Cold start issue. Can someone help?

Elu · 08-25-2005, 06:16 AM

I have a 1974 911. The engine and trans , a 2.7 liter, rebuilt about 32000 miles ago. The engine is strong and runs great. However, when I get in it in the morning it wont turn over right away. I always have to pull the choke all the way up and let the fuel pump run for about 30 seconds and then a short turn of the key. Sometimes it starts the first time to a spatter and chug until it clears it's throat and sometimes I have to do a short turn of the key two or three times after letting the pump run.

I have read a few posts on this but none really seem to help me out. My pressure regulator was just replaced...brand new so I know that's not the issue. I know there is a cold start sensor in the fuel injection mechanism and I'm wondering if it may need to be replaced.

Or....does the 2.7 liter engines just do that when they are cold??

Can someone...preferably someone with some great knowledge help me out? My mechanic doesn't seem to notice the issue and or doesn't find it unusual.

Tooth911 · 08-25-2005, 07:21 AM

Iam know expert however Ive had a 77 2.7 could be a combination of little things.But first thing is to have a shop check fuel pressure when cold (wich means leave car overnight) and untill warm to verify all components are in order. Cis is very touchy but works great when adjusted properly.

azasadny · azasadny's Garage

Elu,
Mine does the same thing and I've learned to live with it. I replaced my WUR, all vacuum hoses, all ignition components, etc... and after spending all that time, effort and $, I still have to crank the car a few times to get it to dstart when the engine is cold. After the engine has warmed up, the car starts the first time, every time. Check your hand throttle and be sure the plastic lever isn't broken. Mine was broken and i replaced it and it seemed to help for awhile, but then the "cold start stubbornness" returned. It's not too bad and I can live with it...

Elu · 08-25-2005, 11:58 AM

bump

Jim Sims · 08-25-2005, 12:27 PM

Read this thread for more insight into your problems:

911 73T CIS issues

Were the CIS pressures (cold and warmed up) checked when the WUR was replaced? What about the fuel pump output?

Jim

Elu · 08-25-2005, 12:47 PM

Thanks Jim...I'm gonna take a look

Jim Sims · 08-25-2005, 12:48 PM

1974 CIS diagrams (In figure 2/3/1 item 24 is the CSV and item 10 is the microswitch):

It Fires...with a little help! Fuel Line Question

Jim

Elu · 08-25-2005, 02:32 PM

Jim,

you don't happen to have the legend for the diagrams do you..or at least know where I might find them? I could really use them. I have found a few wires disconnected back that way, not to mention a few vacuum lines not connected as well. I would have thought the mechanic would have gotten that one. crap. See what happens when you dig in too far??

azasadny · azasadny's Garage

Jim,
What does the microswitch (#10 in the diagram) connect to?

Jim Sims · 08-25-2005, 05:50 PM

"What does the microswitch (#10 in the diagram) connect to?"

In what sense? Mechanical or electrical?

Jim Sims · 08-25-2005, 06:05 PM

"you don't happen to have the legend for the diagrams do you"

I have them but they're not scanned into electronic format. The legends mainly list part name, Porsche part number and sometimes the size of a hose or size and strength grade of a fastener. They do not show wiring hook up; one needs to consult a wiring diagram for that information. There is a usable wiring diagram for a 1974 in the Haynes manual. The exploded parts diagrams (what I posted and referenced in the thread) show the hose hookup; some of the hoses are vacuum but several also are fuel. In 1974 there are only a few electrical connections to the engine CIS system: WUR heater wire, CSV connector, microswitch connectors and connectors to the thermal time switch. Perhaps I can answer your questions.

Jim

Early_S_Man · 08-25-2005, 08:41 PM

Elu,

I suggest checking Voltage at the Thermo-Time Switch pictured below ... the Yellow wire should have +12 Volts during cranking, and the other should have continuity to ground when engine is cold.

azasadny · azasadny's Garage

Jim,
I don't know what the electrical connections to the microswitch should be as mine is disconnected. I have difficulty reading electrical schematics, especially the electrical connections to that particular microswitch.

bigchillcar · bigchillcar's Garage

elu,
old cis cars have a reputation for being hard 'cold starters' in general. these cars lack electronic ignition, etc. and we've become rather spoiled by modern, more sophisticated engine management systems. in other words, don't be too hard on your car..it won't ever start like a new one. that said, the hand throttle, which you incorrectly refer to as a 'choke', is simply a mechanical link to the throttle cable. all it does is move the cable (watch your accelerator pedal) some as if you are holding a little 'gas'. for starting: the hand throttle is SUPPOSED to be in the full up position. a warm car won't require this, but a cold one definitely. check for calibration of the hand throttle at a temperature of 180 degrees - pull it all the way up and see what rpm it gives you. it should be in the 2500-3500 rpm range. if not, there is an adjustment that is made (try a search) that will allow it to be reset..also it's possible that the hand throttle has 'disintegrated'. it is made of plastic and they sometimes fail. you need this part if you have a hand throttle equipped car for your cold starts. good luck!
ryan

bigchillcar · bigchillcar's Garage

art,
i believe that the thermotime switch reports temperature of the engine, and depending upon that, ultimately a signal is generated that fires the cold start valve. again this is working solely from memory. the microswitch plays a role in this too..i'll need to pull my books back out to refresh my memory though..
ryan

Jim Sims · 08-26-2005, 05:49 AM

See the referenced threads; one of them has a detailed description of the CSV circuit (including microswitch) and troubleshooting including wire color, at least for a 1974, but I believe the wiring colors are valid over several years.

hbf · hbf's Garage

If your car starts fine when warm then check the cold start fuel injector.

It squirts fuel into the inlet to richen on start. It is located at the back (front?) of the airbox near the throttle mechanism.

It only works if the throttle is depressed or if the hand throttle is raised. these two mechanisms close the little micro switch at the throttle stop which activates the injector. Additionally it is wired to a circuit to the starter motor so it only works while the engine is being cranked.

If the injector is not working then it is likely to be the electrical side of the circuit, not the fuel side.

As I remember it, the 74 has an electric temp cut out in the injector circuit so that the enrichment does not happen when the car is warm. Check this as well.

It sounds like your car is not getting the fuel it needs from the injector to get the engine running. Fuel from the fuel distributor can only flow to the cylinders if the air plate is raised. The air plate is only raised if air is being drawn through the inlet. Air is only drawn through the inlet if the engine is running. So, to get the engine running when cold, it needs a little help from the inlet injector. From the description above you will realize that the cold start injector is not dependent on the air flow so it can give the engine the initial fuel to allow it to run and so get air flowing and the mechanical CIS system working.

My 99k engine starts sweetly every day of its life, hot or cold.

bigchillcar · bigchillcar's Garage

nice explanation, ray..succinct and to the point.
ryan

Elu · 08-26-2005, 07:15 AM

you guys rock!

I am going to check the thermo time switch first. So if what I have read is correct and I've even looked at my Haynes manual...which never really says much...pulling the "Throttle" all the way up will turn on the micro-switch which will only spray fuel when the thermo time switch sends the signal that it is cold, and only during start up, (the starter cranking) which will tell the micro switch to spray.

Am I correct?? I will check with a volt-meter that the thermo time switch is getting power during the crank and if it is getting the power, then I will check the secondary side of the thermo time switch to see that it is sending power on the red and black wire to the micro switch. And, if power is not being sent through the red and black wire, I need to replace the thermo time switch??

I did find all the vacuum line connections. Someone had disconnected the vacuum line to the distributor and the one to the auxillary air intake. The aux air intake was plugged on both ends. Why would anyone want to do that?? However after doing this I need to adjust the idle because it is slower now.

vash · vash's Garage

that lever isnt a choke, right?

i dont think it is the thermoswitch. if it was, the 30 second pump wouldnt make a diff.

i think you need to hook up CIS gauges for an educated guess