[MGS]

Hi all, I need your help before I drive myself off a cliff with my GT (3.2). I sold my 3.0 GTV last year to buy my GT and the more I drove the GT the more I was surprised that it felt slower than the GTV and not just by a bit, the 3.0 felt significantly faster throughout the bottom end right through the rev range. The GT is still a quick car don't get me wrong but it felt a way off my GTV. Note the cars have the same kerb weight (GT is actually a bit lighter so it should be faster by all accounts at the worst at least as quick).

The cars both have the same spec, CF2 Manifolds, stainless cat back exhaust, custom remap. Q2/Quaiffe. I love my GT in every way the handling, the looks and the sound, but after lots of driving I've realised it has a definite power issue which is exasperated under specific driving conditions (mostly on an uphill stretch of road/under load). Here's the best way I can describe it:

At part throttle, going up through the revs from 2000 RPM, at around 3500 RPM it feels like the car is being 'choked back' or restricted as if its being starved of fuel. Its as if the power is trying to unleash but its being reigned in massively so the revs feel like they're rising much flatter than they should be. It feels like just before its meant to pull away its getting choked back. Here the work its had done:

Fuel pump replaced
MAF replaced
Spark plugs renewed
Air Filter cleaned
Cam Belt Timing adjusted
Checked air hoses to plenum chamber for air leaks
Injection/Fuel Cleaner used
Pre-cat Lambdas replaced and ECU reset (one Lambda was white and dis-coloured)

After all this, the problem is still there and its driving me insane. The car starts on the button and never fails, it just has this power issue. The computer doesn't ever have any errors, it doesn't misfire its just flat and being held back. Most people would drive it and think I'm mad as it is a very powerful car but I know its not running as it should be.

I know this because I drove it a couple of weeks ago and for 15 minutes from start up its power was completely unleashed, it felt like a completely different car that would have left my GTV for dead. Then after turning it off and the next start up the power issue came back. The only difference that I can think of to normal was that it was very low on fuel (as it was about to have the fuel pump replaced).

I have also discussed this it in another thread where I was comparing the power difference of a GT 3.2 to a GTV here:

http://www.alfaowner.com/Forum/alfa...26-alfa-gt-3-2-faster-than-gtv-3-0-litre.html

but started this thread as I now know there's a mechanical issue. I really would appreciate some thoughts and ideas before I book it into my Alfa specialist again as I'm all out (of ideas and money)!

 

[Mitch916]

I'm suggesting this as a long shot and without any GT knowledge do don't shot me but has it got an electronic accelerator? I had a similar issue in my old V6 166 years ago as that was fixed by resoldering on the accelerator pot if my memory serves.

 

[MGS]

I'm suggesting this as a long shot and without any GT knowledge do don't shot me but has it got an electronic accelerator? I had a similar issue in my old V6 166 years ago as that was fixed by resoldering on the accelerator pot if my memory serves.

Mitc916 sorry pressed quote button by accident - Thanks for reply yes the GT does have fly-by-wire throttle and I have wondered if it could be the cause but its not throwing any errors although this doesn't always mean there's no issue. Its also had an ECU reset which I presume resets the throttle so guess apart from cleaning the throttle there's not much else I can do?

 

[dominic2115]

Throttle reset procedure is described in this thread forth or fifth post.
http://www.alfaowner.com/#/forumsite/20947/topics/962746?page=1

 

[FAssarsson]

I'd say replace the 2nd pair of lambdas and if that doesn't work try swapping to another throttle body.
May seem like a far stretch but a faulty throttle body can lead to strange behaviour. (On the engine side, not yours..)

 

[AussieAlex]

Just throwing this out there as a last resort to look at. But you said it has a custom remap?

Has the car driven this way ever since you purchased the car? If so, there is a chance that the map may be the source of your problems. But definitely check all other options like throttle reset before going down this route. But it wouldn't be the first time that a custom map has caused issues.

 

[115686]

At 3500 rpm it should be just about to go mental with the TC light coming on if you are booting it in low gear.

Was there any diagnosis that led to the parts being replaced, or was it a case of 'I'll replace all the likely candidates'?

How many miles? With all that lot done the next step has to be a compression test.

 

[Aramis]

my GT also does that, only at about 3,500 does it kick in and takes off like a rocket...nothing wrong just different acc. curve to your old gtv

 

[MGS]

Thanks all for replies.

FAssarsson - I was under the impression the pre-cat lambdas are the only ones worth replacing as the second set just monitor how well the CAT is running (and the CAT has been tested and is fine). I definitely think looking to swap the throttle body might be the way to go next.

AussieAlex - Yes the issues was definitely there before the MAP - in fact the MAP confirmed the issue as the output graph for before and after showed an erratic 'up and down line' (rather than smooth) in the rev range I'm experiencing the issue.

RXE - Yes most likely parts were looked at by specialist, and some (like MAF and Lambdas) replaced from my own (albeit limited) knowledge of Alfas. Its done around 75K and as from memory compression test came out strong on all cylinders.

Aramis - It does behave like you say but it definitely does hit a flat spot as if choked.

UPDATE : I only had the Lambdas changed yesterday (and ECU reset) and when I drove it home yesterday (only a few miles) it didn't feel any different. However today I have given it a good run and the power is absolutely immense, it feels noticeably more powerful. I'm not sure how long the self learning on the ECU takes to kick in and although I have still only done limited miles, it really does have a stack load of horses back.

BUT the 'choking' under certain conditions is definitely still there. I'm now wondering if I have/had a combination of two issues, lack of power and 'something else'...The Lambdas seem to have sorted the power issues out so I'm going to take a good look again for an air-leak as that what my gut says.

Thanks all for responses will drop an update later today.

 

[GavinH]

Good to hear it's improved a bit.. if not solved fully. Be very careful if you are cleaning carbon off the throttle body as if you reach in and move the actual throttle plate manually, you're forcing the gear mechanism inside.

There is a way to move the plate without damaging the mechanism, it involves removing TB, unclipping the cover, and then taking out one of the plastic cogs... but it's a VERY delicate job to manage not to damage the electronics. There are 4 or 5 little "needles" inside that contact a exposed circuit board..if bent out of shape it is knackered. Can't recommend this unless you know what you are doing.

Far safer to try cleaning by removing the TB (remove concertina section and undoing the 4 x 5mm allen bolts) and then spray with an aerosol carb cleaner from both sides. That way you should shift nearly all of the carbon. Also, take care not to lose/break the gasket between the plenum and the TB.

 

[MGS]

Good to hear it's improved a bit.. if not solved fully. Be very careful if you are cleaning carbon off the throttle body as if you reach in and move the actual throttle plate manually, you're forcing the gear mechanism inside.

There is a way to move the plate without damaging the mechanism, it involves removing TB, unclipping the cover, and then taking out one of the plastic cogs... but it's a VERY delicate job to manage not to damage the electronics. There are 4 or 5 little "needles" inside that contact a exposed circuit board..if bent out of shape it is knackered. Can't recommend this unless you know what you are doing.

Far safer to try cleaning by removing the TB (remove concertina section and undoing the 4 x 5mm allen bolts) and then spray with an aerosol carb cleaner from both sides. That way you should shift nearly all of the carbon. Also, take care not to lose/break the gasket between the plenum and the TB.

Thanks GavinH, I'm going to go with the Carb cleaner method you've suggested. Just been out again and the power is definitely back, I mean its back with a vengeance... It pulls really really hard right through the revs and gets to license breaking speeds really quickly...I'm not counting my chickens just yet because I've been at this point so many times. I need to give it several more runs before confirming the power side of things is ok.

It still has the slight 'choking feeling' at times (although better than before) when at part throttle which I'm now convinced is an air leak (if not throttle body related).

The piping from the air filter to the throttle body all looks good no signs of any leaks but I'm now starting to wonder about the carbon fibre plenum.

I had a plenum fitted as an upgrade a while back and it had to be replaced due to an air leak which was giving similar symptoms. I'm wondering if this one is again leaking air causing the same symptoms. I reckon the lambdas and a possible air leak together were exasperating the issue and now the lambdas have been replaced its resolved part of the problem.

I was going to take the plenum chamber off completely to check it thoroughly for an air leak but I don't want to run the risk of doing it any mischief and unsure about how tight bolts and everything else should be when bolted into carbon fibre so my plan is:

1. Get some carb cleaner now and give the throttle a quick spray
2. Get it booked in to my Alfa Specialist to have the plenum chamber checked over.

Will keep you updated I don't think its far from getting resolved (fingers crossed)!!!!

 

[Mymatemarmite]

Whilst you've got the carb cleaner out try giving it a suirt around any areas of the plenum that you suspect of leaking....if it's sucked into the plenum you'll notice a change of note to the idle.

 

[GavinH]

As per previous poster, this is a very good idea. If you have a custom plenum I would definitely give this a once over to be sure there are no issues there. Tricky to handle if it's made of soft material though!

Is the car idling smoothly? The effect of an air leak (in theory anyway) should be most noticeable at idle. This is because the relatively small amount of air that can travel through the leak become proportionately less at higher revs, and thus has less impact on the combustion process.

 

[MGS]

GavinH - great thank you and yes it does actually idle pretty smoothly.

I took the air hose off the right hand side of the throttle body and sprayed copious amounts of carb cleaner which dissolved a load of gunk and it looked spanking clean on this side. I put the hose back on and started the car, cough splutter, splutter, (because of the carb cleaner) then it started fine and then engine management light has come on (presume this will clear after a few restarts???).

But the 'choking' hesitation itself issue has got more pronounced again, think this is getting closer to the problem. I don't have the kit to check the error code but I would bet its throttle related.

I didn't even get to cleaning the left hand side of the throttle body I'm going to take a stab at that tomorrow.

So new plan is:

1- Carb clean left side of the throttle body
2- Find out what error code is and get it cleared.
3- Carb cleaner on plenum as per Mymatemarmite recommendation to check for air leaks (thank you kindly)
4 - If all above fails look at replacing the throttle body

Will drop an update soon as I have one.

 

[GavinH]

If it is the carb cleaner, hopefully the fault code should disappear by itself after a few miles. I wouldn't go to bother spending money having it read, it's probably just a misfire fault, the cause of which you know anyway.

If you're getting a new TB, try 2nd hand (from likes of Autolusso) because the cost of a new one is scarey...or if you have a mate with a v6 ask him nicely can you swap temporarily and see if that fixes things!

 

[MGS]

Thanks GavinH comments most appreciated. Update to follow tomorrow!

 

[MGS]

Ok turned her on this morning- no engine management light, happy days! Took the throttle body off the plenum, fairly simple job.

The throttle body was absolutely blackened on the left side. I carb cleaned the hell out of it and put it back together.

Can't believe the improvement it's made, the power is immense and throttle response is so much crisper.

I'm going to do some proper tests before I know the second issue is sorted as it only does the 'choking' issue under certain conditions.

Further update to follow!

 

[115686]

Switch the ignition on, put a brick on the accelerator. The throttle butterfly will open and you can easily clean both sides.

 

[Marko1960]

GT 3.2 Lacking Power -...

I aint no techie, one thing I do know however is that the GTV 3.0 litre engine is a proper Alfa Romeo engine and the GT 3.2 is a shared engine that can be found in such mundane cars as Vauxhalls etc. maybe thats it

 

[_The_Editor_]

I aint no techie, one thing I do know however is that the GTV 3.0 litre engine is a proper Alfa Romeo engine and the GT 3.2 is a shared engine that can be found in such mundane cars as Vauxhalls etc. maybe thats it

Certainly not the case!

The 3.2 V6 in the GT is the same that's in the 147/156 GTA.... Last of the big V6 Busso's...

Definitely not the same GM 3.2 JTS engine that's in the Brera!!