So, for the last 4 months, my car has had a terrible vacuum leak.
The car wont idle on its own, gets terrible mileage, terrible power, and reaks like gas.
It has been like this since I rebuilt the motor over Xmas and did the S5 manifold swap.
Ive replaced the gasket between the engine and the lower manifold, between the lower and upper, between the dynamic and upper, and even RTV'd between the dynamic and TB.

I caughed up $25 and bought a pressure tester. I was then able to trace the leak down to under the upper manifold. I capped the vac source for the oil injector vac spider and it made no difference at all. If I apply air to the pressure tester, there is a HUGE hiss coming from under that portion of the manifold. After localizing the leak, I took the upper off AGAIN and found absolutely nothing, so put some RVT on the lower to upper surface hoping that was it again, but it did nothing.

Now that I know where the leak is coming from (well, i cant see under there, but can feel air around the primary rails) I was wondering, could such a huge vacuum leak originate there but have no signs of leaking fuel?? Im stumped

-Alex

 

I've had the same thing. Forgot to line up the rail and one of the injectors was stuck on the o-ring itself. It still sprayed fuel and such into the engine; however, it had a horrific vacuum leak...
Yes, I couldn't see the leaking fuel but I could definitely see the injectors wasn't directly on the hole.

 

Well, i know for a fact that the injector isnt leaking. I had them rebuilt with new o-rings before I put them in and there was zero sign of fuel around them when I tore the upper off Saturday.

 

maybe the primary injector air bleed line has a leak? or the OMP holes in the housings are not blocked off properly?

 

The OMP injectors are tightened down properly and everything but whats needed has vac caps on it. My real question is whether loose injectors can cause a LARGE intake leak?

 

yes absolutly..if the rubber gromet that seals the bottom on the injector (pintle cap end) is not sealing then u will have a huge vac leak, not to mention fuel spraying past ur injectors into ur engine bay on boost.. very dodgy.. I had the same issue a while back as i tried to be cheap and not use the correct size groment for the aftermarket injectors i bought... ended up having to use very accurately applied electrical tape to make them seal whilst I sourced the correct size groment...

if ur still using stock injectors, then buy the stock gromets... mazdatrix sells them here :

http://mazdatrix.com/c-6.htm
http://mazdatrix.com/getprice.asp?partnum=13-2570-N326

 

That's probably where mine is leaking too. Nice.

 

You said you upgraded to the S5 manifold - did you keep your S4 injectors and use the S5 fuel rails? Did you change out the injector grommets on the top & bottom? Did you keep your s4 BAC, block it off or use the s5? Did you use RTV on the lower to mid manifold? Did you use the S5 lower manifold or the S4? There are some clearance issues involved with this swap. All of the above questions could be a problem for you. I just did this swap and when I used some RTV on the S4 lower to S5 mid my massive leak disappeared and everything worked great. I had to grind down the back of my S6 alternator quite a bit to get the manifold to go on correctly and even then it is VERY tight. It was tough to get the fuel rail on EXACTLY right with my S4 BAC. Also did you use all new vacuum lines? I found the old ones were pretty stiff and hard. There's alot of stuff under there that has to be sealed good to work properly. I did some mix-n-matching on the injector grommets - I think I kept the ones in the manifold S5 and used the S4 tops for the fuel rails.

Ramses666

 

same problem here. i also think it is my fuel injectors as i've sealed the manifolds pretty good. my car in the morning idles at almost 2k. thats too much.

 

UPDATE!!!

Sooo, after TONS of headaches trying to track down my vacuum leak I found it!

It turns out that when I had my injectors cleaned, they put the wrong sized grommets back on it.
It was hard to see, but the grommets didnt sit in the primary ports like they should.
I managed to find the old grommets and put them back on.
PRESTO! No more vacuum leak!

I hope this can help out someone else in the future.

 

i had the kind of same problem for so long but i removed my manifold 4 time and everytime i put the seal on than after a day driving it was faliing in the hole so i knew something wasnt right. I went to the guy who i bought it from and he had a old engine which was got it of a mine right before i bought it.I looked inside and there was a spacer things still inside i took them of put it back in and i was ok.
I dont thing u do but u might have the same problem after the rebuild

 

Well, my problem is solved. It was just the wrong grommets around the bottom of the injectors.

 

I hate those freaking grommet. The are so easy to lose! Mine cracked over the summer my engine caught fire. Man did I **** my pants and almost lost my eyebrows. Great to hear you solved the problem.