rough start up breakthrough for dk and spaniel

[supercharged spaniel]

i plugged mine into a vag com thingy a while back and nothing noticable came up but that was just a fault code reader....what other sensors could make the ecu add more fuel?

[Dirrt]

I don't want to divert this thread [so just go round me and my annoying shit] but I have to ask - What is the blue temp sensor and what does it do?

[hayesey]

fault code reading on a G40 is useless, you need to look at the measuring blocks section in vagcom and actually watch the readings the ECU is seeing from various sensors when the problem is occurring.  It's not going to be a five minute job to do though.  Plus there are some oddities to look out for such as the fact that vagcom reports the air temp sensor reading at something like -20deg all the time if it's working correctly! 

blue temp sensor is in the thermostat housing below the distributor, it is blue and has a blue connector.  It tells the ECU what the coolant temperature is and the ECU adjusts fuelling accordingly.  Colder = more fuel enrichment adjustment to the map.  The ECU also contains several different fuel maps for different conditions, when it first starts up from cold, the cold temp reading makes it use a "warm-up" map.

[scotsjohn]

Look back to my post on 13th on this . I reckon the ECU is holding a memory of the old senders output and needs some sort of zeroing. You can re-boot the whole ECU to some extent so why not one individual component of it ?

[dubmanic]

another option is a dodgy wiring loom.  checking that involves a long session with a multimeter checking the pins on various sensor connectors back to the ecu connector, there is at least one thread I've written in the FAQ sections about doing this.  Plus checking the earth crimp inside the loom.  Although to me, it doesn't make much sense that it would only happen when cold and everytime it's cold.  Unless it was a break in a wire which fixed when some heat went into it to soften the wire insulation, it seems pretty unlikely though!

Has either of you had a VAGCOM on it yet to watch sensor values when the problem happens?

if polo g40`s have vag com were do you plug in to?

[hayesey]

they have a diagnostic connector yeah.  It's two, two pin connectors clipped behind the dash where the indicator relay is.  Under the glovebox.  You'll need an ODB to 2+2 adaptor (available on fleabay)

[PeteG40]

Look back to my post on 13th on this . I reckon the ECU is holding a memory of the old senders output and needs some sort of zeroing. You can re-boot the whole ECU to some extent so why not one individual component of it ?

g40s ecu isn't that technologically advanced...  if the sensor is faulty it will log it and not use it. if you replace the said sensor, it'll start working properly again whether you clear the code or not

[hayesey]

yeah it doesn't really store codes like more modern ECUs do.  You just need to fix the fault and then after about 10 mins of driving the ECU realises that signals are back within tolerances.  So you don't need to clear fault codes like on more modern stuff.

[DKnight]

well i examined my connector last night and the plastic wire outer crumbled and snapped, and i sheered the plug connector off

so i botched some wires on and hooked a multimeter on this morning and it wouldnt start, tried again same

so i unplugged the multimeter and it fired, ran rough for about 10seconds, then it was fine...

i feel a bit stevie wonder with this tho, im still sure the problem lies with the blue temp sender, i think it maybe the connector, which spaniel thinks the same, im going to get a replacement one today and see how it fairs.

[supercharged spaniel]

its got to be that plug/loom/sensor...if the wire/plug is corroded even slightly it will alter resistance ever so slightly which could be giving duff readings when very cold..

[PeteG40]

fingers crossed for you2.

I have about a billion blue temp senders i can test and give you to try if you like.

Pete

[hayesey]

which connector are you talking about where the insulation crumbled off?  the ecu connector or blue temp sensor?

[supercharged spaniel]

the blue plug connecting to the sender

[DKnight]

well i swapped my plug for a new one, got on machine and checked the emissions and it was running very rich

so tweaked the co2 pot acordingly and it was running nicely, moved timing to suit aswell, my mechanic didnt want to do the timing from the crank or the cam as he said it wouldnt be accurate.

and we couldnt get in on the spy hole on the gearbox

i mentioned about the co2 pot setting that it needs to be, and he just said, thats a base figure and with all the extra bits changed etc it needs adjusting accordingly

so he did and im running it now, and it feels nicer, gota wait till morning to see how it starts

[hayesey]

i mentioned about the co2 pot setting that it needs to be, and he just said, thats a base figure and with all the extra bits changed etc it needs adjusting accordingly

yeah absolutely, I keep saying this too.  Only proper way to set it is on a gas analyser.  Fingers crossed for tomorrow morning then.