Engine missing when cold?

GuidoK said:
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.
Click to expand...
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?
 
samZ4M said:
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!
Click to expand...
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?
 
Steve84N said:
How does it get to the point where there is way less fuel in the cylinder cavity by idling compared to driving?
Click to expand...
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?
Click to expand...
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: ).
 
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.
 
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.
 
jimmybell said:
Anyone else read this topic as 'Engine is missing when cold' ... maybe it doesn't like winter driving?
Click to expand...

-"It's how cold??? Right. I'm off mate, sort yourself out with a minicab or something, will you?"
 
samZ4M said:
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!
Click to expand...

I take back my earlier comment. Mine's nothing like that - that's not right!
 
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:)
 
It is only for those 30 or so seconds it does it though. Literally off the drive, into 2nd, and hit 2600rpm (I then do pedal to the metal) to see if it's going to do it. Any other time it's absolutely fine and enjoys going through the rev range, it shouts to go higher. I'll see if I can setup my camera to record.
 
You must log in or register to reply here.
Back
Top Bottom