No boost after engine/turbo upgrade

[gmac78]

So, a quick test with the trip computer not working and the diff lock engaged resulted in NO automatic unlock at 15mph. Also on VCDS the speed is stationary at 4km/h, no increase as the car is moving. 20 or so miles further down the line i take a relatively sharp left hander which at speed which seems to have brought back to life the trip computer. Hmmm a loose wire somewhere perhaps?

So i quickly stop, engage the diff lock, drive off and this time the diff disengages at 15mph. I stop again, clear the G68 code to see if the speed increases on VCDS but no joy, stationary at 4km/h with no increase as i drive off. Within a few 100 yards the dash light is back on with the G68 code stored. So even with trip computer working and the diff disengaging as it should i am still seeing no speed increase on VCDS and the fault code being generated??

Whats your thought on this?

[twoqu]

Does sound like a loose connection. Did you have to repopulate pin 50 with the VSS when you converted. I guess the trip computer needs this signal to calculate so thats why it came back to life. As the speedo works it can only be the output through whatever connects it to the ecu/diff lock.

Looks like it would be something to do with the blue dash cluster connector perhaps. Not sure whether you have disturbed the cluster. It will be white/blue wire.

[gmac78]

You've just jogged my memory there and perhaps hit the nail square on the head!!!! I did repopulate pin 50, however it doesn't terminate anywhere as i think i asked the question a few months back and came away thinking it was something to do with launch control for the 7400 chips i bought and GALA, or something along these lines. This wire is rolled up and tucked away with only one end connected at the ECU!!! The other end of the cable is simply taped up. Arrrrgh!!!

I take it this in an ECU input and not output?

[gmac78]

But then why would my trip computer come to life all of a sudden?? Perhaps there is a loose wire elsewhere? the cluster has not been out in ages, certainly not this year anyway.

[twoqu]

Well its Halloween so perhaps thats accounts for spooky stuff!
Without doubt pin 50 should be connected to the speedo output. So yes its an input for the ecu. The VSS goes to various places and one schematic I looked at implied possibily a crimp in the loom where it might branch from.
It seems logically that the reason the ecu is not seing the signal is because it is not physically connected!

If you have a redundent VSS at the radio I guess you could try a lash up to the ecu to prove it's just lacking the signal.

[gmac78]

Yes i totally agree, i remember connecting pin 50 to the blue/white wire at the radio connector a few months back, i'm just wondering was that around the time i checked VCDS for the speed movement because i defo remember observing VCDS as i pulled away out of my drive and seeing it working. Theres just so many wee issues i've had of late that i forget now. Tomorrows first job will be to connect that wire up and go for a spin, i'm hoping for good things!!

Cheers mucker, much appreciated!!!

[newsh]

Fingers crossed, you're onto it [emoji51]

[twoqu]

Of course it will only that stalling issue on the V stream. There is mention of a rev limit of 5320 rpm being applied if that code is logged. Not sure whether you have experienced that.

[newsh]

My car goes so quick from 3k to 4k5 I rarely rev above 5k!

[gmac78]

Evening lads, well, so much for trying the VSS wire first thing, turned out to be the last job of the day. Unfortunately it made no difference, i was rather rushed because i was knackered after a long day so i'll need to double check i connected the wire from pin 50 to the correct wire behind the radio. It was a connector with 3 or 4 cables in it and i spliced in to the blue/white wire.

Now then, last night without this wire connected, my trip computer started working as it should and at the same time my diff lock would auto disengage when activated. Since i connected this wire tonight, the trip computer and diff auto disengagement has not worked on the drive home. I'm just wondering if and when the trip computer starts working again will i get a VCDS speed read out. The laptop will be with me in the car to pounce as soon as the time comes.

Whats your thought on these findings?

Had my hopes up for this one, however nothing but disappointment!!

Back to the drawing board.

[twoqu]

Think it should be white with blue tracer stripe in case there is another wire there.
It does seem logical that any speed dependent system (trip/ABS) would need a signal. So as you say its a bit odd that they worked intermitantly unless purely by chance the taped wire made a connection when you went round the bend.
You would need to work out if they are fed independently with the VSS. If so then a diconnected ecu would not matter.

[twoqu]

Not sure there is anything of interest here. Haven't read it myself yet!

http://www.s2forum.com/forum/showthread.php?t=45307

[twoqu]

I'm not sure what year your car is but a supposed 3B schematic shows that the VSS appears to exit the cluster and splits to the Radio and connector T10/9 which is on the aux relay plate I think and the motronic loom connects to that for the VSS with the large black wiring connector.

[twoqu]

Think I am getting confused because you adapted a 3B loom. Did you have to add a VSS feed to the ecu or did the 3B use it as well. Can't seem to find it on a 3B pin out?

Right I can see that you need to add it and I guess the radio is the easiest feed!

[newsh]

No boost after engine/turbo upgrade

The other possibility is that there's an intermittent short to ground somewhere (as I think was the case with mine). Somewhere behind the radio or in the feed to the diff switch in the centre console