911SC will not idle when hot. Exciting graph inside!

[dino_jr]

Hi again... The graph from before is void... i'd forgotten to plug the TTV back in

OK so new graph... Weather is good, about 24 deg C in the UK right now.



Things to note:
* The solid line is volts to the TTV connector. (using the axis on the right). Notice I did NOT have 12V constant until 6 mins. I also noticed my FP relay was buzzing until 6 mins also. I assume the TTV and FP relay share the same Power supply.
* To cause the TTV & FP relay to buzz requires the airflow sensor plate to oscillate... Which of course it IS doing as the idle is lumpy. FP relay buzz means intermittent fuel supply, causing a lumpy idle... I have a vicious circle of issues!
* When (I assume) the WUR and AAV have warmed and closed, the FP relay and TTV both then stick to 12V from the 6 min mark. This improves the idle obviously.
* For 6-8 mins: My MAX Warm system pressure is 4.5 bar, vs the 3.8 bar using the hand vacuum. I assume this means the engine vacuum is very good into the WUR.
* Engine off at 8 mins

So I am still stumped... The airflow plate switching the FP relay in/out makes me think air leak in the system. I tried squirting soapy water at connections while pressuring the sys. I saw no bubbles, but to be honest I think my airlock test was amateurish and needs another go.

I don't want to adjust the airflow plate as I have read the new issues that can bring. Also, why would it have changed its behaviour anyway? It moves up/down smoothly, as it has always done.

Finally, The TTV was 12V for 30 secs last time, engine off. However with engine running, TTV is 12V All the time. Should it be "powered" at all times? I'd love a cct diagram with the TTV on it... I am yet to find one. Its not on the Fuel Pump relay drawings, so have no idea what its supposed to do.

[Vereeken]

You are confusing things. (or me at least).

It is the thermal valve that holds off vac to the 089 WUR. We also have a TTS thermo time switch. Only plays at start.

Yes the thermal valve needs 12 V all the time if the engine is running.

The graph is no good. You can not have 4.5 control pressure (you can but we will disgard that for no).

You need to read up first on system pressure and control pressure. For all I know you have the pressure test wired incorrectly.

You want to see fully warmed up 3.7 bar controle pressure and 4.8 system.

Please forget about the graph.

Do this test (after reading on system and control pressure).

On a dead cold engine (8 hours or more):
1. Note the ambient temp.
2. apply 450mbar of vac to the left horizontal port of the 089 WUR.
3.Disconnect the 12 V feed to the Wur.
4. Bridge the FP relay so that FP runs when contact is on II (but engine is not started).
5. Put contact to II FP should run.
6. Read system pressure and note
7. change switch on pressure gauges and read control pressure.

Do not go changing anything before you gave us 3 numbers:
Ambient Celcius
System pressure
Cold COntrol Pressure.

No engine should be running during this test.

[dino_jr]

Hi Vereeken

It is the thermal valve that holds off vac to the 089 WUR. We also have a TTS thermo time switch. Only plays at start.
Agreed. The TTS and TTV are not the same. However I cannot find the wiring diagram for a TTV... Do you know of it? The TTV and FP relay both buzzing with engine running has confused me a bit.

Yes the thermal valve needs 12 V all the time if the engine is running.
OK good. That is what I have

The graph is no good. You can not have 4.5 control pressure (you can but we will disgard that for no).
Agreed this number looks like system pressure, not control pressure

You need to read up first on system pressure and control pressure. For all I know you have the pressure test wired incorrectly.
My System pressure is setup (1), Control is setup (2)


On a dead cold engine (8 hours or more):
1. Note the ambient temp.
24 deg C

2. apply 450mbar of vac to the left horizontal port of the 089 WUR.
I applied 500mbar before. I assume that was near enough?

3.Disconnect the 12 V feed to the Wur.
Done

4. Bridge the FP relay so that FP runs when contact is on II (but engine is not started).
Done

5. Put contact to II FP should run.
Done

6. Read system pressure and note
4.6 bar

7. change switch on pressure gauges and read control pressure.
2 bar (Cold WUR), 3.7 bar (Warm WUR, after 5 minutes)

[Vereeken]

Well congratulations.

You have a perfectly good 089 WUR.

From these numbers the car should start straight away. (ok bar the CSV but we will deal with that later).

The system pressure is on the low side but within spec.

Now you can do the second test. Start the car and let the TV replace the vac pump. 12 v connected to WUR and TV

You should get the same results....within 0.1/0.2 bar.

[dino_jr]

That's what the graph at the top shows (6-8 minutes area when the FP Relay stopped buzzing). As you say, the 2x dotted lines should match but they don't... I have warm WUR pressure at 4.5 bar, engine running. 0.8 bar higher than when measured engine off, and the same number as my system pressure measured when engine off.

[Vereeken]

I understand the graph now.

That is an issue.

You need to focus on the return o fuel to the tank I believe.

Also the WUR has two little screens on top of the fuel lines that go in. They can get clogged.

I must admit that I have never encountered a higher WP when running so this is new to me as well.

BTW how is the vent to atmosphere connected to the wur and the throttle body?

[boyt911sc]

Originally Posted by dino_jr

[COLOR="Blue"]...............................................(ed it).....

7. change switch on pressure gauges and read control pressure.
2 bar (Cold WUR), 3.7 bar (Warm WUR, after 5 minutes)

Dino,

Correct me if if I am mistaken. The above fuel pressure readings were taken as:

2 bar (29 psi.).................no vacuum applied (?).

3.7 bar (53.7 psi.)...........with vacuum applied (?).

Note: Engine was not running, only FP.

Thanks.

Tony

[dino_jr]

Hi Tony, Both numbers were measured with a 500 mbar vacuum manually applied.
FP on, engine off.

To get a better idea of the pressures I first need to stop the buzzing FP Relay. Looking at the FP Relay cct, the pump runs from the N/C Relay contact... So to keep the pump ON the relay must stay OFF. so I must disconnect the airflow SW connector so the relay coil stays dead. I'll try that tomorrow and recheck the fuel pressures.

[dino_jr]

Hi me again, sorry to be a bore.

Here's a thing... to stop the FP Relay buzzing, I bridged the relay contacts like I normally do for engine OFF testing. I thought I'd leave the bridge in the car and turn the engine ON, never tried this before.

Well I have engine idle. I then carefully drove round the block to warm up the car. At no time did it stall

New theory: the airflow sensor plate (AFS) has either "sagged" or its damper is failing. So it oscillates more than normal and "bounces" on the SW that controls the FP Relay coil. Hence the relay buzz. This will also explain why the car stalled when lifting off throttle. The back pressure moves the AFS down too far, affecting the fuel pump.

So I have AFS questions, do I:
* replace the damper spring in the AFS. A new spring will probably keep the AFS off the FP Relay SW. The oscillation should reduce too.
* adjust the height of the AFS so it stays clear of the FP Relay more often.
* leave the AFS alone but adjust its SW position? (Is this one even possibles?)
* check the fuel accumulator: its supposed to smooth out fuel flow correctly? It could be causing the AFS to oscillate.

Is there any video of AFS movement, when manually lifted & released? I'd like to compare the damping of mine vs others, thanks.

[boyt911sc]

Dino,

You are posting data that do not make sense. Please review your data well before putting them out. Everyday you have new revelations. Find sometime to read DKLever48's thread about FP relay troubleshooting. This would be a good reference for your investigation.

Not sure how the FP relay makes the buzzing noise but I've never encountered one before so this is something new to me too (?). Refrain from removing the AFS plug during troubleshooting. You want this plugged during the test. Start your diagnosis at the PF relay socket where the ignition switch is connected. Use a 12- old test light.

It is imperative that you understand how the FP relay works. There are terminals that are NC (normally closed) and NO (normally open) for the relay. If you have any question, just ask and be patient.

Tony