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Rich running / CTS Replacement

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Candycj1
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Joined: Thu May 17, 2018 10:22 pm
Location: London

Rich running / CTS Replacement

Post by Candycj1 » Sun Jul 22, 2018 10:20 pm

Hi all

My 88 E24 has been running very rich - starts fine, idle ok (cleaned the ICV which seems to have addressed a previous stutter). Has had a recent service with fluid & filter change, new plugs etc. Garage suggested its probably the AFM but reading here the CTS sounds a likely culprit. I put a meter on it (assuming i'm checking the right thing :D - lower of the two sensors in the pic and got no reading at all, i.e. open circuit - i'm no auto electrician but i'm pretty sure that's bad.
Image
Few q's then:

- Am i looking at the right thing? (and what's the blank plug between the two connectors, was there a sensor here that's not used in later cars?)
- Am i right in thinking this will cause the brain to think the engine is always cold, hence explain the rich mixture?
- Do i need ti drain the coolant to change it over?
- How likely am i to damage the housing in taking it out, any tips?

Advice appreciated, this is my first foray into tinkering in the oily bit...

Cheers
James

ron
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Re: Rich running / CTS Replacement

Post by ron » Mon Jul 23, 2018 7:27 am

Ensure no pressure in the cooling system. Unscrew (you shouldn't lose much coolant) and replace with new one.
They are ALWAYS rustier than you thought!!!!!!
'88 High line.
'85 M #228
'85 M #207
'80 735i

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Brucey
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Re: Rich running / CTS Replacement

Post by Brucey » Mon Jul 23, 2018 8:04 pm

yes If the CTS is read open circuit that results in 'stone cold engine' type fuelling which is so rich the engine won't even run when it is warm and suddenly sees this fault. Actual failure of the CTS is far less common than a dodgy connection to it, BTW.

The part is not expensive but carries a small risk to the tstat housing; they occasionally crack when a sensor is removed.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Candycj1
Posts: 43
Joined: Thu May 17, 2018 10:22 pm
Location: London

Re: Rich running / CTS Replacement

Post by Candycj1 » Thu Jul 26, 2018 10:34 pm

Happy to report the CTS came out willingly, slight coolant spillage but nothing i couldn't soak up with a cloth and top up later. Old one looked pretty ropey, shiny new one now in place.

First test drive afterwards - i'm almost hesitant to report it seems like a different car. No stuttering at all when i put my foot down, no wet tailpipe and it doesn't smell like a filling station (still a whiff of fuel in the engine bay but can't see any leaks anywhere). Can't quite believe that's all it was but it does seem to have done the trick. Very happy!

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Brucey
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Re: Rich running / CTS Replacement

Post by Brucey » Fri Jul 27, 2018 10:49 pm

yay, good result!

fingers crossed it stays 'fixed'.... :wink:

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Candycj1
Posts: 43
Joined: Thu May 17, 2018 10:22 pm
Location: London

Re: Rich running / CTS Replacement

Post by Candycj1 » Fri Sep 21, 2018 6:02 pm

Brucey wrote:
Fri Jul 27, 2018 10:49 pm
yay, good result!

fingers crossed it stays 'fixed'.... :wink:

cheers
Brucey i'm pretty sure when writing that you knew it probably wouldn't...

...after i came back from a 3-4 week break she *seemed* ok on starting but a couple of miles in suddenly started to stutter again; this seemed to coincide with decelerating (as in lifting off from around 50), since when she's back to a similar behaviour as before. Starts first time and idles ok at around 800 but even going a short distance she soon starts to stutter when accelerating; less so when at constant speed but even does it a bit when back at idle - and again smells rich. Any suggestions on where to (re)start investigations? No obvious air leaks but that would cause lean running anyway wouldn't it? Could it be AFM and if so how would i test...?

Thanks
James

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Brucey
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Re: Rich running / CTS Replacement

Post by Brucey » Sat Sep 22, 2018 3:41 am

one check you should make is that the CTS reads the same under the bonnet as it does at the ECU connector. If it doesn't, it means the contacts are bad, probably in the plug that connects to the CTS. My guess is that the CTS connections may have been corroded to start with and worked for a while with a new CTS and then corroded again. If you don't want to disconnect the ECU and want to have a stab at fixing the problem without proper diagnosis, I'd suggest just checking/cleaning the CTS plug contacts.

Problems of this sort are so commonplace that I recommend cleaning and lubing these contacts at least every year as a matter of course.

Of course it is possible that there is an unrelated fault of some kind but it is best to chase down the obvious/likely things first. Do one thing at a time and test the car again; that way you will know what the problem was when you fixed it. Going shotgun at it may fix it but leave you none the wiser as to the cause.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Candycj1
Posts: 43
Joined: Thu May 17, 2018 10:22 pm
Location: London

Re: Rich running / CTS Replacement

Post by Candycj1 » Sat Sep 22, 2018 10:42 am

thanks for the advice Brucey - i had wondered if somehow the replacement had stopped working as it seemed to have reverted to the same state as before; bad contacts / connection would explain it so i'll get some cleaner on it and see if that fixes it before messing with the ecu...

Candycj1
Posts: 43
Joined: Thu May 17, 2018 10:22 pm
Location: London

Re: Rich running / CTS Replacement

Post by Candycj1 » Thu Oct 04, 2018 10:37 pm

Gave the contacts a good clean but tbh they looked ok to begin with - sadly made no difference. still starts fine and pulls ok cold but after a minute or two will stutter under acceleration as if missing a cylinder. Suggestions on what to check next?

As an aside the connector to the other sensor on the housing is a bit loose, tho again the contacts themselves seem fine - the issue is that the plastic surrounding the terminals on the sensor has cracked so the plug doesn't lock squarely like it should. I think this is the thermo time switch which wouldn't be the cause here (?) even if the connection wasn't being made (which i i think it is)?

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Brucey
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Re: Rich running / CTS Replacement

Post by Brucey » Fri Oct 05, 2018 10:35 pm

need to check sensor values at the ECU plug using a multimeter to be 100% sure of them

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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