Author Topic: sensors  (Read 3474 times)

Offline z3i

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sensors
« on: May 17, 2013, 09:41:50 pm »
what should happen at idle when i unplug the co pot sensor? and the lambda sensor? as i unplugged them and nothing changed at all. am trying to diagnose why suddenly when i take the blue temp sensor plug off it doesnt go into service mode, the revs drop instead of increase

also  noticed the lambda and pot sensor wiring are the same and the can both reach each other, plugged them into eachother with no difference. how can i check they are going to the correct sensors and someone hasnt played around with them

the only thing ive done is change the throttle but cant see this affecting anything

thinking about taking the car to VW and getting a mastertech to look at it, getting really close to my trip and the car still isnt running right :(
many thanks taylor

Offline PeteG40

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Re: sensors
« Reply #1 on: May 17, 2013, 10:25:51 pm »
Plug on co got a different spring on it. More like dizzy plug than lambda which is sprung like blue temp sender


 Got a cam in it???

Offline z3i

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Re: sensors
« Reply #2 on: May 17, 2013, 10:37:44 pm »
Plug on co got a different spring on it. More like dizzy plug than lambda which is sprung like blue temp sender


 Got a cam in it???

ah! i see what you mean :) cheers, will check tomorrow when its light
yeah a PSD cam, dont know the durations. but it cuts out when cold on idle, and just put it down to an aggressive cam and chip

Offline PeteG40

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Re: sensors
« Reply #3 on: May 17, 2013, 10:47:08 pm »
what voltage is at the battery? then run crap with a poo alternator

Offline z3i

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Re: sensors
« Reply #4 on: May 18, 2013, 07:57:23 am »
Sorry, i meant knock sensor has the same wiring, had lambda on my mind and typed it stupidly
the knock and co pot sensor wiring is identical

No way! Checked my battery vvoltage about a week ago and was 14.5v

just checked this morning on a cold start, everything on was 12v at about 920rpm
held the revs at 1500 ish and goes to 13.5
gotta be duff alternator, do they just go overnight?
also doesnt the ecu rely on 5v or is that more modern cars
thanks for the help
on the plus it didnt cut out this morning, revs did drop too 800 lumpy as hell, but didnt cut out :)

Offline PeteG40

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Re: sensors
« Reply #5 on: May 18, 2013, 10:41:11 am »
Knock has similar spring to blue temp sender.  Id say maybe cam not dialed with vernier quite right or alternator on its way out. I have an alt u can borrow next time yr up or find a local refurb place.... place round us charges 50 quid. Good for peace of mind

Offline z3i

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Re: sensors
« Reply #6 on: May 18, 2013, 11:07:43 am »
Dont have a vernier, should i get one?
The knock and co pot wiring a definitly the same, could both be interchanged and you couldnt tell the difference
cheers mate :) i remember looking at the alternator when i changed the manifold and it looked crusty and old
will get it looked at by a place down the road, specialize in starter motors and alternators
thanks for the offer bud :)

Offline PeteG40

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Re: sensors
« Reply #7 on: May 18, 2013, 03:08:12 pm »
hmm -  well time to check out the wire colours in haynes

Offline z3i

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Re: sensors
« Reply #8 on: May 18, 2013, 06:10:55 pm »
Good shout, i never think to do the simple things. Turns out they are on correct, so isnt something simple. Any more ideas?

How can you check the co pot sensor is working? Ive set the resistance and checked the temprature part of it by checking the resistance. But nothing happens when i unplug it, should i unplug it and drive, see if that makes much difference

Offline hayesey

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Re: sensors
« Reply #9 on: May 28, 2013, 03:04:32 pm »
why do you want to unplug the CO Pot anyway?  I'm not sure unplugging that is supposed to make a difference.  Unplugging the blue temp sensor is the way of putting it into service mode which should affect the RPM - they'll only rise if it's timed up OK.

If you remove the blue sensor and nothing happens then it's a concern because it means the ECU isn't going into service mode (usually because it has a fault registered for one or more other things).

Get yourself a £10 VAGCOM lead and the free VAGCOM to see what faults it has (although I'd assume none if the revs change when the sensor is disconnected).  You can use the VAGCOM to see what readings the ECU is getting from various things.


Offline z3i

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Re: sensors
« Reply #10 on: May 28, 2013, 04:26:06 pm »
Its all timed up ok as i double checked it from last time as it was out
it used to go into service mode around a month ago and then since fitting another throttle body which actually sealed instead off leaking and changing the lambda sensor it doesnt go into service mode anymore

i wqs thinking about getting the vagcom as i read your post about diagnosing, but i cant find the lead that it plugs into

though a couple of days ago i checked my voltage at idle and it was 12v with everything on, must have died over a few weeks as i checked it not too long ago and was fine

took it off and the bearings are fecked, so got one coming tommorow
would low voltage at idle cause rough running? As when i rev it the voltage goes up to 13v
Sorry for the long post, and thanks for your help, will order that lead and have another look for the plug
would be good to see the readings as like you say, you can check if any are miles out
next thing will be to check resisitances between ecu and the sensors

Offline hayesey

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Re: sensors
« Reply #11 on: May 28, 2013, 04:34:35 pm »
low voltage will cause all sorts of problems yes. 

there is a post I put in the FAQ somewhere which says how to wire up your own diagnostic connector if yours is missing (as some cars randomly didn't have them fitted).

Offline Andy

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Re: sensors
« Reply #12 on: May 28, 2013, 05:23:56 pm »
If your idle speed is incorrectly adjusted that can cause lots of issues with 'service mode' too.

Offline z3i

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Re: sensors
« Reply #13 on: May 28, 2013, 05:34:04 pm »
That may not be helping, i dont think my idle speed is set correctly, but cant put it into service mode to set it
actually that might make sense as its only started happening since changing the throttle body so if the idle is out and your saying it wont go into service mode with it out
it does seem a bit low, i will have a play when i get my alternator and shes running again

yeah i just found it paul :) cheers, mine must be one without it, its j reg so one of the earlier ones,
Thank you

Offline z3i

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Re: sensors
« Reply #14 on: May 30, 2013, 06:34:14 am »
Andy you were right mate :) had to bring the idle speed screw out alot and now it goes into service mode :)
however it seems to cut out more and idle even worse in the cold, and the dash lights flicker at idle, even with my new alternator and with the engine warm
thanks for all the help :) appreciate it