Another cold start challenge

[keithbkeller]

Ok so here's the deal, This car (1981 911 SC) runs and idles perfect at warm to hot operation. The cold start is a mess. I don't see how any of the great recommendations I read on various threads could apply when the performance is so good at warm to hot operation ? I don't have any missfires, hesitations, stalls, or anything else once I get this baby warmed up. SO it must be the WUR Right? The car barely runs at cold start and dies out two or three times before it starts warming up. {Please help if you can}
Many Thanks! Keith

[Nick Triesch]

OK, my friends 84 Carrera did the same thing. Great when warm. Horrible warm up. After much testing it was found to be the brain. Yup!They cost a ton but he was able to locate a used unit. After the new computer was pluged in, the car went right back to a great startup and idle. Just like that. Nick

[keithbkeller]

The only thing that causes me confusion is that if the "Brain" is bad then how can the car run so good at every thing after warm up?

[RarlyL8]

The 911SC has CIS which has no brainbox ('84 Carrera has Motronic FI).
If your SC runs perfectly in all situations except start-up then yes the WUR is most likely the culprit. To test this you need a set of fuel pressure gages. There is a spec range which is dependent on temperature which you need to verify. I'll guess that your cold fuel pressure is on the high side which is lean. If so the engine will crank but not catch then when it does catch will chug chug to life with a low idle that improves as the engine warms. The engine will not respond to throttle inputs well until warm. If this is the case the fix is to press in the cold pressure plug on the top rear of the WUR while watching the pressure on the gage until it is in the middle of spec.

[steely]

Welcome Keith - The Brain, or DME has among other things some circuitry that is used during warmup to control the idle control valve (ICV). I am taking a guess here that this could be related to the issue that Mick mentioned. The DME is the heart of the L-jetronic injector control system introduced in 84.

You however do not have a DME or ICV, and your car uses the K-jetronic system - unfortunately someone smarter than me will have to chime in here to address your original question. But the WUR sounds like a logical start.

try searching here too.

(on edit - man I must type slow - see Brian's post)

[al lkosmal]

The 1st thing that I would check is that the cold start valve/injector is functioning. Verify that it is receiving 12V.....and if it does........does it spray fuel.....etc.?

If it does not spray fuel....well there you go. It could be a bad valve/injector.................or a bad thermotime switch, which provides the valve with 12v, depending on the engine temps.....................or the source of 12V to the thermotime................I.E. you may need to trace 12V back to the source to see what's up. A wiring diagram will be your friend.

regards,
Al

[mca]

Could be a vacuum leak.

I'd start with a CIS pressure test to make sure your pressures are within spec. This will help you determine if the warming element on the WUR is working.

Also, I'd pick up a oxygen sensor relay and install it. Keep the old one as backup. When mine started to fail it was only apparent during cold starts. That lasted for a week until it finally failed under normal driving conditions.

How long has this been going on?

[mca]

Also, if the car fires up then it ain't the cold start valve.

The OXS relay is under the passenger seat.

[boyt911sc]

Keith,

You got a very good explanation by Brian regarding your cold start problem about the WUR having a rather high cold control fuel pressure. First, measure the cold control fuel pressure. However, if the the CCP (cold control pressure) turns out to be good, the lean condition during cold start could be attributed to unmetered air or CSV (cold start valve) not operating. All the above tests could be done without running the engine. Keep us posted.

Tony

[mca]

Tony - if it cranks it isn't the CSV right? Sounds to me like it cranks fine but then dies.

[boyt911sc]

Originally Posted by mca

Tony - if it cranks it isn't the CSV right? Sounds to me like it cranks fine but then dies.

Craig,

What do you mean by 'crank'? Engine turning during start phase or engine idles momentarily and dies immediately? A fully charged battery could easily crank or turn an engine even with the fuel system totally disconnected. According to the poster, engine would run after several attempts during cold start. This could be caused most likely by a LEAN condition but we don't know unless we test the condition.

So what could cause this problem?
a). High CCP (WUR).
b). Unmetered air causing mixture to go lean (air leak).
c). CSV not injecting fuel during a cold start.
d). Or something else.

If the engine starts to run and stall immediately during a cold start, the CSV is working. So we need to test and verify.

Tony

[timmy2]

Go get yourself a pressure gauge set up, read the instructions and once set up provide the resultant numbers in bars:

Valve closed pump running pressure is what? (system pressure)

Valve open pump running pressure, wur unplugged pressure is?(cold control pressure)

Valve open pump running wur plugged in pressure?(warm control pressure)

Valve open after warm pressure check, turn off car and residual pressure reading immediately and then after 30, 60, 120 seconds and then 10 and 30 minutes?

This thread has some good info in it for hooking up the tester.
CIS pressure test, question

[keithbkeller]

Many thanks guys! I will have to buy the pressure gauges, I thought I would just take off the WUR and see what I can see as far as and contamints, gum, or crud in the unit visible to the eye. Is that not a logical first step??

[timmy2]

If the wur was gummed up you would probably have issues all the time. The device actually regulates the fuel pressure all the Time. The name wur is poor, it's a constant pressure regulator...
Get the gauge and the pressure readings and then go from there. Anything else is just guesswork without analytical tools.

[RarlyL8]

Keith,
Your issue is described as only occurring during cold start so that is where the focus needs to concentrate. I see palm trees and note your location so the Cold Start Injector can be eliminated as a possible issue; it is not even activated at your ambient temperature. There is nothing to see on the WUR. If you are confident that no vacuum leaks exist and that the AAR is functioning properly then measuring the cold control pressure is the next logical step. Adjusting is very simple with the gages attached. I'm going to guess that the part number on your WUR ends with -072 or possibly -090. I probably have one on the shelf if the degradation gets to the place where you need to swap yours out.

[keithbkeller]

Thanks Guys! I guess I can get the pressure guage at my local automotive store. Is there a certain type? Keith

[Bob Kontak]

Originally Posted by RarlyL8

I see palm trees and note your location so the Cold Start Injector can be eliminated as a possible issue; it is not even activated at your ambient temperature.

CIS Primer says 113F. Sitting in the sun should have no problem exceeding that where palm trees can grow. Phonix - In the shade will kill it.

[timmy2]

Buy the one from our host, it has the right fittings and you help support this awesome site...

[RarlyL8]

113°F must be a typo, that would imply the CSV is active when the engine is not fully cooled down. The CSV is on a thermo time switch which remains open until <15°C. This can be varified in the Porsche shop manual. Years ago when I moved from IL to AL the CSV was disabled from my engine as it is not needed in this climate.

One important thing we haven't covered is history. When did this condition begin, what symptoms occured as it progressed, and was anything done to compensate for the symptoms. If anything has been done to compensate it must be un-done to help find/fix the root cause or you'll be chasing your tail.

[keithbkeller]

I found that the #5 spark plug was loose then after tightening it I found that one of the cruise control vacume lines was unplugged. Now, as far as the cold start problem it has been getting worse since I started driving it again. But in fairness I have stored this car in my garage and have not use it much in recent years. I took off the WUR today and removed the back plate and blew it out and got some tiny particles of dirt out. Now that I have reinstalled it, it still coughs and sputters and eventually comes to life albeit only after the motor heats up a little. I don't think I have seen anything in my visual inspection of the WUR that indicates that it is even working. But I really am just a newbe to all this. Thanks, Keith