911 2.7s cold start problem

[adomakin]

hi, ive just rebuilt my '75 911 2.7s engine and it refuses to start from cold. if i use some easystart it will (after about 30 secs) catch and run on its own (although real lumpy for the first min or so) then when its been running for a couple of mins it wil idle real nice and rev pretty clean. is this a cold start injector prob? does the cold start injector get power as soon as the ignition is turned on or does it only get power when the starter motor is turning over? does anyone have any ideas?

Thanks

Andy domakin

[Targa77]

Did you verify the timing and the point gap/dwell angle?. My '77 had the same problem as your car until I set the timing to the correct setting. Now it fires right up in the cold. I would check this before suspecting the WUR, Thermotime switch, etc. One note: If you are using a Permatune CDS unit, you do NOT have to worry about dwell angle, just the gap.

[bonedaddy]

Can't argue with Targa77. Once you verify that ignition parameters are okay, if you still have the problem, either the cold start valve or thromo/time switch should be checked. Is the microswitch that energizes the cold start valve properly set? If that switch is not closed when you pull up the hand throttle, you won't get that extra dose of petrol on a cold start.

One easy way to bypass all the diagnostic steps is to unbolt the cold start valve and let it spray into a container to prove whether or not it's working. This is easier said than done, as it's very difficult to access. You have to stand on your head and use a mirror.

The warm-up regulator is also a possibility, but you'll need a test guage to really diagnose that possibility.

I assume the car was starting properly before the re-build, so I would double check all the wiring to the microswitch, thermo/time switch and cold start valve. Perhaps something wasn't reconnected? Let us know how it's coming.

[adomakin]

thanks for the info targa77/bonedaddy.
wots a WUR? wots a THERMOTIMESWITCH?!? and did that car in 'back to the futre' have one??!! also, i didn't even know i had a hand throttle! my car is actually a 68 with a 75 2.7 911 engine and 915 box. is the microswitch on the side of the throttle body?
sorry about all the questions!!!!

[Targa77]

These knowlegable fellas here will correct me if I'm wrong but the Warmup Regulator and the Thermotime switch help with cold starts. Your car will run rich initially so it can start and warm up properly (a cold engine requires more fuel to start). As it warms up, the thermotime switch will tell the WUR to start leaning the mixture out a little.
Like bonedaddy stated earlier, to test these, you will need specialized equipment/tools. The reason that I mentioned timing is that to rebuild your engine, you had to remove the distributor. If you didn't put the dist back where it's supposed to go, your timing could be off. If your timing is correct, then I would have the WUR , CO level and the T switch tested. By the way, you have checked the point gap? This will definitely cause starting/running problems.

[warment]

I'd check the "cold start solenoid" that sits atop the fuel filter on the left side when facing the engine. You can remove this thing and hot wire it up to a 12 volt battery to make sure that it moves correctly.

Bill

[wckrause]

As it warms up, the thermotime switch will tell the WUR to start leaning the mixture out a little.

Actually, the thermotime switch controls how long the cold start injector runs while starting the car. The cold start injector is a seventh injector mounted on the back of the air box. The thermotime switch has nothing to do with the warm up regulator. On some SC's there is a thermovalve which does work with the WUR on cold starts. The warm up regulator controls its own timing and will start to lean out the mixture as its internal bi-metallic bar heats up.

Get Probst's book on Bosch Fuel Injection. It's a good source for info on all of the different types of Bosch FI.

[Targa77]

Like I stated, these guys are the experts. Thanks for the correct info.

[bonedaddy]

Hmmm... I assumed you had a '75, but I believe the earlier models had a hand throttle also. If you do, it's mounted on the tunnel next to the heater control levers between the seats. When you pull up on it, a linkage engages a stop on the throttle rod located in the tunnel which has the same effect as pressing slightly on the accelerator. This moves the linkage on the side of the throttle body, slightly opening the throttle and simultaneously engaging the microswitch that is also located on the side of the throttle body. When this microswitch closes, it enables the cold start valve through the thermo/time switch. As stated in an earlier post, the thermo/time switch controls the amount of time that the cold start valve is active; it's located on the left chain housing cover. If you don't have a hand throttle, well...

Is this a recent transplant, or have you run the car before with the '75 2.7 engine? The answer to that question could help figure out what may be the problem.

[AUSTmike]

Hi Guys!..i have same problem too with the cold start valve!...I took out the cold start valve and tested it by hooking it up to a 12 v battery and all i get is one click sound and thats it!...so i'm not sure if the valve needs to be clicking continually or just the one click for it to work properly!...the next thing i did was to screw back on the fuel line to the cold start valve and placed the cold start valve in a glass jar and turned over the motor on a cold start to see if there is any fuel coming through the valve and there was hardly any coming out!...Off coarse i let the fuel pump run for about 10-15 sec before i cranked the motor....I think i have same issue with adomikin or it may be a separate issue.My nest test will be to test the wire that connects the cold start valve with a multi-meter to see if there is a current going to the valve!

[HarryD]

Andy: when the power to my cold start injector fell off, I had the same symptoms.

You need to study this web page. 911 CIS Primer - Index

I believe you will find most if not all of your answers here.

You CIS is like mine in most cases. You DO NOT have a thermotime switch, that was started ini 1976 and beyond. you need the hand throttle to start the car.

You DO NOT have a cold start solenoid, that was for the MFI system that CIS replaced.

[T77911S]

the CSV gets its power from the starter. start there. make sure the wire is connected and connected to the correct terminal on the starter.

then power goes to the CSV. they don't usually go bad. make sure it is connected.

then power goes to the thermo time switch (TTS) on the left front timing cover of the engine.
there should be 2 wires connected to it. the TTS provides ground for the CSV>

you need to verify fuel pressures.
cold and warm.
you could also check the inlet screen of the warm up regulator (WUR). if it gets clogged that will raise the cold control pressure (CCP).
also check for 12v at the WUR.

the CSV stops working after it starts. I would really look into a pressure problem if it runs bad after it starts and is cold.

dwell is not a big deal with these cars. the points are just a switch for ground to the CD unit.
just make sure the gap is close, maybe error on the big side. I always just eyeballed mine and it ran great.