Cold Start-again

[starrbs]

Another question about the cold start issue. My 83SC has difficulty on initial start up when cold. I looked through the rennlist archives and sounds like a thermotime switch or cold start valve. I tried reaching behind the fuel injector lines on the pax side but couldn't feel any wires running to anything in that area. Am I missing something here, any other ideas or easy tests?

[lagoon]

Your cold start valve only comes on in relativly cold temperatures - i think 50 degrees. check your warm up regulator.

[wckrause]

The cold start injector works at a much higher temp than 50F. I think Warren posted in an earlier thread that it keeps working up to around 90F. He said that it ought to be called a "not-hot start injector"... anyway...

What are the symptoms of your car. Does it fire up, but then idle ruff? Or does it crank for a long time before firing? Does it ever backfire?



------------------
Bill Krause
'79 911SC Euro
MY PELICAN GALLERY

[starrbs]

Car History: It's been doing this for about a year, I've just been dealing with it. The car cranks for several seconds before finally sputtering to a start. It then idles fine, but won't take throttle for another 15-20 seconds. Recently replaced several injectors that were clogged/poor spray pattern, and this did not help. Car will start and run perfectly all day long after this initial start.

[wckrause]

I think your inclination to check the thermotime switch and cold start injector is on target.

Do you have the Bentley manual?



------------------
Bill Krause
'79 911SC Euro
MY PELICAN GALLERY

[starrbs]

I havent't been able to get a good deal yet on the manual, so unfortunately, no, I don't have one yet. Is this topic covered pretty nicely? Thanks for your input, by the way.

[wckrause]

There's a procedure for testing the thermotime switch, and the cold start injector.

Here's the thermotime procedure

------BEGIN BENTLEY---------

- Make sure engine temperature is below 45C (113F). Preferably engine should sit for several hours.

- Disconnect electrical connector from CDI control unit.

- Disconnect cold-start valve harness connector and connect a test light across connector terminals.

- Have a helper actuate starter while observing test light.

Test light should light for several seconds, then go out. (the amount of time the light is on depends on engine temperature.)
If test light does not illuminate, check for voltage at yellow wire at thermo-time switch with starter actuated. If voltage is not present, check yellow wire between thermo-time switch and starter.
If test light does light but cold start valve does not receive voltage, thermo-time switch is fault and should be replaced

- Reconnect cold start wiring connector and CDI control unit when finished.

-------END OF BENTLEY MANUAL-----

------------------
Bill Krause
'79 911SC Euro
MY PELICAN GALLERY

[SepiaBrown]

I am fighting the same problem. My mechanic first started with a fuel pressure test to see if the check valve in the fuel pump was leaking down, then the WUR, cold start valve and fuel distributor. This was after we thought the airbox was cracked. I installed a new airbox (the original was not cracked) and replaced the cold start valve then as well. Still a pain in the @#$&* on cold start! I replaced the WUR, had the injectors cleaned, put in new ignition wires, manifold runners, cleaned the throttle body, new fuel lines, and still the same. Of all the gin joints!!! I change out my fuel filter and that fine black river bottom sediment flows out. Oh my....My fuel tank is rusting out inside and gunks up my fuel ditributor! How much torture does one have to go through? Whats left I ask? I will try the distributor and thats the last straw. My 73.5 does not have the thermotime switch. Maybe you'll have better luck.

Regards
Bob
'73.5 T

[starrbs]

Thank you for your help with my postings, Bill. I'll copy the instructions and give it a shot this weekend. Maybe with a little luck and a beer or two, I'll get lucky. Thanks again.
Brian

[stormcrow]

Guys,

I have a similar problem with my 78 911 Sc Targa but I know what I did to cause it.
You may be running a little lean on your fuel distributor.

Before I did any adjusting on the fuel side, the car would start up with no problem. Stay at high idle and then drop down to 1000 rpm.

What I did was adjust the co2 mixture to lean out the car a little. You know, the little adjusting screw between the fuel distributor and the throttle body.

Ever since I leaned it out the car stalls on start up. It will start after the second try.

Now, if you adjust the fuel distributor, you may need to adjust your sensor plate also. When you do this, make a note where the settings are so you can use that as a starting point. Make small adjustments at a time on the fuel distributor first, and then on the sensor plate. When both the fuel and air sensor are adjusted right, the engine starts right up cold without stumbeling or sputtering. Hope this info helps.

Regards

Steve

[wckrause]

what adjustment on the sensor plate are you talking about?

You should get your mixture set using a exhaust gas analyzer.

------------------
Bill Krause
'79 911SC Euro
MY PELICAN GALLERY

[stormcrow]

If you look at page 256 in the haynes manual, item #34. There is an allen screw underneath to adjust the fuel mixture. Clockwise increases fuel, counterclockwise leans it out.

Steve

[wckrause]

OK, that's the mixture adjustment, that one I understand. What is the adjustment on the fuel distributor that you mentioned? I haven't heard of that one.

------------------
Bill Krause
'79 911SC Euro
MY PELICAN GALLERY

[stormcrow]

That screw does adjust the height of the piston inside the fuel distributor.

There is a piston inside the fuel distributor with slots in it. Each slot is for each of the lines going to the fuel injector.

When the piston is in it's normal position with the engine off, it closes off fuel to the slots.

When you start the car, the sensor plate lifts up ever so slightly and at the same time lifts the piston in the fuel distributor thus allowing fuel to go to the injectors.

The pressure inside the fuel distributor is controlled by the pressure regulator and the pressure bypass on the back side of the fuel distributor which goes back to your fuel tank.

Steve