Cold Start When it’s Hot

[Funracer]

For those of you with CIS cars that live somewhere as hot as I do. It’s 98F (36.7C) here today.

Is a cold start (first of the day) the same as a cold start when its cool outside? By that I mean starts near instantly, goes to 1400-1500 rpm, then drops to 950-1000 over the next couple of minutes as the WUR raises pressure and the AAR closes.

My 83 stock CIS is not starting that way in this heat. Starts first or second crank, goes straight to 1000 rpm and stays there. Drives great.

I noticed that charted WUR “cold” pressures at very high temps are close to warm pressure specifications (both about 3.4 bar) so the WUR is already warm and already leaning the mixture. My AAR is never really open more that 1/3, but I am rarely able to check it under 40 degrees. At these temps it is less than 1/4 open to start and I would guess closes quickly.

So is this a normal cold start in very hot weather?

Thanks

[Alan L]

The CSV does not work above a certain temp. Not sure of exact number, but would be close to your ambient. You can check if the TS is working at that start by putting ohm meter across the switch terminals prior to start. Circuit = active. It is on or off for the start. The AAR is progressive. You can see if it is contributing by pulling the hose off and torch/mirror take note of opening in slit compared to warmed up. Or, remove and put on bench , apply 12V and watch if it closes.
Alan

[Funracer]

Originally Posted by Alan L

The CSV does not work above a certain temp. Not sure of exact number, but would be close to your ambient. You can check if the TS is working at that start by putting ohm meter across the switch terminals prior to start. Circuit = active. It is on or off for the start. The AAR is progressive. You can see if it is contributing by pulling the hose off and torch/mirror take note of opening in slit compared to warmed up. Or, remove and put on bench , apply 12V and watch if it closes.
Alan

Pretty sure all my components are working properly. CSV is new, and I have no problem starting cold or hot.

My question is, are the start characteristics of the 911 with CIS the same if starting in 35F as they are starting at 98F? It’s over 96 every day this week. My car is starting instantly then going immediately to 1000 RPM. Is this normal when its very hot outside?
Thanks

[Schulisco]

Originally Posted by Alan L

The CSV does not work above a certain temp.

This is true for the old electro-mechanic Thermotimeswitches. In the meantime Porsche/Bosch developed and sell the all new fully electronic version only. This version always let inject the CSV for approx. a second while cranking, independent on the temperature.

@Funracer: Did you checked both the control pressure and the fuel system pressure on your car? The cp on a warmed up WUR should comply with the specified values for your car.



And yes, in general the car should start "cold" on 98°F/37°C as good as it starts warm and ice cold. If your car falls to 1000 rpms right after start at 98°F it's okay, because the the increase of fuel due to lower cp on lower ambient temperatures is to keep the engine running when cold, because some of the gas condenses on the cold intake runners. When the ambient temps getting higher more and more less fuel will condenses at the intake runners less fuel is required to get it start and idling when cold. The increased amount of fuel on lower ambient temps also requires more air to get this burned, and therefore the idle rpms increase a bit. Also higher rpms when engine is cold helps the engine to warm up quicker.

Thomas

[Funracer]

CP, SP and WP are all within published limits. Sounds like my car is starting normally given the extreme heat. Thanks for your reply.