# Tight Plug Gap = Low Vacuum? **URL:** \ **Category:** NYSpeed Automotive\ **Created:** [October 18, 2007, 3:04pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217 "2007-10-18T15:04:56Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![9ONA3OOZX](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/9ona3oozx/32/7242_2.png) [@9ONA3OOZX](https://forums.speedlife.net/u/9ONA3OOZX)\ **Post date:** [October 18, 2007, 3:04pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/1 "2007-10-18T15:04:56Z")
So as many people know, i’ve been having mild vacuum issues for a while…and if you didn’t know that, now you do. This got me to doing some homework, and i found a very good writeup: [http://www.atlanticz.ca/zclub/techtips/vacuum/](http://www.atlanticz.ca/zclub/techtips/vacuum/) but what concerns me is that my vacuum is drifting between 14 and 16…which, according to that writeup, means i have too close of a gap. i’m just curious if somebody on here can explain to me exactly how plug gap could effect vacuum readings? and on a side note, i’ve been playing with different plugs and gaps for a while, trying to find a happy mid-way point…but can’t seem to do so. If i open up the gap at all, i get spark blowout at and ONLY at fully boost (which feels similar to misfire), but when i tighten the gap at all, i get this poor vacuum reading. the car makes/holds boost great, just at vacuum it seems a bit low, and i’m flying through plugs (running pig rich). ---
**Author:** ![psphinx81](https://avatars.discourse-cdn.com/v4/letter/p/e9a140/32.png) [@psphinx81](https://forums.speedlife.net/u/psphinx81)\ **Post date:** [October 18, 2007, 3:07pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/2 "2007-10-18T15:07:21Z")
have u done anything to the plugs since we changed them? ---
**Author:** ![9ONA3OOZX](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/9ona3oozx/32/7242_2.png) [@9ONA3OOZX](https://forums.speedlife.net/u/9ONA3OOZX)\ **Post date:** [October 18, 2007, 3:10pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/3 "2007-10-18T15:10:59Z")
[quote=“psphinx81,post:2,topic:37217"”] have u done anything to the plugs since we changed them? [/quote] besides that one time we called your brother, and he told us it was spark blowout and to tighten the gap…no. but that’s around when i started getting lower vacuum…that was the first time i changed the plugs this summer, and i’ve been flying through sets ever since. the set i had in before that, which were also coppers, i had for literally 15K+ miles, and they still looked good when i took them out, but i knew it was time to change them. i just wish i hadn’t thrown those plugs out before checking to see what they were gapped to. :hang: ---
**Author:** ![psphinx81](https://avatars.discourse-cdn.com/v4/letter/p/e9a140/32.png) [@psphinx81](https://forums.speedlife.net/u/psphinx81)\ **Post date:** [October 18, 2007, 3:12pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/4 "2007-10-18T15:12:16Z")
;sfd’asfk;a i swear this car has some kind of curse on it!! ---
**Author:** ![Justin](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/justin/32/7459_2.png) [@Justin](https://forums.speedlife.net/u/Justin)\ **Post date:** [October 18, 2007, 3:16pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/5 "2007-10-18T15:16:49Z")
As far as I know, plug gap has nothing to do with vacuum. ---
**Author:** ![9ONA3OOZX](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/9ona3oozx/32/7242_2.png) [@9ONA3OOZX](https://forums.speedlife.net/u/9ONA3OOZX)\ **Post date:** [October 18, 2007, 3:17pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/6 "2007-10-18T15:17:18Z")
i’m tired of messing with it so much. i bought a fitting that fits into where the maf/intake is, and it has a pressure gage on it, as well as a tire valve… using a compressor, tried filling it with air, but the gage built NO pressure at all…gage works fine, tried it out…but the thing is, i didn’t hear air leaking out anywhere…i know there’s a shit load of piping to fill on my car, but still…if it was leaking, i would have heard it. as i said, i’m tired of guessing and using my car as a guinea pig for everything i’m trying to figure out for the first time…Melissa’s dad has a shop, and he’s doing lower ball joints for me this weekend, i’m gonna see if he can find a vacuum leak anywhere… ---
**Author:** ![9ONA3OOZX](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/9ona3oozx/32/7242_2.png) [@9ONA3OOZX](https://forums.speedlife.net/u/9ONA3OOZX)\ **Post date:** [October 18, 2007, 3:18pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/7 "2007-10-18T15:18:03Z")
[quote=“01AudiS4,post:5,topic:37217"”] Plug gap has nothing to do with vacuum. [/quote] ``` Idle (mildly low with constant small drift) ![http://www.atlanticz.ca/zclub/techtips/vacuum/12.jpg](http://www.atlanticz.ca/zclub/techtips/vacuum/12.jpg) When needle drifts slowly between 14 and 16 it generally indicates that plug gaps are too close, or breaker points are not properly synchronized. ``` ---
**Author:** ![Carnut](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/carnut/32/7590_2.png) [@Carnut](https://forums.speedlife.net/u/Carnut)\ **Post date:** [October 18, 2007, 3:25pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/8 "2007-10-18T15:25:11Z")
If you have poor combustion then yes it could affect manifold vacuum. Put the gap at .28"-.30 and call it a day unless you are running boost higher than 20lbs on a stock ignition. If you are misfiring (again something that will affect combustion) you will have lower than normal vacuum. random misfiring will cause that. Check your plug boots and coils for signs of arching to ground. It will look like white marks on the coils like a blast radius from a bomb. Also 300ZX are vacuum leak nightmares. I went over an looked at woodys one day and I was able to pull just about every vacuum line off. The underhood temps get high and as a result the vacuum lines dry up and crack. You should replace every vacuum line you can physically see. These will also be boost leaks. So you get the added benefit of not destroying your turbos once they are fixed. ---
**Author:** ![Onyx\_Z32](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/onyx_z32/32/7581_2.png) [@Onyx\_Z32](https://forums.speedlife.net/u/Onyx_Z32)\ **Post date:** [October 18, 2007, 5:03pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/9 "2007-10-18T17:03:04Z")
Andy, do everything in this thread: > **[The 6 Ps: Proper Preparation Prevents Piss Poor Performance\>](http://twinturbo.net/net/viewmsg.aspx?forum=technical&msg_id=922678)** > > This is a compilation produced for anyone comtemplating any upgrades on their car or for those wanting a thorough troubleshooting procedure. These tests will track down as many of the potential powerp... Use a smoke machine instead of compressed air. Then you can _see_ exactly where the leak is. Your plug gap should be 0.035. ---
**Author:** ![9ONA3OOZX](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/9ona3oozx/32/7242_2.png) [@9ONA3OOZX](https://forums.speedlife.net/u/9ONA3OOZX)\ **Post date:** [October 18, 2007, 5:04pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/10 "2007-10-18T17:04:38Z")
[quote=“Onyx Z32,post:9,topic:37217"”] Andy, do everything in this thread: > **[The 6 Ps: Proper Preparation Prevents Piss Poor Performance\>](http://twinturbo.net/net/viewmsg.aspx?forum=technical&msg_id=922678)** > > This is a compilation produced for anyone comtemplating any upgrades on their car or for those wanting a thorough troubleshooting procedure. These tests will track down as many of the potential powerp... Use a smoke machine instead of compressed air. Then you can _see_ exactly where the leak is. Your plug gap should be 0.035. [/quote] i tried .035 with the stockers and with the coppers…got blowout both times…030 is the largest gap i can run where it doesnt blowout. :gotme: ---
**Author:** ![2TurboZ](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/2turboz/32/7577_2.png) [@2TurboZ](https://forums.speedlife.net/u/2TurboZ)\ **Post date:** [October 18, 2007, 5:06pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/11 "2007-10-18T17:06:19Z")
![http://i7.photobucket.com/albums/y288/SilverZ32/FAILZ1.jpg](http://i7.photobucket.com/albums/y288/SilverZ32/FAILZ1.jpg) ![http://i7.photobucket.com/albums/y288/SilverZ32/Fail-z1.jpg](http://i7.photobucket.com/albums/y288/SilverZ32/Fail-z1.jpg) Just quit with it already…the car sucks and you know it. Go back to driving Hondas! ---
**Author:** ![Onyx\_Z32](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/onyx_z32/32/7581_2.png) [@Onyx\_Z32](https://forums.speedlife.net/u/Onyx_Z32)\ **Post date:** [October 18, 2007, 5:08pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/12 "2007-10-18T17:08:28Z")
[quote=“90NA300ZX,post:10,topic:37217"”] i tried .035 with the stockers and with the coppers…got blowout both times…030 is the largest gap i can run where it doesnt blowout. :gotme: [/quote] Who says it’s “Blowout” anyway? If you’re car doesn’t run with the plugs where they should be, then it MUST be another issue. Maybe your PTU is shot? Have you tested it or had anyone test it? ---
**Author:** ![9ONA3OOZX](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/9ona3oozx/32/7242_2.png) [@9ONA3OOZX](https://forums.speedlife.net/u/9ONA3OOZX)\ **Post date:** [October 18, 2007, 5:11pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/13 "2007-10-18T17:11:55Z")
[quote=“Onyx Z32,post:12,topic:37217"”] Who says it’s “Blowout” anyway? If you’re car doesn’t run with the plugs where they should be, then it MUST be another issue. Maybe your PTU is shot? Have you tested it or had anyone test it? [/quote] i replaced my PTU when the swap was done…i didnt think really to check it again since they shouldn’t crap out that fast… ---
**Author:** ![woody](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/woody/32/7191_2.png) [@woody](https://forums.speedlife.net/u/woody)\ **Post date:** [October 18, 2007, 5:21pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/14 "2007-10-18T17:21:13Z")
i think its pretty evident that your car’s problems go deeper than just spark plug gap… if youre not holding pressure in the intake, you have big leaks, whether you can hear them or not. use the smoke machine like onyx said. dont end up like me 🙂 ‘spark blowout’ or a similar misfire at high rpms / at full boost can be caused by boost leaks. you apparently have plenty so i would say that is your biggest problem. i would start with that and get that out of the way before you dive any deeper. its the simpliest (in anything but a z) step to take. take care of them before they blow up your car and change your name to woodrow II. ---
**Author:** ![Onyx\_Z32](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/onyx_z32/32/7581_2.png) [@Onyx\_Z32](https://forums.speedlife.net/u/Onyx_Z32)\ **Post date:** [October 18, 2007, 5:25pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/15 "2007-10-18T17:25:38Z")
[quote=“90NA300ZX,post:13,topic:37217"”] i replaced my PTU when the swap was done…i didnt think really to check it again since they shouldn’t crap out that fast… [/quote] It could be many things. Maybe you replaced the PTU, but maybe there is a short in a wire somewhere and you’re not getting proper voltage under load. Or maybe your ECU is shot, who knows. All I know is that you always have problems, lol. You should really take some money and have someone diagnose your problem. Either stop by Licata’s and talk to Jeff or find a good Z tech on TTNET and drive to them. You need to talk to a Z-Pro and don’t take advice from random people who keep steering you in the wrong direction and don’t know these cars _specifically_. (this is NOT directed at you angry Don! lol) ---
**Author:** ![9ONA3OOZX](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/9ona3oozx/32/7242_2.png) [@9ONA3OOZX](https://forums.speedlife.net/u/9ONA3OOZX)\ **Post date:** [October 18, 2007, 5:27pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/16 "2007-10-18T17:27:07Z")
[quote=“Onyx Z32,post:15,topic:37217"”] It could be many things. Maybe you replaced the PTU, but maybe there is a short in a wire somewhere and you’re not getting proper voltage under load. Or maybe your ECU is shot, who knows. All I know is that you always have problems, lol. You should really take some money and have someone diagnose your problem. Either stop by Licata’s and talk to Jeff or find a good Z tech on TTNET and drive to them. You need to talk to a Z-Pro and don’t take advice from random people who keep steering you in the wrong direction and don’t know these cars _specifically_. (this is NOT directed at you angry Don! lol) [/quote] i’ll be due for inspection soon…so it’ll be at Licata’s anyway…i guess now is a good time to find out where my problems lie since i’ll have all winter to play around with it soon… ---
**Author:** ![Onyx\_Z32](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/onyx_z32/32/7581_2.png) [@Onyx\_Z32](https://forums.speedlife.net/u/Onyx_Z32)\ **Post date:** [October 18, 2007, 5:28pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/17 "2007-10-18T17:28:33Z")
Seriously man, you’re making us all look bad, haha. ---
**Author:** ![woody](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/woody/32/7191_2.png) [@woody](https://forums.speedlife.net/u/woody)\ **Post date:** [October 18, 2007, 5:30pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/18 "2007-10-18T17:30:50Z")
did i just get completely overlooked? boost leaks cause misfire ---
**Author:** ![9ONA3OOZX](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/9ona3oozx/32/7242_2.png) [@9ONA3OOZX](https://forums.speedlife.net/u/9ONA3OOZX)\ **Post date:** [October 18, 2007, 5:31pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/19 "2007-10-18T17:31:58Z")
lol i know…i give the Z cars this rep…but i dont get why? i’ve daily driven the thing for over 2 years now (not winters obviously)…and don’t have near as much down time as people may act…sure it has frequent, small problems…but it’s a 17 year old car! it will do that… for what it is, a jdm swapped 17 year old twin turbo car…i’d say i’m doing damn good with it. :gotme: ---
**Author:** ![Onyx\_Z32](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/onyx_z32/32/7581_2.png) [@Onyx\_Z32](https://forums.speedlife.net/u/Onyx_Z32)\ **Post date:** [October 18, 2007, 5:33pm UTC](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217/20 "2007-10-18T17:33:38Z")
[quote=“woody,post:18,topic:37217"”] did i just get completely overlooked? boost leaks cause misfire [/quote] Yes. Yes you did. 🙂 Like I said above, he needs to go over the 6-Ps, then come to us if he still has problems. [Next page](https://forums.speedlife.net/t/tight-plug-gap-low-vacuum/37217.md?page=2)