GrayZee Posted November 13, 2005 Share Posted November 13, 2005 Well I took the turbo Pathfinder on it's maiden voyage today. Hit about 5psi but only if I accelerated very slowly. If I hit the go pedal really fast the engine would fall flat on it's face when the boost gauge hit zero. It felt like it was starving for gas. Making me question a couple of things... I decided to keep the stock fuel pump for the time being figuring that it must be fairly similar to the z31 pump. Would a pump designed to feed a 140hp Pathy engine really run that lean on the Vg30et on low boost? I have wired up a few turbo swaps and never bothered with the fuel pump modulator. I understand that it simply limits the voltage to the fuel pump to run quieter in low load situations. Is it possible that my Pathfinder also has a modulator somewhere and is making the pump run at low voltage? (low of course being the default position I'm assuming) I am using the original Pathfinder fuel pump relay and just ran my z31 engine harness to trigger the relay. Perhaps now that my original ecu is no longer hooked up or functional there is nothing telling the modulator to increase voltage? Any thoughts? I wish I had a good Pathfinder wiring scematic. Quote Link to comment Share on other sites More sharing options...
mc Posted November 13, 2005 Share Posted November 13, 2005 Congradulations on the maiden run...even if it still has some bugs in the system...i put a remote[rear] turbo on my 88vg30 200sx and the fuel pump has kept up fine so far...it also hits 5-6 on the boost guage.I kept the factory harness stock though.Does yor set up start easy,go to fast idle[cold] and idle down when warm???? Quote Link to comment Share on other sites More sharing options...
Clifton Posted November 13, 2005 Share Posted November 13, 2005 I turboed my Toyota truck (V6). The pump on that had a shut off pressure of 50 psi. The volume was also lacking. As the revs went up under boost the pressure would drop, was running 12 psi at the time. I put a Walbro 155 l pump in . You're only at 5 psi though so I doubt that's your problem, you should check the pressure under load though. What are you using to control fuel under boost? Z32 turbo ecu?I run an aic with 2 extra injectors. Once I had the pressure switch loose a signal and I could not run over 2 psi without it falling on it's face. Quote Link to comment Share on other sites More sharing options...
GrayZee Posted November 13, 2005 Author Share Posted November 13, 2005 Yes, the engine starts, warms up and idles fine. My ecu is a 89 z31 that has been re-tuned. The ecu was working in my L28et with 480cc injectors just fine, so I can't see the tune being that far out with the Vg30et. The fuel pressure regulator is from a turbo z31. I guess the only components that are from a n/a vehicle is the upper manifold, including fast idle controller, pcv valve, ect. I'm not using the AAC or EGR valves. I found out that a Pathfinder does not use a fuel pump modulator, but I still suspect fuel pressure drop. Is is possible that a fuel pump designed for use with a TB unit is that much weaker than multiport? I can't really see it being that weak, but I guess you never know.. I guess I'll have to figure a way of mounting a gauge against the window so I can see what's going on. Quote Link to comment Share on other sites More sharing options...
GrayZee Posted November 13, 2005 Author Share Posted November 13, 2005 Ok, I took it out for a drive again. This time I hooked up a fuel pressure gauge by the windshield. It was reading 38psi under full throttle and at 5psi. I guess the fuel pump is not the problem. I am using a 21 year old wiring harness to run the engine, I am wondering if there are some gremlins making a home of my harness? I guess next step is to get it on a wideband and laptop to see what it is doing. *SIGH* how come it never works 100% the first time around?? Quote Link to comment Share on other sites More sharing options...
mc Posted November 14, 2005 Share Posted November 14, 2005 Since your using the turbo ECU that has been retuned,does it still allow you to check the stored trouble codes and what the o2 sensor is reading???? Quote Link to comment Share on other sites More sharing options...
GrayZee Posted November 14, 2005 Author Share Posted November 14, 2005 No, the O2 sensor feedback and diagnosis on that ecu was disabled last year. I do have a new theory on what the problem is however. I took it for another drive and noticed that the problem really has nothing to do with boost. The engine falls on it's face at full throttle. I was at a very slow roll and put it to the boards and it did the same thing once the throttle went all the way down, even with no boost. This lead me to believe that I had issues with the TPS. I had a 240sx TB that I was gonna bolt on but gave up on the idea as that that TB plate actually rotates the opposite way that a Pathfinder TB does. It can be done but the throttle cable has to be mounted at a goofy angle, I did not think it was worth the trouble as the 60mm isn't THAT much bigger than a Pathy throttle. Anyway, getting back to my theory.. I believe that because the Pathy throttle is moving opposite compared to a sx or z31 TB that the off idle indicator is coming on at full throttle rather than off idle. I am told if this is true, the ecu will go into idle mode and release control of the timing and fuel maps, and goes to a preset idle program. This would certainly make the engine fall flat on it's face. To fix this, all I have to do is flip the outer wires on the TPS plug around. I'll give'er a go tomorrow hopefully. Quote Link to comment Share on other sites More sharing options...
GrayZee Posted November 14, 2005 Author Share Posted November 14, 2005 Well I was right, the problem was being caused by the TPS. I flipped the outer wires around on the plug and now it's fine! I took it for another drive and hammered it up to 60mph and it hit 5.5psi. Definatly a improvement from the stock throttlebody injected Vg30 that was in there, but considering all the work that went into it.. well it's a little disapointing. 5psi in a Pathfinder just isn't that interesting when you have a 15psi 280z! Obviously the next step is to start increasing boost. I'm sure once I get the alcky injection going and run 15psi, it will be alot more interesting. Stay tuned.. LOL Quote Link to comment Share on other sites More sharing options...
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