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Thread: Vacuum leak, but not a boost leak? Possible?

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Posts: 11-20 of 27
2012-10-24 05:24:54
maybe the timing had something to do with it, but idk.
2012-10-24 05:27:57
maybe, I know for certain the only variable that was changed that day was the base tune in the chips and I saw a difference, In the latter days was when the other work was done.
2012-10-24 05:48:25
The way a motor is running can affect vacuum very much so. Mainly if the engine is stumbling from running say too rich or timing off or whatever the vac will be much much lower. A smooth running engine, idling at its proper rpm will give you the best reading. Its not necessarily timing so much but just how smooth the idle is.

But if the engine is running smoothly and vac is low then the problem is elsewhere.
2012-10-24 05:52:01
thanks ashton, theres no reason for me to say something thats not true or at least to the best of my knowledge and what I have experienced, in my mind it makes sense is putting it down where I choke. but i think you pretty much nailed what I was trying to get across.
Last edited by xavi1320t on 2012-10-24 at 05-52-16.
2012-10-24 05:57:42
Yeah, two smooth running engines with different tunes should not make any difference. Again only if the engine is not running correctly which I doubt is even the issue in this case. An inconsistent idle can cause it, stumbling, and/or excessively rich condition causing stumbling.

A smooth idle is what makes for a good vac reading. If the idle air control has to keep opening and shutting to keep an idle smooth, that will affect it. Lots of variables.
2012-10-24 13:26:05
broken piston ringland
2012-10-24 14:45:30
It can't be my tune. That's hasn't changed in a little over 2 years.

Like I said on my first post, the car is running perfectly fine. It idles like it should and no hesitations or stumbles. I have a wideband and its not horribly rich or anything.

There's just hardly any vacuum. And worse gas mileage.
2012-10-24 15:44:52
My warm idle is like 750/800 rpm with about -14 vac...i'm going to replace some exhaust gaskets and replace my BOV (as i had to drill out some of the screw to take it apart once so I dont trust that its holding as good as it should)....i'm building a leak tester this weekend, gonna try the cig smoke trick...(engine off blow smoke into the intake, and pump air into it through the leak tester and see where the smoke comes out). I have reason to believe im running rich tho myself, but i dont yet have a wideband
2012-10-24 17:46:23
Yeah mine is at -11 to -10 at 800 rpm.

In a nutshell what is bad piston ringland?
2012-10-24 18:02:25
Its if you had detonation and the ring lands crack between the top and second ring. This will usually but not always cause blowby and/or smoke to come out of the breather of the valve cover and definitely cause lower vac as the efficiency of the motor goes downhill from there due to improper ring seal.

Easiest way to check is for one compression check and two just remove the hose from the breather on the right side of the valve cover and see if you have any smoke coming out while the engine is running.

Again not always will you have smoke coming out but if the ring lands are cracked enough or several you most definitely will. Give it a couple blip revs and stuff like that. You shouldnt have any smoke. You can also place your thumb over the breather and if your still running a pcv you should start getting suction on your thumb. If not your getting too much blowby for the pcv to keep up with and another good likelyhood of cracked ring lands.
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