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View Full Version : Low vacuum!!! Im out of ideas! please help

rps13drift
06-02-2009, 03:36 PM
So ever since I started my motor this past winter from doing some upgrades I have been plagued with a very weird(to me) low vacuum situation. I have done countless boost leak tests/leakdown tests and even this past weekend I ended up ripping my topspeed intake manifold off to redo every intake side gasket and put the stock intake manifold back on. As for the car it starts and runs pretty good actualy but it only pulls 6-7 in/hg ? I got to drive it only once at a drift event and it slid and made power allright it just didnt seem as fast as I thought it would be.

Engine
sr20det redtop
hks 264 step 2 cams
apexi 1.1 headgasket
gt3076r
jwt ecu

My guesses on why it has low vacuum but seems healthy and please feel free to tell me if they are wrong

1- I have a thicker headgasket than factory and I never decked or shaved my head or block. I did the headgasket to this motor when it was running perfect so I didnt get to deck it ike I wanted. Could the added thickness lower my compression thus resulting in lower vacuum numbers?

2- I never bled my lifters when I had them out??? I admit I totaly forgot this step when doing my valvesprings and while searching about this problem all week I came across a thread where someone didnt bleed theirs and they had blowby and lower vacuum? But at the same time my head makes no loud noises what so ever?

other than these 2 guesses I personaly have no Idea on what could be doing this? On paper the motor checks out to be healthy and it also starts/idles and drive fine! Im just paranoid about my vacuum numbers! So if anyone has any Ideas pretty please helphttp://www.freshalloy.com/forums/images/smilies/biggrin.gif
S14DB
06-02-2009, 03:44 PM
Get a Dyson. I hear they are good vacuums.

Did you degree the cams?
rps13drift
06-02-2009, 03:56 PM
Get a Dyson. I hear they are good vacuums.

Did you degree the cams?

yup! i tried looking over everything that I could think of and now im stumped

http://i220.photobucket.com/albums/dd107/rps13drift/IMG00020.jpg

http://i220.photobucket.com/albums/dd107/rps13drift/IMG00022.jpg
S14DB
06-02-2009, 03:59 PM
Did you check the angle at .050"?
rps13drift
06-02-2009, 04:02 PM
Did you check the angle at .050"?

No sir! Care to explain please:o
S14DB
06-02-2009, 04:06 PM
Let me google that for you (http://lmgtfy.com/?q=how+to+degree+a+camshaft)
slider2828
06-02-2009, 04:09 PM
How low is low, and how are you reading vacuum. I have HKS264 Step 1's and didn't need to degree them
rps13drift
06-02-2009, 04:47 PM
How low is low, and how are you reading vacuum. I have HKS264 Step 1's and didn't need to degree them


I agree! i didnt think degreeing these cames was necesary when using stock cam gears? Oh and Im getting like 6-7 in/hg
slider2828
06-02-2009, 05:46 PM
Yeah that is crazy low... thats only 3psi..... should be getting over 2x of that....

********* How old is your gas? ++++++++++
aNskY
06-02-2009, 06:46 PM
1- I have a thicker headgasket than factory and I never decked or shaved my head or block. I did the headgasket to this motor when it was running perfect so I didnt get to deck it ike I wanted. Could the added thickness lower my compression thus resulting in lower vacuum numbers?



Yes, how thick is the hg?

also could be lots of overlap on the cams, those cams are definately not perfect (you need to degree them with adj. cam gears) im running the same cams, havent got to do it yet but i know theyre off. how are your egt's?
rps13drift
06-02-2009, 08:35 PM
Yes, how thick is the hg?

also could be lots of overlap on the cams, those cams are definately not perfect (you need to degree them with adj. cam gears) im running the same cams, havent got to do it yet but i know theyre off. how are your egt's?


I dont have an egt gauge at the moment and I have only realy driven it once because its my track car. what type of vacuum readings are you getting with your set-up?

Also upon messing with it and re-ripping everything apart I stumbled upon my knock sensor wire be pretty much destroyed! Could this have any effect on my motors vacuum if its going into limp mode or what ever? I know it retards timing and dumps fuel from that situation? Im running a JWT tune. Also researching a bunch on here a guy posted a situation similar to my with a new build and he said the knock sensor not working caused a lot of problems with vacuum and lag?
rps13drift
06-03-2009, 06:21 AM
to the top
djcobra
06-03-2009, 07:47 AM
I didn't think you need to degree HKS step 2 cams, unless you go with something really aggressive such as 272 duration. Now what if you have a S14 VTC motor? I believe Slider2828 and I have similar setups, only diff is that i'm using Step 2's 256in/264ex. You can't degree these cams if your going to retain the NVCS on our cars. One thing i had to do was rotate the CAS clockwise towards the engine (almost all of it) to get it to 15deg via timing gun @ around 850rpm idle. Argh.. cams are a pain....

Steve.
rps13drift
06-03-2009, 08:20 AM
Yeah! I never heard of degreeing them either? Any who im super curious now if my bad knock sensor wiring was causing alot of the gremlins?
djcobra
06-03-2009, 08:52 AM
I honestly don't think the knock sensor would be the issue. Only way to check is try someone else knock sensor with harness, or you can check the ohm reading from knock wire plug/harness. I believe it should be between 500-620 kohm reading....

here i've searched for ya :)

http://zilvia.net/f/tech-talk/257474-knock-sensors-pics.html


Steve.
slider2828
06-03-2009, 09:32 AM
Knock sensor usually is 1 wire hooked up I believe as long as that wire is connected just like the fuel pressure wire... you should be fine...
rps13drift
06-03-2009, 09:59 AM
Knock sensor usually is 1 wire hooked up I believe as long as that wire is connected just like the fuel pressure wire... you should be fine...

It was completely destroyed somehow? I will be doing the resistor trick this weekend to see if it changes anything.
aNskY
06-03-2009, 03:41 PM
I dont have an egt gauge at the moment and I have only realy driven it once because its my track car. what type of vacuum readings are you getting with your set-up?



i dont have an egt gauge either - my ex. mani and turbine housing were GLOWING after only 1 or two short pulls with the cams zero'd out.. i advanced ex 2 degrees and it no longer glows and boost comes on sooner. although that was like, winging it, i need to degree them...

im seeing -20psi at idle now... i forgot what it was before

I didn't think you need to degree HKS step 2 cams, unless you go with something really aggressive such as 272 duration. Now what if you have a S14 VTC motor? I believe Slider2828 and I have similar setups, only diff is that i'm using Step 2's 256in/264ex. You can't degree these cams if your going to retain the NVCS on our cars. One thing i had to do was rotate the CAS clockwise towards the engine (almost all of it) to get it to 15deg via timing gun @ around 850rpm idle. Argh.. cams are a pain....

Steve.

im running a built s13 motor... fuuuck nvcs
SoSideways
06-04-2009, 08:09 AM
Yeah I'm low on vacuum too, but my car's got a stock blacktop S13 motor with stock cams.

I've followed Enthalpy Scott's instructions on how to put the cams on the car, and all that, and I only get like 17inHG of vacuum at idle...

So I probably have a different issue than you do.
rps13drift
06-04-2009, 08:23 AM
try a boostleak test! you probably have a small leak
SoSideways
06-04-2009, 08:28 AM
Nope.

No boost leak.

That's tested by both blasting air in through where the MAF would go with a boost leak tester, and by hooking the car up to a smoke machine through the same place to try to smoke out any type of leaky area.

Didn't see anything.

BTW this has been going on forever... since I got the car started the first time. Thought I had a defective boost gauge, but I've had 2 that had the same reading now...
Sleepy240
06-04-2009, 08:50 AM
i dont have an egt gauge either - my ex. mani and turbine housing were GLOWING after only 1 or two short pulls with the cams zero'd out.. i advanced ex 2 degrees and it no longer glows and boost comes on sooner. although that was like, winging it, i need to degree them...

I was under the impression REGARDLESS of what cams you put in you should degree them to some point. I don't believe any "drop in cam" is perfect. Also do you have a boost gauge installed? If so where is it t'ed into? Its going to sound dumb but I would double check your BOV and flange. Mine was leaking on the cold pipe and it took me forever to catch it:rl:
slider2828
06-04-2009, 09:43 AM
Yeah I'm low on vacuum too, but my car's got a stock blacktop S13 motor with stock cams.

I've followed Enthalpy Scott's instructions on how to put the cams on the car, and all that, and I only get like 17inHG of vacuum at idle...

So I probably have a different issue than you do.

That is pretty close to normal though...
SoSideways
06-04-2009, 10:06 AM
That is pretty close to normal though...

"Normal" is around 20inHG of vacuum at idle, and drops to like 25in or more during decel in gear.

I get around 17inHG of vacuum at idle, then drops to like 20in during decel in gear. If it was really hot outside, my vacuum drops to around 18inHG during idle, and drops to around 21-22in during decel in gear.

Someone told me it could be my valves are not sealing all the way, thus causing this low vacuum issue.

Could be true, since I don't think my stock cams are out of time.
slider2828
06-04-2009, 10:44 AM
Could be, do a leak down test..... that will tell you
teamsprock
06-04-2009, 11:39 AM
20 inHG is normal on a fresh engine, plenty of good condition engines run around 16-20. I wouldn't worry if your around that level. My old engine had 16inHG and made 400hp all day long and ran for years with no problems, I finally built that motor but it was still in great running condition.
rps13drift
06-04-2009, 12:55 PM
I was under the impression REGARDLESS of what cams you put in you should degree them to some point. I don't believe any "drop in cam" is perfect. Also do you have a boost gauge installed? If so where is it t'ed into? Its going to sound dumb but I would double check your BOV and flange. Mine was leaking on the cold pipe and it took me forever to catch it:rl:


My boost gauge is installed on my FPR line. I am also not running a BOV at all.
slider2828
06-04-2009, 01:30 PM
Yeah I get about 19-20, motor runs strong no problems there....
clark
06-04-2009, 01:54 PM
dude, take the tee out of your FPR line and use a different vacuum/boost source.

are you positive you don't have a faulty boost gauge? as a sanity check, throw one of your buddies boost gauges onto there.
SILVIA_KIDs14.5
06-04-2009, 02:01 PM
Yes, how thick is the hg?

also could be lots of overlap on the cams, those cams are definately not perfect (you need to degree them with adj. cam gears) im running the same cams, havent got to do it yet but i know theyre off. how are your egt's?
google mercury in/hg is inches of mercury


sounds like a vac leak to me you should be gettin a lot more in/hg than just 7 i'd check your lines first be for anything then for shits and giggles check the boost lines i'b been there done that the car ran ok vac was all over the place and wacked out and fyi you should be getting a negitave reading at idle.
SoSideways
06-04-2009, 02:09 PM
google mercury in/hg is inches of mercury

Are you confusing him saying "hg" to convey "head gasket", by thinking about he misconstrued "HG" as in mercury?
aNskY
06-04-2009, 03:59 PM
I was under the impression REGARDLESS of what cams you put in you should degree them to some point. I don't believe any "drop in cam" is perfect. Also do you have a boost gauge installed? If so where is it t'ed into? Its going to sound dumb but I would double check your BOV and flange. Mine was leaking on the cold pipe and it took me forever to catch it:rl:

Yes, as i said, i KNOW i need to degree them.

Of course i have a gauge. how would i know what my idle vac is without a gauge?

dude, take the tee out of your FPR line and use a different vacuum/boost source.

are you positive you don't have a faulty boost gauge? as a sanity check, throw one of your buddies boost gauges onto there.

there is nothing wrong with t'ing the fpr to a gauge. i've had mine that way on every sr ive had.

google mercury in/hg is inches of mercury



Do you really think i would ask "how thick is your idle vacuum"? :tinhat: he asked a question relating to his HEAD GASKET.
slider2828
06-04-2009, 04:07 PM
LOL!!! AHahaha
SILVIA_KIDs14.5
06-11-2009, 09:59 AM
Are you confusing him saying "hg" to convey "head gasket", by thinking about he misconstrued "HG" as in mercury?
no not trhing to confuse him mm/hg or in/hg is a measurement you'll get if you use metric units for pressure i work in at a process control plant and thats what but my bad if i misunderstood you
wangan_cruiser
10-10-2009, 11:49 PM
sorry for bring up this thread. but my car idles on 15 im hg and my car still pulls strong.

running stock intercooler with atmospheric bov.
GSXRJJordan
10-11-2009, 03:04 AM
sorry for bring up this thread. but my car idles on 15 im hg and my car still pulls strong.

running stock intercooler with atmospheric bov.

There's an extremely small difference between 15 in/hg and 20 in/hg in terms of gauges (could just be the gauge)... most likely, your car is fine.

If you really cared, you could pull the head and do a valve job.