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506 Posts
Discussion Starter #1
bout to go rent a compressor and do it myself, but having second thoughts

i took a look at the piping diagram on the internet...dang are tehre a lot of those connectors, hoses clapms and etc, and most of them u can't get to by hand unless you take off a fair amount.

from those that have done it before, where's the hardest spot/hardest to see hardest to reach that i should keep in mind?

506 Posts
Discussion Starter #3
what are you talking about???

giving it half what, i asked about the boost leak testing and help on locating the leak

the piping from the 300zx diagram shows a very intesive intercooler tract, i just wanted to know the hard spots that i should look out for

10,895 Posts
Thumper 300zx's Guide to Common Boost Leak Areas



If you own a Twin Turbo, you've probably seen a lot of talk about BOOST LEAK. And if you've ever posted a question about "lack of power" or "low boost", you've certainly had a response that reads "Do you have a boost leak?"

This article assumes that you know how to perform a boost leak test, and that you have the appropriate tools (compressor and boost leak tester) to do so. It also assumes that you have an aftermarket boost gauge so you aren't guessing what your boost really is. A good boost gauge IS A MUST! I also suggest at least a fuel pressure gauge.
Gauges provide you with certainties (eliminating variables) and generate accurate data for evaluation. Be very familiar with the terms and concepts provided in Ash's "The 6 P's" (AutoFaq on TT.net). You need to know if your car is UP TO PAR so you aren't wasting time and money trying to get more power out of a car that won't ever provide it. Plus you could damage your car modifying what isn't ready to be modified.

Despite many good articles on how to perform a boost leak check, I have yet to see a writeup that specifically discusses the "common boost leaks", where to find them, and how to fix them. Another tt.net member posted back in '03 asking for info like this, but there was not a single response:

"Boost, Leaks and the rest..."

Hopefully this writeup will fill a void. The info here would've helped me a lot while looking for answers. There is also a Q&A section below (not complete) that might help explain some misunderstood boost/vacuum leak concepts.

Though a boost leak test will effectively point out leaks, it's nice to have a head start by knowing where leaks might show up. Since the goal is ZERO BOOST LEAKS, I have also developed a complete checklist of components that can be under vacuum/boost along with vacuum hose diagrams (CLICK HERE) so you can check each of them (if you want to!)


As noted in "The 6 P's" (see link above), this should be part of continual maintenance. Often you will not be able to perceive boost leaks unless you test for them. If you continually perform boost leak tests, you will be ready to tackle them when it becomes convenient. One example - if your EGR valve is leaking, you are not likely going to pull the engine, tranny, or plenum/lower intake to replace it. However, if your clutch goes out and you know you need to do the EGR, you'll know it! Makes life a lot easier to replace these kind of things when bigger work is being done. At the very least, if you are going to do major work, do a boost leak check beforehand. So, keep doing boost leak checks and you're life will be made easier and your car will always run nicely.


Once a few months ago I performed a boost leak test and found only one leak. It was at the back of the engine. I never pinpointed it and didn't fix it. Even though I had the leak, my gauge (Autometer) indicated a solid 15 psi of boost (w/fuel pressure holding 60).

Then one day after completing some non-related work on my Z, I took it out for a quick drive and found that I had lost boost entirely! There are a few things that cause zero boost:

•Very bad boost leak (detect and repair)
•Blown or siezed turbo (repair or replace)
•Stuck wastegates or recirculation valves (rev trick, adjustment, repair or replace)

Knowing very little beforehand about how the whole intake system is designed, I started on a fairly involved investigation. Ultimately what I found was three boost leaks: 1) Turbo outlet driver side hose 2) Turbo outlet passenger side hose 3) IAA (Idle Air Adjust unit). The outlet hoses were significant enough to drop boost to ZILCH, NADA, ZERO.

I fixed all of these leaks (explained below in detail). As a reward for doing so my car is running better than ever! With the same boost jets (.045) my gauge now indicates 16 PSI solid and turbo response time is much better than before. I have since retested my system and found ANOTHER leak, which is from the EGR. This is a common leak, and very tough to fix. It requires a plenum pull to bypass and a tranny drop or engine pull to remove/replace! And, the buns about it, many need to keep the EGR for emissions!

If you think your can is running perfectly, but you've never done a boost leak check or tightened all your clamps, DO IT NOW! Note that I intend to run 14 PSI...been needing a set of .050 jets or a drill to open up a .045, although I may soon get an EBC instead. I also have race fuel in the car right now (remnant from drag strip), so running 16 isn't too ridiculous. I can't wait to get back on that strip, drop my 60', and get a respectable time slip : )


A normally aspirated (non-turbo) intake is always under vacuum (negative pressure) except during acceleration when near zero pressure might be reached. A turbo intake is also under vacuum until acceleration -- but on a forced induction engine, the turbo (or alternatively, a supercharger) creates boost putting everything beyond the turbo outlet (including the intake manifold and anything attached to it) under POSITIVE PRESSURE. Only the section of intake between the air filter and turbo outlet remains under vacuum.

If you have a vacuum leak off the manifold under negative (vacuum) pressure, it can turn into a boost leak under boost. When you do a boost leak test, you are artificially boosting the entire intake tract. Any leak detected should be fixed because it will either leak boost or suck in unmetered air.

Vacuum leaks generally cause hesitation or inconsitent component operation (ie, idle valve). They can also cause a LEAN condition as the car will suck in unmetered air, which is any air entering the intake system beyond the Air Flow Meter. A lean condition can, and likely will, manifest itself as detonation!

Boost leaks generally cause poor performance (loss of power) and a RICH condition as metered air is leaving the system while the fuel to be injected has already been calculated. Even if you can hit full boost (with a boost leak) you are losing out -- the turbo has to work overtime (spin faster) to maintain peak boost. This will tend to increase intake temps, too. So a boost leak, which will tend to make you run rich, can actually lead to detonation as well!


Anything in the intake tract from the air filter to the cylinders has the potential for boost/vacuum leak. However, the most common leaks found are associated with loose hose clamps on the large intake pipes. Even if you don't find leaks, you may want to tighten down all clamps as a matter of continued maitenence.

When you do your boost leak test, use the pictures/graphics provided below to determine where the leak may be coming from. If you can hear a leak, but can't pinpoint it, use some soapy water solution and you should be able to detect the leak precisely. If the area is not visible, you can use a length of vacuum hose to pinpoint leaks. Just "stick it in your ear", move the hose around, and when you are close you'll hear it. This is how I found that my EGR was leaking!

A list of possible boost leaks would include:

Most Common: Large piping (soft and hard pipes) and their associated clamps
Turbo's themselves
Turbo Intake-Outlet hoses (VERY COMMON)
ANY device or hose attached to the intake manifold (EGR, IAA/IAVC, AIR REGULATOR, BOOST SENSOR, aftermarket boost gauge, anything else pulling a vacuum line off the manifold, etc). CLICK HERE for a complete list!
Manifold itself (along gaskets)
The pictures immediately below show the location of readily visible intake clamps. The legend defines the colored dots. The dots indicate clamp location and the pressure state of the associated piping when intake manifold pressure is positive (under boost). Again, you may as well tighten them all even if you don't hear a boost leak, just to avoid future problems. The white arrows show the direction of air flow.

Side note: all the hose clamps on my '91 TT have flat head slots with 8mm heads.

The intercoolers are located at the front corners of the car (one for each turbo). You can see them if you duck down and look through the intercooler scoopes on the bumper cover/fascia. There are other clamps and hoses not seen here, such as those down by the turbos and intercoolers.

Here are some pictures from alternate angles. They shows the pipe coming from the respective turbo and going to the intercooler. You can see a hose clamp down there that could need tightening.


Some TT.net members have made close estimates of the linear footage of our intake piping from intake to throttle -- it's about 23 mind-boggling linear feet! Here is a list and some graphics of this piping. This info should help you to locate tougher leaks you may have. Note that once the intake TEES off after the Air Flow Meter, you basically have two indentical 11'6" tracts (pass side and driver side). Aside from some appending vacuum lines, barbs, connectors, and shaping, there are no differences between the tracts. There exist an equal quantity of pipes & clamps, a turbo, an intercooler, and two gaskets.

Itemized List of INTAKE TRACT
from Filter to Throttle Body

does not include appending hoses/devices

AFM (w/velocity stack) - CLAMP
PLASTIC TEE (2 equal tracts) - CLAMP

To summarize, that's 13 independent hose clamps PER SIDE of the intake tract (filter to throttle), two shared clamps, and two gaskets for each turbo. This doesn't include recirc valves and various hoses that tap off of the piping! Below are visuals of this information (numbered as above for identification). I used Nissan Fiche diagrams -- the top graphic shows FILTER to TURBO. The bottom graphic is the continuation from TURBO to THROTTLE BODY.

Tip: Refer to your own engine bay simultaneously with these diagrams

Listed above are parts 1-15 on the DRIVER SIDE. Listed below is the continuation, but shown from the passenger side (just because it is more easily followed).


After indentification, the fix for most boost leaks is very easy. Find the leak, tighten the clamp or replace the necessary vacuum line. If you have located the leak then you can probably determine how to get a tool on it. Only one set of hose clamps is rather pesky -- the clamps on the passenger side turbo outlet.

The more difficult leaks to find and fix are components: intercoolers, idle control (IAA), EGR valve, recirculation valves, turbos, or the main pipes in the tract. You will have to repair or replace these items if they have a leak. With some of the components, extensive work would have to be done for a fix (ie, turbos, EGR, intercoolers). Have fun with that : (

As time goes on, I will try to compile some repair info for some of these harder components. I did a fix on the IAA (see here) or click the link provided further down. Recirculation valves shouldn't be too tough to replace, and are instructions for Intercooler replacement, which have failed on some cars. Repair info for turbos may be available on TT.net, but I'm not sure - it could be rather involved. Most people just buy and install a replacement.


The turbo outlet clamps are among the most common that come loose. They are hidden down by the turbos. These clamps hold on a small section of rubber hose, ~4-5 inches long just above the turbo on each side on the intake side (remember that turbos have an intake side and an exhaust side - the intake side is oriented toward the front of the engine).

On the driver's side, the hose clamps are easy to get to (see pictures below), especially if you have removed the PRVR system (debated whether it is o.k. to remove this auxiliary system). You can see the hose by looking down toward the turbo from the clutch reservoir. When I tightened mine down, I cleaned up the working area as well as I could (always clean when doing a repair - shows you love your car). The clamps were loose enough to move without loosening them further! The clamps have a connecting bracket, spacing them apart on the back side. This is a nice feature because it keep the clamps distanced properly for a good fit on the hose ends. I repositioned the clamps and tightened them down. Each of these clamps took about 3 full turns to tighten. THAT'S REALLY LOOSE! If you have hose clamps as loose as this, you will likely enjoy the performance difference after the fix.

On the passenger side turbo intake-outlet you have the same setup, but the clamps are tougher to get to. The lower clamp is particularly tricky, oriented oppositely, facing the front of the engine. For easier access and vision, remove the battery. Make sure the clamps are positioned well on the hose. Then tighten down the lower clamp. To get to it, use a 1/4" universal joint (u-joint) with a LONG extension and a socket driver. If you use multiple extensions, you should probably tape them together so you don't lose disconnected pieces. The angle of attack is around the area shown in the picture below. Get the extension down there and peek from the battery side to manuver the socket onto the clamp head. If you have an old, loosened u-joint, it will be tough to get the socket on the head. Once you get the socket on, keep good pressure once you get it on, and tighten down. Mine took 2-3 full turns. Again, VERY LOOSE. The upper clamp is cake if you have the battery out. Just tighten down. This one also took 2-3 full turns.


There are a few components that have been found to leak. Component fixes are obviously going to be more difficult than tightening a hose clamp. Remember that components an under your peak boost pressure, so an adequate fix will need to be made to keep them from leaking. In the case of a split intake hose, you will need to remove the hose and replace. Some hoses are going to be tougher to replace than others.

Quite a few people have found that their IAA/IAVC unit is leaking. It is located at the back of the engine of the driver's side. There is a great writeup on TT.net for removal/replacement. You might find it handy.

Another leak that has shown up for quite a few Z owners are the recirculation valves. There may be leaks in one of three hoses (two larger, one smaller) leading to it. There may also be a leak in the unit itself, which will be tougher to repair or may require replacement. As someone develops a fix for a recirculation valve, I will get it added to this page.

An intercooler is designed much like a small radiator, though it flows air rather than coolant. A boost leak can manifest itself along a seam, plastic end tank, or along the intercooler rails. [url=http://www.ttzd.com/tech/ictech.html]Here are instructions
to remove the IC. I will post a link to repair as soon as I find one.

You can visit this page to see a FULL LIST of components that could leak -- please email me with any additions that you think of!


The following Nissan engine diagrams and pictures of a removed (JDM) engine to refer to (thanks to "eBAY" for engine pics : ) I find it helpful to understand engine geography to locate other items. It may also help you to locate boost leaks as you will have a map and reference points to follow as you peek around the engine to find things.


Information taken from thumper300zx.com


Post Edited (Feb 17, 7:22pm)

506 Posts
Discussion Starter #13
if u take a look at the intercooler/piping diagram u can see ther's tons of hose clamps

could be any of those and some of those are hard to get to man

aniways yeah, 20 something degree weather, kinda a long time to spend out in the cold man, i don't know about you but i don't like the cold too much

if someone else can do it for a cheap price, i would be more than willing to pay them so i can be inside and be warm.

if it was summer time i wouldn't mind and do it myself, but its cold as **** here in MA

3,685 Posts
Red, I think you'll find that the crap you used to give in the Z31 forum is not appreciated here.

Have a nice day.
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