Low Vacuum, Ideal?

[jukematt]

This is for my 99 GSX. Whenever my car is on, whether cold or warm, my vacuum sits at 5 hg at idle. I can boost fine (still stock level). It used to be about 15 before my clutch got replaced. I did find a boost leak by my smic so thought that was the cause but after I replaced the stock tube with all steel upper and lower, no change.

Does anyone know what causes the vacuum to be so low?

What is the ideal vacuum pressure?

I do know that there's a wiring issue with them lighting up and the EGT doesn't even work correctly but the boost gauge is mechanical. Suggestions? Thanks.

 

[coltanostra]

I found out some interesting thing. If the Balanceshaft(s) is out of there correction Position, the Vacuum is getting low and dont reach stock Level. I used this Method sometimes to check 4g63 Cars before i by them.If you dont have no longer Balance Shafts in, then we have to search further.

 

[68442]

15 to 20 is the norm. Get another guage and hook up to another vacuum port. Could be a bad guage or a bad line to it.

 

[Absit]

Ideal vacuum at idle is around 16-18inHg, my car sits at 14inHg with 143k on the original engine. You're WAY off.

Did you repeat the boost leak test after fixing the one you found?

 

[jukematt]

I still have the balanceshafts. How do you check if they're out of their correct position?

I am getting Prosport gauges soon for Boost and Oil Pressure. I actually haven't even checked where my current one is hooked up since it was on the car when I bought it.

I have not repeated the boost leak test. I was getting 5 psi of boost and now I can get 10 after installing the hard ic piping. And I can feel the greater power. But the main reason I haven't repeated the test is because we had a REALLY hard time getting those couplers on the piping. Before we did the test by removing the hose off the j pipe and blowing toward the smic. Not sure the best places to do it. Also, the lower ic pipe was designed for the T25 turbo and I have a 14B. We used the stock tubing as a coupler to bend around from the j pipe to the ic pipe.

But still, the vacuum sits the same as it was before changing the piping.

Thanks for the help so far.

 

[tsi87889095]

I have the same problem rebuilt and installed a 2g head and now vac sits at -8 or so. Boost is set at 9psi? While I'm in the throttle it holds at 9psi with no problem. I will be curious as to what the problem is so maybe i can fix mine. Sorry to jump into the post with the same problem but didn't want to start a new one. Thanks

 

[jukematt]

That's fine if you jump in here. That is better than starting a duplicate post. I posted the thread last night then went to bed shortly after so couldn't get back until this morning. Still waiting for a response again.

 

[boost69]

i had the same problem and my timing belt jumped one tooth, reset timing and was all better

 

[standard235]

My gauge says 20 inHG on a 120k mile motor and 24inHG on the MAP sensor...

I'm thinking timing. My car used to do the same thing.

 

[jukematt]

Well I am saving up to have the timing belt replaced. Belt looks good but since I don't know when last it was done, be a good idea. Alright, thanks. Hopefully everything will be fine until I get that done.

 

[gst96spyderman]

Get a kevlar timing belt. They are crazy tuff. A little bit more expensive... But deffinately worth it.

 

[jukematt]

I've heard of those. So do they last longer or something so not as much of a risk? And where do you buy them?

 

[gst96spyderman]

i honestly forget where I got mine. I always goto extremepsi.com, but they don't sell them. rbwtrans suggested to me where to buy, but that was like 2 years ago... pm him, or googloe it. I just did and the 4th tab was for a 4g63 engine kevlar timing belt. heres the link. Power Enterprise 4g63 Kevlar Timing Belt (DSM / Evo) - Modern Automotive Performance I'll do some more research for you.

Kevlar timing belts are amazingly tuff. I've seen parts of the belt be tore off but still fully functional. Like if a tooth on a gear breaks at high rpm, then knocks about a nickle sized portion of the timing belt off it will still hold. Still looking for you on the best place to buy. good luck.

 

[jukematt]

Cool thanks I'll look around too but let me know what you find. My laptop just went to the wayside so I have to wipe it and reinstall Windows. I'm on a friend's laptop right now but I won't be able to get online as much until I get that done so thanks!

From what I've read it's also good to get a new waterpump too when I get that done? And what do you think about the whole balance shaft eliminator? Y/N?

 

[gst96spyderman]

Sorry about not posting lately. I just suffered a lose. My spyder was totlated this past sunday. So I've been busy looking for replacement

Anyways, Greddy makes a kevlar timing belt. Thats what I had on my gst (RIP) Not sure where it was pruchased. But now you have a title to search with.

As for the water pump... That is a big affirmative. It is a pain in the ass do get to, and a lot more accessible to replace when timing belt is being replaced.

Balance shaft eliminator... simply, yes. Do it.

Good luck and keep us informed

 

[jukematt]

Thanks for the advice and help, sorry for your loss and hope you find another soon! I like the sypders but decided not to get one due to the extra weight. Maybe you can find a GSX/TSI AWD now!

 

[gst96spyderman]

Not looking for 500hp, just around 300-350 DD. The verte looks so sweet. Plus the ladies love riding in them. I'm a spyder man. Used to have a TSI AWD at about 370awhp... I loved the launch and handling around those hairpin turns, but open top on open road... can't beat it. Maybe an awd conversion on a spyder... We'll see

 

[agentorange313]

you guess should consider small problems that are causing the bad idle

Idle vacuum should be anywhere form 18-22.

Have you check for vacuum leaks? Any unmetered air will screw up your idle.

Have you checked you IAC?The stepper motor could be bad and not competely retracting when you go into idle allow the correct amount of air into the chamber.

Bad idle is also a sign of engine performance. With bad idle, you are able to determine sometimes if the rings are bad in a chamber. If the chamber can not hold compression it definitely can not create vacuum on the intake stroke.
Do a compression check just to make sure.

 

[jukematt]

...open top on open road... can't beat it. Maybe an awd conversion on a spyder... We'll see

Well got me there I have not experienced that but yeah an AWD conversion would be sweet.

 

[4g63oncrack]

have you done a no crap boot leak check?

 

[jukematt]

agentorange313,

How do you check for vacuum leaks?

What's an IAC? ...just checked acronyms, it says that is only on 420a cars.

I was going to do a compression test this weekend but my friend never told me when he was available. If we don't do it, I'll do it with another friend when I go back home for Thanksgiving break. Since I've never done it and don't know how.

 

[gst96spyderman]

another alternative.


Took me blowing HG and needing to look for new timing belt to get back to you. Here's a link.

Super Strong Timing Belt

Whats come of it so far?

<-----new spyder... new problems

 

[jukematt]

Wow I haven't been on for a while. So first, my laptop I was fixing turned out to have some hardware issues so got a new laptop. Alienware

As for the vacuum problem, staying about 9 hg now for some reason. Still haven't got the new gauges due to other expenses that are more important.

Still haven't done a compression test. My one friend wasn't available except once but it would have meant me picking him up from clear across town in rush hour then taking him home again and was already getting late, and I was really tired. The other friend back here at school has been pretty busy. He did pick up a '90 GSX and I was helping him get it up and running. Took all day to do just a couple of things but next time we have some free time (and good weather) we'll try and finish then do the compression check on both cars.

Other than that, it's fun pulling up to these RSX's or Honduhh's who think they're all that and blowing them out of the water with my near-stock GSX HAHAHAHA.

Oh and congrats gst96spyderman on the new spyder. '99 hmm? Sweet!

 

[agentorange313]

I never checked back, sorry about that

Get a boost leak tester, you can look up how to make one or buy one online. It will tell you if you have any leaks on the charged air side


IAC/ISC Idle air control/idle speed control: It is a stepper motor located on your TB. It moved in and out in steps that allows for certain amount of air to pass into the throttle body allowing for the right A/F at idle when the TB plate is closed.

There is a tech article on how to test it.
http://www.dsmtuners.com/forums/articles-tuning-ecu/386663-dsm-isc-motor-testing-replacement.html

If it is non functioning this is where you can buy a new one. Cheapest price
DSMISC Automotive (New ISC Supplier)

goodluck

 

[misterjose]

make sure you have no leaks on your TB. between your TB and intake. when i replaced my tb i had a huge leak i guess the gasket did hold or what not but i put rtv all around that sucker and wallahh it was fixed.