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Perhaps I can elaborate on this topic as I have a wealth of information on it.Unfortunately there is no short, simple answer.
The fuel pump control circuitry is rather simple. In the NA there is only a single control line from the ECU to the FPCM (fuel pump control module). When this line is pulled to ground, the NA controller will operate in low speed. When this line goes open (floating input, neither ground nor positive voltage input), the controller will run in full speed (battery voltage). In the TT there are two control lines. One of them is the same pin/wire as what you find in the non-turbo system, with the addition of another control line coming from another pin at the ECU/harness. Below is the logic table: (P1 and P2 are the two output lines from the ECU to the FPCM, G=grounded, O = open, P1 is the same line used in the NA system (black/white), and P2 is the second line added to the TT system (purple)). P1 P2 PUMP SPEED
G G LOW
O G MID
O O HIGH So what happens when you use an NA ECU in a TT vehicle? Well, since the NA ECU lacks the internal circuitry to handle the P2 line, this output is always open, and this causes a problem. Because of how the input logic circuits are constructed in the fuel pump control module, at any point if P2 is open, the controller will run the pump at full speed regardless of if P1 is grounded or open. This results in the pump running at full speed all the time. With a stock fuel pressure regulator and a twinturbo fuel pump, this condition will overrun the regulator's ability to bypass fuel back to the tank and result in an elevated fuel pressure in any load condition below ~10"Hg. Over a period of time the closed loop system will adjust to compensate fuel delivery in these conditions, however, it will put a beating on the pump over time. The bottom line here is that when you do a conversion or have to replace any of these parts in your Z, you need to make sure to keep the ECU, fuel pump control module, AND both the EFI and body harnesses consistent with each other. You cannot mix and match any of these parts. If you are doing an NA-TT conversion and want to take advantage of the 3-speed control that the TT offers, you must use a TT FPCM, TT ECU, and run the second control line from the ECU to the FPCM. The alternative to this would be to use the NA ECU and NA FPCM in your conversion and retain the 2-speed control. Ideally you want to use the 3-speed control though; and here's why:
- In the 3-speed control system, pump speed is controlled based on the following criteria:
-At startup, pump speed is 100% duty and held for 5 seconds after the start signal is released. (i.e., you release the key from "start")
- At idle condition (TPS closed throttle = ON), and after startup sequence, pump speed = LOW
- TPS closed throttle = OFF, any throttle position, manifold pressure below ~5psi, pump speed = MID
-TPS Closed throttle = OFF, manifold pressure > ~5psi, pump speed = HIGH
*(For those of you who have a deeper understanding of how our ECUs operate and know that our ECUs do not base any control algorythms on manifold pressure, but rather, a load calculation, please understand that I am aware of this simplification.
Since a vast majority of the vehicle's use will actually be in an "off idle, less than ~5psi boost", without the 3-speed control you will force the pump to run at full speed for most of its life. I prefer the 3-speed control; less wear on the pump, less wear on the alternator, less wear on the belt, etc etc. In addition, Nissan didn't build the TT with a 3-speed pump control system just for kicks - the NA and TT fuel pumps may look the same, but they differ quite a bit in flow. The 3-speed system in the TT was built to cater to this - the TT pump in a 2speed control will overrun the factory regulator during a cruise condition - where the pump is at full speed and manifold vacuum is ~10-12" Hg. So taking the recommendation further, if you use a TT fuel pump, you should also use the TT FPCM, TT ECU, and have both control lines from the ECU to the FPCM.
From the symptoms you describe there are just far too many variables to nail down what is going on with your car. There are a number of tests that will have to be performed in order to eliminate the possibilities; I would start with the 6 P's and go from there. If you go through all of those tests and still dont isolate the problem, relay the results to me in an email and I will be happy to assist you further. :)
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
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