Boost

[JSeaman]

About a week ago I upped my boost to 10-11psi (Using stock gauge) and ran fine for 3 days. One morning I booted it and hit fuel cut, from then on I kept on hitting fuel cut even when I lowered the boost. I am getting creepage so I think the wastegate is knackered which is not helping.

Anyway, I lowered the boost to about 7 psi just to be safe but got a problem on Saturday night that when I hit 4.5k revs. Tried in 2nd and 3rd, pulled to 4.5 ok then spluttered (best way I can describe it). If I then accelerated I could get past it but if I held it at 4.5 then it stayed spluttering. This was gradual increase in revs so boost wasn't really present.

I decided that the bleed valve could be causing the problem and that when I hit WOT the car ran rich enough to correct it ie runs richer - purely speculative 'cos I have no air/fuel gauge and got no warning lights. Needless to say I instantly turned the bleed valve to off and presto problem gone. Can't find any boost leaks and 5psi sucks - any thoughts anyone?!

[G.T]

I personally have never trusted bleedvalves not to introduce boost spikes, they certainly aren't in my mind a reliable way to increase your boost, plus the length of pipe run to the valve can affect things, all too random for my liking. Get a EBC on there, what spec are you running?

[JSeaman]

Yeah, the bleed valve wasn't something I fitted but I figure 'cos it's there ;o) The pipe is longer than I'd like as well.

I'm going to get an AVC-R soon anyway so I might bring that forward. If the bleed valve was causing boost spike then is it conceivable that it was knackering up the air/fuel mix at that rev range?

Forged pistons, mhg, stock CT26

Cheers

James

[Adam W]

James, is the check engine light coming on when it's sputtering?

It does sound like a classic boost leak to me, I didn't notice any old-looking hoses but one of them could have split somewhere. It could also be some sort of AFM problem, try checking the ECU error codes to narrow it down.

[Lofty]

Anyway, I lowered the boost to about 7 psi just to be safe but got a problem on Saturday night that when I hit 4.5k revs. Tried in 2nd and 3rd, pulled to 4.5 ok then spluttered (best way I can describe it). If I then accelerated I could get past it but if I held it at 4.5 then it stayed spluttering. This was gradual increase in revs so boost wasn't really present.
How are your plugs and leads?

[G.T]

Correcto mundo, too much boost=momentarily too much air, not enough fuel=lean running, in other words not healthy. Also, if you aren't running a boost gauge capable of displaying how high the boost is spiking, you have very little , if any idea how high the spike is running. Personally, I'd remove the bleed valve.

Also, I think the two things aren't linked. The spluttering you mention does sound like a boost leak, be worth as Adam says, checking all pipework is sealed properly. Check your HT leads are seated properly too.
What grade plugs are you running? If 6s try 7s, this made a difference for me.

[JSeaman]

Adam, Nope, no engine lights. I'd assumed the afm could be at fault but the wiring looks fine. Might have a spare one knocking about - will check tonight. I'll have a full check for boost leaks later too.

New plugs and Magnecor leads Lofty.

GT, I figured that was the case. Can't really do anything in the way of boosting until I've got a boost gauge which is up to the task so I've killed the fun for now! Adam, do you know what grade those plugs were?

What grade plugs are you running? If 6s try 7s, this made a difference for me.
Boost leak was my first thought but I couldn't guess why it would happen at 4.5k revs in either gear with really low boost?!

Thanks for the feedback guys

James.

[Adam W]

I put 7's in I think James, you can pull one out and read off the code on them to check but I'm 99% sure.

[Nick@TC]

They were 7's

James, got a nice GReddy boost gauge here :wink:

[JSeaman]

They were 7's

James, got a nice GReddy boost gauge here :wink:

NO!


How much :)

[Nick@TC]

£90 which is nearly half price (it's my personal one that I never used) 60mm peak/hold/warning white face

[JSeaman]

Is it PSI or bar? Fitting stuff? Does it light up pretty colours?!

[Nick@TC]

Is it PSI or bar?

2bar


Fitting stuff?

It's brand new never been out of the box, so yes, complete with fitting stuff.


Does it light up pretty colours?!

When's the sex change happening again?? :p
Lights up green iirc

[JSeaman]

Sod off! :)

(Still too noisy by the way!!)

I was after a -30 +30 psi one really. I can get a cheap and cheerful autometer el one for £70 but I'm tempted to go for the greddy one .. because it's a greddy. Not that I have any money at the mo - gave that all to you guys!!

Will let you know, cheers

James.

[Lofty]

from then on I kept on hitting fuel cut even when I lowered the boost.
This does sound like a boost leak. Have you checked your IC pipes (especially the turbo -> IC), 3000 -> TB, BOV, vacuum hoses? If it is a boost leak then you will be running very rich which could account for the poor performance.

[Adam W]

Sod off! :)

(Still too noisy by the way!!)

I was after a -30 +30 psi one really. I can get a cheap and cheerful autometer el one for £70 but I'm tempted to go for the greddy one .. because it's a greddy. Not that I have any money at the mo - gave that all to you guys!!

Will let you know, cheers

James.

You'll do well to pull - 30psi vacuum, I don't think anyones managed that before :) I was wanting a gauge that read in PSI but went for the Greddy because the font and lighting etc is such a good match for the stock gauge. You soon get used to thinking in bar.

[JSeaman]

Lofty, will check all pipes tonight if I get any free time at all for a change. Checked the top end (3000 pipe area) etc but will check again - very easy to miss them. Hope it is just a boost leak.

Adam, I do a lot of driving 8,000 metres below sea level. OK, I don't but that's how all the 30psi gauges are that I've seen - either 0-30 or -30 +30. I'm sure I would get used to bar but I like psi! It's smaller increments so easier to spot deviations from normal but I guess I'll just have to get used to fat 14.5psi jumps instead .. assuming I can get any money to pay for it!

Thanks for the help guys, will get back to you tomorrow.

[Adam W]

The greddy gauge measures in 0.1bar increments James, it doesn't go 0, 1, 2 :cheeky:

[JSeaman]

The greddy gauge measures in 0.1bar increments James, it doesn't go 0, 1, 2 :cheeky:

No sh*t?! Well I'll get one then :)

Good news guys - I'd developed a small boost leak (about the size of my head) which was only opening under pressure. I've also removed 8-10" of hose from the bleed valve set up. Left it installed though so I can go to my ~10psi ish and keep a big fat smile on my face - awesome cars these supras ... when they're running right!

Thanks to all who contributed in this post - big help.

What a great start to the day :yes:

[Lofty]

Sounds like you better start selling your body parts to get saving. A new gauge and some hard pipes looks on the cards. But why stop there - you may as well get a new IC while you're at it. :cheeky:

which pipe was the hole in?

[JSeaman]

Yeah but I've got a big brake conversion, new turbo, lots of internal stuff, stereo stuff and a million other things on the list too!! Plus I've got someone holding various parts for me for next month - need to sell a lot of body parts!!

Turns out it was the 300->throttle body, only checked that it was tight at the weekend but when I removed it, there was a tear all the way round the bottom between the two jubilee clips.

[Lofty]

Not uncommon. I have some black Samco silicone the right size (70mm) if you have trouble finding a replacement.

[JSeaman]

Not uncommon. I have some black Samco silicone the right size (70mm) if you have trouble finding a replacement.

Cheers for the offer lofty but thankfully I had kept the 3000 pipe from the spares car so I just did a quick swap and all's fine now. Appreciate the gesture though, thanks.