Why do camshaft/crankshaft sensors fail?

[Mordan]

how many miles/start stops before a failure?

I think it is happening to my 15 years old 50k miles M50 (first hand driven by a senior before me).

[shogun]

heat maybe over so many years. But on my 750 they are now 21 years old and still fine. Some weeks back we did an E31 850 intake reseal job and the plug of the cranshaft CPS sensor broke into 2 parts. As it was a Sunday and no stock, we re-glued all the small parts of the plug and let it dry over night, still works fine, although a new CPS sensor is now available.
In this case, DO NOT buy after market CPS sensors, a lot has been written about trouble with these cheaper after maket CPS sensors.

[Jehu]

heat maybe over so many years. But on my 750 they are now 21 years old and still fine. Some weeks back we did an E31 850 intake reseal job and the plug of the cranshaft CPS sensor broke into 2 parts. As it was a Sunday and no stock, we re-glued all the small parts of the plug and let it dry over night, still works fine, although a new CPS sensor is now available.
In this case, DO NOT buy after market CPS sensors, a lot has been written about trouble with these cheaper after maket CPS sensors.


A friend of mine in the States shared an interest in buying an 8 Series and many others warned him about frequent failures in many systems.
Is the 8 series any more problematic than any other ageing used car? Do you know of a detailed knowledge base I can share with him to assist his search thru the 8 Series BMWs?

[Mordan]

heat maybe over so many years. But on my 750 they are now 21 years old and still fine. Some weeks back we did an E31 850 intake reseal job and the plug of the cranshaft CPS sensor broke into 2 parts. As it was a Sunday and no stock, we re-glued all the small parts of the plug and let it dry over night, still works fine, although a new CPS sensor is now available.
In this case, DO NOT buy after market CPS sensors, a lot has been written about trouble with these cheaper after maket CPS sensors.

thx. would it be my camshaft sensor when cold start is easy and hot starts are quite difficult?

I don't understand why a hot start can be hard when cold start is fast. what is the reason? Cold starts don't use camshaft sensor input?

cheers

[shogun]

hot start bad? Maybe not the CPS but the fuel tank check valve
http://www.bimmernut.com/forum/showthread.php?t=40658&highlight=check+valve

@Jehu,
see my website below, under other diy links there are the sites of wuffer, Timm and Mwrench, they have all you need for checking an E31. Wuffer even has a prepurchase check list
and
http://www.8er.org/
http://forums.bimmerforums.com/forum/forumdisplay.php?f=55

[shogun]

and more copied here
Subject: 318 cold run problem
Author: ufarley : Posted on: 2009-11-11


Any help would be great, this belongs to a friend. where should I go next?





Subject: 95 BMW 318i (Cold Running Problem)

95 318i that when initially started in the morning, or after letting it set and cool completely down, has initial running issues. When I start it cold, it idles perfectly, but when I give it a little throttle, about 1500 rpms it starts to spit and sputter, possible detonation. I get no check engine light, and no codes (Code 1444), unless I really try to throttle it, then it occasionally gives a knock sensor code (1286). If I let the car warm-up completely, before driving, it runs perfect, with no signs of any issues, at all speeds, city & highway. I assume if it were a fuel delivery problem, at high speeds (85 MPH +) there would be issues, but none, runs great. I have tried & and changed out numerous parts, hoping to fix this issue. Could this possibly be a CAT problem? All other e36's that I have researched have the opposite problem, they run poorly when the car is warm, where mine runs poorly when cold. I have buzzed about every wire or componant that I can think of, according to the Bentley Manual and cannot come up with the fix. Symptoms started about 2 weeks after Crank Position Sensor failed and I had to change.

NEW/SWAPPED-OUT PARTS & THINGS TRIED

New O2 Sensor
New Cam Position Sensor
New Crank Position Sensor
Cleaned Idle Control Valve (IDLES PERFECTLY)
Swapped out DME (NO CHANGES)
Swapped out MAF with two other known working (NO CHANGES)
New fuel filter
New fuel level control (Cracked on top and leaking)
New vacuum lines (CHECKED EXTENSIVELY)
New Valve Cover Gasket (NO LEAKS)
Cleaned the Air Intake Sensor with approved cleaner (NO CHANGES)
New PCV Valve
New Hose from valve cover to PCV
New Hoses under intake manifold, (ICV Hoses & fuel injector hoses)
New Intake Boot (From MAF to Throttle Body)
New Plugs (Iridium)
New Coolant Temp Sensor
New Fuel Pressure Regulator
New Thermostat
New Throttle Position Sensor

Thank you in advance
---------------------------------
and here the solution explained by him:
http://www.bimmerboard.com/forums/posts/729514

[Tiger]

There is a possible good aftermarket one. I was looking at rockauto and they have a Standard Part for less than $50. It looks exactly like OEM... which is unlike all the aftermarkets that we see... looks quite different from OEM.

I think I will try that when my CPS fail.

[93 525 Paul]

how many miles/start stops before a failure?

I think it is happening to my 15 years old 50k miles M50 (first hand driven by a senior before me).

The 93's CPS went last year at 16 years of age and 170 something thousand miles. Driving along, pulled out to pass, and the motor shut off. Coasted to a stop and it would crank and crank but not a hint of firing.

(I wish ours had 50k mi on it. Lucky dog...)

[Mordan]

thx all for the input.

initially thinking about the CPS, it seems more to be a fuel pressure problem.

it never occured to me before, and don't remember reading it, that you can just put ignition on and wait for pump to pressurize the system to sort out of a hot start problem.

well in my case, engine hot starts fine when waiting for pump to prime the system.

so it is either check valve of fuel pump or fuel pressure regulator!

cheers.