidoK
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Engine missing when cold?

Post by GuidoK » Thu Jan 12, 2017 8:24 am

^ I dont agree with that for the full 100%.
First of all its not cold that induces wear, its lubrication (or lack of) and differences in tolerances.
Secondly, forces when driving (even when driving gently) are in an order of magnitude bigger than when idling.
Oil can take some time to refill all the passages, sometimes up to a half a minute or so (you can see that when you have had an engine apart and start it up again it takes some time to get oil pressure) . In that situation you want as little force on the wear surfaces as possible.
Also when things heat up more quickly, it means that some parts heat up more quickly than other parts as it takes time for heat to travel through the metal. That can mean that some things expand more quickly (due to heat) than other things that they wear upon to, changing clearances.
The general advice to drive straight away is that it causes less pollution. A heated up engine is less polluting, and driving straight away means you use the energy otherwise used as idling directly for driving.
There was once a video by engineering explained where the argument of when a car starts cold, it makes the mixture extra rich which can cause droplets of fuel on the cylinder wall infilcting wear and that more quickly heating up the engine will make the mixture lean more quickly.
In a way that is true, but all modern car has a so called open loop and closed loop state. In closed loop the mixture is adjusted to its need, and in that situation the statement of engineering explained is true. However, every car waits for around 50sec-1min for the lambdasensors to warm up to go to that closed loop state (without the lambda sensors working properly, it doesnt work). This is a set time (there is no temperature measuring involved). Until that time, the car runs in open loop. That means it has a non adjusted pre-set mapping that is thus not adjusted by the need of the mixture. The amount of mixture is injected by measurement of the inlet temp sensor/MAF and the throttle position and not adjusted by the lambda sensor (that can measure if all fuel is burned or not), so for that first 50 sec-1min the mixture is rich anyway, regardless of driving or idling. And if that preset mapping is set correctly, you get to the point that there is way less fuel in the cylinder cavety when idling than when driving, which means there is less fuel to condense on the cylinder walls and because less air (and less gas) is let into the cylinder all together (because of the closed throttle body), the vapour point is even more shifted, resulting in even less chance of fuel condensing on the cylinder wall.
That that guy didnt even mention closed or open loop says to me that he overlooked that. Only in closed loop the engine can lean itself out, but that only starts to happen 1 min after its started.

Thats my view on it anyway.
So when really cold, let it idle for about a minute imho.
Also a z4m will take a lot longer to get hot/to get to operating temperature because of the iron block (iron is a bad heat conductor and has more heat capacity, so it needs more energy to heat up and it gets that energy more slowly). This means heat is distributed more slowly through the engine.
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Engine missing when cold?

Post by pHilli0 » Thu Jan 12, 2017 10:37 am

TomK wrote:For me that doesn't sound normal at all. Mine is fine when cold, obviously treating it with a bit of respect. No flat spots or misfiring here.
When was the car last serviced op? Could be the sign of a plug or coil on its way out?
I'm with Tom. My engine is fine from cold, runs normally and no hesitation at all. It is not eager to rev much. I would say the transmission is terrible when cold but soon warms enough to be normal. Your describing a problem with the engine somewhere, something is not correct but it is being hidden. The S54 gets away with so much as people say it ticks, and does this and that, when actually they are avoiding a problem.
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Engine missing when cold?

Post by D4dawg » Thu Jan 12, 2017 11:04 am

Steve84N wrote:Letting it sit when cold before driving it is actually not the best thing for it as it stays colder for longer. Driving it gently straight away warms everything more quickly and it's when it's cold that more wear occurs.
Only meant a couple of mins buddy
As does damage to car otherwise:)
Just like oil to move around a few times
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Engine missing when cold?

Post by samZ4M » Thu Jan 12, 2017 11:18 am

Still get very flat spots at about 2600rpm. It does it long enough, I can put my foot to the floor and the engine just sits at those revs, then picks up slowly (at which point, I ease off the gas). When it's warm, at about 2800rpm the power changes for the better!

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Engine missing when cold?

Post by DMC63 » Thu Jan 12, 2017 12:03 pm

Doesn't matter how cold it is, car covered in frost and scraping windscreen. When I turn the key the car starts first time and purrs. No, judders, coughs or splutters. I keep it under 2500rpm until it's warmed up. An engine shouldn't start to play up because it's cold. I'd take it to bits, piece by piece and put it back together. If you have any parts left over and it still runs then it's obvious those parts were to blame. :thumbsup: Seriously tho' I'd get it looked at. That's not normal.
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Engine missing when cold?

Post by Steve84N » Thu Jan 12, 2017 1:47 pm

GuidoK wrote:The amount of mixture is injected by measurement of the inlet temp sensor/MAF and the throttle position and not adjusted by the lambda sensor (that can measure if all fuel is burned or not), so for that first 50 sec-1min the mixture is rich anyway, regardless of driving or idling. And if that preset mapping is set correctly, you get to the point that there is way less fuel in the cylinder cavety when idling than when driving, which means there is less fuel to condense on the cylinder walls and because less air (and less gas) is let into the cylinder all together (because of the closed throttle body), the vapour point is even more shifted, resulting in even less chance of fuel condensing on the cylinder wall.
How does it get to the point where there is way less fuel in the cylinder cavity by idling compared to driving? Driving achieves operating temperature more quickly and surely the preset map over injects fuel at all throttle positions? If you're driving more will be burnt and it's all relative so there will always be some left over. Yet, the most important thing has to be getting the engine warm ASAP?
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Engine missing when cold?

Post by Buckz » Thu Jan 12, 2017 2:00 pm

I don't find the engine that bad from cold! gear box is a pita sometimes tho :poke:
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Engine missing when cold?

Post by TomK » Thu Jan 12, 2017 2:15 pm

samZ4M wrote:Still get very flat spots at about 2600rpm. It does it long enough, I can put my foot to the floor and the engine just sits at those revs, then picks up slowly (at which point, I ease off the gas). When it's warm, at about 2800rpm the power changes for the better!
There is something very wrong with your motor then, it really shouldn't do that.
Have you not taken it anywhere to get it checked out?
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Engine missing when cold?

Post by GuidoK » Thu Jan 12, 2017 2:27 pm

Steve84N wrote: How does it get to the point where there is way less fuel in the cylinder cavity by idling compared to driving?
When the car idles the throttlebody is closed, so less air and less fuel gets into the engine. So the mixture itself might be in the same ratio, but there is just less of it :wink: . And because the manifold pressure is much lower, gas has less tendency to condensate and more tendency to evaporate (vapour pressure is higher at low pressure (cq. boiling temp is lower at low pressure)).
The higher the vacuum in the cylinder, the more the petrol wants to evaporate. and the higher teh vacuum in the cylinder, also the less petrol is injected in the first place.
Driving achieves operating temperature more quickly and surely the preset map over injects fuel at all throttle positions? If you're driving more will be burnt and it's all relative so there will always be some left over. Yet, the most important thing has to be getting the engine warm ASAP?
As long as the lambda sensors are in open loop, the mixture is not adjusted for running too rich or too lean. During that time (so that is the first 60 seconds, determined by the ecu) its best to let as little fuel and air into the cylinders as possible, because of the above reason.
Imho there is much more condensation of fuel when throttle is applied than when its idling. The engine may heat up more quickly, but during that time there is much more wear imho, from both more chance of condensation and far greater forces on the components.
Otherwise, why not give it full throttle? that'll warm the engine up much more quickly.
Especially the switch from open to closed loop is a big difference imho.

The reason a lot of people give that warming up your engine is a left over reminence (now myth) from the carburettor time, is for me a sign that those people have no idea what a choke is all about (every carburetted combustion engine has a choke). And at the later stages of the carburettorengines they got automatic chokes (bi-metal controlled)

In one story (about how its best not to warm up the engine) it said "The best thing to do is start the car, take a minute to knock the ice off your windows, and get going."
Why? :roll:
So imho: that minute gets the oil flow going, and gets the lambda sensors up to temperature (mind you, not because of the engine heat but because of its internal electric heater) and after that switchpoint, the engine can lean out its mixture accordingly by actually measuring the exhaust afr.
So the engine doesnt have to idle so long that its up to full operating temperature (that will take a pretty long time, at least 20 min or so), but that first minute is different because the ecu acts completely different.

But the ultimate question on what level is engine wear (and this is specifically piston ring wear or scoring of the cylinder walls) an issue on modern cars.
Most modern cars are discarded nowadays either because of rust or because of wear on various parts (suspension etc), but not often on piston ring wear or cylinder wall scoring (unless you have a porsche :lol: ).
Last edited by GuidoK on Thu Jan 12, 2017 2:51 pm, edited 3 times in total.
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Engine missing when cold?

Post by Steve84N » Thu Jan 12, 2017 2:33 pm

Would be interesting to see some tests around this. However, the reality is it probably doesn't make a big enough difference to GAF as otherwise we'd all have manufacturer's instructions to idle in cold weather. Not driving it hard until warm is just to limit the wear to acceptable levels as I'm sure it must not be a linear scale between revs/load and wear meaning modest use avoids most of the wear.
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Engine missing when cold?

Post by monaco_blue » Thu Jan 12, 2017 3:34 pm

I remember an article years ago about the showroom stock racing category in the US. This was a racing category where virtually no mods were allowed - literally cars as they came out of the showroom. Perhaps cages and seats but absolutely no engine mods. One very wealthy team experimented with how to get the fastest Corvette. Consistent answer was to drive it like you stole it from 0 miles. No break in, no warm up. Might not have done much for engine longevity but was the answer for most (short term) power.

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Engine missing when cold?

Post by jimmybell » Thu Jan 12, 2017 4:24 pm

Anyone else read this topic as 'Engine is missing when cold' ... maybe it doesn't like winter driving?
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Engine missing when cold?

Post by ga41 » Thu Jan 12, 2017 5:02 pm

jimmybell wrote:Anyone else read this topic as 'Engine is missing when cold' ... maybe it doesn't like winter driving?
-"It's how cold??? Right. I'm off mate, sort yourself out with a minicab or something, will you?"
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Engine missing when cold?

Post by MrPT » Thu Jan 12, 2017 10:35 pm

samZ4M wrote:Still get very flat spots at about 2600rpm. It does it long enough, I can put my foot to the floor and the engine just sits at those revs, then picks up slowly (at which point, I ease off the gas). When it's warm, at about 2800rpm the power changes for the better!
I take back my earlier comment. Mine's nothing like that - that's not right!
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Engine missing when cold?

Post by D4dawg » Fri Jan 13, 2017 12:02 am

Sam your cara not repeat not sounding healthy buddy!!
Should rev freely
Mine only is Lumpy for say 30 seconds and that's on a very cold day as air is cold more sense and damp

Get it to bmw

Ref this go from cold hhaha
Not in any of my cars too many mates in car world etc
Valve stems oil seals pistons etc etc all get abuse with no lube and gaps all bigger and risk of shattering bits when cold
Idle for a few mins drive gently:)
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