Cold start problem on 1974 911 2.7L CIS

[jeff m]

I have a mfi but the electrics are similar.
It works like this. you op the starter, 12v is sent to the Thermo time switch, it starts timing (it will remove a ground from other side of switch after a time delay to prevent excess fuel)
The starter also sends the same 12v to one side of a relay #52 the rear most on my car. the other side of the relay 52 gets the ground from other side of thermo time switch. Relay operates and sends 12v to op your cold start solenoid.

It's really two very simple circuits.

to test COLD car, I took the fuel feed from my cold start solenoid and directed it into a small container, ignition on press relay 52, you should gat fuel from your fuel hose.
Get someone to turn the starter, (put back the feul hose first)
and kneel down and watch the armature of relay 52 it should operate especially as you have a new thermotime switch.

If it doesn't operate then clean your 14pin plugs, Pins 1 & 7 on my car but just clean them all. if it still doesn't work repost. but be prepared to get your meter out!
good luck
Jeff
911T

[azasadny]

The original starting problem has returned. I managed to start the car after about 50 cranks and several loud backfires, then it started and ran great. I drove it about 60 miles to a Porsche event and I stopped at a gas station. Restarted the car with the first crank. After letting the car sit for 30 minutes, it's extremely difficult to start again. I'm goint to test the pressures using my recently acquired gauges. I'm going to search the PP archives for the testing procedure and take it from there. I'm not going to start replacing parts again and evidently my mechanic didn't fix the problem, so I don't think I'll be taking it back to him.

[Dana_Drury]

Um, Sounds to me like your Warm Up Regulator actually???

I had that exact same problem. As soon as I took it into my Porsche Mechanic he knew straight away, they replaced it and it starts great. Exact symptoms that you have. You should also replace the thermotime switch as well.

[jk911]

azasadny, when I read your post Its as if you are talking about my car !

I have a 1975 CIS 911 the set up is just like yours.

I have had and still have the exaxt same problem.

I have replaced every single part of my fuel injectionCIS system from new fuel pump right through to new injectors. 1.5 years later and my car is better but still not properly fixed.

I also replaced my cold start valve, thermo timeswitch, WUR, check valve everything, even a rebuilt fuel distributor and it still doesn't start easily when cold or at rest for >15 min.

Now my car starts for a second or two dies and required 3-4 tries before it starts (after a rough bit). Ie cold start is working.

I believe the problem with our cars is the fuel pump location. Is yours at the rear of the car like mine ??

Then you start it cold can you hear a little noisy fuel pump then it clears up ??

I believe my problem is the fuel between the pump and the tank runs back (just a bit) causing air to get in and then that cuases the starting problems.

Try filling your tank up FULL and see if that makes any difference. It should make a small difference.

I believe that If we moved our pump to the front near the tank that should solve our problem ! Correct me if im wrong .

[azasadny]

JK911,

Wow, now I'm really discouraged. You're replaced just about everything and still have the same problem I have, that doesn't bode well for me. My fuel pump is at the front of the car just behind the gas tank. I'm going to install a fuel pump check valve this week to see if that helps. Replacing the WUR helped because prior to replacing it I could get the car to start even if I sprayed starting fluid in the airbix, but yesterday I was able to start it after spraying the starting fluid in the airbox. Once the car "catches" and starts to run it idles smooth and it runs great. I just can't take it many places because if I stop for 30min or more, I'll have a very difficult time starting it and I'll usually get a few backfires before it eventually starts, pretty embarrasing!

I can't get the fuel line fittings loose on the WUR or fuel distributor to attach my newly acquired pressure gauge. If this continues, I'll have to get it to a shop that is knowledgeable about CIS, but so far in the 11 months I've had the car this is my only problem, but it's a PITA! Hope you get your worked out. Please let me know when you find out what finally fixes it. Thanks!

[jk911]

In 1974 fuel pumps were rear mounted which means someone in the past has moved yours to the front. ( I was planning on doing this to mine but if you still have a problem I might exclude any other possibilities first)

Does it buzz or make a load sucking sound at all when you go to start the car ?

Other possibilities for both our cars I have considered is a slight fuel leak in the fuel line going through the middle tunnel of the car.

Does your car smell like fuel at all ?

Mine does slightly but I have always attributed this to my open ventilation tube from my fuel tank ?

Another possibility is that our 74 -75 model 911's have this

[jk911]

In 1974 fuel pumps were rear mounted which means someone in the past has moved yours to the front. ( I was planning on doing this to mine but if you still have a problem I might exclude any other possibilities first)

Does it buzz or make a load sucking sound at all when you go to start the car ?

Other possibilities for both our cars I have considered is a slight fuel leak in the fuel line going through the middle tunnel of the car.

Does your car smell like fuel at all ?

Mine does slightly but I have always attributed this to my open ventilation tube from my fuel tank ?

Another possibility is that our 74 -75 model 911's have this


Number 20 A throttle pressure regulator
(hope that that is not the problem cause its not easy to replace)

Keep me informed, I will !

[azasadny]

jk911,

Thanks for the advice. I'm going to replace the check valve on the fuel pump one night this week. I just got back from a nice, spirited drive (to burn off gas so the tank will be as close to empty as possible). Any excuse I can get to drive on a beautiful evening is OK with me! I hope it's just the check valve and not the other parts that are hard to get to... I'll let you know how it goes, thanks again!

[jk911]

Sorry
For some reason I thought you had already changed the check-valve.

That's probably your problem !
Good luck.

Don't worry if there is fuel in the tank( you will never be able to get it all out anyway) just clamp the hose off with a handheld rubber tipped clamp you can buy from a hardware store.

What type of pump do you have ?

[ruf-porsche]

You Guys replace just about every components on the CIS system and you still have the problem. Did you guy do any testing before replacing the components and did you guys do any testing after you replaced the components?

The fact that you can start the car with starting fluid point to a fuel delivery problem.

You guys replace the cold start valve but did you test to see if the old cold start valve was bad? Did you test to see if the new cold start valve is any better? You can test the cold start valve by pulling it out and turning on the ignition switch to see if any gas is coming out of the valve(get a beaker or measuring cup to determine how much gas comes out before the thermotime switch cuts out the flow. If you have nothing than you have to determine if you have pressure or if the electrical connection to the cold start valve is the problem.

If the cold start valve is fine, you should check the position of the sensor plate when the engine is not running. Make sure that it is free to rise and fall. I know after thousand of miles, the sensor plate get awfully grungy. I use carb cleaner to clean it out.

Were the cars like this when you first brought them or did these problems started after you own the cars for a while?

[azasadny]

Ruf,
My car was purchased last June and always had a cold start problem since I've had it. I know this isn't the "proper" way to troubleshoot, but each time I replaced the suspicious component, the symptoms either changed or the problem went away for awhile. I didn't know how to test anything when I began this endeavor. I tested to determine the WUR was bad and my mechanic confirmed that. Now, I have a fule delivery problem and I'm going to figure out where it is. I have a difficult time getting to the parts (cold start valve was a pain to replace!) and I don't have the right tools, so that's a challenge. I'm learning alot in the meantime, but I'm getting closer to getting this problem resolved. The PO took it to the shop all the time and never did his own work, so he really wasn't able to tell me anything about the car.

[jk911]

Ruf
You have made a very good point.

I don't know if I am jinxed or the previous owner was very smart in offloading the car to an unsuspecting porsche fanatic novice.

I am no expert and but no longer a novice when it comes to the cis system. The guys at the porsche centre now know me on a first name basis . They perfomed the tests ateempted repairs a couple of times and $1000's later you are back at square 1 you either give up or attack it your self. I chose the latter option.

Porsche started me off by telling me the following form testing my car

System pressure = 3.75 Bar
Control pressure = 3.1 Bar warm & 1.8 Bar cold
Leak down test = 30 sec = 1.45 Bar

1 min = 1.0 bar
2 min = 0.75 bar
5 min = 0.7 bar
1 hour = 0.6 bar.

No voltage to Warm up Regulator. Relay for W U regulator was faulty. Recomend flush / clean injectors.

So I started by replacing these with new one's, and the story kept going as you can see from my previous posts.

My cold start valve now works. no doubt about it.


The only other thing I havent done since changing my fuel pump is adjusting the mixture. It was done 1 year ago with the old fuel pump !

But even that won't solve my problem of a bit of air in my fuel pump when starting up !

[ruf-porsche]

One thing my father taught me was that you need the right tool to get thing done. He was an ASE Mechanic working for Dodge, Chevy,and Chrysler dealerships his entire career. He help me synch the carbs on my 340 six pack Cuda. That car could really fly in a straight line. Probably could outrun Nash Bridge fake Hemi Cuda

He hated foreign car although when we brought him an Austin American he loved that car. Probably because it was one of the first front wheel drive car available and it had a 4 cylinder engine.

Most of what I know about cars is what I learn from my father. And the tools he left me I will always cherish

[ruf-porsche]

JK911 and Azasadny

Do your cars have popoff valves? If it does make sure the valve is seated correctly. I would also check to see if the expoxy at the base of popoff valve hasn't crack to allow a leak in the airbox. You can remove the air cleaner and spray some carb cleaner around the popoff valve while the engine is running to confirm if you have an air leak.

JK911 how do you know that you have air in the lines?
Do you use the hand choke when you start the car? (lever by the handbrake, not the heater levers) I know Azasadny is missing a few parts.

I don't remeber my 74 having a starting problem except when the fuel pump finally died.

[jk911]

Ruf

when I go to start the car after its been sitting for a while the fuel pump makes a buzzing sucking sound for a second or two then buzzes quietly as normal.

When i replaced the fuel pump my car started a bit better and progressively got worse again. I returned the pump back to the manufacturer who tested it and siad the pump was 100% o.K.

Im assuming its air that is causing this.

p.s I have emptied the fuel tank, replaced all fuel lines (except the tunnel lines), tank filter was as clean as a whistle.

[azasadny]

Guys,
I replaced my hand throttle lever and it's working fine. My fuel pump is original (I think) and I need to install the check vallve I have and I'll do this one night this week. My airbox has a pop-off valve and it's in excellent condition, no cracks or leaks. Once the car starts, it runs flawlessly with no backfires or misses. I replaced almost all of the vacuum lines last summer when I got the car. I can hear the fuel pump "buzz" when I turn the key and I always give the pump 10-15 seconds before starting the car. If I spray starting fluid into the airbox, the car starts right up.

[Dana_Drury]

But have you replaced your warm up regulator?

[ruf-porsche]

Originally posted by jk911

when I go to start the car after its been sitting for a while the fuel pump makes a buzzing sucking sound for a second or two then buzzes quietly as normal.

Im assuming its air that is causing this.

From what I can remember of my 74 that sound about right, inital buzzing sound from the fuel pump (to pressurize the lines) and then quiet buzzes afterward.

JK911 how long do you crank before the car start? Does it start immediately if you spray the intake with starting fluid?

Afterward does it run fine no hesistation, pull from 1000 rpm to redline?

Have you check the sensor plate location?

[azasadny]

Dana,

Yes, the WUR was replaced last month. Prior to that, the car wouldn't start even if I sprayed starting fluid in the airbox. Now, I have to spray starting fluid if the engine is cold or after the car has been stopped for 30min or so. The car starts immediately when "hot" (stopped for less than 30min).

[bigchillcar]

Hi Art,
Problem back, huh?

Hmmm...This could be a fuel check valve problem alright. From the sound of it, it isn't maintaining positive fuel pressure in the lines. Sounds like after sitting 30 minutes or more the fuel has escaped. I believe that our '74's have fuel pumps with an internal check valve. This could possibly indicate replacement...I'd try a search on the board for fuel pump/check valve, etc. You've replaced your thermotime switch, but I can't recall if you replaced the cold start valve it controls? It should operate when the engine is cold and could possibly explain why it's so hard to start unless really warm. You've replaced the WUR, but I never actually suspected it since the car ran well once started...that suggests a good WUR...it only takes over AFTER the car has started and serves to lean out the 'rich' starting mixture. My suspicions would center on the fuel pump/check valve or cold start valve hypotheses. Does the engine smell gassy or not after multiple starting attempts? Is the new hand throttle set correctly? You could check by holding down the accelerator a little with your foot to simulate. If that allows it to start cold, it could be your problem. Mine probably would struggle cold without the hand throttle being used. Remember, it has to be up and working for start - this is unique to the '74 - later editions have a vacuum valve to control starting and warm idle conditions...AAV I think is the name.
Ryan