CJM: Ultimate 370z Fuel Pump Thread

[phunk]

It was all moved to a PDF on our website, in the tech section.

[Jayhovah]

Just installed the CJM fuel tap with mini pressure gauge... My fuel pressure at idle at just over 60psi with my 255 lph pump.

What is the downside of not performing the idle pressure fix? Is it safe to assume I would need a retune if I did it?

[phunk]

That pressure spike is the down side.

You wouldn't need a retune if you fixed it. But you don't need to fix it if it's not causing a problem. It come right back down to spec as soon as you give it some gas. But if it's making you idle rich or giving you startup issues you might want to address it.

[Jayhovah]

Originally Posted by phunk

That pressure spike is the down side.

You wouldn't need a retune if you fixed it. But you don't need to fix it if it's not causing a problem. It come right back down to spec as soon as you give it some gas. But if it's making you idle rich or giving you startup issues you might want to address it.

Thanks! The car runs fine so I will just leave it =)

[VSS370z]

I've been having start up issues for 2 months now after i upgraded from a walbro 255 to a aeromotive 340 fuel pump and is always when the car sits for hours and it never did it with the 255 fuel pump. I am starting to think i need to do this Idle Pressure thing to possibly sort things out but first i need to find that PDF.

[phunk]

Originally Posted by VSS370z

I've been having start up issues for 2 months now after i upgraded from a walbro 255 to a aeromotive 340 fuel pump and is always when the car sits for hours and it never did it with the 255 fuel pump. I am starting to think i need to do this Idle Pressure thing to possibly sort things out but first i need to find that PDF.

I would recommend getting a fuel pressure gauge in the car so you can see pressure at idle and startup. This would help indicate if there is a possible problem there.

[Jayhovah]

Originally Posted by phunk

That pressure spike is the down side.

You wouldn't need a retune if you fixed it. But you don't need to fix it if it's not causing a problem. It come right back down to spec as soon as you give it some gas. But if it's making you idle rich or giving you startup issues you might want to address it.

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.

[ChaseZ]

Originally Posted by Jayhovah

I am running the Walbro 255....

Might that not be the crux of your problem right there?

Perhaps a bigger pump and good regulator?

[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.

[Jayhovah]

Originally Posted by phunk

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.

Thanks for the response! I'll try removing that bottom venturi piece and report back. I appreciate your guidance!

Sent from my Nexus 6 using Tapatalk

[Jayhovah]

Well.. I disassembled the pump and I found one problem - I drilled too far through the venturi:


And you can see how big the hole is:


1) Is this damage repairable? If not, recommendations?
2) If I drilled all the way through, we would expect to see much lower idle pressure, no?

A couple of other disassembly pics:
I don't recall this strainer being so black before....


And where did all this crap come from?


I am going to reinstall without the black venturi just to see the test result. Will report back in a few.

[Jayhovah]

Removing the black venturi piece does not seem to have affected anything, at least as far as reported by the gauge.

Prior to turning the car on, the gauge read 0psi.

After turning the car on, but not starting the motor:


After starting the car:
http://www.the370z.com/attachment.ph...1&d=1482777206

After the motor comes up to temp (water temp one dot short of middle.. This is also when my idle starts to go wobbly)
http://www.the370z.com/attachment.ph...1&d=1482777217

And after shutting the car off:


Any ideas? Based on your previous post, its likely either the gauge misreporting or a problem with the OEM regulator... I'd imagine the gauge is behaving properly, but I put up the pictures in hopes you can confirm one way or another... So probably the OEM regulator?

Should I go ahead and start hunting for a new fuel pump assembly? Are they the same for the Z and G?
Edit: The part#s are similar, but different. G37: 170401NC0C 370Z: 17040-1EK0B

[phunk]

Running without the venturi installed or running it with the extra hole in it has ruled out the venturi as the source of your pressure spike. Unfortunately Nissan does not sell the venturi jet, so the only way to replace it is to replace the entire fuel pump housing. It will need to be replaced or repaired since the additional hole will either entirely defeat the venturi system or render it too weak for standard use. The car will fuel starve from not being able to recover fuel on the driver side of the tank.

All the black gunk/debris in the fuel pump canister is normal. I dont know where it comes from but its in every stock 370z fuel pump I have ever opened. The strainer being darker probably isnt a big deal yet, looks pretty normal for a well used one. It wouldnt effect the fuel pressure spike anyway as the most it could ever effect, if it were completely clogged up, it would restrict the pumps intake resulting a pressure loss rather than pressure spike.

Since your fuel system is stock, the only possible way for fuel pressure to exceed the regulator setting is if the regulator cannot vent out well enough, or if the regulator itself is damaged/clogged. You have eliminated regulator venting from the equation, so there are only 2 possibilities left. Your regulator is bad or clogged up, or the fuel pressure gauge is reading high.

I would replace the fuel pump module with another one since this is inevitable at this point*, and then if the fuel pressure is still too high according to the gauge, i would either try another gauge or I would just ignore it and write it off as the gauge just reads a few psi high.

*: unless you can find a way to plug that extra hole up with something that will not dissolve in gasoline. Such as machining a custom plug on a lathe and pressing it in, or something.

Another thing you can try, is drilling out the outlet on the stock regulator. I have never had to do this but I do not generally use a stock fuel system. All the cars I work with are using return kits. But I believe that Stillen has their customers drill the outlet on the regulator so it itself can vent better. This might be worth a shot as it could not hurt anything so long as you do not drill too deep into it.

[Jayhovah]

Originally Posted by phunk

Running without the venturi installed or running it with the extra hole in it has ruled out the venturi as the source of your pressure spike. Unfortunately Nissan does not sell the venturi jet, so the only way to replace it is to replace the entire fuel pump housing. It will need to be replaced or repaired since the additional hole will either entirely defeat the venturi system or render it too weak for standard use. The car will fuel starve from not being able to recover fuel on the driver side of the tank.

All the black gunk/debris in the fuel pump canister is normal. I dont know where it comes from but its in every stock 370z fuel pump I have ever opened. The strainer being darker probably isnt a big deal yet, looks pretty normal for a well used one. It wouldnt effect the fuel pressure spike anyway as the most it could ever effect, if it were completely clogged up, it would restrict the pumps intake resulting a pressure loss rather than pressure spike.

Since your fuel system is stock, the only possible way for fuel pressure to exceed the regulator setting is if the regulator cannot vent out well enough, or if the regulator itself is damaged/clogged. You have eliminated regulator venting from the equation, so there are only 2 possibilities left. Your regulator is bad or clogged up, or the fuel pressure gauge is reading high.

I would replace the fuel pump module with another one since this is inevitable at this point*, and then if the fuel pressure is still too high according to the gauge, i would either try another gauge or I would just ignore it and write it off as the gauge just reads a few psi high.

*: unless you can find a way to plug that extra hole up with something that will not dissolve in gasoline. Such as machining a custom plug on a lathe and pressing it in, or something.

Another thing you can try, is drilling out the outlet on the stock regulator. I have never had to do this but I do not generally use a stock fuel system. All the cars I work with are using return kits. But I believe that Stillen has their customers drill the outlet on the regulator so it itself can vent better. This might be worth a shot as it could not hurt anything so long as you do not drill too deep into it.

I'll dry drilling the regulator, seems like I don't have much to lose at this point and may as well experiment. As for plugging the hole on the opposite side of the venturi - JB weld makes a couple of epoxy putty products that they say can be submerged in gasoline.. might see if that does it. If I do manage to repair the damage, do you think I drilled out the venturi too much for the 255lph? If I did, what would the symptoms be? low idle pressure? or low pressure while driving? Could I then correct the problem by just upgrading to a 340lph?

Any recommendations on getting a new fuel pump assembly? Used units for the G37 seem to be much less expensive, but the part number is slightly different. Do you know if they use the same venturi piece or regulator?

Also, do I need the little venturi piece if I upgrade to a return system? A new assembly is $350..might be better put towards an upgrade.

Thanks for continuing to provide feedback. Really appreciate the advice! Hope the documentation of my experience in this thread will help someone else!

[phunk]

If you find an epoxy to plug the extra hole with, may as well use it to also bring back down the size of the original hole.

Symptoms from making the venturi too large is that the venturi will become weaker as you will have lowered the pressure differential. The venturi system is used to fill the fuel pump canister, and to transfer fuel across the tank from the driver side. A weaker venturi will do this slower, or not at all. The perceivable side effect would be the vehicle acting like it is out of fuel when it is not. Power cutting out, fuel starvation, etc.

Most G37s use almost the same fuel pump module, but its several inches shorter and not tall enough for the Z tank. You would have to hybrid it together and use your Z top hat and rods with the G37 lower half, or just take the venturi part you need and move it over.

Some G37s use a 350z fuel pump module, which would be entirely useless for you. So you will want to see a photo of the one you are buying first, and make sure it looks just like the one you have. The 350z module looks entirely different on the fuel tank side, so there would be no way to mistake them unless you only saw them from the very top (such as not removed from the tank) in which case they look nearly identical.

The venturi system is still used with a return fuel system, so you would still need to either repair or replace this component.