S2 ABY black smoke and misfire on boost, temp sensor?

[Cossie7]

hi all

well with a rocky start to s2 owner ship with water problems that have now been adressed i'm still left with this problem. the car was fine with good boost no smoke etc but then its started doing this again there is no power as sson as the turbo starts to come in the car splutters and kicks black smoke out.

also at the same time the car has started to give the red temp warning on the clocks (car is not overheating)and i have traced the problem back to the 4 pin temp sensor. when i tried to get the plug out it just crumbled and one of the wires was rotted off (black with a blue stripe). obviously this needs replaced and as soon as i find one i will do it.

what im wondering is could the temp switch be the cause of my boost issues? just this is the first s2 ive had but have owned plenty of cosworths and vaux red top turbos and i have had the same issue with the red top turbos if the temp switch acted itself it played havoc with the mixture and it would result in this exact same problem but i dont know if it would effect an s2 the same way?

and help would be greatly appreciated

cheers

colin

[Rikki Kitto]

Is it a missfire or a boost cut, how bad does it feel when you are trying to accelerate a boost cut is fairly violent as the turbo starts to kick in it feels like you are gonna go through the windscreen if it feels like this do a boost leak test

[Cossie7]

Hi thanks for the reply

I'm pretty sure it's not boost cut as it's no violent I can bearly feel it and it does it as soon as it starts to build boost ie 5psi it basically won't take any boost at all

Cheers

[rynaqui]

Definitely a boost leak. Look around the engine bay for oily patches and check the boost pipes for signs of leaks.

[twoqu]

If you are getting an overheat symbol then its possible the MFTS (the sensor with the 4 pin plug) is malfunctioning. This will cause the vehicle to have mechanical boost only and is designed to save potential engine damage IF there is a genuine overheat condition.
Remove the 4 pin electrical connector and try again. You will lose the coolant temperature gauge but nothing else is effected.

[twoqu]

http://forums.quattroworld.com/s4s6/msgs/22584.phtml

[Cossie7]

Don't think its a boost leak as had it on the ramp today and checked all pipes and they all look good, also thanks twoqu that is exactly what I wanting to know as I said the red tops used to do exactly the same and it was strange how it was running fine until the temp warning came on. I'll try and unplug it, I would of done so earlier but was unsure of the effects it would have on the car.

I don't suppose any one has any recommendations on where to locate a new sensor and plug? Or am I better with a second hand item as I don't think the 4 pin units are available anymore

Thanks

[Cossie7]

Just had a look at the link, thanks that's great ����

[UrS4boy]

Just had a look at the link, thanks that's great ����

The replacement F76 MFTSs are only 3 pin but they still work fine. The link that twoqu provied was written by me and it contains the pin-out for the 4 pin plug and a PN for the plastic portion of the plug that you might be able to buy and get your plug back in shape.

[UrS4boy]

S2 3B and ABY and RS2 ADU Boost Leak Testing

Have a read on this:

S2 3B and ABY and RS2 ADU Boost Leak Testing:

http://www.s2forum.com/forum/showthread.php?t=63974&highlight=boost+leak+testing

[andy10v]

Just unplug the MFTS to check, takes a couple of seconds. Car will run fine, just no water temp on the dash so keep an eye on oil temp.

I had that on mine, would boost fine, then the red coolant light would come on and no boost. You can buy a new MFTS plug and new contacts with a wire for the plug from Audi for not a lot of money. A lot of the 3 pin MFTS do not read correctly.

If you want to check for boost leaks a visual inspection will not work, you need to pressurize the entire intake system.

[Error404]

Dodgy MFTS will not cause the car to throw smoke or run badly it will just limit boost to spring pressure.
You probably have a boost leak. Pull the codes first. Do a full leak test, visual check is no use.

[Cossie7]

Hi all thanks very much for the advice, I couldn't wait so have just had the car out after unplugging the MFTS and the first few hard throttles the car was great but then back to the same situation so I think you may be right I must have a boost leak or it's blowing spark out or maybe a cool pack breaking down when it gets hot? I just can't understand if it's a boost leak why the odd time it will boost properly? Also have read fault codes and nothing apart from lamba the odd time but I'm putting this down to how right it runs when it starts missing

Thanks again for all the help so far I've never known a forum quite like it.

Cheers

[Error404]

Post the codes.
You say lambda, that means it's not achieving the mixture the ECU is requesting. 99% of the time that means boost leak.

[andy10v]

You may well have a few issues. Once you unplugged the MFTS the ecu would boost again, if you have a boost leak it would boost, the ecu would see target boost was not reached and then the ecu would stop it boosting again.

If you have not leak tested the intake you will probably have boost leaks.

If you have a boost leak the MAF meters the air in, the ecu fuels accordingly, but you are loosing air out and hence rich.

Once its boosting properly you may then run into coil issues if they are tired as well.

I would

Read fault codes
Clear fault codes
Boost leak test
Test drive
Read fault codes

Remove the crank case breather from the MAF hose and plug the MAF hose, pressurize the entire intake system, spray down with soapy water to find small leaks (check around injector seats etc), large ones will be audible. I would just replace all the small bore vacuum hoses.