Boost issues... please help !

Angus · 12-19-2008, 12:36 AM

I have an aw11 4agze with oversize crank pulley which usually hits 11.5psi on my boost guage WOT in 5th gear. However after a recent track day (where it performed awesome ALL day) it started only boosting half, EXACTLY half?!

so now, if i floor it, it shoots up to about 6-7psi on the guage then after one second levels off to about 5 psi

so i know your thinking intercooler pipe leak right ?

i took off the intercooler and the pipes from the SC to the throttle body all look sweet, so what else could it be ???

cheers guys

328FTW · 12-19-2008, 01:05 AM

Belt is not loose and slipping? There is not a huge amount of things I can think of to cause that. Either that or the supercharger clutch could be starting to slip which I don't know how to check for other than pulling it apart.

Jackstand Queen · 12-19-2008, 01:39 AM

clogged intake (air filter)

THE USUAL SUSPECTS:
leak in IC, or intake piping to and from SC to head. Including intake manifold. Loose, missing, or unplugged vacuum lines.

I don't know is the safety experts would approve, but I spray brake cleaner on, and around suspected leak areas. Do this in moderation, don't allow puddles of the spray to form. Do it while idling the engine. If the engine idle "wobbles" or reacts to the presense of the brake cleaner . . . there is your leak.

If you can't find an intake restriction, or leak . . . pull the SC out. Disassemble it, and see if the rotors are melted, warped, or have too much clearance from the case's interior.

Good Luck Bloke!

Angus · 12-20-2008, 02:03 PM

Quote:

Originally Posted by 328FTW

Belt is not loose and slipping? There is not a huge amount of things I can think of to cause that. Either that or the supercharger clutch could be starting to slip which I don't know how to check for other than pulling it apart.

When i first put the the oversize pulley on it had a new belt so initially used to slip alot, so i know what that sounds like, and it not slipping now

cheers for the thought though

my mechanic cant figure it out, so like many other times, i come to you guys for help

Angus · 12-20-2008, 02:08 PM

Quote:

Originally Posted by Jackstand Queen

clogged intake (air filter)

THE USUAL SUSPECTS:
leak in IC, or intake piping to and from SC to head. Including intake manifold. Loose, missing, or unplugged vacuum lines.

I don't know is the safety experts would approve, but I spray brake cleaner on, and around suspected leak areas. Do this in moderation, don't allow puddles of the spray to form. Do it while idling the engine. If the engine idle "wobbles" or reacts to the presense of the brake cleaner . . . there is your leak.

If you can't find an intake restriction, or leak . . . pull the SC out. Disassemble it, and see if the rotors are melted, warped, or have too much clearance from the case's interior.

Good Luck Bloke!

The symptom seems such a dead ringer for pipe leak ay, the boost guage shoots up to 0.5bar then backs off to 0.4 bar and holds there, and it does exactly this every time. Compared to when it used to shoot up past 0.6 and at high rpm it reached 0.8

ill look at the air cleaner, probably needs a clean, and re-oil by now

I really appreciate the thoughts guys

curvesrgood · 12-20-2008, 05:13 PM

I know you said you checked the IC and SC pipes, but did you check the rubber coupling down low coming off the S/C and going to the charge pipe or whatever that thing is called? Of course that one is the hard one to reach, but when I had the same type deal happen I found a 1 inch or so long gash through my lower pipe. I replaced all 4 rubber sections with hard rubber radiator hose of the same size and boost increased 1.5 lbs over what I had been boosting and throttle response improved slightly under boost

. Cheapest performance mod bang-for-your-buck wise for the S/C car I've ever heard of. It sounds so simple, and is total common sense, but really seems to work great!! If you've got those off, go ahead and try the radiator hose straight pipe instead of the ones with the bulge... the bulge kills aero and creates a slight delay as each pipe bulges under boost. I think it cost me maybe 8 bucks for the 4 sections of pipe from NAPA and I have run them for over a year with no problems... have removed and checked a couple sections to verify that they are holding up well, and they are so far.

Angus · 12-26-2008, 01:27 PM

Thanks heaps guys

finally got around to looking at it again, and i checked the super to intercooler pipe from underneath the car and it was all good, so started checking the vacuum hoses and the one going onto the ABV was not on tight, so i pushed that on fully and when for a drive and its all good again, full boost !

Had to believe something that minor could cut the boost in half.

So she is back in business, and im a very happy man again

Happy holidays !

12-19-2008, 12:36 AM	#1 (permalink)
Angus some skills Join Date: Oct 2007 Location: New Zealand Posts: 93 Thanks: 11 Thanked 5 Times in 4 Posts iTrader Rating: (0/0% )	Boost issues... please help ! I have an aw11 4agze with oversize crank pulley which usually hits 11.5psi on my boost guage WOT in 5th gear. However after a recent track day (where it performed awesome ALL day) it started only boosting half, EXACTLY half?! so now, if i floor it, it shoots up to about 6-7psi on the guage then after one second levels off to about 5 psi so i know your thinking intercooler pipe leak right ? i took off the intercooler and the pipes from the SC to the throttle body all look sweet, so what else could it be ??? cheers guys

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12-19-2008, 01:05 AM	#2 (permalink)
328FTW Get your -_- face on Join Date: Aug 2008 Location: New Zealand Posts: 2,156 Thanks: 17 Thanked 127 Times in 111 Posts My Google Map iTrader Rating: (0/0% )	Belt is not loose and slipping? There is not a huge amount of things I can think of to cause that. Either that or the supercharger clutch could be starting to slip which I don't know how to check for other than pulling it apart.

12-19-2008, 01:39 AM	#3 (permalink)
Jackstand Queen Cage Fighter Join Date: May 2008 Posts: 691 Thanks: 53 Thanked 56 Times in 53 Posts iTrader Rating: (1/100% )	clogged intake (air filter) THE USUAL SUSPECTS: leak in IC, or intake piping to and from SC to head. Including intake manifold. Loose, missing, or unplugged vacuum lines. I don't know is the safety experts would approve, but I spray brake cleaner on, and around suspected leak areas. Do this in moderation, don't allow puddles of the spray to form. Do it while idling the engine. If the engine idle "wobbles" or reacts to the presense of the brake cleaner . . . there is your leak. If you can't find an intake restriction, or leak . . . pull the SC out. Disassemble it, and see if the rotors are melted, warped, or have too much clearance from the case's interior. Good Luck Bloke!

12-20-2008, 05:13 PM	#6 (permalink)
curvesrgood three mk1's Join Date: Feb 2006 Location: NC Posts: 453 Thanks: 8 Thanked 31 Times in 26 Posts iTrader Rating: (0/0% )	I know you said you checked the IC and SC pipes, but did you check the rubber coupling down low coming off the S/C and going to the charge pipe or whatever that thing is called? Of course that one is the hard one to reach, but when I had the same type deal happen I found a 1 inch or so long gash through my lower pipe. I replaced all 4 rubber sections with hard rubber radiator hose of the same size and boost increased 1.5 lbs over what I had been boosting and throttle response improved slightly under boost . Cheapest performance mod bang-for-your-buck wise for the S/C car I've ever heard of. It sounds so simple, and is total common sense, but really seems to work great!! If you've got those off, go ahead and try the radiator hose straight pipe instead of the ones with the bulge... the bulge kills aero and creates a slight delay as each pipe bulges under boost. I think it cost me maybe 8 bucks for the 4 sections of pipe from NAPA and I have run them for over a year with no problems... have removed and checked a couple sections to verify that they are holding up well, and they are so far.

12-26-2008, 01:27 PM	#7 (permalink)
Angus some skills Join Date: Oct 2007 Location: New Zealand Posts: 93 Thanks: 11 Thanked 5 Times in 4 Posts iTrader Rating: (0/0% )	Thanks heaps guys finally got around to looking at it again, and i checked the super to intercooler pipe from underneath the car and it was all good, so started checking the vacuum hoses and the one going onto the ABV was not on tight, so i pushed that on fully and when for a drive and its all good again, full boost ! Had to believe something that minor could cut the boost in half. So she is back in business, and im a very happy man again Happy holidays !