The 6 Ps: Proper Preparation Prevents Piss Poor Performance

This is a compilation produced for anyone comtemplating any upgrades on their car or for those wanting a thorough troubleshooting procedure. These tests will track down as many of the potential powerplant issues as I have seen as well as ensure that your car is prepared to safely meet the demands of upgraded component installation. Failure to perform these tests may lead to destruction of your engine – something that will cost thousands of dollars to repair, perhaps only to go out and just do it all over again if the problem still exists.

These tests are not only beneficial for those who plan to upgrade, but should be a battery of tests that one continually abides to performing. As your horsepower output increases, so does the demand for maintenance. Just like 3000 mile oil changes are a MUST with these vehicles, it is suggested that there be an interval to test these specifics as well.

This document primarily caters to the twinturbo owners, however, differences will be pointed out for the non-turbo guys as well.

The primary concerns one should have when they begin modifying the original design parameters of their vehicle is simple.
1) Is it getting enough fuel
2) Is it getting proper ignition
3) Is it getting proper air

These three components are what enable your engine to produce power. With only one of these components missing, the engine will not run at all. With any one of these improperly ‘configured’, it could mean poor gas mileage, poor drive ability, or much worse – catastrophic engine failure. It is up to you to perform these test to ensure that everything is in good working order.

The weapons of war:


These are the required components to effectively perform the tests outlined in this document.

Timing light: the thing that looks like a gun – this is used to check the base ignition timing value.

Fluid pressure gauge: This was acquired from Autozone for about $20. It is used for oil pressure testing, but that’s inconsequential – it tests up to 100psi with 5psi increments. Perfectly suited for testing fuel pressure as well. A “T” connector for 8mm (5/16″) was acquired to allow easy “T-ing” into the fuel line. The “T” connector was soldered to the end of the pressure tester fitting and a 4″ piece of hose and a hose clamp were used to secure everything together.

10mm socket, 3/8″ ratchet: This will be used to loosen the bolts on the CAS to allow for you to adjust the base timing.

Compression tester: This is used to determine the condition of the combustion chamber and its ability to compress the air and fuel that enters into it.

Induction piping pressure tester: This is actually a speaker magnet with a hole drilled through the centre of and a wheel valvestem has been installed. You can get creative here as well and build your own, or you can get one from Turbotrix. He produces a pressure testing kit that you can purchase inexpensively and it comes with a pressure gauge mounted.. This will allow you to easily isolate any intake tract leaks and fix them.

Feeler gauges: This tool is simply an assortment of metal strips of various thickness. Each one is labelled as to its thickness and it will be used to gauge the gap of the spark plug.

Ignition Timing:

Ignition timing is the point when the spark plug is being fired in relation to the position of the piston and crankshaft. The unit value used is angular degrees. In the VG30, the base timing (or the timing reference at idle) is 15 degrees. This means the ECU is making the engine fire at 15 degrees BTDC, or Before Top Dead Center. This is in relation to the position of the piston and crankshaft. BTDC means that as the piston is in its upward motion on the compression stroke, the plug is being fired when the crankshaft is 15 degrees before the piston reaches top dead center of the cylinder. The object here in setting base timing is to make the ECU and the timing mark on the pulley agree with each other.

Typical timing lights use an inductive pickup to detect when the plug is being fired and when it detects this, it causes a strobe light to fire off. This basic principle allows us to see exactly when the plug is being fired off in relation to the crankshaft position. On the front of the engine just above the crank pulley is a timing indicator which shows a range of degrees on what looks like a ruler. The values go from 0 to 30, from right to left. There is a mark on the pulley that indicates the position of cylinder #1. When the mark is lined up to “0” on the indicator, this means the #1 piston is all the way at the top of the cylinder.

Timing lights also require power in order to fire the strobe light off so be sure to connect the power leads.


The inductive pickup:
NOTE:! Using this point as the pickup has been found to be the quickest and most accurate method of hooking up the timing light. There is also a black loop on the PTU harness that is supposed to be used for this, however, on a number of occasions it has given vary peculiar results – sometimes getting two points of indication on the pulley and sometimes it being so far off you can’t even see it. If you see any oddities like this, use the procedure in Figure 3.Try this method first. If for some reason you aren’t getting a signal, verify that your power terminals are connected and wiggle the pickup around a little on the wire. You should get a pulse. If it still doesn’t want to behave, you will need to pull the coil pack out and use a plugwire extension and put the inductive pickup on the high voltage line going to the plug. The inductive loop has been known to do weird things which makes it difficult to trust with something like ignition timing.


Once you have everything properly hooked up, point the light at the pulley and observe. You should see the same as pictured



It is not hard to set it dead on 15 degrees and it is highly recommended to get this setting right.To adjust the timing, the CAM ANGLE SENSOR, or CAS for short, it used to adjust the base timing.

  • There are three 10mm bolts that hold the CAS in place. Loosen these with the engine off.
  • Since the engine rotates clockwise, turning the CAS clockwise will retard the timing whereas turning it counterclockwise advances the timing.
  • Move the CAS in the appropriate direction to adjust the base timing.
  • The engine must be running to test it and once you have the CAS loose, you can start the engine and then begin moving the CAS to get the timing mark aligned to 15 degrees.

This process ensures that the timing values in the ignition timing map of the ECU are in fact, correct. All the CAS is for is simply to calibrate the engine with the ECU such that the values in the ECU agree with the actual timing that the engine is running at. The timing light allows you to verify what the actual timing is because it flashes the light off when the plug fires and the markings on the pulley allow you to see what the position of the crankshaft is.



In order to check the fuel rail pressure, you need a pressure sensor put inline with the fuel line to the fuel rail. The pressure sensor defined above will allow us to do this, but we have to connect it in. Since the fuel system always holds some degree of pressure, even when the car is not running, we must ensure that we dont disconnect a line and spray raw fuel into a hot engine bay. The best way to do this is to relieve the pressure in the fuel tank by removing the gas cap and let the car sit for about 20-30 minutes while the pressure in the lines bleed off. It is highly recommended to wrap a shop rag around the hose when disconnecting it to absorb any residual fuel that may come out. Ideally, one would do all of this while the engine is cold and the car has sat overnight.
Once done, place your rag as follows, loosen the hose clamp and remove the hose from the filter (Figure 6).

In the VG30, as well as most other fuel injected vehicles, have an operating fuel pressure of ~3bar. 1bar = 14.5psi so 3bar is effectively ~43.5psi. Since the tip of the injectors is inside of the manifold, this means that the vacuum or pressure that the injector tip ‘feels’ affects the fuel delivery. The ECU controls the duration of time that the injector is held open and it assumes that a given opening time of the fuel injector will always deliver the same amount of fuel. In order for this to work, there must always be a 43.5psi difference between the fuel rail pressure and the manifold pressure. This is to ensure that no matter what vacuum/pressure the manifold is under, a ‘x’ millisecond pulse of the injector will always deliver the same amount of fuel. (Figure 7) 7.
Ok, now that you have everything connected, you are ready to test your fuel pressure. You can see in this picture that there is about 10psi of pressure on the guage. The engine is not running here and hasn’t been started since the install of the gauge.Now, in this picture you can see that the fuel pressure is appx 35psi. Remember the pressure differential I was talking about? Well, at idle, the manifold is at about -10psi of pressure. In order to maintain linear fuel delivery, there must always be a ~43.5psi pressure differential; so 35 + 10 = 45psi. We are good here. 8.
This next picture is a demonstration of how the fuel pressure regulator works. The hose I am holding in my hand is what connects the fuel pressure regulator to the manifold. The fuel pressure regulator is the device that maintains this ‘pressure differential’ such that the fuel delivery is linear per pulsewidth of the injector. Since I have unplugged the FPR(fuel pressure regulator), the FPR ‘thinks’ the manifold is at 0psi. You can see here that the fuel pressure has now raised to ~44psi, as it should. (Figure 9.)
I want to point out that since the fuel pressure control systems are a mechanical, passive system that is not actively regulated by closed loop circuitry, there will always be slight variations in fuel pressure from what you see here. However, there should not be anything greater than about a 5psi difference from what the calculated pressure should be. This is primarily what makes the difference between one Z and the next – some fuel systems simply work a little better/worse than the next Z, but the actual effect on the system as a whole is typically marginal.
The fuel pressure guage has been setup as well as a manifold pressure guage to demonstrate how the fuel pressure regulation system works in finer detail.Jerry-Rigging is PETZ acceptable for very temporary setups like this – do not Jerry-Rig your Z under any other circumstances.

You can see here that the fuel pressure is slightly higher at 0psi of manifold pressure than it was in the original test. This is due to the fact that the ECU ALSO varies the fuel pump voltage (which affects its output). You can see here that at 45MPH with the manifold at 0psi, the fuel pressure is at 55psi. This is actually a little on the high side as we should be seeing a fuel rail pressure of ~45psi at 0psi of manifold pressure. At the time these pictures were taken, my Z was equipped with a non-turbo fuel pump controller which has different control voltages for the pump speed. However, this is not bad, if anything, it is simply safer. In this condition you should see at least 44psi at the fuel rail. If you see less than 44-45psi, you have a problem and it must be fixed

The next test is running the engine at 7000RPM and 15psi of boost. You can see that the manifold pressure is at ~15psi and the fuel rail pressure is at ~65psi. This is consistent with what we should see.
IMPORTANT!!: I am running the engine at 7000RPM here in the above photo. This is when the fuel system is at 95% of its expected delivery rate. You have to consider that as the engine RPM increases, so does the fuel rate. When I converted my non-turbo to turbo, I used the non-turbo fuel pump. It worked great at ~14psi. However, when I raised the boost to 16psi on the non-turbo pump, as the RPM increased to around 5500RPM, I began noticing the fuel pressure falling off all the way down to 45psi! This is VERY BAD! The reason this occured is because the non-turbo fuel pump was unable to keep up with the demand of fuel at higher RPM. It maintained ~65psi until around 5000RPM and then sharply fell off at 5500RPM down to 45psi at the fuel rail. This is a catastrophic failure waiting to happen because when the fuel pressure falls, so does the fuel delivery. This is not a problem with the fuel pressure regulator, this was simply the non-turbo pump falling on its ass. I corrected this problem by putting a twinturbo fuel pump into my car.

You want to ensure that the fuel pressure is maintained ALL THE WAY THROUGH THE RPM RANGE that your engine operates within. If it does not maintain this pressure, the fuel delivery will fall and this will cause a lean condition. Lean conditions lead to detonation, burned and broken pistons, burned valves; basically, catastrophic engine failure.

This test concludes the ‘fuel delivery’ aspect. If your fuel system does not maintain proper pressure, you simply need a bigger pump.



This is one of the three vital components to proper engine performance. Just as much as a dirty air filter will affect performance, a leak in the intake system will also promote piss poor performance.

The intake system of the Z, in both the non-turbo as well as the twinturbo version, consists of a multitude of intake plumbing components. In the non-turbo Z there is a total of ~10 feet of piping between the air filter and the throttle bodies. The twinturbo variation has over 20 feet of plumbing. Unfortunately this system is not composed of a single pipe. In fact, there are a dizzying number of clamps, hoses, and pipes that comprise the intake system.

In the design of the 300ZX(Z32), the engineers employed a Mass Airflow Sensor with the ECU (Engine Control Unit). This sensor measures the intake air so as to determine proper fuel delivery, as well as a multitude of other control parameters. Since this system relies so heavily on the accuracy of the measured intake air, it is critical to have an ‘air tight system’ in order for it to properly perform. In order to ensure that the intake system has no leaks, we can use Sir. Bernoulli’s principle: PRESSURE

The test is simple and requires simple equipment. For those who have a single intake, removal of the MAS and filter and installation of the ‘plug’ is easy. Those with dual intake systems need to dig up their original intake “T” and use it for this test. The hardware is installed as such:

In Figre 14 the plug is installed and the system is under pressure. It only takes a few psi of pressure to find a leak and 5psi should be your maximum.
DO NOT EXCEED 5PSI DURING A BOOST LEAK TEST! The reason I only have the intake system at 5psi and no more is because of the fact that 1/4″ of the intake system is not subjected to positive pressure. None of the non-turbo intake system is under pressure. In addition, since the intake system is also part of the PCV system (positive crankcase ventilation), you do not want to overpressurize the crankcase for fear of blowing out the oil seals along the camshafts and crankshaft. 5psi is enough to hear any leaks and not too much to blowout seals. Once you have the system pressurized, you will be able to easily locate any boost leaks. Typically it only involves tightening the loose hose clamps that hold the system together. Locate all leaks and fix them.


In the stock configured 300ZX(Z32), the NGK (japanese manufactured) platinum tipped plugs are used.

NA stock = PFR6B-11 gapped to 0.044″ (1.1mm)
TT stock = PFR5B-11B gapped to 0.044″ (1.1mm)

While these plugs perform well under stock configuration, they do not perform well under a modified, high output configuration.

The nomenclature used in the plug numbering denotes several aspects of the plug’s design and performance. What interests us the most is the 4 character in the naming scheme. The NA is a “6” and the TT is a “5” in the above examples. This number denotes the ability of the plug to diffuse heat away from the tip and into the plug body, where the cooling system absorbs the heat. The higher the number, the better the plug’s ability to keep the tip ‘cooler’.

As you increase the output of the engine, the cylinder temperatures also increase. What this means is that you need a spark plug that also increases in its ability to dissipate the heat. By not changing the plug’s thermal dissipation when you increase the output of the engine, you raise the likelihood of ‘spark knock’. This phenomenon is analogous to detonation and it should be avoided at all costs.

To mitigate the posibility of ‘spark knock’, you should use a spark plug that has a higher ability to dissipate heat. This simply means you need a plug with a higher ‘thermal dissipation’ number. Here’s the breakdown:

NA stock: PFR6B-11 ; upgrade to the PFR7B-11
TT stock: PFR5B-11B ; upgrade to the PFR6B-11B


For the NA guys, this is all you need to do. However, for the TT guys, there is an additional parameter that you must concern yourself with.

Since a stage3+ upgrade to a twinturbo ALSO includes running higher boost pressures, we have to account for the higher air/fuel densities in the combustion chamber.

In the stock configuration, the plug gap is set to 0.044″ (1.1mm). While this performs well in both low and high load conditions, it will not perform well in high load conditions when you raise the bar.

The higher density of air and fuel in the combustion chamber (a result of running higher boost) requires a higher voltage for the spark to ‘jump’ the gap. Since you do not have the ability to easily increase the spark intensity, you must resort to alternative, and less expensive methods of promoting proper ignition. Instead of increasing the spark intensity, one can simply reduce the gap tha the spark has to jump thereby allowing a spark to jump at all under high boost.

The typical plug gap is 0.044″, but by reducing the gap to 0.035″, one can increase the chances that the spark will actually ‘jump’ the gap. -0.035″ has proven to be an ‘ideal’ gap to set the plugs to. Conversely, if you make the gap too small, you will notice misfiring at low load/cruising conditions as the spark is simply too small to ignite the low density of air and fuel in the combustion chamber. This is why you dont set the plug gap to 0.010″ and expect it to perform well – just about everything is a tradeoff and this one falls at mid-road of the equation.Using the feeler guage pictured in the “Weapons Of War”, you can properly gap your plugs.


Since you already have your plugs out because you are changing them to the proper plug and gapping them to the right spec, you are already set to perform a compression test.

A compression test simply shows you the engine’s ability to perform one of its most vital functions: compressing the air and fuel mixture sufficiently. The reason the engine compresses the mixture of air and fuel is because it optimizes the oxidation of fuel to create pressure and heat energy to push the piston, which is connected to the crankshaft and eventually to the wheels. A worn out engine will yield lower compression numbers simply because the cylinder or rings are no longer producing an ‘airtight’ seal, or the valves and/or valveseats are burned/broken. Since the non-turbo engine has a different ‘compression ratio’ than the twinturbo, you will be expecting different compression values between the two. Here are the factory specs:

non-turbo: 186psi is ‘perfect’, minimum of 136psi.
twinturbo: 174psi is ‘perfect’, minimum of 121psi.

If you perform a compression test and you see numbers lower than the minimum specified, your engine is worn beyond spec and you need to rebuild it before you plan on upgrading it.

If your test yields higher numbers than ‘perfect’, there is likely a problem with your compression tester and you should acquire a new unit and perform the test again.

Typically you will see ~150psi for a twinturbo in good shape and ~165psi for a non-turbo in good shape. If any given cylinder is significantly lower than the rest, this is bad news – Nissan only allows a 14psi maximum difference between any two cylinders, regardless of position in the engine. Low compression on a single cylinder is indicative of broken ring lands, burned valves, or a burned piston. Unfortunately, the only fix for this requires the engine to be disassembled.


The Z32’s ECU is equipped with OBD, or On-Board-Diagnostic capabilities. These capabilities allow the ECU to determine when a sensor in the system has a fault of some sort. It does a pretty good job of detecting critical failures as well as other failures that may go unnoticed. Since not all failures will result in the engine running notably poorly or not at all, you should ensure that there are no errors in the system. The process as well as diagnostic codes are defined in the link below.
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If there is any problem detected, this should be rectified BEFORE any upgrades are put in place. There are a number of different codes that will put the vehicle into ‘safety mode’ of which will inhibit performance. Correct the problem first, upgrade later.

At this point, if everything checks out OK, you are ready to upgrade your vehicle. If any one of these tests come out ‘substandard’, the problem should be corrected before upgrading is even considered.