car runs better before warm up?
Thread Starter
Joined: Sep 2002
Posts: 51,241
Likes: 20
From: NV
Rep Power: 813 
car runs better before warm up?
Has anyone else noticed how much better the car runs before completely warming up? I especially could tell during the summer. I was wondering if the ecu somehow alters the fuel mixture or changes the timing. Rumors were going around about something happening to warm up the catalyst faster. Any ideas?
it's not the less pressure typically, it's that the colder air is more dense, so it has more oxygen in it for the engine. Possibly after it warms up, the engine bay is warmer, slightly lowing power compared to right when you start up?
Yes, it's an Acura EL
iTrader: (23)
Joined: Dec 2002
Posts: 8,248
Likes: 0
From: 416-905, Ontario, Canada
Rep Power: 369 Someone once told me the ECU settings aren't really in full effect while warming up, hence air/fuel mix isn't ideal (rich? smells like it when starting up). I dunno, just something a friend told me. Does it make sense?
coolant temps are lower, therefore colder coolant is running through the throttle body and not heating up the intake mani.
also, engine bay is not warm, so cooler air running through there ...
also, engine bay is not warm, so cooler air running through there ...
Registered!!
Joined: Jun 2004
Posts: 24
Likes: 0
Rep Power: 0 
When you look at the fundamentals of the engines, engines would be more efficeint and producing more power when the temperature difference between the temperature of gas burning and outside of the engine(engine bay) gets bigger. (Does this make sense?) Anyways,
When the engine is not warmed up, the engine bay temperature is lower, but the burning gas's temperature won't change(of course when more gas is put in, it will be higher). For, example, if the gas burns at 400 degrees( assuming, dont know the exact temperature) and engine bay temperature is 70 degree, the difference will be 330. if the car is warmed up and engine bay temperature goes to 120, the difference is 280. so it concludes that when the car is not warmed up, it should make more power.
BUT. since car's are controlled with ECU, it's probably not true. What i said was just the theory of it. And plus i don't think it's good idea to drive hard when it's not warmed up, just like you cannot run right after you wake up in the morning. Everything needs warm-ups.
When the engine is not warmed up, the engine bay temperature is lower, but the burning gas's temperature won't change(of course when more gas is put in, it will be higher). For, example, if the gas burns at 400 degrees( assuming, dont know the exact temperature) and engine bay temperature is 70 degree, the difference will be 330. if the car is warmed up and engine bay temperature goes to 120, the difference is 280. so it concludes that when the car is not warmed up, it should make more power.
BUT. since car's are controlled with ECU, it's probably not true. What i said was just the theory of it. And plus i don't think it's good idea to drive hard when it's not warmed up, just like you cannot run right after you wake up in the morning. Everything needs warm-ups.
Registered!!
Joined: Oct 2004
Posts: 118
Likes: 0
From: Austin, TX
Rep Power: 0 When your vehicle is cold and coolant temperatures have not yet reached 180 degrees, youe ECU is in what is called "open loop." It is "open" since the circut is not complete, your ECU is running off of a set fuel map with no used feedback from your O2 sensor. This means that it is not adjusting for a stoiciometric 14.7:1 air/fuel ratio. More often than not, the open loop fuel map is tuned rich for safety in this aspect.
Once your coolant temperatures have reached acceptable levels, the ECU switches to Closed Loop and uses all the engine sensors to adjust fuel and timing trims to cycle the engine quickly between 14.5:1 and 14.9:1 to acheive an average of 14.7:1.
Stoiciometric air/fuel ratio is desirable since at this level the cylinder temperatures are too cold to produce many oxides of nitrogen (NOX), the combustion is also hot enough to cut down on Hydrocarbon emissions (HC).
To answer the question, you may perceive the engine to run better when "cold" since the ECU is using a richer fuel map and allowing you to burn a slightly better power mixture. However, during this time your engine is not operating efficiently. Also, keep in mind that your oil will not be up to operating temperature either, and will not lubricate bearings or your head as effectively as it should.
Once your coolant temperatures have reached acceptable levels, the ECU switches to Closed Loop and uses all the engine sensors to adjust fuel and timing trims to cycle the engine quickly between 14.5:1 and 14.9:1 to acheive an average of 14.7:1.
Stoiciometric air/fuel ratio is desirable since at this level the cylinder temperatures are too cold to produce many oxides of nitrogen (NOX), the combustion is also hot enough to cut down on Hydrocarbon emissions (HC).
To answer the question, you may perceive the engine to run better when "cold" since the ECU is using a richer fuel map and allowing you to burn a slightly better power mixture. However, during this time your engine is not operating efficiently. Also, keep in mind that your oil will not be up to operating temperature either, and will not lubricate bearings or your head as effectively as it should.
Registered!!
Joined: Oct 2004
Posts: 118
Likes: 0
From: Austin, TX
Rep Power: 0
Originally Posted by TeLLy
Someone once told me the ECU settings aren't really in full effect while warming up, hence air/fuel mix isn't ideal (rich? smells like it when starting up). I dunno, just something a friend told me. Does it make sense?
Originally Posted by MugenRacer
When you look at the fundamentals of the engines, engines would be more efficeint and producing more power when the temperature difference between the temperature of gas burning and outside of the engine(engine bay) gets bigger. (Does this make sense?) Anyways,
When the engine is not warmed up, the engine bay temperature is lower, but the burning gas's temperature won't change(of course when more gas is put in, it will be higher). For, example, if the gas burns at 400 degrees( assuming, dont know the exact temperature) and engine bay temperature is 70 degree, the difference will be 330. if the car is warmed up and engine bay temperature goes to 120, the difference is 280. so it concludes that when the car is not warmed up, it should make more power.
BUT. since car's are controlled with ECU, it's probably not true. What i said was just the theory of it. And plus i don't think it's good idea to drive hard when it's not warmed up, just like you cannot run right after you wake up in the morning. Everything needs warm-ups.
When the engine is not warmed up, the engine bay temperature is lower, but the burning gas's temperature won't change(of course when more gas is put in, it will be higher). For, example, if the gas burns at 400 degrees( assuming, dont know the exact temperature) and engine bay temperature is 70 degree, the difference will be 330. if the car is warmed up and engine bay temperature goes to 120, the difference is 280. so it concludes that when the car is not warmed up, it should make more power.
BUT. since car's are controlled with ECU, it's probably not true. What i said was just the theory of it. And plus i don't think it's good idea to drive hard when it's not warmed up, just like you cannot run right after you wake up in the morning. Everything needs warm-ups.
A good shot at it, since efficient combustion is soley determined by amounts of air and fuel. Normal cylinder temperatures can range from 2200 to 2400 in most vehicles. temperatures below that indicate a rich mixture, and temperatures aboove indicate a lean mixture.
With a cold engine and an ingress of colder air past the valves since the intake and intake manifold have yet to heat up much combined with a richly tuned closed loop ECU map is the exact combination you need for more power. More air and more fuel make more power (in proper ratios
) 
Originally Posted by ctx66
i wouldnt know.. i treat my car like baby untill the temp needle gets past a few white lines.. never over 3k until it warms up.. driving hard when the engines cold aint smart..
... and he had the sf turbo 
Thread
Thread Starter
Honda Civic Forum
Replies
Last Post
CarStuff
Safety/Security Items - SRS, Keys, Immobilizer, airbags, ABS
6
Dec 6, 2020 12:52 PM
mistermenphis22
Mechanical Problems/Vehicle Issues and Fix-it Forum
5
Apr 3, 2016 08:06 AM
