odd cold-start issue
 

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

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!

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?

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

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?

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?

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.

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

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

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!

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.

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

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!

Thermotime switch........
 

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

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.

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

Just for you........
 

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

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

Columbus, Ohio........
 

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

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:).

Tony come to Ohio - HA.

He's going to have to if his son and daughter-in-law are moving here.

OK, so I checked the cold start switch and it is functioning. I see about 26ohms across it cold with the wires pulled off it, did not check it warm though. I measured (briefly) 12volts as I hit the starter at the yellow wire and again on the other terminal post so I'm good there. I was looking at a post Vereeken had on AAR's and read that they should be wide open at 0 degrees C. I'll need to check that. I do know that at 16 degrees C it was about half way open and it does close after a couple of minutes with 21 ohms of resistance measured at the bi-metal. So assuming that the system checks out and that the AAR needs to be letting more air through to lean out the mixture so that the cold run rpm would be closer to 1800, how would I go about that? PS, my CCP was 1.3bar @ 14.2 degrees C which is within spec for the WUR.

Warren

AAR test........
 

Warren,

This is how I test the AAR. First measure the heating resistance (Ohms).
1). Place it in an oven @ 300°F for 15 - 20 mins. and observe if the valve has closed up. If it has fully closed, then it passed the oven-test.
2). Cool the AAR to room temperature and place it in the freezer for 30 mins. Observe that it has partially opened. If it has partially open (50%-60%), then it passed the freezer-test.
3). Allow the AAR to cool to RT (room temp.) and compare the aperture opening at freezing and RT. Insignificant difference. Apply 12-volt to the heater's terminals. Record the time (mins.) for the aperture to close. What I found out from numerous tests is that on the average, a good AAR would start to close approximately close to 4 mins. Some would take longer like 5 minutes.

The objective of the above tests is to determine if the AAR is opening or closing with thermal application and applying 12 volts to the heater. The actual time it would take for the AAR to close when installed on the engine is less than the bench test time. What is critical is the time it would take to close the aperture during cold start.

BTW, the AAR's do not open fully and never seen one that is fully open since I started investigating them more than 15 years ago. I have boxes of these AAR's that I have tested and used in the experiment. My data point is not based on a couple of AAR's but boxes of them. And still doing the tests as of this writing.

Keep us posted with your test results.

Tony

Tony,

I ran the AAR test when my problems first arose back in October the way you described above and the AAR checked out good. So at this point the only adjustment I'm going to make is to lean out the WUR just a little and see what happens. I'll do that tonight after work. I will also check throttle plate rest position and make sure that is correct.

Warren

the AAR has NOTHING to do with mixture. it does not lean it out, it only raises the idle when cold.
many people seem to have this misconception.

if you notice, both sides of the AAR are connected AFTER the AFM, so the air it bypasses around the TB has already been metered, or measured.

Very true. But very counter intuitive. Took me a while before my penny dropped!

Got it. The AAR is bypassing metered air that has already been accounted for. So I will lean out the WUR CCP a little and confirm the throttle plate rest position. Good news I already know what was too lean because that's what the old incorrect WUR was doing and I have the CCP data from that valve.

Thanks

how was the mixture set when you put the new WUR on

As I recall CCP was 1.3bars @14.2C. WCP was 3.5bars. I have not checked mixture. As I said above the car aside from this issue is running well. If I don't get the desired results from adjusting CCP then when I have access to a CO tester I'll be able to confirm mixture.

I am assuming your Thermal valve still works and is holding off vacuum to the WUR for about 30-45 seconds?

If that is the case and you do not mind resetting the CCP set it to 2 bar at that temp (I would even go as far as 2.5).

I know it is out of spec but I can only tell you by experience that it works on a 83 SC with a ROW engine and a 089 WUR. And I am not concerned about running too lean at that CCP since I have a AFM hooked up constantly.

Perhaps it says something about my engine but I do not know what as everything else checks out.

Michel

if your pressures are within spec, you may just need to lean it out a tad.

i dont know if tony modded your WUR so that it is adjustable or not, but you might go an 1/8 to 1/4 turn lean first.

V,

Thermal valve is working (got it with the WUR from Tony as it was missing from the car) and does hold off vacuum for 30 seconds. Set CCP last night to 1.6bar with vac on @ 13 degrees C. According to 089 graph I'm at the high edge of the range for that ambient temp. I let the car sit over night and started this morning b4 work. Started resonably well so I think I'm pretty close. Going to see Shank Racing tomorrow with the MOPCA so I'll get a chance to drive it with the new settings.

Warren

Ok Was that 1.6 with the vac applied or with the vac held off. I am willing to bet that with a CCP of 2 your car would start very well. I know it is against the graph, but it works for me....same car same temps, same WUR...

Michel

V,

I got 1.6bar with the vac on and 1.1bar with the vac off. I'll post a follow-up on this after I drive the car which is the true test afterall. I think though if I am any leaner I will start having issues with hesitation and backfiring through the intake (which I want to avoid for obvious reasons).

Warren

Warren

Vacuum test........
 

Warren,

When you get a chance, could you check if the idle speed drops down when you remove the oil filler cap off with the engine fully warmed up? Or pressure test for vacuum leak/s.

Tony

Tony,

Yes, rpm drops when I remove the oil cap. I've had a vacuum gauge on the system at idle and I get a nice steady 12-13" of vacuum at idle. Just out of curiosity, I left the guages on the system overnight and did notice that system pressure had dropped to zero when I checked it this morning. I had run the car last night around 9:00pm and have done a residual pressure test which was OK. Is it normal that the system would eventually drop to zero after an extended period of time?

Warren

I do not think that is a risk. The CCP is out of the equation after 3 to 4 minutes anyway. And at that bar setting I do not think you would be lean. Perhaps if the CSV would not work, maybe....but I let Tony comment on that.

I believe that the driveability of the car is linked with the WCP. I have mine also at 3.5 and I feel this is better then the 3.8 I had before....

Residual fuel pressure..........
 

Warren,

Yes. The residual pressure test determines the rate by which the fuel pressure deteriorates over time. As long as residual pressure stays up on the gauge for 20 - 30 mins. you'll be OK. After several hours (??), it would drop to ZERO. This is normal.

Tony

Thanks Tony and Vereeken. RP is good. As I recall last night, I finished testing and went in to watch TV for awhile. I came back out probably an hour and a half later and I think I still had better then 1 bar in the system.