TwinTurbo.NET: Nissan 300ZX forum - Have any of you had problems with overheating fuel?
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Subject Have any of you had problems with overheating fuel?
Posted by NNayak on June 28, 2018 at 1:28 PM
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Message Hey guys,

I'm having some trouble with my Z that appears to be vapor locking/fuel boiling in the fuel pump, and I was wondering if this is a somewhat common problem on modified Z32s.

My car has GT2560Rs, full breather mods, 3" turbo back exhaust, nismo 740CC/min injectors, NA ECU/FPCU, and a TT fuel pump.

The two times that I've driven my car for long distances after finishing my NA-->TT swap, I've gotten symptoms that feel like loss of fuel pressure after driving for roughly 1.5-2hrs. The onset of symptoms is gradual and gets worse with time. The car will initially cut out or lose power at ~3500rpm or ~30% throttle, and will slowly stop building boost. It initially feels like the car is hitting a soft fuel cut rev limiter in the sense that the engine speed will not increase, power will fall off, but there's no popping or banging out of the exhaust which would indicate the presence of unburned fuel.

If I continue to drive the car past this point the symptoms get worse. Rather than feeling like the car his hitting a soft cut, the car will start bucking and the power comes on/off like a light switch at 3500rpm/30% throttle. At this point, the fuel pump becomes very noisy and I suspect there may be cavitation at the pump inlet which would indicate hot fuel boiling in the pump inlet. Obviously, the car is not vapor locking in the fuel lines because EFI fuel pressures are too high for that to really occur. I have read that 120F is the fuel temperatures threshold above which this boiloff can begin occuring.

If I let the car cool off overnight, the symptoms go away entirely, as does the fuel pump noise, which leads me to believe that something is happening specifically when the car has heat soaked for a couple hours.

My car has the driver's side fuel/brake line heat shields and exhaust manifold heat shields in place in the engine bay, but does not have turbine or downpipe heat shields as the aftermarket parts do not have provisions for the OEM heat shields. The test pipes also do not have any heat shielding, and there is no shielding between the exhaust and the fuel tank. I did use the OEM isolators when mounting the fuel rail to the engine.

Have any of you guys experienced this with your modified cars? If so,what was your solution to the problem? I am considering adding insulation wrap to the fuel lines and fuel line heat shields in the engine bay and on the frame rails.

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