Weak Cold Start Trick

[Funracer]

Starting another thread with this update

To recap all my cold start issue WUR and fuel pump specs are good, AAR works, timing 5 degrees BTDC no air leaks etc etc. I ran the car for about 3 months with the FP gauge in place so I could check the WUR pressures whenever and they are always in spec vs temperature. Also did a flow check all six lines at once without injectors all volumes were equal with each other. CSV also removed and tested and working. After the initial start all other starts are instant.

So now my cold starts are taking 5-6 seconds to fire, then it idles up to 1500 then down to 1000 over the next couple of minutes. Drives perfectly. This seems worse than the 3-4 seconds it was taking a few months ago.

Anyway here is the cool part. I removed the FP gauge after weeks of leaving it on the motor and reattached the OEM half hard/half soft line. IT FIRED INSTANTLY from dead cold. First time its done that in 6 months or longer. I mean first or second crank. Let it run, shut it off. My thoughts were maybe the extra volume in the FP octopus setup was the issue and now with the OEM line back in place it was fixed.

Next morning I had high expectations. No such luck. 6 seconds to start again. Shut off left overnight.

Next day I removed the OEM line, drained out the maybe half teaspoon of fuel, put it back on and it fired INSTANTLY again. So for the last 10 days I have done the following:

Odd days I do nothing, just put the key in and start. Every time it takes 6 seconds. Too long.

Even days I crack the FD/WUR line at both ends, let the bit of fuel dribble out, retighten and it starts instantly every time.

Not sure where to go with it now.

[mike sampsel]

Wonder if it’s a bit too rich at first?
Might try slightly leaner on the odd days to see what happens?

I’m just throwing spaghetti on the wall here, no expert and I’m happy to have my thoughts corrected anytime!

[Schulisco]

Sounds weird.
I experienced a bad fuel accumulator years ago. Cannot confirm that it had the same behaviour due to other starting issues. But: I examined the FA more closely with air pressure outside of the car. I closed the overflow output (not urgently required, but I wanted to remove any possible leak), attached a pressure gauge on the output and gave some air pressure on the input with a compressor. I pressureized the FA as Porsche specs saying (max. 5bars). I could hear the diaphragm is moving. No leak, held the pressure. Good so far. Then I opened the input so that the pressure immediately dropped. I could feel and hear that the diaphragm rested for a second or so in the pressurized position before it slammend down by releasing the spring! So it retarded heavily the release of the diaphragm!!
In other words: It could be possible that the FA hangs (due to corrosion or wear) after parking the car and releasing the fuel pressure over time. This creates a vacuum in the CIS system. When you release the connection, the now smaller vacuum is removed and can be easily refilled by the fuel pump. If you don't open the fuel line, the vacuum (or even capacity) remains and the volume to be refilled is bigger and this takes more time to be refilled and pressurized. After the fuel pressure is high enough the engine will start directly...
Check with a fuel pressure gauge how the pressure behaves when cranking the engine without opening the fuel line to prove that it slowly increases as expected. Then crosscheck it, open the line, and have a look on the pressure gauge again. It should increase directly...
Just a thought.

Thomas

[Funracer]

Originally Posted by Schulisco

Sounds weird.
I experienced a bad fuel accumulator years ago. Cannot confirm that it had the same behaviour due to other starting issues. But: I examined the FA more closely with air pressure outside of the car. I closed the overflow output (not urgently required, but I wanted to remove any possible leak), attached a pressure gauge on the output and gave some air pressure on the input with a compressor. I pressureized the FA as Porsche specs saying (max. 5bars). I could hear the diaphragm is moving. No leak, held the pressure. Good so far. Then I opened the input so that the pressure immediately dropped. I could feel and hear that the diaphragm rested for a second or so in the pressurized position before it slammend down by releasing the spring! So it retarded heavily the release of the diaphragm!!
In other words: It could be possible that the FA hangs (due to corrosion or wear) after parking the car and releasing the fuel pressure over time. This creates a vacuum in the CIS system. When you release the connection, the now smaller vacuum is removed and can be easily refilled by the fuel pump. If you don't open the fuel line, the vacuum (or even capacity) remains and the volume to be refilled is bigger and this takes more time to be refilled and pressurized. After the fuel pressure is high enough the engine will start directly...
Check with a fuel pressure gauge how the pressure behaves when cranking the engine without opening the fuel line to prove that it slowly increases as expected. Then crosscheck it, open the line, and have a look on the pressure gauge again. It should increase directly...
Just a thought.

Thomas

My pump, filter and accumulator are new, WUR and FD rebuilt professionally. I did not test the new accumulator prior to install but I did test the old one and it was good.

This is clearly, to me anyway, a fuel or air supply issue. I will reinstall the FP gauge and run the pressure test as you suggest.

Thanks

[Funracer]

Originally Posted by mike sampsel

Wonder if it’s a bit too rich at first?
Might try slightly leaner on the odd days to see what happens?

I’m just throwing spaghetti on the wall here, no expert and I’m happy to have my thoughts corrected anytime!

I’ve been all over with the mixture, from so rich it wont start at all no matter how much you crank, to so lean it will start immediately on the CSV shot, run for 1 second then shut off because its too lean to run, and many places in between. Mixture is super important but not the culprit here IMO.

Thanks