CIS Cold Start Problem Did Pressure Tests Now What?

[WyattEarp]

I'm new to working on CIS and have done a bunch of reading. Did the fuel pressure tests with results below. Symptoms after.

1983 911 SC with 105k miles stock motor
WUR 090

4.7 bar System Pressure

Ambient air 67 degrees
1.0 bar Cold Pressure
1.25 bar @ 1 minute
2 bar @ 1:30
2.75 bar at 2:00
3 bar at 2:30
3.5 bar at 3:00 and holds steady there

1.7 bar 10:00 residual pressure and holds for over an hour

Problem is the car is either extremely hard to start or won't start when ambient air is less than about 70 degrees. When it gets into the 50s it usually wont start cold. It will crank and crank and sometimes sputter just a bit as I let off the key. Crank too much and smell fuel. If it does finally catch and run it will idle a little low for about 30 seconds. If I give it some revs it runs just fine. After running for a minute or so the car runs excellent. Revs great, idles great and then comes back to idle great. Once its been running even for as little as say 30 seconds if I turn it off it will immediately fire back up and run well at first turn of the key. All of this goes away if the ambient air is in the mid 70s and above with the exception of maybe a bit of a low idle when first started.

So looking at the charts in my Bentley it looks like system pressure is within spec of 4.5-5.2 bar. Residual Pressure is good being over 1.1 bar. Control Pressure warm is within spec of 3.4-3.8 bar. So looks like the problem is the cold pressree. Looking at the graph it says I should be at about 2-2.4 bar.

So where do I go from here knowing I have low cold pressure? What do I need to do to get it to start when its cold and cold outside?

[HarryD]

Is your cold start valve connected?

I had a similar problem with my car until I discovered the power connector for the cold start valve had fallen off. Plugged the cable back in and all is well.

If it is connected, are you getting power to it when you crank? It is powered by the same power feed to the starter motor and switched by the thermotime sensor on your timing chain cover. Is your thermo time sensor working?

If you are getting power, is the valve working? Not sure how to test.

Wiring diagram:

[911bruce]

Where is the cold start valve, mine does this occasionally.

[HarryD]

Originally Posted by 911bruce

Where is the cold start valve, mine does this occasionally.

On my 1973.5 it is behind the throttle body.


This thread may be helpful to the OP: 76' cold start valve troubleshooting.. need help

Testing a Cold Start Valve/Removal & Replacement

[HarryD]

Jim Sims posted this info for a 1973.5 911 and "should" be similar to your car.

Originally Posted by Jim Sims

…



FRONT TOP of 73.5T CIS




73.5T CIS Cold Start Valve (CSV). Should be same on SC.




… The line to the CSV is actually externally braided hose.

Cheers, Jim

[boyt911sc]

Wyatt,

What is the heater resistance (Ohms) of the WUR-090 when the engine is cold? Keep us posted. Thanks.

Tony

[juanbenae]

calling pmax and ADDvanced! this is a formal CIS string band request for you guys to hum your tune some. where ya?

[QueWhy]

Originally Posted by juanbenae

calling pmax and ADDvanced! this is a formal CIS string band request for you guys to hum your tune some. where ya?

Hahaha. They say carbs are too complex...

[tirwin]

Wyatt,

I’m not near the Bentley book but your numbers seem normal. Even if they were slightly off, it is doubtful the car would be as hard to start as you describe.

Tony asked a question. It would be good to follow up.

Good thought on the CSV. The cold start valve is the “7th injector”. It provides extra fuel on cold starts. It’s located on the back side of the throttle body. It looks like this:

https://www.pelicanparts.com/More_Info/91160610701.htm?pn=911-606-107-01-OEM&gclid=EAIaIQobChMItKOh4LaP3wIVlFmGCh23wQIyEAQYAiAB EgLdWvD_BwE

After CSV, I would start thinking ignition. When was the last time plugs, plug wires, cap & rotor were replaced?

If you pull the coil wire and you ground it (being careful not to get electrocuted) while a helper cranks the car, is there a strong blue spark? How does the car drive once warmed up?

[WyattEarp]

Originally Posted by boyt911sc

Wyatt,

What is the heater resistance (Ohms) of the WUR-090 when the engine is cold? Keep us posted. Thanks.

Tony

I did not test the resistance cold because apparently I am not smart enough to get the electrical connector off and didnt want to break it. Any tips on removal? I can make out a little metal clip that I can see on the drivers side of the plug but couldn't figure out how to release.

Originally Posted by tirwin

Wyatt,

I’m not near the Bentley book but your numbers seem normal. Even if they were slightly off, it is doubtful the car would be as hard to start as you describe.

Tony asked a question. It would be good to follow up.

Good thought on the CSV. The cold start valve is the “7th injector”. It provides extra fuel on cold starts. It’s located on the back side of the throttle body. It looks like this:

https://www.pelicanparts.com/More_Info/91160610701.htm?pn=911-606-107-01-OEM&gclid=EAIaIQobChMItKOh4LaP3wIVlFmGCh23wQIyEAQYAiAB EgLdWvD_BwE

After CSV, I would start thinking ignition. When was the last time plugs, plug wires, cap & rotor were replaced?

If you pull the coil wire and you ground it (being careful not to get electrocuted) while a helper cranks the car, is there a strong blue spark? How does the car drive once warmed up?

Seems pretty far off at cold. Bentley chart says it should be at about 2.2 bar where as I am seeing only 1 bar. ????????

CSV looks just about impossible to get off without an engine drop any tips on this?

Car run excellent after it warms up. Zero issues. Pulls strong idles smooth.

Plugs, wires, cap and rotor were replaced about three years ago and only have about 2k miles on them.

[tirwin]

Sounding more and more like something that is just starting related. The WUR pressures are only going to really come into play in the moments right after starting when the engine transitions from start to run state. You’re not getting past starting. It sounds like you’re fuel starved when cold. Cold air is more dense than hot air, so when the ambient air is colder you need more fuel to compensate for the fact that there is more air per unit of volume. Hence the reason for the CSV.

Once the engine has started, and the engine is cold, you are in the warm-up state. The WUR adds more fuel during this time and gradually backs off to normal running state once the engine is warmed up.

A lower cold control pressure means you’re getting a richer mixture on cold start. If everything else is functioning correctly you would just have some white smoke on startup and the smell of unburnt fuel in the exhaust. What you are describing is hard starting so while the cold control pressure is off, it is likely not the source of your problem. I would make adjusting the CCP a second priority at this point.

Getting to the CSV can be a pain. But the first thing to do is check the easy stuff. Someone already suggested making sure the connector on the back side is connected. Next step would be to verify power and ground. The CSV fires when certain conditions are met. Engine is cranking AND engine is cold. Do you have the Bentley? If so, do the diagnostics associated with the Thermotime Switch. If the TTS has failed the CSV won’t fire. The tests aren’t hard and the TTS is easier to access. The TTS is located on the left side chain cover housing in the far left corner. It has two wires going to it. If the TTS is good then it’s pointing back to CSV and you’ll have to verify CSV is firing when cold and cranking.

Getting to the CSV may require a partial engine drop. You may need just enough clearance to remove the “pope’s hat” and have some room to work.

To remove the electrical connector on the WUR just grab it by the base and pull straight up.

[WyattEarp]

Originally Posted by tirwin

Getting to the CSV can be a pain. But the first thing to do is check the easy stuff. Someone already suggested making sure the connector on the back side is connected. Next step would be to verify power and ground. The CSV fires when certain conditions are met. Engine is cranking AND engine is cold. Do you have the Bentley? If so, do the diagnostics associated with the Thermotime Switch. If the TTS has failed the CSV won’t fire. The tests aren’t hard and the TTS is easier to access. The TTS is located on the left side chain cover housing in the far left corner. It has two wires going to it. If the TTS is good then it’s pointing back to CSV and you’ll have to verify CSV is firing when cold and cranking.

Getting to the CSV may require a partial engine drop. You may need just enough clearance to remove the “pope’s hat” and have some room to work.

To remove the electrical connector on the WUR just grab it by the base and pull straight up.

Yes I have the Bentley manual. I saw the instructions on testing both the Thermotime switch and the CSV. I will get my hand back there and double check that the plug is on the CSV first and then run the test on the thermotime switch. Going to be a day or two before I can get to the tests and will report back.

[Bob Kontak]

Originally Posted by tirwin

To remove the electrical connector on the WUR just grab it by the base and pull straight up.

Isn't there a spring type clip around it? I never did understand those things and am always in there with a scriber type tool trying to remove the clip.

[stlrj]

Originally Posted by WyattEarp

I'm new to working on CIS and have done a bunch of reading. Did the fuel pressure tests with results below. Symptoms after.
So where do I go from here knowing I have low cold pressure? What do I need to do to get it to start when its cold and cold outside?

Check your thermo time switch and make sure it is connected. Next, check the red/black terminal to make sure it is grounded. If all checks out, it should fire up!


Cheers,

Joe

[tirwin]

Originally Posted by Bob Kontak

Isn't there a spring type clip around it? I never did understand those things and am always in there with a scriber type tool trying to remove the clip.

There is but I’ve never had difficulty disconnecting mine. It’s a statistical sample of one though so take it for whatever that’s worth.

[Bob Kontak]

Originally Posted by tirwin

There is but I’ve never had difficulty disconnecting mine. It’s a statistical sample of one though so take it for whatever that’s worth.

Maybe WyattEarp could test.

[pmax]

Originally Posted by Bob Kontak

Maybe WyattEarp could test.

It's just a spring clip, folks.

[pmax]

Originally Posted by juanbenae

calling pmax and ADDvanced! this is a formal CIS string band request for you guys to hum your tune some. where ya?

Originally Posted by QueWhy

Hahaha. They say carbs are too complex...

LOL, there are at least half a dozen regulars here who understand this inside out. Just sit back and watch them work.

I do want to add though that the resistance of the WUR does not affect the initial startup, it comes into play only after the engine springs to life.

[Bob Kontak]

Originally Posted by pmax

It's just a spring clip, folks.

You call it a spring clip. What does that imply? Just pull as Tim suggests? I have seen BMW spring clips that have a little press thingie to allow removal of the connector.

[pmax]

Originally Posted by Bob Kontak

You call it a spring clip. What does that imply? Just pull as Tim suggests? I have seen BMW spring clips that have a little press thingie to allow removal of the connector.

Disengage, release, pry out ... the metal clip on the sides then pull.


Here ... it's Saturday morning, why not