PSE doesn’t turn in when first starting cold in open loop
05-07-2021, 01:28 PM
#2
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Because it's vacuum operated and there is no reservoir.
(edit)
To add a bit more explanation, the exhaust valves are operated by a vacuum drawn from the intake manifold, and the solenoids are normally-open, which releases the vacuum in the lines against the actuators, probably for wear purposes. Without a reservoir to store vacuum pressure to introduce to the valve actuators, the engine needs to build vacuum in the intake manifold before it can actuate the valves.
As far as why it takes it like 10-15 seconds to do so is not well explained by this though. Vacuum exists shortly after the engine is started. Could be a cold start emissions thing -- more flow, SAI, overinjection, all to get the cats up to temp -- but that's just conjecture on my part. Hasn't bothered me enough to investigate further. When I convert the valves to a proper dump instead of the crappy PSE setup I might look into this more.
(edit)
To add a bit more explanation, the exhaust valves are operated by a vacuum drawn from the intake manifold, and the solenoids are normally-open, which releases the vacuum in the lines against the actuators, probably for wear purposes. Without a reservoir to store vacuum pressure to introduce to the valve actuators, the engine needs to build vacuum in the intake manifold before it can actuate the valves.
As far as why it takes it like 10-15 seconds to do so is not well explained by this though. Vacuum exists shortly after the engine is started. Could be a cold start emissions thing -- more flow, SAI, overinjection, all to get the cats up to temp -- but that's just conjecture on my part. Hasn't bothered me enough to investigate further. When I convert the valves to a proper dump instead of the crappy PSE setup I might look into this more.
Last edited by asellus; 05-07-2021 at 01:34 PM.
05-07-2021, 10:27 PM
#3
PSE appears to be disabled on starts until the ECU lowers the idle speed after start.
Why the higher revs at cold start? I never have liked it due to wear and tear on a cold engine. Sure it’s emissions related.
Why the higher revs at cold start? I never have liked it due to wear and tear on a cold engine. Sure it’s emissions related.
05-07-2021, 11:48 PM
#4
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If you're worried about wear and tear on a cold engine, start it up and go out and drive it right away like you're supposed to!
05-08-2021, 07:17 AM
#5
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Originally Posted by BSO
Why the higher revs at cold start? I never have liked it due to wear and tear on a cold engine. Sure it’s emissions related.
05-08-2021, 10:46 AM
#6
It has been documented for some time that most engine wear occurs on cold starts, and while heating the cats for emissions is needed, I'm not convinced that those higher revs when cold are inconsequential.
Cold starts in colder climates has been mentioned as a factor associated with cylinder wall scoring (if credence is to be given various forum posts on the topic).
The other issue is that many experience valve train noise on cold start, if the car has been sitting for a few days, not happy with that either. Prior to owning my 911, the only cars that I saw this on were high mileage cars with worn valve trains. When this happens, I drive quite sedately until the noise dissipates.
Luckily, my 911 rarely sits that long. Right now it is sitting, as the "love bug" season is in full swing where I live. My SUV will fill in the role of "love bug" killer until the swarm subsides (lasts several weeks).