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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. :)

Hmm, this theory may have some merit.


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.


If your theory of CKPS to flywheel gap is correct, this can explain why the problem has resurfaced for me (although I can't explain why the problem initially went away).


Now are you telling me to replace the CKPS, I will need to drop the transmission again? :eek Please don't say that! It cost me an arm and a leg to get the clutch replaced.


I also found this from back in 2005 -> http://www.m5board.com/vbulletin/e3...d-my-m5-only-wants-run-after-2nd-start-2.html


Seems the problem has afflicted people for quite a while.
 

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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.

By the way, the sensor is quite often damaged during a clutch swap if it isn't removed before dropping the tranny. It can get crunched against the flywheel while finagling the tranny off the dowels.

Malcolm
 

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This is what I think happened to mine as the induction end of the sensor looked like it had been damaged also slightly.

Anyway as Malcolm said - CKPS is the easiest thing you will do on the beast and I'm not reporting any issues still after doing mine.
 

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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.


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?


Thanks.
 

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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?


Thanks.
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.

You could buy a set of dial calipers. They're about CAN$40 here, so not a huge outlay. They measure down to 1/1000". With them you can measure the distance from the mounting face on the bellhousing to the face of a flywheel tooth. Then measure the length of the CKPS nose from the end to the mounting face and subtract the two measurements.

If you have a good eye, you could put a small lump of modelling clay on the nose of the CKPS, install it, remove it and measure the thickness of the crushed clay with the calipers.

No, there's only one CKPS on the bellhousing.

Malcolm
 

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Just to make things ultra confusing again, since my car has been at the body shop with no use for 6 weeks, upon return I have had ZERO cold start issues.

Before it went in for repair, cold start fails were a certainty.
 

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Work was only done down bank 5-8 side of car if that helps, the bulk of the damage was on the section closest to the bottom left door after the object glanced off of the wheel.
 

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I have no idea what is going on with these down under cars. We have tried everything I could think of. On some it seemed to work but on most it did not. Maybe it is so simple we are missing it. It is like your drains spin the wrong way but not for you because you are on the other side of the equator. At this point all I can think is a gravity problem that BMW missed which is super important on the other side of the equator. There are quite a few engineering principals that change once the world spins the opposite way.
 

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mine was caused by poorly charged battery, once fully charged problem has disappeared. water now flows down drain same as northern hemisphere :D
 

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It does not, your world spins opposite to mine.your toilet spins to the right mine to the left or maybe it is the other way. There is one thing that is never a question the women south of the the equator are the worlds most attractive.
 

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Well cold start issue came back :( that was a nice month or so.
 

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Thanks to all who've contributed to this thread, very informative and hopefully useful.
I've read through this whole thread over the past few days, a bit surprised to see I'd posted in it!
Anyway, at the end of March this year I replaced my old oem pump for a new Quantum 340lph (QFS-340FT) fuel pump - which, as I later discovered, is apparently just the same as an aeromotive one. I was concerned that my old pump was getting on a bit and didn't want to be stranded anywhere!

Prior to the change, my car would fire up happily on the first attempt.

Having made the change, it hasn't been so keen to fire up, but always on the second attempt (hence my reading through this thread).

If I turned the key to position2 and left it there a moment to prime, eg whilst doing up the safety belt, it would start but would take a few rotations to do so, not instant but most times would start on the first attempt. I don't mind this, as it does prime the engine with oil in those few turns, can't be a bad thing. Hoewever, it's still not 'right'.

If I get some time, I'll have a look at the connections in the tank to see if they hold, just as is described in the quote below. My gut feeling is that the connecting pipe from pump to float unit is leaking, either split or clamp/s not holding. I've got some fresh ones to fit. It would make 'sense' if there's a small leak, as it would prime but not hold the full pressure. Car drives fine, so enough is getting through to run the engine.


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!

Cheers!
cherrsagaicherrsagaicherrsagai

I also sometimes get the 7F tank leak diagnosis system failt (read on my i910 reader that's always in the car). I think this translates to a P1451 error code.
I have a fresh tank vent valve on the way, which I hope will sort it for good. If it's not the valve, it's most probably going to be a blocked pipe. Iis there an 'open to atmosphere' vent pipe in the system? If not these, then I'm not sure...

I'll rrport my findings.
 

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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.
 

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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.

Thanks for your reply and thanks for your thoughts and suggestions, they are really appreciated.
I'm sure I've been getting the code for well over a year, it's been coming and going and I've just been keeping an eye on it and resetting as and when required. I did some initial research and wasn't too bothered, but I now feel it's time to sort it by now.

The 'non starting' started when I installed the pump, it was pretty much perfect 1st time starts prior to this and I've a feeling that I didn't clench the clamps enough, it all adds up nicely. I'm pretty sure it's at the pump end and it will be easier than checking the check valve pressure (I haven't got a suitable 'fuel' pressure gauge and I'd have to raise the car etc). I'll probably lift the float section off the tank and watch what happens when it's primed, just as the other poster did. It will be nice to get confirmation of the leak

If this doesn't work out I'll look in to the pressure raised by the system...
 

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An update to my problem:

I finally had time to remove the tank 'lid' and had dad work the key to prime the pump and inspect my possible leak.

At first it was rather difficult to see anything, and as it happens, I was very fortunate that my tank with less than half full. This allowed me to see the top of the pump which was clear of the fuel (this turned out to be very important). I asked dad to turn the key to prime the fuel system whilst I peered at the pump. After three or four times I realized that fuel was coming out from the pump exit (barb or nozzle) and getting past the transparent flexi pipe. If more fuel was in the tank, I would not have been able to see this.

Pump was then removed, single clamp removed and two clamps fitted tightly instead. No way could any fuel get past this (I thought!). I blew into the pipe as hard as I could, no apparent leaks and it was re-fitted.

Here's a pic of the twin clamped barb:




I thought it better to just prime the system once before closing it all up. Again dad 'did the honours' and turned the key whilst I peered. To my dismay, fuel managed to leak again. I left it for the night and had a think.

Following day, I thought that maybe if I gave the pipe a bit of help in sealing, all would be fine. I bought a tube of blue Hylomar, which is fuel resistant, and took the whole lot out, cleaned and used a dab of 'blue' to seal it. In thinking this would be ok, I only used one 'O' clip this time.

Here it is all sealed up and ready to go:




With the blue Hylomar, which has finally changed packaging:




Hopes were high and it was all fitted again. This time a prime was definitely on the cards, but I thought all would be good.
On turning the key, a large gush of fuel was pumped and no leaks, weheeey. That lasted about two seconds.. A prime lasts three! just as it finished, fuel gushed out past the barb again. I was drained and fed up of this, but wanted to get to the bottom of things, so it was removed and inspected again.

I thought that during all of this time, the other end of the pipe, connected to the plastic 'end' underneath the tank 'lid' hadn't leaked a bit.

I had a look at fuelperfomance's website (pump supplier) and found their page on the clear flexi hoses:

Convoluted Fuel Flex Hose

This gave me some numbers. The pump's barb was measured to be 8.25mm. The original pump's barb was also 8mm or so and I'm sure it never leaked. I had used the new clear flexi hose as supplied to me with the pump. I measured the old one, both ends were for 8mm barbs.

Fuelperformance sell a short, 160mm long, flexi with 8mm at both ends. The 220 and 260mm long ones had one end at 8mm and the other at 9mm. Their 280mm one is 9mm at both ends. The supplied pipe is 260mm long...

I removed the pipe from the pump and, sure enough, it had a 9mm end. The other end, fitted to the tank 'lid' was the 8mm end, no wonder it didn't leak.

Here's a picture of both ends of the supplied pipe:




This pipe is supplied and is said to be specific to BMW's (and a few other manufacturers). Turns out it isn't! I never thought of checking the pipe diameters, I presumed they were correct. As this kit is so similar to the Aeromotive, it might be a good idea to check the pipe that come with their kit, I'd not be very surprised if it's the same!

Anyway, I left there for the night and returned the following day. I fitted the old 'clear' (but now petrol stained brown) pipe. Both ends were a nice tight fit. Both ends fitted with one 'O' clip and clenched reasonably tight.

All fitted and again checked. This time, not a single drop came out and the fuel movement sounded more positive, I'm sure more fuel returned to the tank, as I noticed it, it was 'noisier'.

Finally, I could finish fitting it all and refit everything.

Car fired up fine, even with some air in the system and has continued to do so since. Finally I can say that the problem is solved!

Incidentally, very little information is given about the original 'O' clips as used by BMW to clamp the flexi fuel pipe.
They are marked '113' and 'JET PAT', 113 referring to their size, 11.3mm 'open' diameter. They are 5mm in width, which I couldn't easily get here.

Here's a picture:




I did get a 10-pack of 11.9mm, 7mm width ones which have worked perfectly with the correct sized pipe. I didn't bother with a picture of these, you can go on ebay and search for 'single ear' 'O' clips, or sometimes known as 'Oetiker' clips. They weren't expensive and it was nice to use the correct type of clip for the pipe.

I want to change the tank vent valve too, as I've had a few codes relating to that but I've not been able to yet. That shall be done in the near future.

If anyone has an Aeromotive or Quantum pump and used the supplied flexi and are getting starting issues, it may well be a good idea to check the hoses. These clamps cannot reduce the pipe size down by a millimeter, the join will leak, quite dramatically if just joined up quickly and without paying too much attention. If this is the case, it may well be that these pumps are working much harder than they should in maintaining pressure etc, it could go some way to explain the high temperature failures.

I did get some heavier, external fuel pipe too. This has a 7.6mm (or so) inner diameter and would have fitted well over the barbs and could be locked with small worm drive clips. However, they are not designed for tight curves so I decided not to use it for the time being, as it might kink! A longer piece could be used to increase the curve sizes so it's not being thrown out yet, but as long as the old oem flexi works, I'll use it.
 

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Finally have got around to change the fuel tank breather valve.
Plenum off and dive in:



New one in position, old one there in the picture.

As most have found, it's a bit of a fight to get the lower hose off, but it will relent in the end. I squirted a tiny bit of Auto Glym's rubber and vinyl care to help get the pipe back on, that stuff will dry in no time and I doubt it will cause any harm to anything, but it did help the pipe to slide on easily.

I had checked the replacement valve, it held pressure/vacuum when blown into or sucked out of and when 12V was applied it gave a strong 'clunk' and free flow or air.

When the old one was removed, I instinctively tried blowing/sucking though it and it held my pressure quite happily. I was beginning to wonder if I'd wasted time and effort. Anyway, later on I hooked it up to my little 12V source and it became clear that it wasn't performing as it should, held a little pressure no problem, but it hardly moved when I applied power to it. Sucking on the lower 'exit' pipe connection (normally under vacuum, it goes to the inlet) it sometimes failed to open, giving an unreliable poor air flow. So, not a waste of time.

I'll have to use the car a few times now to confirm that this issue is properly sorted. It gave the code - 7F - tank leak diagnosis system when read with a small handheld scanner, code P1451 I believe from a generic scanner.

Seeing that the valve was obviously faulty, I'm pretty confident that this will have solved the issue. If not, I'll report any developments here.

Incidentally, the valve is just the same as any other bmw tank breather valve. Any one from any supplier will fit, there's plenty of room there for any of them, even though the M5 one is a tiny bit shorter.

BMW part number is:
13907830766 (think expensive)

However, 1 748 875 on the lower part of the unit, this is probably an old number for the valve.

I had a look on Febi's webcat.
Febi make a fuel tank valve, no. 46426, but it's not listed for the M5...

Febi also list this as an equivalent to:
13 90 1 433 603
13 90 1 433 602
13 90 1 744 150
and 13 90 1 748 875 - this is the same shape as the M5 version, this number is on the m5 unit! So, the Febi valve would/should work in the M5.

I'm hoping now that my starting and eml issues will have been solved. Time will tell.
I hope this will help someone else too.
 

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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.
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.


Go figure!
 
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