amg guy

iTrader: (1)

Quick question, I've already taken the car into the dealer while my warranty was still in effect. They claim it is a noise coming from the rear differential and it is normal. I have a whistle noise coming from what sounds to me like a vacuum leak under deceleration at about 80 mph. Goes away at 75 mph. When I drive long distances on cruise control with distronic I set it at 80 and when I have to disengage or distronic kicks in the noise exists from 80 down to 75 in drive. I've tried to duplicate it in other gears with no success.

I'm wondering if this is a intake gasket leak? Anyone? Would like to get this nailed down before I add a pulley and tune.

shardul

iTrader: (1)

Simple way to find out of you have a boost leak is plug in a obd2 scanner and see what boost you are making. On a car with a stock crank pulley it should be 10 to 11 psi.

amg guy

iTrader: (1)

Ok, cool thanks. I have a ODB2 scanner I'll check.

amg guy

iTrader: (1)

uh, scratch that, what I have is just a code scanner.

Any recommendations on which one to buy? Seen several that are bluetooth capable to a laptop? Looks like a good way to go

Thanks Shardul

jmb614

You may be able to get away with monitoring peak boost with a kiwi wifi and an app like torque for the droid. The problem is that the sample rate can be slow depending on how many pids you are monitoring. The best solution is to install a datalogging system like the zeitronix or innovate and hook up a map sensor.

amg guy

iTrader: (1)

Ok just got my data logging software and ran it. 11 psi on stock pulley. Guess that is not the problem... Any ideas what that noise could be?

shardul

iTrader: (1)

check all the PCV hoses from the valve covers and follow them to the bottom of the TB.

ls1_mast

i know it is an old thread but i didnt wanna start a new one . any one had issues with boost leak? and any common places that i should check ?

why you think PCV hoses can cause a boost leak ? correct me if i'm wrong here but from what i know it might cause a vacuum leak but boost is after supercharger roots which means any thing leaking before that will only be vacuum .. can affect idle and crousing but not full throttle behaviour.

GinDistiller

You're correct PCV does not relate to boost, but the OP posted about a noise and loose PCV hoses can mimic what sounds like a boost leak at times.

The only spots for actual boost leaks would be the two rubber couplers behind the TB, IAT sensor seal, surge tank gaskets, and supercharger gaskets. Sometimes a poor seal underneath the supercharger where the intercooler mounts too.

If you have low boost though - I'd look into belt slippage first, especially if the boost curve jumps around.

ls1_mast

what u said about the potential boost leak places is very helpful i will defiantly check them out one by one , thanks the thing is my boost levels are around 14.7 on the third gear. which is quite low considering my mods ( 180mm CP and 84MM Supercharger Pulley) i was expecting 16 to 16.5 PSI . it goes like this ... at 5000RPM its 14.7 then at 5500 RPM its 13.9 then at 6000 its 14.5 which to me means that there is no belt slip since if there is ( from what i know and experienced in another car) the boost should drop dramatically after belt slip start to accrue. so i suspected a minor boost leak.