The CKPS is a pure inductive sensor, a coil around a permanent magnet. When a flywheel tooth passes the sensor, the magnetic field in the sensor ramps up and generates a voltage in the coil.
It seems this type of magnetic circuit is sensitive to air gap, in this case the gap between the sensor and the flywheel. The bigger the gap the weaker the signal. And the effect is not linear.
Say the gap was a bit too large on a cold engine, so the signal to the DME is weak. First crank fails. Next crank, the DME uses the CMPS signal. Then when the engine has warmed up, the gap between the CKPS and the flywheel decreases and the signal improves, satisfying the DME every time.
I must admit I struggle with my own logic here because the flywheel is steel and the bellhousing where the CKPS is mounted is aluminum. Aluminum has a coefficient of thermal expansion twice that of steel, so if the flywheel and the bellhousing heated up to the same temperature, the air gap would increase even further. But say the bellhousing is cooled by the air flow over it, whereas the flywheel is so heated up by conduction from the engine and clutch operation that the gap closed?
So in summary, get the shop to check if the CKPS to flywheel gap is in spec.
No need to drop the transmission. The CKPS just screws into the bell housing from the outside. It's easy to change.
And I'm not even suggesting changing the CKPS, I'm suggesting checking the gap. The TIS manual specifies a range, somewhere around 0.028", IIRC. I replaced mine and had to shim it to get the gap in spec.
TIS says gap should be 0.55 mm plus or minus 0.2 mm, so 0.35 to 0.75 mm. That's 0.014" to 0.030". Not much, so tough to measure by eye.Ok thanks.
How do I check the gap between it and the flywheel if the CKPS screws into the bellhousing? I wouldn't be able to visually see the gap?
I've also read threads that suggest the CKPS is in front of the engine. Do we have 2 CKPS on our cars?
So, I've had this problem since 2012, it has been so rare so i have'nt done anything about it. 2 months ago my fuelpump died, I replaced it with original Pierburg pump, and that was when the s*it really hit the fan. I started having starting problems EVERY time car stood still over 3 minutes, and it was allways 3rd attempt when it fired up. I tried to figure it out, no luck. Long story short, I ended up in situation where my backseat is off, fuelpump cover and right side sensor are out, but the pump and all fuel lines and electrics attached. So there I am wathching what happens inside my fueltank when my friend turns on the ignition: Pump starts building up pressure, and emmediately fuel starts leaking from the fuel line/pump connection. When ignition turned off, the leaking continues slowly untill the fuel line is empty/out of pressure. I was sure I tighteded the clamps properly when I changed the pump, and I did, but the fuel line from the pump to the fuel level sensor was so hardened that it didn't tighten anymore. Next I cut 1 cm out of the old pump end fuel line, and changed the hose clamp to smaller one(10-16mm-> 8-12mm). Then we did the same test again; pressure built up much faster, and no leaks. And for me problem solved, not a single second start after that. This got me thinking, this all could happen without a pump change. If the fuel line hardens, it can cause the same leaking problem even with the original pump. And it also makes sense if you think about the pattern this usually comes up! So I encourage all of you with this problem to CHECK YOUR FUEL PUMP/FUEL LINE CONNECTION!
Have you just been getting that code since the install of the pump? I would agree you are not holding pressure. You could check at the regulator valve how much pressure you have and watch if it falls and how fast after you turn the car off. It could be the new pumps check valve is not working well and the fuel just flows back thru the pump. Unless there is a leak outside the tank that does not explain the 7F. The tank and system is sealed basically. The tank can only vent to the engine but air can be drawn into it when there is a vacuum, but it is not open to the air.
My last update in Feb 2016 indicate that the problem had resurfaced for me since a clutch change. The discussion thereafter was around the crank position sensor however I never got around to replacing it because for the past few months, without having done anything, the car has been starting perfectly on first start, even after sitting for 3 weeks.Have owned mine for almost 3 years. Previous owner had the exact same problem and mentioned it to me on purchase. I inherited the problem but magically, for no explainable reason, after approximately 12 months of ownership, the problem stopped occurring. Just like that, out of the blue. I was able to start on first go. 6 months ago, I got my clutch replaced. After that work, the problem has reoccurred and has continued to occur since then.