DIY: M70 Crankshaft Sensor Replacement
Glad I can contribute from this site, instead of just being a parasite
I researched a lot on this site and it seems the answers lead to the repair of my M70 engine problems, so thank you everyone for posting what your problems have been in your past.
My Car:
1991 850i (03/90 build date), auto, with 212k kms (Jpn model) ASC+T system (relevant info for my PS Pump loosening)
My Symptoms:
-RPM gauge would just stop even when engine was still on, and car moving.
-HORRIBLE Idle at start up (if at all)
-backfiring when idling
-Trans Fail Safe Prog would engage a lot.
Possible solutions:
I looked at/replaced DK motors, fuel pumps, fuel filters, Spark Plugs, Spark Plug Wires, Ignition Coils, Distributors, Distributor Rotors but nothing solved my problems.
Solution:
Crankshaft Sensors (P/N # 12141720307) two purchased from Autohauz @ $45 each
Tools needed:
6mm socket (for removal of hose clamps, if non-factory clamped)
8mm socket (for removal of plastic dirt guard)
10mm socket (for a few bolts removed)
13mm socket (for most bolts removed)
17mm socket (for belt tensioner removal)
hex key (used for crankshaft sensor nut)
Process:
Sorry, I do not have pictures, but I'd be happy to describe the process I had to go through, in case people need to repeat this for themselves.
It took me 5 hours (yes, I know a long time, but I did things with scrutiny and researching when I hit a snag), BUT If I had to do this again, I'd be able to do it again in about 2 hours max.
1) remove the fan blades/clutch assembly.
2) remove fan shroud (i disconnected small coolant return line on left side of rad and line to expansion tank (hidden under shroud) but kept the line to the engine block attached), these were 6mm hose clamps on my car.
3) remove expansion tank from fan shroud and just push off to side. You may find it useful to remove ignition coil wire for extra travel to the expansion tank hose.
4) lay fan shroud on top of engine.
5) remove coolant hose from top of left side of rad and from water pump. 6mm hose clamps on my car. Be prepared to loose a litre or more of coolant from hose and engine block. this removal is necessary to access top crankshaft sensor removal.
6) Loosen three 13mm bolts on the Power steering pump pulley.
7) use a 10mm socket to remove the long tension bolt that keeps the shock for the idler/tension pulley in place. This will cause slack in the serpetine belt.
8) Remove the serpentine belt from the PS Pump/Alternator system. REMEMBER HOW THE BELT WAS LOOPED.
9) The Shock for the idler pulley was still in my way a bit, so I removed the 13mm bolt that held the idler pulley to the engine block as well.
10) Continue to remove the three 13mm bolts from the power steering pulley.
11) Jack front end of car and place on jack stands.
12) slide under and remove plastic dirt guard that is held in place with four 8mm screws to give access to lower crankshaft sensor and removal of other parts in the way.
13) the second (or lower) Crankshaft sensor is attached to the engine block very closely to the PS Pump (remember, I have the larger PS pump since I have ASC+T, you may not require to loosen your PS pump). This Pump must be loosed from its holding brackets (front and rear), but not needed to be removed from the PS system/hoses. Once you've removed the pulley from of the PS pump, there are three 13mm bolts that hold the front of the pump to a bracket. There are also two 10mm bolts on the BACK of the pump holding it secure to the engine block. One bolt is just in a bracket holding a hose to the pump (must be removed to allow hose to be pushed out of way). The second bolt is hidden quite well at the top of the rear of the pump. Its a twisted L shape bracket that holds the rear of the pump to the side of the engineblock. I had to use REALOEM to see this part and how the PS Pump system was attached to the engine. Its awkward to get to, but doable with a long 10mm socket OR extension of some sort. With all 5 bolts removed, the pump is slightly moveable but still connected to lots of hoses.
14) NO PS Pump hoses need to be disconnected from pump, BUT slack MUST be given to these hoses. Two 10mm nuts hold a PS line to the lower front of the engine block. These must ber removed and the hose pulled off to give slack.
15) a 10mm bolt that sits just above the PS pump front bracket must be removed too to give slack to the hoses.
16) you can now wiggle the PS pump away a bit from the Crankshaft sensor. It will be tight but you will have to hold it away as you pry/wiggle out the crank shaft sensor from its holder.
17) The wire that runs from back of sensor to top of engine block is also held in place at two points along the front of the engine block (trace wire up) with 10mm bolts that need to be removed. The top 10mm bolt (which holds two crankshaft sensor wires) is easily removeable. The lower one, just above the lower crankshaft sensor is almost impossible to remove cause of its placement, SO I just cut the wire since I'm replacing the sensor/wire anyhow.
18)A Hex key is required to remove the small bolt that holds the sensor to the engine block. Once Hex bolt is removed, pry on the PS pump down and towards the left tire and with other hand wiggle sensor out of its holding spot. Once sensor is out, clean up the holder for the new sensor before you install it.
19) install new sensor and tighten hex bolt.
20) remove top sensor and clean the holder (brake cleaner spray) before installing new sensor and tightening hex bolt.
21) now with both sensors in place, run wires up engine block and secure with the 10mm nut/clamp. The wire is so rigid that the lower sensor will not need to be secured at the lower position as well.
22) Re-Mount Power Steering pump to the bracket with three 13mm bolts on front. Re-mount 2 brackets on the rear of the pump with 10mm bolts (top hidden bolt is difficult but honestly, its doable, just be calm). replace the 10mm bolt that was above the PS Pump front bracket (held hose in a bracket) and re-mount PS line to lower front of engine with 10mm nuts.
23) replace PS Pump pulley and put the three 13mm bolts as tight as possible (will fully tighten a bit later once belt is bck on and causing tension). Tighten properly when the serpetine belt is replaced and causing tension on the pulley.
24) re-install small plastic dirt guard to bottom of car and lower to ground.
25) replace idler pulley and shock system with 10mm and 13mm bolts (13m bolt held pulley brackey to engine block).
26) replace serpetine belt
27) set tensioner/shock. the 17mm socket is rotated wounted-clockwise, causeing tension on the belt, and a 10mm bolt is tightened to hold the tensioner in place permanently. Fuly Tighten the three 13mm bolts on the PS Pump pulley.
28) re-attach coolant hose from rad to water pump.
29) replace fan shroud and re-attach two coolant lines. One end to the top of rad, and other end to the expansion tank.
30) make sure expansion tank is sitting properly in its holster on the fan shroud.
31) re-install fanblade/clutch assembly.
32) replace ignition coil wire, if you needed to remove it earlier.
33) fill expansion tank with more coolant and purge system as shown in other DIY's on Bimmerforums.
34) lastly connect crankshaft sensor plugs to their female counterpart bracket just below the Oil Fill spout.
35) turn car to accessories two position for a few second before starting car, to let car computers recognize new sensors. Start up car and run for a minute. Continue smiling.
I swear, my cars are like a girlfriend.
Sometimes its a rough ride, sometimes its smooth motorin'.
Sometimes she doesnt like how i treat her and sometimes i dont like how she behaves.
BUT at the end of the day, she loves it when I am inside her.
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