CIS Cold Start Trouble, ready for new ideas

[iboughta911SC]

Background: 81 911 SC, 12K miles on rebuilt engine. WAS starting immediately, cold, warm and hot. Cold, warm or hot, runs excellent, pulling fabulously. -Was at Porsche Palooza in Arkansas in November. February is my oil & filter change, but since it had been about 10K miles, I adjusted the valves (they were all still about .004). I installed new spark plugs too, although the Bosch I pulled out looked nice and evenly tan.

In January, I installed a new fuel filter and new accumulator - was having questionable 60 minute park warm start extra cranking required. I believe the accumulator solved that issue as it fires immediately upon cranking if warm or hot.

Trouble - no longer starts/fires during cold cranking. To get it to fire, I have to give it about 1/2 throttle pedal travel and then it catches and runs great with no drive-off hesitation, pops, etc. So once running, the idle goes to 1250rpm or so and after about 30 seconds, it drops to 1000. No drive away troubles, pulling normally.

So, went to the checklist found elsewhere in these forum pages.
WUR - I rebuilt and properly configured my WUR a few years ago. But I tested the cold pressure just in case: (‘81, US delivered, WUR p/n …090..)
Valve closed - fuel pump pressure - 74psi.
Valve open - 57F, vacuum pump at 14psi on intake port, fuel pressure is 26psi, which is basically in the middle of the range for 57F and this model WUR

Maybe a vacuum leak? - did a smoke leak test - no leaks.

Engine fully warm - very steady vacuum of 15 in hg at idle of 1,000.

Thought maybe the NGK plugs were the trouble - so I pulled them back out and reinstalled the tan Bosch but no help.

Further note: I had my hands around backside of throttle assembly checking connections hoses, etc. and didn’t find anything amiss.

Thoughts: It takes opening the throttle to get it to fire so the engine wants more air. Could my cold start injector be injecting for some reason (this morning it was 65 so the cold start injector should not be operating)? One thing I will try is to disable that injector.
Could a weak spark be not igniting the cold start fuel? (The plug wires are not new but recently cleaned light corrosion off the contacts of the rotor and dist cap, but again it runs so well once running.
More: A few years ago, I had the engine out to replace the intake manifold so I also tested the auxillary air flow and other cold start devices and they were working well.

Where to go from here? Thanks in advance for your ideas.

Charles in Dallaas.

[kevbo]

If you don’t have it already, pick up the book on Bosch continuous injections systems. Has all kinds of good info on what might be happening

[sigchuck]

I’m sure experts will chime in, but did you check to see if AAR (and AAV) are functioning? No idea how to check AAV, but AAR is relatively easy with a 12v source and freezer. I think they have a tendency to gunk up over time and the sliding disc may have stuck closed. I think it takes some creativity to get it off an SC runner, but you could probably check position of the disc with a mirror by disconnecting the big hose and seeing if it closes any more by applying voltage. I don’t think that they ever completely close, but you should probably see some movement on a cold/room temp engine vs 3-5 minutes of applying voltage.

Another Charles in Dallas

[PeteKz]

If it starts and runs well when warm, then rule out spark issues. It sounds to me like your cold start valve is not operating when cold. I think that when you give it about 1/2 pedal, that draws more air through the air sensor, which increases fuel from the fuel distributor, and then it starts. But you shouldn't have to do that.

I would check that the CSV is getting voltage from the thermo-time switch. If it is, then take out the CSV and apply 12 volts to see if it squirts fuel. Then report back here.

[targa80]

Disclaimer: I might be wrong but from my own experience, when the engine is cold (not run for at least several hours) there is no residual fuel pressure in the fuel distributor (FD) system. The cold start valve will open and inject fuel directly into the manifold to allow the engine to start before residual pressure has developed. Once the engine is warm the cold start is disabled and the FD residual fuel pressure has stabilized. Since you state the engine runs fine when warm and starts normally when warm how does it start after resting for 30 to 45 minutes? I would suggest you verify that the cold start valve is functioning properly.

[iboughta911SC]

ah ha! the Cold-Start valve is activated when engine temperature is below 113F. I thought it was much much lower such as 32F. I remember it incorrectly.
That combined with the idea that providing lots of throttle increases the fuel flow from the distributor, combined with easy starting when engine is not cold leads me to believe I messed up the connection back on the cold start valve when I had my hands back there. This morning I’ll get out there and first, check the harness is properly attached to the cold start valve.
If it is, then I’ll disconnect it, connect a trouble light across its contacts, disconnect the CDI, and have my wife crank the engine. I’ll be watching for the light to come on thus confirming the signal from the Thermo-time switch is working….or not working.

back in touch.

[iboughta911SC]

Ok, So I saw my blue harness connector on the cold start valve. Looked correct. Unplugged it, disconnected the ignition (as if engine would start on test cranking, haha). It is about 65F and I haven’t run the engine today. As my wife cranked the engine, the test light illuminated and turned off after about 2 seconds. Signal good to cold start valve. I plugged it back on (using a mirror and light), heard it snap in place, and gave it an extra gentle wiggle.
Enabled ignition, turned key and engine fired immediately! Yay! If anything changes in the next few cold start days of driving, I’ll report back.
Conclusion: While thinking about the fuel pump operation (during process of valve adjustment), I was trying to disconnected the air flow sensor kill-the-fuel pump switch (thinking about operation of the fuel pump, disregard this thinking).
By mistake, I had disconnected the Cold Start Valve but thought it was back in place properly, however, it must not have been seated properly making good contact.

Thank you for your ideas, Targa80, PeteKz, Sigchuck and kevbo.

Charles in Dallas.

[HarryD]

Glad you found the culprit.

This is a good lesson to others. When things stop working, revisit everything you touched recently. It is easy to forget to plug something in or not verify it is fully seated.

[PeteKz]

Ditto what HarryD said, and thanks for reporting back on problem resolution.

[iboughta911SC]

Guys, bringing this thread back to life. The 911 SC has not had my full attention in the last few weeks but I will point out, that 80% of the time, I’m having difficulty starting. I do have my WUR pressure set properly and believe the next thing for me to try is to change the Bosch cold start injector plug end. When I look at the female connectors of this plug, one side is missing part of the spring connection and what is left is suspect. I’m thinking it is time to make a jumper harness to see if my starting trouble can be solved. Is this a standard Bosch injector plug end I can get on ebay or other?
My plan is to run temporary new wires from the thermotime switch to this new plug, which of course I’ll connect to my cold start injector.
Thanks!

Edit: found this: https://www.fuelinjectionproducts.com/products/wire-connector-for-most-bosch-auxiliary-air-cold-start-valves-late-70s-on

[proporsche]

have you ever looked at the adjustment of the sensor plate and after the fuel mix.?

Ivan

[boyt911sc]

Originally Posted by iboughta911SC

Guys, bringing this thread back to life. The 911 SC has not had my full attention in the last few weeks but I will point out, that 80% of the time, I’m having difficulty starting. I do have my WUR pressure set properly and believe the next thing for me to try is to change the Bosch cold start injector plug end. When I look at the female connectors of this plug, one side is missing part of the spring connection and what is left is suspect. I’m thinking it is time to make a jumper harness to see if my starting trouble can be solved. Is this a standard Bosch injector plug end I can get on ebay or other?
My plan is to run temporary new wires from the thermotime switch to this new plug, which of course I’ll connect to my cold start injector.
Thanks!

Edit: found this: https://www.fuelinjectionproducts.com/products/wire-connector-for-most-bosch-auxiliary-air-cold-start-valves-late-70s-on

Charles,

What are your control fuel pressures (CCP & WCP)? When the engine cold, what is the WUR heater resistance (Ohms)? Thanks.

Tony

[iboughta911SC]

Originally Posted by boyt911sc

Charles,

What are your control fuel pressures (CCP & WCP)? When the engine cold, what is the WUR heater resistance (Ohms)? Thanks.

Tony

The heating element of my WUR is 20 ohms. Right in middle of range I think. (something such as 18-22 is acceptable?)

This morning at 65F/18.3C, my WUR is sitting at 26psi/1.79bar.
This is with 15 inHg pulled with my Mitivac on the WUR.
Fully warmed up, my fuel pressure is 46psi.

My 81 SC is a US delivered, still have O2 sensor and computer working.
I believe it should have a WUR ending p/n 090. But mine is a 089 with a vacuum port.

As I have said, this thing runs fabulously cold, warming up, and when fully warmed. When restarted while still warm/hot, it hits/runs immediately.

What I don’t have a record of is where my cold WUR pressure was prior to messing with it a month ago. I thought it was in my records from when I rebuilt the WUR a few years ago, but it isn’t.

[boyt911sc]

Originally Posted by iboughta911SC

The heating element of my WUR is 20 ohms. Right in middle of range I think. (something such as 18-22 is acceptable?)

This morning at 65F/18.3C, my WUR is sitting at 26psi/1.79bar.
This is with 15 inHg pulled with my Mitivac on the WUR.
Fully warmed up, my fuel pressure is 46psi.

My 81 SC is a US delivered, still have O2 sensor and computer working.
I believe it should have a WUR ending p/n 090. But mine is a 089 with a vacuum port.

As I have said, this thing runs fabulously cold, warming up, and when fully warmed. When restarted while still warm/hot, it hits/runs immediately.

What I don’t have a record of is where my cold WUR pressure was prior to messing with it a month ago. I thought it was in my records from when I rebuilt the WUR a few years ago, but it isn’t.

Charles,

You have the WRONG WUR. Using WUR-089 will not prevent it from running but your enrichment management would be severely compromised. Try finding a good WUR-090 and experience how a properly sorted SC CIS performs on the road.

If you are interested, I could lend you a WUR-090 that you could test on your car without any obligation to purchase. Send it back to me when you are done with the test.

Tony

[Walt Fricke]

Tony
You may recall that my '82 US replacement engine (purchased from someone in Seattle and shipped to me in Boulder in maybe 1990) had the 089. I think Charles mistakes the air vent for a vacuum port (the hose just allows the upper chamber of the WUR to connect to the filtered air which is above the throttle body).

This ran just great, at least before I started adjusting the WCP to try to get race air/fuel readings at high track RPMs. Eventually, a shop redid the engine and replaced with an 090 just because that is the parts book part for the model. Ran great with it, too.

Eventually, all I could figure was that the specs for the 090 for these small port US SCs might not be the right specs for an 089. The 090 presupposes the Lambda system and its controls of the CP, and doesn't need any altitude/barometric compensation other than what the Lambda provides.

But I don't believe it is just coincidence that two engines of reasonably well known provenance have the same "wrong" WUR. Anyone else seen this on these models? And up until recently, his engine ran fine with the "wrong" WUR. And still does, other than this starting issue. Maybe our Porsches are like our bodies - some of us have our heart on the right side, not the usual left? Still work just as well.

However, I'd put my $ here on an issue with the cold start system. If not the sensor (which is pretty easy to check), then maybe the plug issue.

[boyt911sc]

Walt,

WUR-089 and WUR-090 have similar control fuel pressures range and using them would not prevent from starting and running a motor. And some unsuspecting owners swear that the motors run GREAT! If that is the case, why are they here at the forum seeking help?

These two (2) WUR’s in particular are built and designed differently. One is vacuum assisted and the other one is non-vacuum assisted. They have different application and they are calibrated differently.

My reply to Charles’ PM was that he has the wrong WUR and if he believes the -089 is performing great, ignore my comment. Wished him the best.

Tony

[proporsche]

i`d start as i have mentioned with the basics that is adjust and check your sensor plate.Must be done on cold engine or empty fuel from the distributor..if the adjustment is off your fuel mix is off too....
On 1st pic arrow points to the unit pic to the right side of the plate.

[Schulisco]

I would give it a cross check with brake cleaner or start spray: Just one shot into the airbox (removed air filter) before start after sitting a night. If it right starts away as usual there might be a problem either on the fuel supply or the csv /tts side.
Did measured how long it takes the fuel pump to repressurize the fuel system while cranking?
On a hanging check valve or a bad / hanging fuel accumulator you probably experience the same behaviour. I don't think that the WUR is a problem while engine runs fine after a successful start. Nevertheless proper fuel pressure in spec is key.

Thomas

[pmax]

Originally Posted by iboughta911SC

Guys, bringing this thread back to life. The 911 SC has not had my full attention in the last few weeks but I will point out, that 80% of the time, I’m having difficulty starting. I do have my WUR pressure set properly and believe the next thing for me to try is to change the Bosch cold start injector plug end. When I look at the female connectors of this plug, one side is missing part of the spring connection and what is left is suspect. I’m thinking it is time to make a jumper harness to see if my starting trouble can be solved. Is this a standard Bosch injector plug end I can get on ebay or other?
My plan is to run temporary new wires from the thermotime switch to this new plug, which of course I’ll connect to my cold start injector.
Thanks!

Edit: found this: https://www.fuelinjectionproducts.com/products/wire-connector-for-most-bosch-auxiliary-air-cold-start-valves-late-70s-on

Yes, making sure the CSV functions reliably is the right plan when having cold start problems.

Many of these components are shared across the "CIS" variants in other makes (Delorean!) and models.

[PeteKz]

DANGER!! Schulisco and others: Do not use BRAKE cleaner! Some brake cleaners are hydrocarbons, but many (most in the USA) are chlorinated hydrocarbons. Burning those will generate phosgene gas. If you are not familiar, look it up. Even small exposures can cause permanent neural problems.

Bottom line: Use CARBURETOR cleaner (or starting fluid or something like that), not BRAKE cleaner.