Jump to content
SAU Community

Recommended Posts

Hey, is there a known restriction in the R34 GTT fuel return? I tested my fuel pressure with a Walbro 255, and have 52 psi at idle, with the regulator vacuum line on and off.

The only time I get 43 psi is if I fully disconnect the return line off the regulator and let it flow out into a bottle, so it seems to be something after the reg causing it.

I've disconnected both ends of the return line and I can blow through it. I went under the car and don't see any dents or kinks in the hard lines. I blew air into the return port of the fuel hat and it's harder to blow through, but I'm guessing that's because of that tank transfer valve attached to it. I’ve replaced the return lines from the reg to the hard lines as well

Any ideas? Thanks

Link to comment
https://www.sau.com.au/forums/topic/484962-er34-fuel-return/
Share on other sites

29 minutes ago, Dose Pipe Sutututu said:

Yeah the venturi/siphon inside the fuel tank lid.

Either you drill it out or replace it with a radium venturi/siphon or go tits out get a FFG fuel tank lid and replace the OEM unit.

Makes sense, I was thinking it had to be that thing. I will try modifying it first and see if I can get it to work. Is it drilling out the fittings on the hat, or drilling out the actual siphon pump?
IMG_1401.thumb.jpeg.327d0ab370bf04413efc17ce4d74b4e8.jpegIMG_1402.thumb.jpeg.91eee0fd4e0a5c42a6f8735e27d1ad9d.jpeg

2 hours ago, tylink720 said:

drilling out the actual siphon pump

It's a nozzle used to generate the suction. It's sized to produce enough suction with the stock fuel flow driving it. If you upsize the pump then you have to squeeze that increase through there. And you get LOTS of suction.

I don't know how much to drill it out. Remember that cross sectional area increases with the square of diameter, so you probably don't want to drill it out a lot, for "only" a 255L/h pump. You're up about 25-30% on stock capacity, so you probably only need about a 10-15% diameter increase.

  • Like 1
  • 2 weeks later...

I've drilled out the siphon pump to a little larger than stock, I think I used a 5/16 bit. Put it back together and still had the 50psi fuel pressure. Took it apart again and ended up breaking one of the fittings on my fuel hat which sucked, but luckily I was able to get a new one within a week. Fit the new hat, and tested the pressure with the siphon pump removed so it just pumps straight back into the tank, still 50psi. 

I have to assume now it's my return line that's the restriction. I was hoping it would be easy to replace the rear fuel lines that connect to the tank, but it looks like I'd have to lower or drop the tank which looks like a crap job. I will try using an air compressor first to blast out the return line and see if it does anything

24 minutes ago, tylink720 said:

I've drilled out the siphon pump to a little larger than stock, I think I used a 5/16 bit. Put it back together and still had the 50psi fuel pressure. Took it apart again and ended up breaking one of the fittings on my fuel hat which sucked, but luckily I was able to get a new one within a week. Fit the new hat, and tested the pressure with the siphon pump removed so it just pumps straight back into the tank, still 50psi. 

I have to assume now it's my return line that's the restriction. I was hoping it would be easy to replace the rear fuel lines that connect to the tank, but it looks like I'd have to lower or drop the tank which looks like a crap job. I will try using an air compressor first to blast out the return line and see if it does anything

You had the same idea I did. If that doesn't do it start measuring pressure at various points in the system, the pressure drops at each point will tell you where the restriction is. Could be an FPR too. If you've hardwired your fuel pump to run full blast all the time the FPR is almost certainly your problem at idle. Nissan used the FPCM to slow down the pump at idle.

Edited by joshuaho96
  • Like 1

Try bypass the fuel dampener to see if there's still an issue.

R34 GT-t uses a couple of them instead of 1x like the R33.

If that solves the issue, then delete the OEM ones and install an aftermarket one like a Radium one.

 

In the past, on S15s (same fuel tank hat/lid as the R34) I enlarge the siphon/venturi and it fixes the issue. Was hoping that was enough for you.

  • Like 1
On 10/4/2023 at 2:35 PM, joshuaho96 said:Could be an FPR too. If you've hardwired your fuel pump to run full blast all the time the FPR is almost certainly your problem at idle. Nissan used the FPCM to slow down the pump at idle.

I don’t think it’s the FPR as I’ve run a short hose into a bottle straight off the reg, and the pressure drops down. Maybe a new reg is a good idea anyway though. I will try doing what you said and test down the line. Although the only spot I can measure is between the hard line and tank, but it’s cramped as in there. I’ll have to lower the tank to get in there. 

On 10/4/2023 at 5:47 PM, Dose Pipe Sutututu said:Try bypass the fuel dampener to see if there's still an issue.

R34 GT-t uses a couple of them instead of 1x like the R33

Yep I bypassed the dampener on the fuel return line too but didn’t help. I still have the dampener on the feed. Maybe I’ll test bypassing that one too as I put the gauge before it. 

15 hours ago, Dose Pipe Sutututu said:

Hang on, are you running the stock FPR? If so, get an aftermarket one

Yep stock reg. Ill look into a new reg, just seems strange that it drops the pressure fine when I remove the return line. Also seen posts on here saying the stock reg is good for mild pump upgrades. It is 25 years old I guess

1 hour ago, tylink720 said:

 Also seen posts on here saying the stock reg is good for mild pump upgrades.

Car still might work however the fuel pressure is probably all over the shop like you've just discovered.

1 hour ago, Dose Pipe Sutututu said:

Car still might work however the fuel pressure is probably all over the shop like you've just discovered.

Alright, I've started looking for an aftermarket reg. This cars been a bottomless pit so far, and I haven't even started the proper power mods yet lol.

thanks

5 hours ago, tylink720 said:

Yep stock reg. Ill look into a new reg, just seems strange that it drops the pressure fine when I remove the return line. Also seen posts on here saying the stock reg is good for mild pump upgrades. It is 25 years old I guess

If you want to run the stock regulator you need to keep some method of making sure you aren’t trying to flow 255lph of fuel at idle. Otherwise you will experience what you’re talking about. 

  • Like 1
2 hours ago, tylink720 said:

 This cars been a bottomless pit so far, and I haven't even started the proper power mods yet lol.

Welcome to Skyline ownership, cheaper and more reliable buying a BMW M2 Comp, but here we all are lol.

1 hour ago, Dose Pipe Sutututu said:

Welcome to Skyline ownership, cheaper and more reliable buying a BMW M2 Comp, but here we all are lol.

Yep lol, half the fun is working on these piles. My brother has a newer BMW and it’s super quick and reliable

Any current recs for a good budget reg? I don’t want to buy some cheap eBay stuff, but also don’t want to drop $500 on just a regulator. I’ve seen some for about $140-$170 like Tomei, P2M, NRG, AEM, ect

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • Hi, i’m making a rb25det coil loom for Vag short coil. Can anybody tell me which Ecu signal wire belong to coil number 1 and 2,3,4,5,6? The connecting switch in above pic is 8 wire i think white is for +12v and black for earth.
    • Was there ever a model of the Stagea m35 that didnt have a badge on the grill? I thought I saw that somewhere, some aero edition or something? I cant find it again? davemoto
    • Its a 2002 vr-x four VQ25DET, silver. Coil overs, lowered, polished alloys and sport exhaust. Bit of a project, was sitting in a shed for a while but runs and drives great.
    • I wasn’t able to replicate the sound anymore. It was a one time sound so maybe it was just coincidence but it was like small pebbles being dropped in a coke can.   should I try cleaning the MAF? It could be it’s functioning but dirty? I don’t know.
    • Update 4: Hi all. The car drives again! Haven't driven for long, only to store it in the garage again, but the test drive was successful. The coolant and oil leaks seem to be fixed for now. Temps on the engine were also very good, while moving I never even saw 80C water during the approx. 30 minute drive. Ate up all the coolant in the reservoir though so will have to fill that even more when I go to the car next time. One thing that pisses me off is that the RPM gauge is still f**ked, I even resoldered the board twice and used copper paste on the silly screws that are used as connections. Next time I take it out I'll take apart the board and fit new components, I'll see if I can get a replacement IC for it.  I have an appointment set for 22nd of September for the engine tune to 370hp. Alignment also still needs to be done. My hope is that I can get all the legal stuff over with by the end of this season. Anyone of you have advice regarding intercoolers? Currently there is an APEXI core fitted, one of those weird hybrid ones, 600x270x76. I don't think it's bad but it's not new and now I still have the chance to change it now to legally include it in the paperwork. Only issue is that the only options that would arrive in time are a HKS Type R intercooler or generic Ebay spec intercoolers comparable to a JustJap one. Ideally I'd order a Plazmaman but it takes over a month to receive which would mean making the car legal has to wait until next season. Would love to hear some input on this. Same story for my injectors, the previous owner was a nunce and put ID 1050x on the engine. They work but are obviously not ideal at "normal" power levels. But I don't see a reason to change them unless the tuner says it's necessary. I read online before buying a different exhaust that the top secret style rear diffusers won't fit due to the size of the rear resonators. My buddy and I made it work by slightly "adjusting the shape" of the mounting bracket and making some spacers out of 3d print for the mounting bolts. Fits like a charm. Just putting this here in case someone has this problem. Even the hefty HKS Silent Hi Power rear can fits without hitting anything.
×
×
  • Create New...