Hard Start from cold

[JSV798]

Car is 1978SC. Hard to start from cold for quite a while when left for a few weeks. So decided to check out the cold start system. I pulled the fuel pump relay as I didn't want to start the engine. With a cold engine I disconnected the yellow wire at the Thermo Timer Switch (TTS) on the left hand chain case and connected a test lamp to the disconnected yellow wire with the other end on an engine earth. The test lamp wire was long enough for me to dangle the lamp over the right rear side so that when I turned the key to start the I could observe the lamp (car is RHD); it did not light.

I checked at the solenoid end. Here the yellow wire is actually soldered to the yellow wire from the ignition switch and both connected to terminal 50 on the solenoid, but I don't see this as a problem. I know it should be connected to terminal 15a.

I tried to trace the yellow wire back from the TTS and noticed that a similar sized yellow wire emerges from the wiring loom near the 14 pin connector at the left of the engine bay. There are 2 yellow wires in the 14 pin connector but these look to be both thicker. The yellow wire that emerges goes into a connector (see photo). There is continuity either side of this connector but nothing between this connector and the yellow wire at the TTS. I'm thinking of running a wire from this single connector to the yellow wire connector (G) on the TTS. Is this a good idea?

Roy

[PeteKz]

Check the connector to the CSV. The yellow wire goes from the starter solenoid to that connector first, then to the TTS. See if you have 12v at the CSV socket. If not, the wire is broken between the CSV and starter. I may be misremembering some of the details, but that yellow wire in the picture should go to the Sportomatic relay (if installed).

Do you have a wiring diagram?

[jimmyjimmy]

isn t that the yellow wire from the blower motor relay?

[JSV798]

Originally Posted by PeteKz

Check the connector to the CSV. The yellow wire goes from the starter solenoid to that connector first, then to the TTS. See if you have 12v at the CSV socket. If not, the wire is broken between the CSV and starter. I may be misremembering some of the details, but that yellow wire in the picture should go to the Sportomatic relay (if installed).

Do you have a wiring diagram?

I do have a wiring diagram (Haynes and Bentley) and know how the CSV and TTS work together, but the CSV is out of sight so started with the TTS. I can try and check the yellow wire at the CSV.

I'll also have another look at the yellow wires in the 14-pin connector.

Very interesting piece of information regarding the yellow wire. The car was originally a Sportomatic but was converted to manual long before I bought it in 1993: so I can ignore that particular yellow wire.

I am thinking that the wire to the CSV from the solenoid is broken and I am contemplating running another wire from the solenoid to the TTS.

[JSV798]

Update:
I now notice that there are two yellow wires near that 14-pin connector. There's the one in the photo and another one out of shot that is disconnected so that must be the Sportomatic connection.

I tested for voltage at the yellow wire junction in the photo and found that the test lamp lights when the key is turned to start, so this yellow wire is connected to the solenoid.

I decided to connect the yellow wire at this junction to the TTS and start the engine. It took the usual 4 or 5 goes to start and then continued to fast idle; normally the idle speed drops after a few minutes. So now I think I have awakened the CSV and it's stuck open! This would suggest the break is between the solenoid and the CSV as connecting to the TTS as I did would provide voltage to both the TTS and the CSV.

My thinking now is that if the CSV was connected to the solenoid it would have operated without the TTS being connected to the yellow wire as the TTS actually interrupts the earth to stop the CSV. So with no voltage at the TTS the CSV would always operate. I going to have to get the CSV out and check it.

Any comments on my reasoning would be welcome

[mike sampsel]

I believe the way it is supposed to work is the TTS forms a ground (when cold) this allows current to flow to the CSV. After some time, the TTS opens, and the CSV gets no current/voltage.

My TTS has a yellow wire and a red and black wire. if either are taken off of the TTS the CSV should not spray. if both wires are on the TTS, the CSV sprays until the TTS will opens up at temp and then the CSV is also not going to spay once the temp is reached.

The TTS is supposed to interrupt the earth at temp, not at cold.

[JSV798]

Originally Posted by mike sampsel

I believe the way it is supposed to work is the TTS forms a ground (when cold) this allows current to flow to the CSV. After some time, the TTS opens, and the CSV gets no current/voltage. .

Yes that agrees with my understanding. The TTS warms up and breaks the ground contact, interrupting the CSV. When the temperature is above 45 deg C the ground contact is broken and the CSV doesn't operate on a warm engine. When cold there is ground contact at the TTS so when the engine is cranked the CSV will spray. After a few seconds the TTS warms up and breaks the ground contact, switching off the CSV.

In my case there was no voltage on the yellow wire at the TTS and also I think no voltage on the CSV as the two are connected. Voltage arrives at the CSV first so can't have been getting there. When I connected the yellow wire from that connector to the TTS I think I awakened the CSV from a long sleep and it's now stuck open.

I'm going to have to remove the CSV and bench test it and clean it with carb cleaner. Not looking forward to getting it off with the engine in situ but believe it can be done. Anyone else done this?

Roy

[mike sampsel]

Originally Posted by JSV798

Yes that agrees with my understanding.

I'm going to have to remove the CSV and bench test it and clean it with carb cleaner. Not looking forward to getting it off with the engine in situ but believe it can be done. Anyone else done this?

Roy

Ive taken it off in situ. You need a good mirror to see what your doing to get it back on. Also, raise the car a few feet to protect your back. You'll want to get new o-rings for the fitting and the CSV.

A good magnet to fish out dropped stuff too. Tony likes to tie ropes to the allen wrenches to make fishing out a dropped one easier.

Enjoy, it's a lot easier with engine out. If it's spraying when activated, it seems unlikely the CSV is the problem though. Without power to it, does it spray? Probably not our you would be flooded and not start. Sounds like it's not the CSV to me.

[Funracer]

Originally Posted by JSV798

Yes that agrees with my understanding. The TTS warms up and breaks the ground contact, interrupting the CSV. When the temperature is above 45 deg C the ground contact is broken and the CSV doesn't operate on a warm engine. When cold there is ground contact at the TTS so when the engine is cranked the CSV will spray. After a few seconds the TTS warms up and breaks the ground contact, switching off the CSV.

In my case there was no voltage on the yellow wire at the TTS and also I think no voltage on the CSV as the two are connected. Voltage arrives at the CSV first so can't have been getting there. When I connected the yellow wire from that connector to the TTS I think I awakened the CSV from a long sleep and it's now stuck open.

I'm going to have to remove the CSV and bench test it and clean it with carb cleaner. Not looking forward to getting it off with the engine in situ but believe it can be done. Anyone else done this?

Roy

Ive done it too but my 83 has hard fuel lines and I thought it was a real pain. I believe you have flexible lines to the CSV? If so I have read somewhere (maybe from Tony?) it can be checked without totally removing it. Not sure of the procedure.
So its doable either way but not one of my favorite jobs. Any time you are using lights (dark back there) and a socket extension to get at something you can only see with a mirror you will need plenty of patience and flexibility. Long arms help too.

[JSV798]

Originally Posted by JSV798

Car is 1978SC.

Can anyone tell me where the red wire with white stripe goes (just visible on the right)? It came adrift when I unplugged the 14-pin connector. I think it came from one of the 3 fuses under the black cover, but which one? Lowest one? Middle one?

Roy

[mike sampsel]

Originally Posted by JSV798

Can anyone tell me where the red wire with white stripe goes (just visible on the right)? It came adrift when I unplugged the 14-pin connector. I think it came from one of the 3 fuses under the black cover, but which one? Lowest one? Middle one?

Roy

Bentley shows R/W from 87 pin on the relay to the Rear window (defogger).

[JSV798]

Update:

I did eventually get the CSV off. I attempted a partial engine drop to give more access but that resulted in one end of the engine support holding the bolt breaking off. I was able to undo the other bolt and got the support welded up. I found that by removing the blower motor and some brackets holding various hoses/cables both under where the blower motor attaches and round at the back where the CSV attaches and using a mirror I could get everything undone. I replaced the CSV with a used one verified as working from Tony. With everything back together I separated the yellow wires in the picture above; the bottom wire became live when the key was turned to start so I connected this to the yellow wire at the TTS. The CSV was now getting voltage from the TTS . And it worked: the engine started almost instantly, something it hasn't done for many years. I did need to use a piggy back connector on the TTS to preserve its correct function. There is clearly a break in the yellow wire from the solenoid to the CSV.

But the blower (ventilator) in the engine compartment no longer worked. I left this alone until recently when I decided I might need heat now that summer has passed. After some trouble shooting I found that to get the blower to work I needed to reconnect those two yellow wires. The wiring diagram bears this out but why is the heater blower switch connected to this yellow wire which becomes live only when the key is turned to start. How is the blower (ventilator) switch getting power? There are two yellow wires coming from the solenoid and the one that I was now using to power the TTS and CSV also goes off to join a number of other yellow wires including one to the blower (ventilator) switch. What is going on here?

Roy

[wazzz]

You are right, the yellow wire becomes live only when key is turned to Start and it is indeed connected to the blower relay coil through the blower switch. The other side of the blower relay coil is connected to Live (+12V). So the yellow wire actually provides a dummy ground to the relay coil, since the solenoid coil has a pretty low resistance and is itself connected to ground. In non-start situation, if the heater is switched on via the heater switch, the blower relay coil is energized and the blower is running. If you start (crank) the car, yellow wire becomes live (+12V) and therefore the blower relay coil is no longer energized, as it gets +12V on both its terminals (meaning it gets zero volts). That way, because all power is needed for the starter, heater blower is cut off temporarily. And so are other secondary car equipment, like AC.

I have posted diagrams with color explanations of this principle some time ago, but can't remember in which thread. Hope this makes sense.

[JSV798]

Originally Posted by wazzz

You are right, the yellow wire becomes live only when key is turned to Start and it is indeed connected to the blower relay coil through the blower switch. The other side of the blower relay coil is connected to Live (+12V). So the yellow wire actually provides a dummy ground to the relay coil, since the solenoid coil has a pretty low resistance and is itself connected to ground. In non-start situation, if the heater is switched on via the heater switch, the blower relay coil is energized and the blower is running. If you start (crank) the car, yellow wire becomes live (+12V) and therefore the blower relay coil is no longer energized, as it gets +12V on both its terminals (meaning it gets zero volts). That way, because all power is needed for the starter, heater blower is cut off temporarily. And so are other secondary car equipment, like AC.

I thought something like this must be going on. I was still have trouble seeing what happens when the key is in the run position. I notice that on the wiring diagram that the blower relay gets it power from fuse 22 which is live when the key is in run, but I was not seeing where the earth was. Then I noticed that it must be earthed at the solenoid terminal 50 with the current going through the winding of the solenoid to earth. I fact I connected that (upper) yellow wire when it was disconnected using my test lamp to earth and the test lamp glowed faintly and the blower started up. It would seem that terminal 85 on the blower relay doesn't need much of an earth.

Thanks for clearing this up.

Roy

[Schulisco]

A hard start is not only caused by a non working TTS & CSV. You wrote "after sitting some weeks": That's why I suspect far more that the WUR control pressure is out of spec together with a bad check valve at the fuel pump and probably some more things are still not right.

Even without a TTS & CSV must a 911SC start. Not so easy as with them, sure, but it has to.

So - for further steps of investigation - pls. define more precise the "hard start": how long does it take to start the engine on which ambient temps? Do you have to push the throttle? Does it remains running after start? Does it surges? Best option is to create a video and put it online here for us to see and hear ...

Background information: Curse and blessing of the CIS that they will run somehow for many years while all parts running out of spec over time. Then almost everything is worn out and culminates in several issues, like a bad start and/or poor performance and gas mileage, bad hot start etc. and then people start to tune this and that without knowing what they do...and in the end almost everything needs to be overhauled. This is the point when it gets expensive ... and people getting annoyed and cuss CIS and replace it with carbs or modern ECUs...
That's the point where you you've pulled the short straw... just for your understanding...

Thomas

[boyt911sc]

Roy,

I suspect that the problem you are having is happening @ terminal #16 (starter solenoid). Either terminal #16 is compromised like loose connection or have an open line. You could test and confirm the problem testing the continuity between terminal #16 (starter) and terminal G (@TTS).

Tony

[JSV798]

Originally Posted by boyt911sc

Roy,

I suspect that the problem you are having is happening @ terminal #16 (starter solenoid). Either terminal #16 is compromised like loose connection or have an open line. You could test and confirm the problem testing the continuity between terminal #16 (starter) and terminal G (@TTS).

Tony

Back in 1997 while on holiday in France the solenoid failed and a local garage obtained and fitted a Bosch replacement. I think the mechanic did some rewiring as now the yellow wire that should go to terminal 16 is actually joined to the yellow wire that comes from terminal 50. This looked OK to me but could this be the problem? I'm not getting my test lamp to light when it is connected to the yellow wire at the TTS (when key is in start position). I'm definitely getting current from terminal 50 (when key is in start position) as detected at the lower yellow wire in that photo. At the moment on my "fix", current is flowing from TTS to CSV (when key is in start position) not the normal route.

Roy

[wazzz]

It seems that the solenoid for SC (starting in 78) is different from earlier years. In 77 and before, yellow wires were all linked together, meaning that current for TTS and CSV was flowing through the ignition switch in Start position. This was may be prone to failures of the ignition switch, as it already had to feed the solenoid.

So starting from 78, it seems that a new version of solenoid was introduced, with a relay switch dedicated to TTS and the CSV. Now the yellow wires were no longer all linked together. There was a separate branch for the TTS and the CSV and another branch for the rest of the system as it used to be before (ignition switch, heater blower relay and solenoid).

My guess is that the local garage in France may not have received the new version of solenoid and had to deal with the older version and rewire it the old way.

See the schematic for 1977 that I am linking here. You can zoom on this file and get a detailed picture. Legends are in French but you can relate them to the English version. See as the yellow wire forms one circuit only, while the 78 version that I'm linking here has two separate circuits.

[boyt911sc]

Originally Posted by JSV798

Can anyone tell me where the red wire with white stripe goes (just visible on the right)? It came adrift when I unplugged the 14-pin connector. I think it came from one of the 3 fuses under the black cover, but which one? Lowest one? Middle one?

Roy

Roy,

It could be the red/white wire coming from Fuse #23 and going to the heater blower relay (J14) from reading the Porsche Shop Manual (SC wiring diagram).

Tony

[JSV798]

Originally Posted by boyt911sc

Roy,

It could be the red/white wire coming from Fuse #23 and going to the heater blower relay (J14) from reading the Porsche Shop Manual (SC wiring diagram).

Tony

Well it turned out that this wire powers the AAR. I left this wire unconnected initially and that was the cause of the high idle mentioned in post #5. I had disconnected the 14 pin connector when I attempted the partial engine drop and this wire came loose. When I connected it to fuse #23 (the lowest one) I had a functioning AAR again. So the high idle that I had attributed to a stuck CSV was a false diagnosis. There looks to have been some rewiring before my ownership (I've had the car 31 years) as there is some non-standard insulation on the thick engine harness in that region out of which that yellow wire with connector appears. At some point I will need to see what's going on there. I might find the break in the yellow wire to the CSV.

Roy