full boost vac leak

[d_money1]

i just bought a car today. the description i got was, the car runs rough, she parked it about 4 months ago, started it 2 months ago after movin' away with her new car, it ran rough and it's been parked and sitting ever since. Now, she was home, i bought the car, it sounds like it has a huge vac. leak, it studders so bad it won't accelerate barely enough to get to 2nd gear. I can't find any loose vac. lines, i hear it toward the back of the IM, maybe under it. I haven't gotten a chance to verify correct cam timing. The car is all stock. First gen., GSX.

 

[snowborder714]

Do a boost leak test and spray soapy water where you hear the leak. The leak will make the soapy water bubble and you'll be able to "see" the leak then.

 

[d_money1]

i don't have access to much of anything where the car is at. I boost leak test may be hard to do right away. The leak sounds like it's coming from the underside of the manifold. Today i was messing with the car a bit more, and it was reading almost 7lbs of boost for awhile, then after revvin' it a bit it dropped to around 10in". It has an aftermarket boost gauge and the stock one, and they're pretty close at both those times.

 

[turbosax2]

The stock gauge is useless and not accurate. It is critical that you do a proper boost leak test to pinpoint the leak.

 

[d_money1]

one thing i forgot to mention was that it reads 14lbs of boost while drivin' it.

 

[laserspeeddemon]

This can be a number of problems from bad spark plugs to a bad ECU.

Lets take care of the hissing first. There are vacuum lines that run under the manifold. You can cap the vacuum line on the throttle body to elminate this as a cause. If you can't get a hold of some caps. Then you can reroute them together in pairs of 2. If you are still getting a hissing sound under the manifold then this is not the problem. Also make sure the brake booster is connecting. This is actually BEHIND the manifold. Double check the fuel pressure regulator line isn't leaking as well. Replace the hose if there is any question.

What does the boost gauge read with the engine off? The gauge may be out of calibration. It doesn't seem likely that you would be getting 14 psi if the engine has such a severe boost leak. When I get home I'll show what to look for with some pics.

 

[d_money1]

the gauge reads zero with the engine off. thanks a ton, i really appreciate the help. I won't get a chance to check out the car again until friday. The plugs look like CRAP!, completely carboned up. I don't know where the aftermarket gauge gets it's boost signal from.

 

[snowborder714]

I would get new plugs (NGK BPR6ES) and follow the line from the boost gauge into the engine bay and figure out where it's teed into to make sure it's a good source.

 

[turbosax2]

the gauge reads zero with the engine off. thanks a ton, i really appreciate the help. I won't get a chance to check out the car again until friday. The plugs look like CRAP!, completely carboned up. I don't know where the aftermarket gauge gets it's boost signal from.

The most common place to tap the boost gauge is the fuel pressure regulator hose. If it's not tapped there already, considering changing it. Do not tap it off the bov line.

 

[d_money1]

thanks again! you guys have been a great support and much help. Hopefully i can get this thing runnin' smooth next weekend and drive it home.

 

[d_money1]

with a miss that bad, any chance of seein' a lack of vac. that large? And, thinking back, i don't think that the aftermarket boost gauge is T'ed into the fpr line, because i checked the fpr line looking for a leak.

 

[turbosax2]

with a miss that bad, any chance of seein' a lack of vac. that large? And, thinking back, i don't think that the aftermarket boost gauge is T'ed into the fpr line, because i checked the fpr line looking for a leak.

This comes back to checking for a boost leak. Doing a proper boost leak test is the first step you need to take as soon as you can do it.

 

[d_money1]

will do it as soon as i get up there. i'm gonna have to bike pump it though, i have access to nothin' up there.

 

[turbosax2]

will do it as soon as i get up there. i'm gonna have to bike pump it though, i have access to nothin' up there.

Ouch, that's going to be rough if you have a big leak. Good luck. Remember the soapy water to find leaks.

 

[d_money1]

yeah, i'm hopin' with some help, as i pump i can have some friends with their ears closer to things, maybe hear a little something. And i'll be packin' the soapy water as well.

so, i found a leak at the TB. the compressor i'm using is just a small one that plugs into your cig. lighter, so it doesn't push a lotta volume. I have trouble getting more than 10psi in there, but i can hear the leak. My biggest question now, since i wasn't able to go ahead and fix that today, before i head back up there, could that be causing all these problems? I mean, could that really make the car run that rough through in all conditions? I understand that it's a vac. leak, and can cause mixed a/f ratios...but the kid who works on the car was saying something about him messing with the CAS a bit, but the car ran fine after that...was just wonderin' if i could get a few more thoughts before i head back up to fix that TB gasket next weekend. Thanks for the help thus far guys,
Neil

oh, and the car is still making boost in neutral, can't figure out what the deal with that is. I checked the timing, timing marks line up, except i can't see the oil pump mark. But crank & cam gears all line up right. TDC when the cams are lined up.

 

[erald01]

After doing the proper tune up for the car, what i would i would get one of those carburator cleaners at the local car store and start spraying it at the vacum lines or where ever you think there is a boost leak coming from. If there is a leak where you spary you will notice the engine rev, then go back to normal. You must have a huge boost leak if the gauge shows boost in neutral, but at the same time those stock gauges are pieces. Good luck and keep us inform.

 

[alice]

I just did a boost leak test on my 2g because I was only pulling 12-13in/hg vacuum. Found the Base Idle Set Screw (BISS) o-ring was hard as a rock and dried out. My car didn't hold 15psi for more than 10 seconds; no good. Quick test for that: Start the car and put your thumb over the BISS screw (you might have to remove the cap/cover) and see what happens. Check if your vacuum goes up. Mine went from 12-13in/hg vacuum to a very steady 15in/hg. I still have some boost leaks to find and take care of but the BISS o-ring is a common place for leaks and good place to start.

Pull the BISS out and see if the o-ring is hard or cracked. If so, just replace it. The o-ring is a number 5 - 3/8x1/4x1/16. <---thanks to VFAQ!! It can be had at most hardware stores. Hope this helps and good luck!! -Jeremy

 

[d_money1]

thanks, i really appreciate the reply. The more i'm looking, it seems that a lot of my symptoms relate more to a CAS problem than just a vac. leak. It has trouble reving past 2500-3000rpm when in gear, stutters and cuts like crazy. Sparatically it will pick up and fall-right on it's face, but for like maybe half-second to a full-second it makes a quick leap, then the same thing, doesn't matter what i'm doing with the throttle. Anything from barely touching it to WOT, doesn't seem to make any major differences in the reaction of the car. I will check out that BISS though.