CJM: Ultimate 370z Fuel Pump Thread

[phunk]

Originally Posted by Jayhovah

Phunk... this holiday I have been trying to fix my wobbly idle and thought I might as well do the idle pressure fix... I have pulled the fuel pump and drilled the venturi 4 times now - the last time with a 7/64" bit. Pressure at idle has only dropped to 59psi (and was only ~62psi before I started) and I am hesitant to keep drilling it in fear I may be doing something incorrectly. Is this out of the ordinary? Seems very large compared to the starting point you provide in your tech article. I am drilling all the way through the oriface.

I am running a walbro 255lph and reading the pressure from the mini gauge on my CJM fuel port.

Any advice you can provide would be appreciated! Happy holidays!

edit: Also wanted to mention I have 650cc injectors too.. otherwise the fuel system is stock. I also tried revving the motor up to 3.5k and the fuel pressure only dropped a few psi.

7/64 sounds large-ish to me for just the Walbro 255. If I found myself in your position, the first thing I would try is entirely removing the black Venturi from the bottom of the canister and reassembling (temporary). This way you can find out if there is any end in sight or if you might go larger until the component is entirely useless just to find it still didn't fix your fuel pressure spike. To take the part out completely will defeat the Venturi system but it will also answer a question, whether any size modification at all could even resolve your condition.

The idle pressure spike generally is only at idle and flattens out immediately when the throttle is touched, so I'm thinking your fuel pressure spike might not be coming from the Venturi system.

If you drilled out and it got you down a few psi, and then you drilled it a little more and it didn't go down more, than I don't think it's going to go down any more. It's a very sensitive setup and the slightest enlargement should have a measurable effect.

I suspect your stock fuel pressure regulator is backing up the return flow itself. But even in that case pressure should drop as soon as you touch the throttle. Which would lead me to consider the gauge is reading incorrectly or the regulator itself is regulating incorrectly.