Afm/vacuum Leak/bleed Valve Issues?

[nsdq]

Hey guys,

Recently my 33 gts-t has developed the following problem in which I will attempt to describe. After driving slightly intense (4500rpm+) the following symptoms develop:

- In idle , revs start to drop to and fluctuate between 100 - 1500rpm, causing the feel of stalling.

- At the same time, the boost gauge fluctuates and shows a reading of 0 to -10psi (normally it sits at -20psi in idle).

- After about 1 - 2 mins, it seems to fix itself and idles normally. Occasionally the car will stall.

I have also tried driving while this is happening and discovered that the car boosts fine in 1st gear. However in 2nd and 3rd, the car would feel very sluggish and boost would rise very very slowly from 3psi or so. At times the car experiences extreme jerkiness, feels almost like boost has suddenly kicked in the out again.

The mods on my car include: 3.5inch Cat-back exhaust; Turbosmart boost tee (not secured to anything, only thing holding it are the vacuum tubes.. not very smart).

After searching the SAU forums, I am guessing either the (1) AFM is knackered; (2) Boost Tee is stuffed/leaking; (3) Air leak between throttle body and AFM; (4) Leak somewhere between intake and turbo.

I'd really appreciate some help - What do you guys reckon is most likely causing the problem? I'd like to self diagnose/fix before taking it to a mechie.

[nsdq]

Reverted the Boost Tee to a stock T pipe. Slight improvement at first but after a while same problem came back.

ANY ideas, thoughts welcome..

[Moodles2]

Fuel pump is the likely suspect, it being close to 15 years old now.. the symptoms sounds like the pump dying, but not completely dead (yet).

[mosquitocoils]

Clean your AAC valve

Or are you using at vent-to-atmosphere blow off valve?

[blk94r33]

Clean your AAC valve

Or are you using at vent-to-atmosphere blow off valve?

^+1

Otherwise maybe something to do with the cam timing as you said it occurs once you take the car above 4500 rpm?

[karma_syke]

is there a good way of testing for vacuum leaks? i'm kinda nervous about spraying propane and carby cleaner at my engine

[nsdq]

Cheers for the replies.. went for another drive today. Car runs normal most of the time, but the problem did occur again - this time as soon as I started the engine back from lunch after driving for about 30 mins. Seems to happen when car is warm..

No, I have the stock plumb back bov. I was also thinking could be aac valve.. although this happened suddenly last week and not gradually over a few months as you would expect from carbon buildup?

I was hope this has nothing to do with the engine but cam timing is possible, in which case it will be a bitch to fix.

The problem occurs only sometimes and not all the time, so if it was a constant boost leak then it would make sense for this to happen all the time?

And Thomas fyi you can test vacuum leak with a air compressor - connecting it to the turbo outlet and blocking off the pipes leading to the throttle body. saw it on mightycarmods a while back.

Anyone else think its a fuel rather than an air problem (or vice versa)? If it's a fuel issue then why does the boost gague going nuts? (sorry not trying to be an arsehole here, just trying to understand the issues.)

Any thoughts appreciated, cheers.

[pineapple]

LOL seem be happining to every one these days mate im in the same boat pritty much

iv tried fuel filter, fuel regulator, coil packs, ignitor, plugs, AFM been cleaned

my fuel pump is in good nick so i dont think its that

tomorrow im gone try leak down test, comp test, o2 sensers and coil pack loom

then monday injectors cleaned prob

so if i get a mirical ill let u know bud

[payback21]

Check the intake pipe going from the AFM to the side of the turbo. They can wriggle off abit being a little loose and can suck air in making the car unable to idle properly and rev correctly.

While wriggling the pipe to check, you may need a torch to see if it has come off from the turbo. Its just a thought to check out.

[nsdq]

Yeh alex, its such a shit feeling when your car is sick, but can't figure out where the problem is.

Took it for another drive, realised when I rev it hard is when the problem starts, which got me thinking fuel pump. But then again you have the same issue and your fuel system is working fine =S ..Am going to mates place and taking apart the front end to check the piping thoroughly and see how I go. I'll post up my findings later tonight haha.

Also keep us posted if some miracle does happen

[nsdq]

Update:

- checked all the intake piping - poured water onto each joint and listening for drops in idle.. nothing. All hoses seems to be intact. So unlikely problem is vaccum leak.

- did some research on fuel pumps - apparently there's no such thing as a fuel pump that's about to die. They either work or they dont. So fuel pump is also unlikely to be the problem.

- took out the AFM and gave it a good clean with carby cleaner. After the clean car runs alot smoother, but the initial problem still exists.

Will give the Aac valve a good clean next wkend and post my findings.

[blk94r33]

Update:

- checked all the intake piping - poured water onto each joint and listening for drops in idle.. nothing. All hoses seems to be intact. So unlikely problem is vaccum leak.

- did some research on fuel pumps - apparently there's no such thing as a fuel pump that's about to die. They either work or they dont. So fuel pump is also unlikely to be the problem.

- took out the AFM and gave it a good clean with carby cleaner. After the clean car runs alot smoother, but the initial problem still exists.

Will give the Aac valve a good clean next wkend and post my findings.

Fuel pumps can start dying giving up all kinds of funny symptoms. Had a VS commo with a fuel sock so clogged with crap, that the car would idle and run OK, generally drive well, but too much throttle and it'd miss and fart and carry on, and occasionally stall, fuel pressure gauge showed the pressure being a maximum of half it's usual, and revving the engine didn't give a nice peaky response, the fuel pressure would slowly drop off and rise.

[mad082]

yeah fuel pumps can slowly die. they either get the sock a bit blocked or are worn inside and don't have the same maximum flow as they should. i've seen cars on the dyno where the fuel pump has been dying and the AFRs are fine until about 2/3 of the way through the rev range where they start to lean out and the further up the rev range you go the leaner it gets. put a new fuel pump in and it's all good again.

[Penitent_Spark]

I am having the exact same issues as nsdq, where you able to solve your problem, or did you ever find out what the cause was?