GT Twin Turbo Decat
 

I wrote about this in a different thread so excuse the repost but no-one answered me. I just had a decat back box and centre section fitted and now the car is dog slow with no power.

The chap who fitted it said it wouldn't need any ECU twiddling but they did remove a device previously plugged into the old centre section which I am told was my rear O2 sensor. The car is an auto which doesn't help and it is now all revs but no go.

Heeelllppp!!!

Screwd.

What year 'n' model is your car?

If the sensor that has been removed was situated in the cat, then it's an EGT.

TT's have 2, one for the primary cat and one for the centre.
It will need this sensor.

Do a CEL check, to make sure nothings a miss else where.

HTH

Mark
UK Twin Turbo Legacy Register

Many thanks Mark.

1993 Legacy GT Estate. I don't know what a CEL check is...
The exhaust centre claim to have done loads of these before but the sight of my old centre section dangling from a wire left me a teensy bit worried. He said it was a temperature gauge. Then I drove the car and it has no torque, revs out though.

Screwd.

Hate to say it, but decatting the centre of a bg5, can cause boost spikes, as the ECU can't read the boost quick enough, it somes times boost/fuel cuts.

Doesn't explain no torque though.

See my website for the CEL check.

Who done the exhaust?

Mark
UK Twin Turbo Legacy Register

Ok. It was Hayward and Scott, Basildon.
Thought they ought to know what they are doing...

I have registered at your site, guess I had better spend more time reading through it. My other thread is suggesting an auto box problem too.

It will still top 150 though (ahem!) but I had better not test this too often until these issues are resolved, I'll have a look at my "check engine light" codes tonight.

Screwd.

Had mine replaced at H&S, but insisted on the cat.
There have been cases of TT's losing engines or popping head gaskets, after decatting the centre.
Time for a boost gauage.

If you want the cat, they have to do more work :)

Even the Impreza needs adjusting after decatting.

The diagnostics for the g/box is also on the site ;)

Mark

Mark, thanks again. I might go back to H&S and see if they will replace this system. I love the noise but I was told (by Ian) that I wouldn't need to do any further mods when fitting this exhaust and now everything points to power loss unless I spend serious money on the ECU etc. Will check CEL as suggested on your site.

Screwd.

All you need is the cat welded back in, with the egt.

Mines running an H&S centre with my cat (no centre box), 4.5" tail BB with extended silencing (no boom).

Lovely deep burble :D

Good Luck

Mark

Thanks again! I will go back and ask. Let you all know how I get on.

Cheers

Screwd.

Hmm. Conflicting information. H&S are saying the sensor they removed is a "hot cat" sensor and imply that there is no problem with removing it. Other information above suggests it is the EGT (rear O2?) sensor and thus VERY important.

I need to be able to prove which sensor it is - with no question marks. I can then go back to H&S to get this sorted.

I'll have another good look around the Turbo Legacy website for detailed info, otherwise any further help much appreciated. I don't want to blow it up proving the ECU has been mortally offended by the removal of this mystery sensor.

Screwd.

Update:

CEL checks out ok, no warnings.
Auto box has been assessed and is also OK.
So it must be the exhaust and/or missing sensor.

For info I took the car to Mister Transmission in SE London. They were recommended to me and now I can recommend them to you: 020 8691 6494

My next step is to find an ECU expert to sort out any gremlins, get to the bottom of the "missing sensor" and present H&S with my findings. My premise is: since I asked them beforehand if I needed to shell out any extra with an ECU remap, they should somehow re-fit the blasted sensor without extra charge...

Somebody tell me if this is all too boring and I should just shut up (Um. That would be somebody not associated with H&S!)

Screwd.

Working on it....

Got there :)

After trailing the wiring diagrams, no luck :(

But some one on the yahoo groups has hacked the TT ECU

And I found this http://www.zen21168.zen.co.uk/ecuwiring.htm

Please note pins 13 & 39

Pin 39 being the sensor you req, sits in the centre cat, which you now no longer have.

HTH

Mark

H&S have already offered to refit the sensor, looks like they were right about it being a temp sensor (or have the wrong information from the same source!). It might well be a different name for the same device...

Either way I will have this refitted and let you all know what difference this makes. I will probably also have the ECU reprogrammed/replaced at a later date to benefit from the free flow exhaust.

Many thanks Mark. You are a star :-)

Cheers

Screwd.

Whacking a big free flowing exhaust is well known to cause licorice all sorts on TTs... Hard to predict whether the car will become a slug (like happened to mine with big HKS pipe on it), or a rocket (which is almost as scary coz it is likely lean and raises the chances for the primary to fail, or for det).

Supporting mods are a must - knocklink, and ecu (subcom or flash) are the minimum IMHO.

Good luck getting it sorted.

Thanks AJ. Can you tell me where and how much for the ECU? PM me ufulike.
Cheers
Screwd.

Sorry m8, no idea on tuning your era as I came into the game on later cars, but the fragility of the TT is something that is pretty well known in the TT community.

When it comes to tuning, the tuner is the key of course, but I've no idea who does them on that era car, or even if a remap (vs sub-computer) is on the cards or not. It may pay to do a bit of a call around to the big names for advice/help: Bob Rawle, David Wallis, Powerstation, TSL et al.

HTH

Update: finally nailed this sensor. Ian at H&S was perfectly correct, my 1993 GT twin has a rear hot cat sensor which only comes into play if the rear cat (now removed) bursts into flames. Thanks to Ian and Pat for sorting this out.

However, having fitted this exhaust, I will undoubtedly need to have the ECU reprogrammed. Moral of the story so far? If you start dicking about with a complex system like this, better have deep pockets.

Having been introduced to Pat, a well known ECU guru, I hope to persuade him to have a go at zapping the ECU in a week or so. I will post updates on a new thread. Many thanks to all at H&S for their genuine concern and offers of help.

Screwd.

Good luck with getting things up to scratch. Pat is indeed a well known tuner. Hope it all goes well.

Please keep us all informed as I would be interested in a re-map for my early MY96 GTV.
Hope you get it all sorted out.

This would be seriously good news if Pat can re-map the std ECU :)

Mark