intermittent starting

harpersimon

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Hello all. Ideas please..
My car had a random habit of not starting. It will crank until the cows come home
But not start. Then for no apparent reason it will start and be fine for a day or so
When cranking it is almost like an imobiliser has cut in and when it does start I am left with
the engine management light on- which clears after a day

It has been suggested as the symptoms or a crank position sensor fault but thought I would run it by
the knowledge here.
If it is, what is failing , can I do anything to temp fix it and how hard is it to change if you are handy with spanners?

I appreciate it prob needs plugging into some diagnostics. I live in lancs so if there is somewhere
Near please advise. Thanks!
 

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Yes as SAM CPS £47 from Bosch or £87 from MB take your pick
 

Alex Crow

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when cranking but not starting, does the rev counter needle register at all? even just bumping off the bottom a bit?

if not, then suspect the crank sensor as my learned counterparts suggest.
 
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harpersimon

harpersimon

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Hello all. thanks for responses. I didn't note the rev counter needle - something I can check tomorrow.
It just did it again, and then once started - on the way to my friends completly cut out - and wouldn't restart at all. Would that suggest same thing? I think it was dodgy, and has now failed completely. I left it for an hour outside my friends house and it started first crank!! Sooo annoying!!
Do they get progressively worse then fail totally?
If it failed completely would that instantly cut the engine out whilst you are happily motoring along?
Got to find somewhere local now that can check it out and repair - anyone know any places in the Wokingham / Bracknell area (where I am stranded!)
 

Alex Crow

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that crank sensor is still the most likely.

there are other possibilities to consider but it would probably not be worth speculating on these. if you are keen to diy it simon you could test the resistance of the sensor if you have a multimeter.

it is located in the 10 o'clock position (n/s) in the very rear of the engine block. it has a plug on which is fairly easy to release with one 'tag' to press, and then pull the connector. the sensor itself should read about 1000-1300 ohms. if you find it is way over this then change it. if it is close or within this range then it could still be faulty but harder to condemn.

usually they come out ok but increasingly we find them rusted in to a greater or lesser degree. if it is free then it's a doddle to change with 1/4 drive ratchet and something like a t6 socket.

good luck!
 
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harpersimon

harpersimon

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Thanks - I read some other posts on here about them and to be fair it seems 99% that is the culprit. I will try finding the part tomorrow and have a go (as am being quoted 2 hrs labour by garage!). be good to make it home as I don't have all my tools with me down south obviously!! but thats 4 hours up the motorway, so could be a long drive if it cuts out. I suppose I could buy one and get a local garage to whack it in.
So that is the position of the sensor on my V6 then yes? If I can find it, I am sure I can replace it myself. Will report back!

Where can I get one? Sort of thing good old Euro Carparts will carry?
 
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harpersimon

harpersimon

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just read some more postings from people who have changed these. When you say a doddle - is it an actual doddle, or do i need to remove half the engine component s first!! there is a tale of 4 hours night after night trying to get it done -although not sure what engine that was.
I am guessing at the least all the top covers are coming off right?
and I will e able to spot this amongst the miriad of other sensors and wires?

currently waiting for places to open to try and locate one...
 

Alex Crow

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easy access on your engine, just remove plastic cover and look exactly where i said. if it is not seized it is a doddle in my terms of reference!! can't guess at your abilities though, but you seem to have done jobs before??
 
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harpersimon

harpersimon

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easy access on your engine, just remove plastic cover and look exactly where i said. if it is not seized it is a doddle in my terms of reference!! can't guess at your abilities though, but you seem to have done jobs before??

Hi - yeah happy with spanners - do all my own work that I can - so shouldn't have a problem there - just locating it and having never owned a merc working out how to get the plastic cover off :)
I am going to get one somewhere so I know what I am looking for and then drive home and look to change. I am lso 99% sure its that sensor as I have the exact symptoms of one failing. Just hope it doesn't decide to cut out up the motorway!
If I get stuck will be on here shouting!
Thanks
 
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harpersimon

harpersimon

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Right - have located one at Eurocarparts - Bosch 0261210170 - can anyone verify that for me?? - its about £40 all in from them.
 
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harpersimon

harpersimon

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Drove 250 miles North this morning, without a hitch!! Tempremental isn't the word!! Even managed to park at the parts place, obtain the part and restart.
Anyway - I have the new part in my hands.. will be fitting tomorrow when I am not so tired (ALOT of driving for work this week) and report back. Least I know what I Am looking for now!

Is it simply remove and refit - no resetting of any ecu or anything required - and away I go?

Pointers to remove the top plastic cover also appreciated.. or I will just figure it out :)
 
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rpe2

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The cover just pulls upwards.

The sensor is plug and play.

Good luck! :D
 
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harpersimon

harpersimon

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Sensor located and (eventually) removed.. you could do with having small hands for this job - to say its tight in there is an understatement. Mine was siezed inplace, but some wiggling, swearing and tugging has got it out. I'll try and clean around the hole although I suspect no such issue getting the new one in. Am taking some pics of location of sensor if anyone might find that useful
 

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pics are always useful to someone at some point!
 
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harpersimon

harpersimon

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how do i add them? as attachments to the post?
 
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harpersimon

harpersimon

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Replacing the Crank Position Sensor - some pics

Sensor replaced and so far so good - although clearly I will need to run the car for some time, and try running on hot days to totally guarantee this is sorted. Here are some pics and a description of how I did it, on a V6 - including the sensor location and what it looks like

1. Remove the top engine cover / filter housing
2. The pics show where you are looking for the sensor - back left of the engine from the drivers seat, on top of the bell housing. Its VERY tight to get to, so I removed a clip holding the top wiring harness so that can be moved out the way
3. with that able to be moved, you can get your hand down the back and unclip the sensor wiring
 

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Alex Crow

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well done simon. told you it was a doddle! nice glove btw, shamone!!!!!!

you say back right of the engine, usually in automotive speak left and right mean when facing in direction of travel. this can cause confusion, hence the usual use of nearside/offside or driver's side/passenger side.

did you have the right socket then??

have had to drill out seized sensors before, can you imagine the fun i have.
 
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harpersimon

harpersimon

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Part two

4. The sensor is held in place with one bolt, I didn't have a torx socket but a 4BA on the end of several 1/4 extensions works fine. You can't see the bolt but with some light can navigate onto it and after cracking off mine was easy to unscrew.
5. The sensor was stuck pretty well - as I was replacing it I put the blade of a large screwdriver in the top part to twist it a bit and free it off. With alot of wiggling and pulling in and out to free it up, eventually it came out
6. Check the new sensor against the old one - just to make sure you have the same part
7. One pic shows the sensor hole and bolt hole next to it - it would be nice to clean up around the hole to provide a nice surface, but its tricky - I did manage some fine sandpaper on the end of my extensions to just rub around the general area.
8. installing the new sensor was pretty easy, getting the bolt in a little trickier - I inserted the bolt into the sensor so I could get it partially screwed in, rather than put the sensor all the way in and try and get the bolt in with fingers - its virtually impossible to twist the bolt once your hand is wedged in!
9. after re installing, make sure you reconnect anything you took off - I took the time to have a general tidy up and even cleaned the top cover.

Hope this helps anyone trying to change the sensor. Total time for me (fairly good with spanners) 4 hours - most of which was getting the old one out and taking my time basically, with a soup break in the middle!
 

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