Engine temp related poor running (VR6)

[dylan0451 10]

Hi,

 

As of the last couple of days ago the corrado has suffered an odd running issue. From cold (and not on every start, though it's getting more common) it starts really rough, lots of power loss and big vibrations. Unlike a coilpack/lead/plug issue, it doesn't surge or kangaroo under full throttle/low revs but just runs rough, no power and a deep bassy tone emits from the exhaust like a Subaru :-s

 

The computer reports approx. 8mpg when it's like this, smells that way too.

 

As soon as the engine gets to around 90-95c the issue disappears suddenly and full power, sound, economy is restored.

 

 

I've replaced the coilpack/leads/plugs last year after the coilpack outer casing started breaking up so am fairly sure it's not that, I'm assuming it must be cam or crank sensor?

[Jim Bowen 1]

I think one of the coolant sensors can do this, blue one maybe.

[Jim 2]

Yeah - does sound likely. Sounds like it's massively overfuelling.

[dylan0451 10]

cheers, coolant sensor you say? I'm thinking that requires complete removal of the thermostat housing?

 

I'm surprised the ecu doesn't just make a conservative estimate when it receives a faulty value rather than just fail massively!

[Jim 2]

Pretty sure you just remove the cover, and pull out the dodgy coolant sensor, and replace quickly before it glugs coolant everywhere - though admittedly have never changed one on a VR before.

[robrado974 1]

No need to remove anything , apart from the plastic housing that covers the sensors and that just slides off . Blue temp sender sends the signal to the ecu . Simply remove the plastic circlip and the plug on the sensor and it will come out . You will loose coolant at this point so have the new one ready to pop in . Take care to make sure the o ring comes out with it , these are provided with the new sensor . Snap down the circlip and replace the plug .

Rob

Edit , good idea to do all three while your at it .

[Stonejag 10]

If you unplug the sensor completely then the ECU should use a default temp of 70ºC - which will give you a very rich mixture until the warmup time elapses.

 

If you have access to VAG-COM then you can double-check it, think the coolant sensor error code is G61. Clearing the codes with the engine running will cause it to rev at around 2000rpm for 2-3 seconds before the ECU decides the fault's recurred and goes back to the default 70º setting. Think the harness is fed to the ECU via the fan controller so it may be worth unplugging it and giving it some contact cleaner on the off-chance.

 

If replacing the sensor, make damn sure you've pushed it all the way home! It's possible for the clip to seat fully into the housing but spread out around the sensor body rather than fit in behind it and hold it in place. If you do this then it will suddenly pop free while you're driving, and all your coolant will spurt out of the hole and strand you in a lay-by for several hours. Ask me how I know... :lol:

 

Stone

Edited August 14, 2014 by Stonejag