Turbo Stutter, Low VAC Question, Air Intake Question

[TheGreatGSX]

Hello everyone, I am new to the threads but a long time DSM Fan! I have searched and searched these problems and found simillar cases but did not really seem to find one that matched mine 100% so I completly apologize if these are common/noobie/stupid questions. (After so much reading I am have a major headache =D)

Ok, so about 6 months ago I purchased a 97 GSX (Last car was a 95 GS) So I am new to the turbo.

-114k miles
-Aftermarket Air Intake
-Looks almost like a self-made MBC
-Boost Gauge (reads up to 30PSI)
-Non-working A/F gauge
-Stock BOV (Pretty sure anyways, looks rusty and old)
-CatBack exhaust

Not sure if it has anything else, it had one owner and the dealer that sold it to me wasn't too sure either...

Problem #1
Driving the car home and for about a week after the VAC read about 20-21. After a short street race I noticed that the VAC was reading about 16-18. Usually first starting it up it will be 18 then after braking it will be 16, if I pump the brake it will even get as low as 14. I am completly new to this so I am not sure if this is normal or not. Now if I am moving and let the it drift in gear (Say its in 3rd gear but I am not giving any gas) The VAC will read 21 all the time but in neutral or completly stopped it will read anywhere between 14-16

Problem#2
When I got the car the boost maxed out at around 15-16psi. I simply left it alone (Afraid to screw anything up) But the mileage completly sucked. I had to fill up at around 220-230miles. And I also didn't see the need of having that much boost on daily driving. So I attempted to lower it. Well...no matter how much I lower it, it still boosts at around 15-16psi, now that it being cold out it seems to even get up to 17psi. As before when it was warm out the lowest I got it was 13-14psi. Any suggestions?

Problem#3
I ordered a cheap air intake for it. I installed it myself (Since they are so easy). On the stock one the guy who had it before me had plugged up a hose that use to be there. There are 2 bigger hoses and 1 smaller hose. He had plugged up the smaller one. Now that the new intake is steel I could not use the plug that he had used with the plastic intake. So just for the time being I just routed the hose to under the air filter and kind of tied it there since I had no idea where it should go. Can this cause any problems for the time being? And where should it go? Can I plug it?

Problem#4
My biggest problem being that it just recently started stuttering/jerking/bucking at full boost. It has never done this and since I get boost happy I typically floor it at least once-twice a week to "clear her throat" . If I gradually accelerate to full boost I don't experience the problem, but when I floor it when it gets to full boost or close to it it feels like the engine cuts off for a second or two then kicks back in with a loud backfire. Sometimes it does it a couple times in one episode but usually only once since I let off the gas as soon as it does it since it honestly scares the poop outta me when it happens. I read up that usually new spark plugs/wires usually solve this problem. I just want the best answer since this economy sucks ass and I am hard for money at the time but need a good running vehicle. And since we're on the subject what plugs/wires do you guys recommend for daily driving/non heavy modified GSX?

Unfortunately we don't have a whole lot of mechanics out here in Morgantown, WV and virtually none that work with modified turbocharged cars. Thank you guys in advance and these forums (I've been to a lot) absolutley kicks ASS.

I will be posting pics very soon and will probably be asking more questions!!

****I realize I need/should do a leak test, but am not confident enough to do it on my own so should I take it to a shop to do this or can a dummy perform this test accurately and safely?****

 

[e85_4g63]

I'm thinking you have a boost leak somewhere. The BLT (boost leak test) is easy to do. There are many threads about them. You could always try pulling the plugs and and seeing if any of them look fouled and re-gap them before reinstalling. Also post a picture of what tube on the intake your talking about. I'm thinking it's the one that goes to the valve cover, but not 100% sure without seeing it.

 

[nlzn]

First thing you need to do is plug any of those hoses if you arent using them.

The bigger hose on the intake tube is probably the BOV recirc.. and that would be considered a big vacuum leak if left unchecked.

On the 1g intake tube (stock) theres 3. Moving from the MAF side, first one I dont remember where it goes, second one reroutes from the intake manifold vacuum source and the third is the BOV recirc. Any and all of those hoses left unplugged are a post MAF intake leak, and the car will be getting too much fuel because it's not getting metered air it thinks its getting.

 

[TheGreatGSX]

I have some pics up and in my gallery. The tube is the one closest to you (If you were standing in front of it). In the pic its a red tube coming under the MBC and going to the left. There is already one going to the valve cover so I am somewhat sure that is not it.

 

[TheGreatGSX]

One tube is going to the valve cover, the other to the BOV.

 

[nlzn]

I think i see what youre talking about.
if its coming out of the intake tube and isnt plugged.. its a leak.

Your stutter @ Wot is probably either fouled plugs (youre getting fuel for air that isnt making it to the motor or fuel cut)

Edit: curious.. im guessing the previous owner just unplugged the BCS with a few other things. Id make sure to go over ever hose under that hood and make sure its connected or capped.. then hit it with a boost leak tester

 

[TheGreatGSX]

Would I be getting fuel cut although I've never experienced it before and have changed nothing?

-And thanks by the way for the help...everyone in this forum seems to rock...it is much appreciated

 

[nlzn]

Heres a real good explanation of fuel cut.

http://www.dsmtuners.com/forums/frequently-answered-dsm-questions/186971-what-fuel-cut.html

Last I forgot to mention.. depending on the setup and with a leak its possible to boost more when its cold out due to simple physics. Cold air is more dense.. iirc correctly the formula was every 10degrees in intake air temp dropping is a around 1% in total HP increases.

 

[TheGreatGSX]

I looked up the terminology but did not find "BCS", what does it stand for?

And also I still need answers for Problem#2 with lowering the boost and does it matter what spark plugs and wires I get since it is not heavily modifed?

 

[DarkMyrakul]

boost control solenoid (BCS) a.k.a. the wastegate bypass solenoid, also the number 2 problem you should be good with some NGK BPR6ES since there are no mods and there are basically 2 types of wires i would go with...Magnacore or the Accel 300+. Also as you can probably tell the answer to the number 2 question is the BCS.

 

[mike_tsi]

It is Boost Control Solenoid. Right under your intake to the left. When looking at the car from the front. Little black box w/two air hoses connected if running stock. I would think you are hitting fuel cut also. With the boost creeping up to 17, I think its due to the cold. Because are cars love the cold weather.

 

[Colt4G63 also]

BCS means Boost Control Solenoid. These guys are correct, it sounds like you have all kinds of leaks in your intake tract. You really need to fix that, because with a turbocharged engine it makes a huge difference.

Don't drive it until you get it fixed. Your engine is most likely experiencing massive knock caused by improper A/F ratio, and that cutting out symptom is your ECU trying to prevent total engine failure.

 

[TheGreatGSX]

So I should hook that tube into the BCS? And the original intake should not of been plugged? That being done and some new plugs/wires will that more than likely solve my problem? Or is the fuel cut due to something else? And I know these are dumb questions so thank you guys for being patient and not getting frustrated...my conscience could not settle with causing people to break their keyboards over there heads =D

 

[TheGreatGSX]

Ok, After going out and checking things out. I realized that, that tube is in fact plugged. Now that I remember, the plug the guy had used did not fit in the new intake but it did fit into the end of the hose (very very well actually) which I did. So all the hoses and tubes are either clamped nice and tight or plugged. Which brings me back to the question as why did this start happening, everything was fine untill it started getting cold out...should I still go ahead and connect that tube into the BCS?

 

[mike_tsi]

Problem 1: Check for boost leaks. Couplers etc. Test it.
Problem 2: Check if your BC(boost controller) is hooked up properly. May not be hooked up to a proper source.
Problem 3: With the new intake you have it should have two nipples on the bov side. Also another nipple on the radiator side(small nipple)Its the smallest hose. All hoses should be plug an play fit snug.
Problem 4: Personally it sounds like Fuel cut from boosting 17, could be that. Check spark plug wires, boost leaks.

By the way your bov is a 1g bov. So it should hold just fine.

 

[dsm908]

BTW your BOV is from a 1st GEN, way better than your stock one so don't get upset and waste money on an unneeded part

 

[dsm908]

oh mike sorry didnt see what you wrote at the end of your reply , its ok everyone laugh at the dummie

 

[TheGreatGSX]

Wow, glad to hear its a 1g BOV, one thing I don't need to worry about. And yes the intake has 2 nipples on BOV side and one on radiator side. The 2 nipples on the BOV side I just plugged them into the exact places where they were before with the original intake (Nice and Snug). The nipple on the radiator side, the stock intake had a plug in this nipple, now the plug was too large to fit into the after market nipple so I just attached the hose to the nipple then put a plug at the end of the hose and routed the hose to the left side of the car (Everything nice and snug). The MBC seems to be installed correctly (It appears the gentleman who had it before me knew some-what what he was doing, more than me anyways, unfortunatley). First thing Monday I will be getting new spark plug wires, getting a BLT done, and getting someone else to recheck the MBC to ensure it is installed properly.

**I appreciate all your guys help very much**

I will update as soon as I get all this done and hopefully I get somewhere and learn along the way.

 

[nlzn]

Well it isnt too hard to hook the boost controller up.

Basically the best way is to have a source from the compressor housing of the turbo (to avoid spikes the closer the better) and the WG. If not Then youll want to use a T from an intake source, mine comes from the BOV that's T'd to the Intake manifold.

See this article: http://www.dsmtuners.com/forums/articles-turbo-system-intercooler/237982-best-way-install-mbc.html

On the spark wires, dont waste your money on Magnecore unless you have extra just laying around. Some NGK or good Accel's will be just fine, just dont get cheap or Bosch ones.

 

[TheGreatGSX]

Just small update:

After reading that article (Thanks to nlzn) the MBC is installed properly and exactly the way the article says. I have the MBC to where if it was screwed any more loose it would come off which the boost was still getting up to 15-17PSI. I triple checked all the hoses and tubes and they all seem to be nice and tight. Still have to wait untill Monday to get a BLT, and hopefully later today I can pick up some spark plug wires and see if that helps any. At least that way the only thing left do is the BLT.

And is it ok that the small nipple on the radiator side of the Intake is plugged? Any pros/cons to that?

One other question, any way I can get the BOV polished to make it looking nicer? Looks kind of beat up. And if so usually what is the price range on that.

Thanks again to everyone.

 

[TheGreatGSX]

I got the plugs and wires. The NGK plugs out of the box recommends gapping at .032 but since I researched the forums and everyone seems to agree that .028 is the way to go that is the gap I'm going with. I will update after I get them installed and take it for a test drive.

 

[TheGreatGSX]

****UPDATE:****

Got the plugs and wires installed. Solved the bucking issue completly.

I messed around a little with MBC and got it to 14psi but still can't lower it anymore than that. So I'm still going to get a BLT done Monday.

To describe the VAC issue in more detail...
When I first start it up, the VAC goes to 21. Now as the RPMs drop down to idle the VAC slowly goes down. Depending on how cold it is outside it usually goes down to around 18 on an average day, or 16 on a warmer day. When I change gears it goes straight to 21 or after revving it up while the RPMs decrease it drops to 21, then once it gets to idle they slowly go back down to 18ish. As I said before it seemed when I first got it, it would always be at 21 (Although not to say I did not pay THAT much attention to it) Is ithis normal? Or does this usually implie there is a Boost Leak somewhere?

T - H - A - N - K - S again to EVERYONE. I love these forums.


Edit: Basically the VAC mimics the RPMs. The lower the RPMs, the lower the VAC (During Idle).
I.E. If the car is idling at 1.2RPMs (Cold outside) the VAC reads 20-21. If it's idling at 0.9RPMs (Normal Idle) then the VAC is reading 18
Normal or usually indicates a leak?