Cold start problem on 1974 911 2.7L CIS

azasadny · azasadny's Garage

My 1974 2.7L CIS has developed a cold start problem. The car requires 5-8 cranks before starting when cold. I have replaced the cold-start valve and o-ring (not fun!!!), checked all vacuum hoses, CIS unit, air box and hoses, rotor, Pertronix "points replacement", plug wires, 2 month old Perma-Tune CD unit, new engine wiring harness, new Bosch plugs, etc...

The problem has progressed from intermittent to "constant", but only when the car is cold (having run less than 10 minutes). Once the car is warmed up, it starts and runs beautifully. Since the cars runs so well, I have not been too aggressive with adjustments, replacements, etc... Everyting seems to be tight and secure, but the cold start problem is starting to drive me crazy.

The car is getting fuel and spark, so something else is going on here. Could it be the warm up regulator? Any other suggestions? Thanks!!!

Early_S_Man · 03:25 PM

The primary device controlling the cold-start valve is the Thermo-Time Switch ... located on your left chain cover ... as shown by the somewhat grungy one in the pic below ...

You can remove it and perform bench tests on it ... between the body (ground) and Terminal 'G' is a heating element that should measure 20-30 Ohms. Between Terminal 'W' and ground are thermostatic-controlled switch contacts that should be closed at room temperature. If you monitor Terminal 'W' while applying + 12 Volts to 'G' and ground ... the contacts should open within two minutes or so.

azasadny · azasadny's Garage

Early_S_Man,

Thanks for the info and helpful picture. My Thermotime switch has two wires connected to it, I noticed that when I redid the wiring harness in the engine compartment. I'll take a look tomorrow and let you know what I find. Thanks again for everything!!!

john walker's workshop · 09-24-2002, 03:46 PM

just to clarify what you mean by start, the starter cranks the engine and it begins to fire. that's the starter, and the cold start valve doing their thing. the warmup regulator takes over from there, and allows the engine to run richer so it won't die repetedly and spit and pop until it warms up. so does it not even fire, or just run crappy and die a lot until it's warm?

azasadny · azasadny's Garage

John,

The engine turns over, but the car requires at least 5-8 trys before the engine runs. It doesn't sputter or run rough at all. The car idles at 1000rpm when cold, but occasionally idles fast 2000rpm) after warming up. The engine acts like it "wants to start", and is getting fuel and spark. Do you think it's the Thermotime switch?

john walker's workshop · 09-24-2002, 06:27 PM

if it runs well when it finally starts, the warmup regulator is probably ok. there's a micro switch with yellow wires that closes as the throttle is just opened, to complete the circuit so the cold start valve will work. it's on the left side of the throttle housing. do you open the throttle just a hair when you try to start it? you gotta do that on the early CIS cars.

azasadny · azasadny's Garage

John,

I open the "manual throtle" lever next to the emergency brake when I start the car cold, but it doesn't seem to help. I'll check all of the wires, connections, etc... today. Maybe I knocked something loose several weeks ago when I replaced the cold start valve?

Dana_Drury · 09-25-2002, 05:11 AM

My throttle level doesn't seem to do much either... hmmmmm

Hladun · 09-25-2002, 06:26 AM

For the n+1+1 time, the thermotime switch must be wired correctly or it doesn't work! It's not just a case of two wires to two terminals!

azasadny · azasadny's Garage

I just checked everythign out. The wires were nice and tight, but there were two wires running to my thermo-time switch and I disconnected one of them (the one that was originally disconnected when I got the car this summer) and the car started on the first try!

Evidently, one of the two wires to the thermo-time switch don't belong (I think it was red with black stripes, but I'm severely colorblind, so I'm not 100% sure). I'm wondering why there are two wires there in the first place. The PO had the wiring pretty mucked up and I had to rewire alot of it and I completed the work in early July. Over the past month, the intermittent cold start problem progressed to "constant" and several weeks ago I replaced the cold start valve, but the problem persisted.

I've ordered a new thermo-time switch from Pelican and I'll replace the ratty-looking one, but I'm curious about those wo wires.

You folks are absolutely incredible, the sheer knowledge you have, along with your willingness to help other "cluless newbies" like me is awesome. I can't thank you enough! My wife is impressed that I haven't had to take the car into the shop and pay some guy named "Johann" in a white lab coat big bucks to fix things! I promised her that I would do as much of the repair/maintenance work myself as I could and you are helping me keep my promise! Thanks again!!!!!

azasadny · azasadny's Garage

Hladun,

I agree with you 100%! I just need to figure out how to properly wire the thermo-time switch. I am colorblind and don't have a wiring diagram that I can decipher (yet). The PO had the wiring looking like a couple ferrets played with the wiring and I've been (very, very carefully) redoing the wiring, one wire at a time, so as not to complicate things...

mperkins · 09-25-2002, 08:00 AM

i had the same problem for months.
should the problem creep up again on you...
install a new check valve in your fuel pump.
the piece costs about $20 from Pelican.

good luck,
Maurice
1980 SC Coupe

Hladun · 09-25-2002, 08:16 AM

CIS Cold Starting Solution

Early_S_Man · 09-25-2002, 08:46 AM

The two wires for the Thermo-Time Switch have two DIFFERENT-SIZED spade connectors ... so the power lead for the heating element can't accidentally be connected to the switch contact! One lead has a normal 1/4" Faston, and the other is a smaller 0.187".

azasadny · azasadny's Garage

Thanks for the advice. I just experienced the "cold start problem" again, but not as bad as before. I'll check the wires (two different spade connectors) and possible replace the check valve on the fuel pump (per mperkins). I'll get it fixed.... eventually...

azasadny · azasadny's Garage

Mperkins,
I just checked, my 1974 doesn't have a fuel pump check vavle, that's for 1980 and newer engines, so I guess I'm starting from scratch again... Thanks for the help!

Bobboloo · Bobboloo's Garage

Your thermotime switch should have a red and black wire that comes from the cold start valve connected to terminal W.

It should also have a yellow wire that comes from the throttle valve switch as well as a gray and white wire coming from the other side of the cold start valve connecting to terminal G of the thermotime switch.

As Warren stated the W connector has the larger spade.

Bobby

azasadny · azasadny's Garage

Bobby,

Yes, those are the wire connections/colors (I think, I'm colorblind). The cold start problem still exists so I'm thinking maybe the ThermoTime switch is bad, since the electrical connections to it are intact. I just ordered a new one from Pelican, so I'll replace it (sure looks easier than the dreaded cold start valve) and see if that helps... Thanks!!!

azasadny · azasadny's Garage

I replaced the thermotime switch with a new one from PelicanParts and the car starts much easier now. It occasionally takes more than one crank to start when cold, but only one crank to start when it's warm. I guess the thermotime switch was the problem. Thanks again to everyone for their assistance, I couldn't have fixed it without your help!

azasadny · azasadny's Garage

Oops, I spoke too soon. After all the work, the problem is back, but is now intermittent. Since I have backfiring upon starting (not all of the time and never after starting), I believe the problem is in the CIS system. I don't have a clue where to begin, but cold weather (and the accompanying salt on the roads) is coming, so I'll have to do the work when the car is stored for the winter...