odd cold-start issue

[wolds]

So I've had my 83SC ROW since August and with the cold weather upon us found some cold -start issues. The initial issue was a lean start when the engine was cold and ambient was around 50 degrees. This issue has been resolved with your help in a previous post and was due to having the incorrect WUR installed on the car. Tony sold me the correct 089 WUR and now cold engine/ambient temperature diveability is very good. The issue I have now is that after the car has sat overnight in a 50 degree garage the engine cranks freely, but tends to not start as quickly as when warmed up which is darn near immediate. It will crank and sputter to life after maybe 5 seconds of cranking. So hears the odd thing. I drove the car to Chicago over Thanksgiving and had to park the car outside for the three days I was there. I was expecting to have a rough time starting the car because morning temperatures were in the high 20's. To my relief the car started quite easily all three mornings... Last night back home and in a 50 degree garage I had the same issue with a prolonged crank before start. I haven't checked the cold start switch or the cold-start valve yet, but I thought I'd post this and get your response and or ideas as to what's going on. The car runs great otherwise and gas mileage is good so this appears to be an isolated issue.
Warren

[jeffs9146]

I am having the same problem and I am thinking it is the cold start sensor is sticking in the warm position until the temps go low enough to free it up!

[wolds]

So when you say "cold start sensor" you're talkng about the cold start switch which I'm assuming is a thermistor. Is that right?

[Bob Kontak]

You ought to be able to test it on the car - the thermo-time switch - with a multi-meter across temperatures.

[wolds]

I'll try that tonight. I'm suffering from sticker shock on what it will cost me to replace if it's defective. Am I right in thinking that this is a thermistor or is it some type of bimetal divice?

[T77911S]

if it started fine in the 20,s, its not the CSV system. make sure your pressures are correct, and that the mixture is set properly.

it never hurts to change plugs,cap and rotor. in fact, thats a good place to start with bad running/starting.

starting in the 20,s makes me think it is too rich, making the 50's harder to start.

when it does start in the 50's, any surging after it starts?

[wolds]

Did a complete tuneup back in August when I got the car along with filters, etc. When I installed the WUR a few weeks ago my CCP and WCP were within spec (don't have those values in front of me). Some surging on startup, lasts for maybe a minute or so. So you're thinking I might want to lean out my CCP a little more? Makes sense. I'll still check the thermo time switch and plot the voltage rise across the terminals as the engine warms up.

[T77911S]

you still need to check pressures first. never make mixture adjustments to fix something until you have done that.

[wolds]

T, did the pressures when I installed the valve, just don't have them in front of me at the moment. Makes sense though that I may have the CCP set too rich for the given ambient. If the TTV checks out OK, I'll probably reset the WUR CCP leaner and try that. If it won't take throttle then I'll know I've gone too far towards lean.
Warren

[jeffs9146]

This sensor measures the temperature at the engine's timing chain cover on the left side. Interestingly enough, this switch also has positive current going to it, which makes it act as a small heating element as well. It only stays powered during cranking and the heating element signals it to stop sending power to the cold-start valve if the engine does not start after much cranking -- to avoid flooding the engine.

I would guess if the switch is stuck in the warm position it will be signaling to stop sending power to the cold start injector thinking the car is already warm!

[wolds]

My understanding of how the TTS works is that as engine temperature rises it stays closed for an ever shorter period of time until at its upper limit (not sure what temp) it remains open and therefore eliminates the path to ground for the CSV (so the valve doesn't open) to prevent flooding the engine.

[Vereeken]

The TTS plays with the make/brake ground of the CSV.

The TTS works under starting only and for a maximum of 8 seconds regardless if the engine has started or not.

The TTS is also out when the temperature is 40 degrees celcius.

I remember your other post well. It always struck me as odd that you had good start at 50 degrees F with a CCp of 0.5 bar.
I never managed to get a good start at that low CCP with a 089.

One thing also worh checking is the rest position of the air flow sensor.

I have the impression that this piece is vital for start-up. The Porsche manual calls for a setting that can not be off by more then 0.5mm. I think of all the CIS specs that is the spec with the tightest tolerances.

Michel

[jeffs9146]

As I said, I have the exact same problem. It isn't a problem except when the temp is between 50'-60' F! Other than that the car starts and runs great all the time!

It always starts on the first click and warms up fine except when it's at that perfect morning temp where it turns over about 5-6 times before firing. Once it starts you can hear it stumble for a second and something catches and all is good again!

PS: My car is kept in a garage and in the central valley, California!

[boyt911sc]

Originally Posted by wolds

My understanding of how the TTS works is that as engine temperature rises it stays closed for an ever shorter period of time until at its upper limit (not sure what temp) it remains open and therefore eliminates the path to ground for the CSV (so the valve doesn't open) to prevent flooding the engine.

Warren,

The TTS is grounded (close) when engine temperature is 45°C/113°F and below. So even if you live in AZ or NV, you would still need a CSV from time to time. When the engine is warm (113°F+), the TTS would have an open ground contact and would not allow the CSV to activate during start. Plus the built-in heater on the bi-metallic would limit the operation of the CSV between 6 - 7 seconds based from testing a few TTS.

Since you had changed the CCP setting that I made on the WUR prior to delivery, I would suggest that you check the fuel pressures. As you mentioned, the car had no problem cold starting in Chicago, so the CSV and TTS were both working.

Do not tweak or tinker the mixture setting unless you have confirmed and tested the absence of significant vacuum or air leak in the system. Once you have done this, check your fuel mixture preferably with a gas analyzer.

Could you re-state for me your current problem/s regarding cold start? Thanks.

Tony

[T77911S]

just to be clear.

the problem has exsisted since the new WUR from tony, correct?
you checked pressures on the new WUR, correct?

have you checked residual pressure? how are hot starts?

check the mixture.

tony if you are reading, i have a task for you. check to see what temp the TTS opens and closes. knowing you , you have already done this.

[wolds]

T,

Not to confuse the issue more, but let me add this bit of info. Currently when I am doing a cold start my initial rpm is around 1100 (after warm-up it settles in at 950). I checked out my AAR when my initial cold engine drivability issue came up (early October). At that time the AAR (which is correct for the car) was opening and closing, but at 50 degrees ambient I would say that it was open about 50%. At that time if I started the car cold and ambient @ 50 degrees with the connectors pulled on the WUR and AAR I was getting close to 1800rpm (which sounds right for a cold start). So now I am seeing a lower initial cold rpm. If the AAR was bypassing more air my now rich mixture would become leaner and my rpm would go up. Does this train of thought make sense? If it does, maybe the issue is with the AAR, not my CCP pressure which as I stated earlier is well within the recommended pressure according to the 089 warm-up graph that Vereeken supplied. So, what can be said about this?

Ain't this fun? Warren

[boyt911sc]

Originally Posted by T77911S

just to be clear.

the problem has exsisted since the new WUR from tony, correct?
you checked pressures on the new WUR, correct?

have you checked residual pressure? how are hot starts?

check the mixture.

tony if you are reading, i have a task for you. check to see what temp the TTS opens and closes. knowing you , you have already done this.

Ty,

Look very closely at your TTS. Stamped on the side of the TTS is the operating temperature. Like most TS (temperature switch) that we use in 911, the spec is indicated on the device.

For example:

Thermotime switch (911-617-117-00-M100) has 45°C (113°F) stamped on it. You could test the device if it is open or close at room temperature or heat the TTS to see if it opens up. Energize the TTS and it would switch off after several seconds.

I sent the WUR to Warren that I personally set at lower CCP than the chart shows. So a few days after installing the replacement WUR, Warren contacted me about the slightly lower CCP. So I asked him if there was any problem with it because I could replace it with a higher CCP. He said no and works fine except he wanted to make the CCP higher. He inquired how he could do it. Explained to him the method I use for adjusting the CCP. End of story.

So I'm eager to see what Warren finds out with his troubleshooting.

Tony

[wolds]

Hey Tony,

When are you coming to Ohio? Stop by and I'll buy you dinner or something. Ya, I didn't notice initially that I was having a starting issue which is why you are just hearing about it now. This is not a major issue as the car will start. I am just trying to smooth out these start irregularities that's all.

Warren

[boyt911sc]

Originally Posted by wolds

Hey Tony,

When are you coming to Ohio? Stop by and I'll buy you dinner or something. Ya, I didn't notice initially that I was having a starting issue which is why you are just hearing about it now. This is not a major issue as the car will start. I am just trying to smooth out these start irregularities that's all.

Warren

Warren,

Very soon. My son and his wife have 2 houses to chose and close the deal.

With regard to your engine, the hardest part is getting a stone cold engine to start on demand and you are well ahead of the game. The rest would be fine tuning. Check you ignition system, vacuum leak, and keep track of your control fuel pressures.

The TTS is very sturdy and they last for many many years. So I doubt if you have any related problem with TTS & CSV. I hope you have not tinkered your fuel mixture setting (?). PM me if you have any question at all.

BTW, the cross country drive from Philadelphia to California in 5 days was a blast covering more than 3,000 miles of hi-way driving. The '87 Carrera performed flawlessly.

Tony

[wolds]

Tony,

No, I know better then to mess with the mixture. If the car was exhibiting other drivability issues I would question the mixture settings, but she runs very well. Took her to Chicago over Thanksgiving to show her off to my sister, b-law, and kids. Put on 1000 miles with no issues. What a great car.