So...vacuum leaks

Topic: So...vacuum leaks (Read 1277 times) previous topic - next topic

So...vacuum leaks

January 03, 2009, 10:00:17 PM

I put the mass air stuff in today and now have an apparent vacuum leak (whistling) coming from the front of the lower intake/distributor area. Due to the lack of removing ambient noise with the stethoscope, I cannot pinpoint the whistling. Any ideas on how to quiet down sounds not coming from the stethoscope hose? I've checked all the intake runners and fuel injectors but the on and off whistling (the idle is rougher with the mass air...) makes it very hard to know if I'm hearing sounds through the stethoscope or ambient sounds.

It really sounds like the distributor but I don't hear anything from it - I'm assuming the sound is actually coming from under the plenum but cannot pinpoint a thing!

Any ideas other than to just pull it all off and replace all the gaskets/fuel injector orings/vacuum hoses at plenum?

So...vacuum leaks

Reply #1 – January 03, 2009, 10:18:20 PM

is the canister purge line installed???

So...vacuum leaks

Reply #2 – January 03, 2009, 10:45:49 PM

Quote from: mjbtbrd;250117

is the canister purge line installed???

The 3-port vacuum tree coming off the intake (Cobra) has one going to the fuel pressure regulator, one goes on the egr/thermactor stuff at the passener side fender, and one to the vacuum tree on the firewall. There is a press in fitting that has a T adapter that splits between the PCV and canister. The one on the drivers side of the plenum has been capped off due to the mass air conversion. There are no vacuum ports on the front side of the intake. The PCV is in very tightly with a customed thicker grommet since the stock ones always get loose after a couple months due to heat. Is there huge vacuum differences between the pcv fitting on the intake and the one for the MAP sensor? Any reason not to get rid of the T fitting I'm using and run the hose directly to the MAP sensor's old spot?

To me it sounds like either upper/lower gasket or the "T" under the upper but I can't get that verified with the stethoscope. The annoying Cobra rockers don't help the noise in that area.

So...vacuum leaks

Reply #3 – January 03, 2009, 10:47:21 PM

Oh, and I didn't hook up the secondary fuel pump relay wire to the computer when installing the mass air, yet it's not throwing that code? This confuses me...

So...vacuum leaks

Reply #4 – January 03, 2009, 11:10:17 PM

I am also only seeing 15 inches of vacuum at idle right now - I assume I should be closer to around 20? This is with gt40p heads with stock valves and trickflow replacement "stock" springs, Cobra intake, stock mustang throttle body and mass air sensaor, full exhaust and headers. I know stock engines are supposed to be around 20 at idle and I assume with the above I should be seeing similar numbers. Upon rev with the mass air, the engine takes half a second before it actually responds. I didn't have this issue with the speed density. Quitting the code reading mode after done almost caused the engine to completely stall.

So...vacuum leaks

Reply #5 – January 03, 2009, 11:27:05 PM

One last note, with the IAC connected, it's a lot better than without. With it disconnected, the throttle body stop screw does very little until it's in quite a bit - this is also a sign of a vacuum leak, is it not?

I'll have to try again tomorrow with the stethoscope and spraying cleaner around the intake but it has been unsuccessful so far...at least this is an easy check for fuel injectors since they sit in their own little crevices that will retain the fluid instead of it running off the side.

So...vacuum leaks

Reply #6 – January 03, 2009, 11:27:43 PM

remove your serp belt and run the engine.... that'll get rid of a lot of noise

So...vacuum leaks

Reply #7 – January 03, 2009, 11:49:41 PM

Quote from: mywifeskitty;250130

remove your serp belt and run the engine.... that'll get rid of a lot of noise

My major problem is the roller rockers - they're fine and quiet with thick oil but once it thins, they get annoying. Can't disconnect them things...

I would try this but I need the engine running for a bit to find this problem and no pumping water = bad. Thanks for the tip though

So...vacuum leaks

Reply #8 – January 04, 2009, 06:53:00 AM

Could it be the famous cobra intake whine, when accelerating you here the whine.

So...vacuum leaks

Reply #9 – January 04, 2009, 08:04:13 AM

Vacuum Leak. Defiantly!! Check all hose connection points under the intake and remove the upper intake again to verify that it is seated correctly and not at an angle plus you did not get something under it when placeing the intake on the motor. You can pinpoint the vacuum leak with a can of brake cleaner, it will almost or will kill the motor when sprayed into the vacuum leak. Just spray it around the area of the suspected leak. he same effects can be had using starting fluid except the engine idle will drastically increase, this way is less safe as the starting fluid can catch on fire. Pull the intake and verify it is seated correctly and the vacuum lines underneath are used or plugged. Oh and BTW, the adjustment screw on the throttle body is not to be adjusted by you.....there is no need to adjust it. Set it back to the initial set point.

So...vacuum leaks

Reply #10 – January 04, 2009, 11:51:03 AM

Quote from: Lightningbird;250145

Oh and BTW, the adjustment screw on the throttle body is not to be adjusted by you.....there is no need to adjust it. Set it back to the initial set point.

I don't follow? This is a strange comment. I know what the IAC is for but the screw if anything keeps the throttle body from closing so much that the blade catches on the housing causing it to stick closed (mainly on quick changed to closed throttle). If not by the mechanic, then what in the world would this screw even be used for?

So...vacuum leaks

Reply #11 – January 05, 2009, 10:38:56 PM

The noise sounds like it's coming from the alternator? I rtv'd the IAC and redid the timing - now I cannot get the lean pop to happen again but I have another problem. With the mass air setup, now I have a delayed throttle response. This was perfect with speed density. What's up?

Stock mass air sensor that is clean. A9P ecu, pins mounted where they should be, and the MAP is open to the atmosphere. TPS changes read instantly in my TCS' software so the computer knows the throttle is opening, yet there is a delay before it revs up. It doesn't make any sense.

So...vacuum leaks

Reply #12 – January 06, 2009, 05:46:59 AM

Is your egr hooked up? if it is, is the diapraghm good?
Sure sounds vacume related.

So...vacuum leaks

Reply #13 – January 06, 2009, 08:52:57 AM

I get code 33 which I've received forever, even after replacing the egr 2 years ago. It's got like 5000 miles on it now and is a Motorcraft piece. It functions normally as tested with a hand vacuum pump.