911 sc cis residual pressure

[Schulisco]

The values I showed above are for the 930/10 (means ROW 3,0SC from '81-'83, no catalyst, no lambda control).

[boyt911sc]

George,

Where are you located? USA or Europe?

Tony

[leonardo911sc]

@ Tony

Just completed FD leak test with pump running. No leaks.
See relevant video.

https://youtube.com/shorts/7usraTLfN3Q?feature=share

The weird thing is that after this test the engine fired at first crank. (7 hours since stop) Engine temp was around 28 c so CSV was activated for sure.

Next is to check sensor plate alignment, just to confirm it's within spec.

Waiting for your comments.

Thanks

[leonardo911sc]

Originally Posted by boyt911sc

George,

Where are you located? USA or Europe?

Tony

Europe Athens Greece.

[leonardo911sc]

Originally Posted by Schulisco

The values I showed above are for the 930/10 (means ROW 3,0SC from '81-'83, no catalyst, no lambda control).

Thanks Thomas!

[Schulisco]

Weird, indeed.

I experienced a similar behaviour: I had to crank the engine much longer after the car was sitting a while due to an "emptied check valve" (no ball and no sppring inside anymore, therefore the fuel ran back to the tank; cranking that longer gave the fuel pump the time to refill the fuel lines) and the bad fuel accumulator as I wrote sooner. BUT: Still the engine started after a few seconds cranking....but your's won't start at all with the CSV connected...

You could check the CSV by plugging it manually with a switch to ground while the engine is running. If the CSV works, it will inject fuel and riches the mixture that much, that a warm idling engine will stall or at least start surging.
While driving / accelarating and powering the CSV you richen the mixture as well. Depending on the current mixture either the car gains or looses power. With this method I diagnosed (wihtout a CO tester) that the mixture on my car is too lean under load. The difference of power while accelerating with a lean mixture compared to a proper/richer mixture is tremendous...

Refer to the schematics on how to put the switch in the circuit for the CSV (similarly to replace the thermo time switch with a manual switch...)





Thomas

[boyt911sc]

Originally Posted by leonardo911sc

@ Tony

Just completed FD leak test with pump running. No leaks.
See relevant video.

https://youtube.com/shorts/7usraTLfN3Q?feature=share

The weird thing is that after this test the engine fired at first crank. (7 hours since stop) Engine temp was around 28 c so CSV was activated for sure.

Next is to check sensor plate alignment, just to confirm it's within spec.

Waiting for your comments.

Thanks

George,

When the problem exists randomly, it would be challenging to diagnose the culprit/s. Double check the setting of the sensor plate before we go crazy looking for unknown culprit. It would be a challenge to align the sensor plate with the AFM (air flow meter) installed in the car. I always do it on the bench but you could do it with more patience.

If I were doing the troubleshooting, I would test for:

• Unmetered air going into the system. Test and verify.
• Residual fuel pressure.

After you have confirmed the setting of the sensor plate, test run the motor and run it for a few mins. and let it cool down. Wait 7 hours more or less and try to re-start the motor. Do not try to start after two (2) unsuccessful attempts. If it starts after a couple of attempts, we’re in trouble.

If the motor failed to start after a couple of attempts, try this:

• Pull out the FP relay.
• Bridge terminals #87A & 30 to test run the FP.
• Allow the FP to run a few seconds to “pressurized” the system.
• Install back the FP relay and try to start the motor.

Keep us posted. Thanks.

Tony

[boyt911sc]

George,

Before doing any adjustment with the sensor plate, try the suggested test procedure. Does the motor start at the first attempt after a short stop? Could you test and verify that the motor would run after:

• 4 hours.
• 6 hours.
• 8 hours.

We need at least 2 data points for each test condition. We have to establish how reproducible is the occurrence of the problem to identify it. Thanks.

Tony

[leonardo911sc]

We will find the solution All together. I am sure about it. We are very close to narrow it down.

In order to summarize.Tests and spares:

1. Check valve and pump are new
2. Residual pressure will be maintained at 1.3 bar for more than 1 hour
3. Cold and warm pressures within spec. Verified many times
4. Csv is new. Tts tested with multimeter and test light with external 12v power supply.
5. New injectors
6. Fd not leaking from plunger or injector ports
7. Checked csv 12v power supply while cranking.
8 Adjusted CO to 2.5%
9. Set ignition timing
10. After 9 hours standstill i jumpered the fp relay to prime the system before i crank it. Same result. Will not start unless csv is disconnected OR after cranking for more that 10-15 seconds (within this time csv is deactivated)
10. Spark plugs are new W3CC
11. Engine will start half crank after a short stop. Even 1 hour later.

To be done:
1. Check sensor plate alignment
2. Test starting after 4,6,8 hours
3. Repeat intake leak test
4. Re confirm CO% level

[boyt911sc]

George,

Perform a residual pressure test for the system pressure (fuel distributor). Test run the fuel pump with the CIS gauge installed (valve open) and you are measuring the control pressure.

Close the valve to measure the system pressure. And switch off the FP. Write down the pressure readings:

• Valve closed and FP running.
• Valve closed and FP off.

Take note of the pressure readings on the gauge:

• Immediately after turning off the FP.
• After 20 mins. (pump off).

Let us know the pressure readings. Thanks.

Tony

[leonardo911sc]

Ok will do.

System pressure with pump running (valve closed) is set to 5.1 bar. Reverting with remaining tests.

Thanks

[leonardo911sc]

Updates.

Today morning ambient was 30c. Engine did not start after over night stay for the first time. 13 hours have passed since engine was stopped.

Started after csv was disabled.

Seems that as ambient temp goes higher the problem is getting worse at cold starts. It is definitely an over rich mixture culprit.

Will try to start after 4 hours parked. Tomorrow will do the 6 hours start attempt.

Weekend will perform remaining tests.

Thanks!

[Schulisco]

You can play with the valve of pressure measuring unit to change the control pressure by half closing the valve. So you can lean the mixture by raising the control pressure....

[T77911S]

is the CSV wired properly at the STARTER

[leonardo911sc]

Below video of start after 4 hours parked.

Started immediately. CSV should be active as i checked TTS ground contact is closed. Used multimeter to check contact to ground.

https://youtube.com/shorts/PWPc8lKGses?feature=share


Thanks

[leonardo911sc]

Originally Posted by Schulisco

You can play with the valve of pressure measuring unit to change the control pressure by half closing the valve. So you can lean the mixture by raising the control pressure....

Good test idea!

And see at what control pressure it starts. Will DO

Thanks thomas

[leonardo911sc]

Originally Posted by T77911S

is the CSV wired properly at the STARTER

Yes.

Have 12V at TTS and CSV during cranking. Will make a lamp adaptor also to test the CSV plug this weekend. If you check previous msgs the engine will start easily when CSV is de activated. CSV is new. Old had also the same symptoms.

Thanks

[boyt911sc]

George,

It is quite difficult to determine the root cause of your cold start problem because it occurs randomly. The “9-hour window” you have observed occurs at random. One day you observe it and other times it’s gone. Focus on solving the COLD START PROBLEM and ignore the 9-hour no start for the meantime.

Eliminating the CSV for cold start is a complete violation regarding CIS principles. You have tested and confirmed that the fuel distributor is NOT leaking. But you have to confirm the basic setting of the FD plunger using the fuel mixture screw. The initial setting is about 1/2 turn (CCW) from open/close setting. Followed by the final mixture setting with the engine at operating temperature.

Our goal is to identify the culprit/s preventing your motor from cold starting. Let’s make it start consistently and worry the other problems. Things I am interested to investigate:

• Spark plugs (brand, type, and appearance after all the tests).
• Is the CSV actually working?
• Residual pressure loss @ FD.
• Unmetered air.
• Etc.

Tony

[leonardo911sc]

Originally Posted by boyt911sc

George,

It is quite difficult to determine the root cause of your cold start problem because it occurs randomly. The “9-hour window” you have observed occurs at random. One day you observe it and other times it’s gone. Focus on solving the COLD START PROBLEM and ignore the 9-hour no start for the meantime.

Eliminating the CSV for cold start is a complete violation regarding CIS principles. You have tested and confirmed that the fuel distributor is NOT leaking. But you have confirm the basic setting of the FD plunger using the fuel mixture screw. The initial setting is about 1/2 turn (CCW) from open/close setting. Followed by the final mixture setting with the engine at operating temperature.

Our goal is to identify the culprit/s preventing your motor from cold starting. Let’s make it start consistently and worry the other problems. Things I am interested to investigate:

• Spark plugs (brand, type, and appearance after all the tests).
• Is the CSV actually working?
• Residual pressure loss @ FD.
• Unmetered air.
• Etc.

Tony

Good day

1. Spark plugs 3wcc bosch. New. Last time removed brown tan color. Will pull out again.
2. CSV is new. Will connect test light to plug and confirm.
3. Residual pressure loss @ FD. Reverting with test results
4. Will do an intake test again

Do i need to do the basic setting of the plunger since i have access to gas analyzer? This will be final setting anyway.

[Schulisco]

George, did you already checked the rubber fuel injector sealing rings and the red injector sleeves? There might be a vacuum leak as well...hard to find if not checked manually.

I guess that we do not have only a single problem. When I recapitulate the facts of starting right away and next time not I guess that a vacuum leak in the past was corrected out by manipulating the CIS and now that or another leak will occur again from time to time and additionally preventing a proper cold start. Also a temperature dependency is given leads me to search for sth. where its getting hot...

Thomas