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carrpet

Getting the fuel pumps running for pressure testing

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6 minutes ago, sopor said:

Even if the flap isn't lifted?

As per Ivan, only if it is spot on.

 

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How do you measure system pressure with the engine running then ?

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3 hours ago, SilverWT said:

Don't need leaky or failed injectors on a CIS engine, all the injectors squirt all the time there is pressure in the system.

Although CIS continuously injects it only does this when it’s metering fuel via the fuel distributor and this only happens when the sensor plate is moved off its rest position (ie drawing air when cranking or running). Provided the sensor plate isn’t moved then running the pumps with a dead engine should not put any fuel into the cylinders. This is why I disconnect the safety switch to make the pumps run. The injectors are mechanical and only open at a particular pressure (high) so if the fuel head isn’t metering then there is insufficient pressure to open an injector. I wouldn’t think a malfunctioning injector is a big concern as you’d already know about this through poor running & running on. 

There is debate about whether you should do pressure tests with the engine off or running. In my experience both work and give the same result. If all is well with your CIS then doing with the engine off won’t dump fuel in the motor. If it isn’t well you’d expect to know this as you’d have a big running issue, although I get that it’s a small risk. On the other hand taking readings at specific temperatures (as per spec) is harder with a running motor......

David 

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11 minutes ago, carrpet said:

How do you measure system pressure with the engine running then ?

Exactly the same - connect your gauge, set the valve to measure system pressure and start the motor. Let it idle. When you switch the valve to measure control pressures the motor struggles to run but continues (or at least mine does). You need to be quick measuring cold control pressures as the motor warms quickly. 

David 

 

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Thanks David,

Right just completed my definitive pressure test at 9C ambient (engine not running)

Cold pressure    17psi

Warm pressure  54psi

System pressure 102psi

Do these look right ?

Peter

 

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Porsche 911 Turbo manual states for a 66 engine at 10C

Cold pressure             11.6 - 17.4 psi

Warm pressure           53 + or - 3 psi

System                         87-97 psi

 

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For a 930/66 your control pressures are just inside the upper spec limits but your system pressure is high at 7 bar (spec is 6-6.7 with an adjusting target of 6.2-6.5). If your gauge is accurate then I’d be looking to reduce system pressure to within spec, although I doubt this creates your cold start issue. 

You should do a min pressure test too - system pressure should be at least 1.6bar after 10 min and 1.4bar after 20min. This would be more an issue for hot start. 

With a cold start issue I’d check the Cold Start Valve next. 

David 

 

 

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1 hour ago, Ian Comerford said:

Looks like it is in spec Peter, now what?

I am still concerned about the high system pressure Ian. I am reading 102psi on a gauge which goes up to 100 psi. It may be higher than that if it has hit the upper stop. The pressure regulator has 3 shims in it - one shim is typically 4psi. I have read that one symptom of high system pressure is that you get an immediate fire but does not catch, which I regularly experience. So I am regretting not having purchased a 150 psi gauge !! I need to find out if it is 102 or higher. Not sure how easy it is to access the pressure regulator. In the pictures looks quite straightforward but it may be hidden round the back of the distributor. I am sure David will put me right on this !

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20 minutes ago, flatsix777 said:

For a 930/66 your control pressures are just inside the upper spec limits but your system pressure is high at 7 bar (spec is 6-6.7 with an adjusting target of 6.2-6.5). If your gauge is accurate then I’d be looking to reduce system pressure to within spec, although I doubt this creates your cold start issue. 

You should do a min pressure test too - system pressure should be at least 1.6bar after 10 min and 1.4bar after 20min. This would be more an issue for hot start. 

With a cold start issue I’d check the Cold Start Valve next. 

David 

 

 

I have done the minimum pressure test and was much better than the minimum standard. I was above 1.4 bar after 1 hour. As I said to Ian I think I need to validate my system pressure reading.

How do I test the CSV and the temperature probe which drives it ?

Also when the engine runs from cold the rpm increase above tick over is no more than 200 rpm. Is that normal ?

Peter

 

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Hi Peter, 

I’m not sure I’d trust a gauge right at the limit of it’s scale so I’d get one with a 150 psi scale and re-test to get a conclusive system pressure before adjusting shims. 

The CSV is an additional electronic injector that’s takes a positive feed from the starter (yellow wire) which is live during cranking. It’s grounded through a thermotime switch on the left chain cover. This opens to ground when the temperature is low. The idea is to inject more fuel for a cold start but only for a short time. 

Check that the thermotime switch has continuity to ground when cold and that the wire to the CSV is OK. Then check that you have power to the CSV when cranking.  

If all is good then you can check that the CSV solonoid is working. It’s easiest ti bench test but I  imagine you can manage in situ (never tried). If the solonoid works and you have fuel pressure to the CSV then it should be working but to properly test you can remove the CSV, leave fuel line connected and apply 12v across contacts. You need to take care to catch all the fuel safely in something. You’d need the pumps running for fuel pressure. This confirms flow and let’s you check that you have a good pattern. 

Take care as you have 7 bar of pressure so make sure you rig to catch it properly if you do this. 

David 

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Removing the CSV looks like a challenge ! Lets check the electrics first !

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System pressure confirmed at 102 psi

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Car starts first time from cold (6C), every time I break into the fuel system, run the pumps, connect the fuel system back up and away she goes. 

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1 hour ago, carrpet said:

Car starts first time from cold (6C), every time I break into the fuel system, run the pumps, connect the fuel system back up and away she goes. 

I don’t know exactly how the fuel head works but there must be a separation of the system pressure circuit, which feeds the injectors and cold start valve,  and control pressure circuit out to the WUR, which you break to install gauges. If you’ve just run the pumps up for the test then residual pressure behind the injectors is presumably higher than a normal cold start so it gets more fuel faster and starts sooner. Guessing really. 

I think this just confirms it’s a fuel issue. CSV operation still most likely cause IMHO. 

Also worth checking your mixture to make sure not too weak  (I have mine at 3% CO with no air pump) and air leaks. Anything that causes the motor to run too lean will make it start hard from cold. 

David 

 

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CSV check on Saturday

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I have now adjusted / re-shimmed the fuel pressure regulator and I now have a system pressure of 94 psi. There 4 shims (not the specified 3 shims interestingly !) totalling 1.95mm of shim. It took me two goes to get it spot on, I now have 2 shims totalling 1.15mm which brought the pressure down by 8 psi. The process went like clockwork once | knew what 0.1mm of shim delivered on my engine. Interestingly my car was set up with the right system pressure for the 68 USA model (mine being a 66). In the Porsche manual there are some specifications which are for the 68 model which are not labelled as the 68 model eg the CO specification. My WUR failed over 10 years ago and I had the car repaired by Porsche Nottingham and I know they played around with "fuel pressures" ten before they replaced the WUR.

All of my pressures are now in spec and I had to increase the idle from 650 to 950 once the system pressure was lowered to 94psi.

I continuity tested the Cold Start Valve's thermo-time switch on the left hand timing chain cover and that seemed to be spot on. I have not yet tested the CSV itself which is very challenging to get at so I thought I would see where today's adjustments got me to and take stock.

Lets see what the cold starting is like tomorrow.

I do have a question mark over the Auxiliary Air Valve or AAV because my fast tickover is a minimal increase over normal tickover. I haven't yet researched how to test the AAV though.

The journey continues and with some good progress today !!

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Good work Peter and logical.  Do you think the FPR was incorrectly set by the OPC or has worn over time?

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11 hours ago, Ian Comerford said:

Good work Peter and logical.  Do you think the FPR was incorrectly set by the OPC or has worn over time?

Hi Ian

The fact that there were 4 shims and Porsche specify 3 means to me that someone has had a go at adjusting this, so I do not think it is wear, especially given the car's low mileage. I would have put 3 shims back in but I did not have a combination of the 4 to give the overall total shim thickness that I needed.

Incidentally the K-Jetronic fuel trouble shooting guide which you sent me indicated that high system pressure was a possible cause for my symptoms ie. fires straight away, does not pick up and then requires a lot of cranking to start the engine.

Peter 

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I checked out the operation of the AAR by removing the inlet hose, blanking off the intercooler connection  and observing the slide valve from cold viewing straight down the throat of the valve. There is a video on one of the forums showing the valve closing over time. Mine seemed to behave perfectly normally. Another bimetallic strip actuated device ! Bosch seem to love these !

Following the adjustment in system pressure, the tickover needed adjusting and I thought the prudent thing to do was to check & adjust the mixture at tickover to give a CO% of 2% to 2.5% or thereabouts (target range is 1.5% to 2.5% for a 66). It was quite a way out on the lean side.

The car now starts first time from cold, the fast tickover is exactly as it should be and I am a happy man.

Thanks for your help getting me there

Peter

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