ChevyChad

iTrader: (50)

A few weeks ago, I finally got around to fixing a slit intercooler rubber pipe that had got damaged scraping something on the road. At the same time, I put a bigger filter on. Before I did all this, I was making 8psi with the leak in the rubber pipe. I had put some duct tape over it and got up to 10psi. Then after I put the new hose on and bigger filter, it went to 12psi. About a week ago, boost started going down again. It got down to 10psi. I did a pressure test by capping off the plenum just behind it (where the MAF would go) and was filling it with air from where the pipe is that comes right out of the head unit. I could not see hear, or feel a leak in any of the piping. So I figured the belt must be slipping. Put a new belt on a couple days ago, and got on it for the first time today. It is now only making ~8psi or so, and there is a high pitched whistle I can hear over the whine of the supercharger the whole time I am WOT. Do you think it could be my bypass valve? I have the ATI red race BPV and it has never leaked before, and I haven't ever messed with the setting on it. If so, why would it all of a sudden not be holding pressure? If it is not the BPV, what else could it be? The whistle is loud, I think that has to be the sound of some pressurized air leaking out from somewhere, but I can't hear it at idle or just revving it while parked standing over it. Could it possibly be the head unit going bad or something?? I sure hope not Someone please help

EPP

iTrader: (22)

The easiest way to find it, at least for us, is to put the car on our Mustang Chassis Dyno, and apply a load to it simulating a mountain grade. I realize this is not cheap for you to do, but if you have a chassis dyno close to you that has eddy current, you will find the problem. Bob

ChevyChad

iTrader: (50)

Thanks for the input Bob. I know there are a couple dynos near, but I think they are both dynojet not mustang.

However, it got worse yesterday. It now sounds really bad. Best way I can describe it is like a table saw cutting a 2 x 4. Bad grinding sound. Not all the time, but a lot of the time. Like anything over 2000 RPM, or when I go over a bump. I wasn't even going into any boost at all! I looked under the hood and didn't see anything rubbing the belt, and the SC belt hadn't jumped a rib (altho it did sound a lot like belts rubbing). I didn't have a chance to look at it last night when I got home, but I plan on taking a look today after work. I sure hope the head unit is not going south

alwaysinboost

You will not be able to 'hear' a boost leak when driving, no matter how big or small. You might be able to see it, as in less boost on your gauge, or feel it because of the reduced power or drivabilty problems, but you will never hear it while you're driving. Trust me, I've blown IC pipes clean off so the engine was basically NA and there was no difference in sound what so ever. It was obvious by looking at the boost gauge what just happened but nothing changed sound wise. The exception to this rule is a turbo car which is a little different animal but thats not here or there.

What you need to do in order to correctly check for leaks is pressurize your charge piping @ the compressor inlet. This is where your air filter would attach to the compressor. If you cap off your compressor inlet and fill it with air from that point, it will simulate the SC making boost just like it does when you are driving and you will be able to tell exactly whats going on. weather you BOV is opening under boost or you have a pinhole leak someplace, whatever the case my be this is the only way to correctly check for it. when testing for leaks this way all your charge piping & vac lines need to stay in place just like when you drive the car on the road. Nothing gets removed except for the air filter in order to place the cap w/valve stem on it.

If you detached one of the charge pipes for testing, like how you did the leak test the first time, when you reconnect that section of pipe you could have a potential leak and that would totally defeat the purpose of doing the test in the first place.

Boost leak tests are a common thing on a FI car and something that should be checked on a regular basis. The more you do it the quicker/better you get at it.

ChevyChad

iTrader: (50)

Well, you are right about not hearing it. I initially thought it was a whistle, but now i know it is something else. I almost think it may be the idler pulley going south. That would explain the sound at least. I'd rather it be the idler than the head unit for sure! It wouldn't surprise me a bit if it was the idler because when my intercooler pipe had slit that first time, I tightened the **** out of the belt trying to get the boost back up...

alwaysinboost

well if you do the leak test like described above and you still have the problem atleast you can eliminate that from the equasion.

ChevyChad

iTrader: (50)

Good advise. I will try it that way

EPP

iTrader: (22)

Good advice! Bob

Whitez406

iTrader: (14)

Ive had the same problem and recently found it. The damn aluminum plenum cracked on the bottom. I know these are common for this but i did not hear it at all till it finally cracked open along the whole bottom.

EPP

iTrader: (22)

Good idea to check it out. A pressure test should show a crack if it is present though. Bob

ChevyChad

iTrader: (50)

Yeah, I haven't had a chance to redo the pressure test this week has been too damn busy. I hope to this weekend. However, there has to be more to it than that for me because I am hearing a very bad grinding noise like something mechanical aint right at all... I will recheck the plenum again if the pressure test doesn't help...

mondi2002

iTrader: (11)

Did you ever find out what was wrong?
I am going thorugh the same thing. Loud whistle/chirp shortly
after I installed a slighly smaller pulley.
My plenum tube blew off last night and I tightned the clamp so much
than the plenum outlet (plastic) started colapsing on the bottom
creating a hump inward where it goes into the tube.
I bent it straight and carefully tightned the clamp again.
Went for a drive and the noise was totally gone!?!
I got to 10psi & it blew off again
But the noise never cam back. I am about ready to glue that sucker on!

ChevyChad

iTrader: (50)

No, I haven't touched anything yet or even looked at it. Its been parked in the garage the whole time. I started receiving my home theater stuff over the last week, and I have been setting all of it up. LOL funny how priorities change when I get fed up with something... It's too hot to drive it right now anyways since I can't use my A/C without the coolant temp climbing to near 230° I'm getting more enjoyment right now by just staying inside where it is 72° watching a 120" screen and shaking the walls down with the speakers than messing around with diagnosing one thing after another on the T/A.

mondi2002

iTrader: (11)

I hear you! I am just too stubborn.
I used some contact cement and clamped it back on.
No leaks so far and I am back to 12psi plus the sound never came back.
Maybe the belt stetched a little more and the sound was coming from
the tensioner pulley?

Pro Stock John

iTrader: (34)

Or Chad you have some bearings dying in your idler or your blower.

ChevyChad

iTrader: (50)

That is my thinking...

And I'm HOPING if that is the case, then it is in the idler! Makes me sick to even think they are in the blower

Slowhawk

iTrader: (12)

Sounds like your idler pulley is grinding against the bracket.Have seen it many times on overtightened belt's.