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Old 18th May 2010, 17:52   #1
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Default Cold start vs warm start, is there a difference?

I've noticed this on my OHC.

If i do a cold start and drive normally, the engine feels a bit detuned even after it has warmed up. It's only when i do a few high rpm runs does the engine get charged up.

But instead of ripping the car through the revvs, if i just come to a halt, shut off the engine and start it again (with a warm engine), it suddenly feels lively.

So is the ECU taking in different readings in these 2 cases? Does a warm start give the engine an aggressive map/setting?

I find it surprising how the engine goes from dull to ultra responsive with just a warm restart.

Shan2nu
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Old 18th May 2010, 18:02   #2
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During cold starts the ecu injects additional fuel to warm up the engine (warm up enrichment) this is typically in process till the engine reaches operating temperatures and has a minimum threshold limit. Also note closed loop will not come on till the O2 sensor is warm enough to start sending out signals. You will also note a higher idle rpm.

Hence when you switch the car off on a warmed up engine and if the minimum threshold is crossed with the O2 sensor warmed up it will work on closed loop. The idle RPM will be back to normal.
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Old 18th May 2010, 18:06   #3
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So the engine being more responsive after a warm start is normal is it? Coz i haven't tried this on other cars.

But what is confusing me is that after a cold start, if i keep driving the car normally (low rpm shifts) till the engine has warmed up, it still doesn't feel as responsive as compared to when i do a few high rpm runs or a simple warm restart.

Shan2nu

Last edited by Shan2nu : 18th May 2010 at 18:09.
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Old 18th May 2010, 18:08   #4
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Quote:
Originally Posted by Shan2nu View Post
So the engine being more responsive after a warm start is normal is it? Coz i haven't tried this on other cars.
Shan2nu
I also have noticed this in my car. If I stop the car and do a warm start, the engine feels more smooth.
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Old 18th May 2010, 18:13   #5
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Quote:
I also have noticed this in my car. If I stop the car and do a warm start, the engine feels more smooth.
Exactly. The engine revs much more effortlessly and needs less throttle input.

Shan2nu

Last edited by Shan2nu : 18th May 2010 at 18:16.
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Old 18th May 2010, 18:24   #6
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I have noticed one more similar thing.

Sometimes rarely during a warm start, I've to keep it cracking for about 3 seconds to get the engine started, the engine coughs up and starts - then the ride won't be smooth at all. To fix this, I have to stop the engine, restart it gracefully where it start in a split second. The ride becomes smooth then onwards.
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Old 18th May 2010, 18:32   #7
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One look at the title, and I thought it is do something with a database server or UPS

Quote:
Originally Posted by clevermax View Post
I also have noticed this in my car. If I stop the car and do a warm start, the engine feels more smooth.
Yes, I too have experienced it with my car (Palio 1.2NV - 5 years old). And, even feel the same about my Gladiator (3 years old). I used to think it had to do something with the ambient temperature in Pune (overnight temperature is about 15-20); glad to see some more people who "experience" these things (I hope you'll agree that it becomes very difficult to pinpoint / specifically explain what we "feel")


Quote:
Originally Posted by Psycho View Post
Hence when you switch the car off on a warmed up engine and if the minimum threshold is crossed with the O2 sensor warmed up it will work on closed loop. The idle RPM will be back to normal.
Actually what I have noticed during cold starts is that the tacho hovers above 1000 RPM and AFTER depressing the clutch to shift from 1st to 2nd, the tacho shoots upto 2000 RPM or beyond (even without any accelerator input) and thereafter, idling settles down to slightly above 1000 RPM. Whereas, during warm start the idling is slightly below 1000 RPM.

Quote:
Originally Posted by Shan2nu View Post
So the engine being more responsive after a warm start is normal is it? Coz i haven't tried this on other cars.

But what is confusing me is that after a cold start, if i keep driving the car normally (low rpm shifts) till the engine has warmed up, it still doesn't feel as responsive as compared to when i do a few high rpm runs or a simple warm restart.
Exactly - has this anything to do with the idling as experienced by me above?
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