Jump to content
SAU Community

High Fuel Pressure

rofocale

By rofocale,
in General Maintenance

 Share

Recommended Posts

rofocale Contributor

rofocale

Posted
Posted

Hi folks,

This is on a 1995 R33 GTR V-spec with a stock FPR and injectors and 2 year old fuel filter. With an unknown fuel pump...initially... and the car is definitely running on the rich side with a powerfc using the base map and the idle routine is complete. It drives okay...but definitely rich (on mixture and pocket!)

Some time ago I bought a mechanical fuel pressure gauge to plug into the fuel line just after the fuel filter before heading off to the fuel rail and injectors. I measured the pressure according to many articles I've read on this and other skyline forums and my results have been:

at idle: ~43psi

at idle with vacuum line to FPR disconnected: ~50psi

These figures I believe are high for a gtr...i've seen posts which basically say it should be 2.5 bar(or 36psi) at idle and 3.0 bar(or 43 psi) with vacuum line disconnected. The R34 gtr service manual and R32 service manual also corroborates these figures(I haven't seen specific references in any Nissan documentation for the R33 GTR)

Now my old fuel pump was never holding line pressure with the power switched off and it was very likely just the stock fuel pump which would make it pretty old so I recently had the opportunity to buy a Nismo GTR fuel pump and I have installed that and also replaced all the pressurized fuel lines(ie the ones from the fuel tank to the metal runners behind the right rear wheel and the ones in the engine bay) with some new high pressure fuel tubing and for good measure I also replaced the fuel filter. So after replacing all the stuff and measuring the fuel pressures I get exactly the same figures...

My thoughts are:

Is this fuel pressure within some level of tolerance and effectively normal? (I doubt this but it might be possible) Hence I need not go any further except get the car tuned.

This fuel pressure is high and hence raising the amount of fuel going into the engine - more than what the powerfc thinks is going in.

If this fuel pressure is too high and should be addressed, I suspect that the only piece left in the equation is the FPR which is just a stock item. By chance I happen to have a nismo adjustable FPR I got some time ago cheap and never had a need to use. Is it worth me changing over to the nismo FPR and setting the idle fuel pressure to 2.5 bar (or 43 psi)? Or would this potentially mask the real problem whatever it may be and not be a good idea (yet?).

Are there any other possible causes for this high fuel pressure? (Other than the mechanical pressure gauge is reading incorrectly... I shall investigate this just in case...)

Any thoughts would be appreciated.

Link to comment
https://www.sau.com.au/forums/topic/411313-high-fuel-pressure/
Share on other sites
scotty nm35 Grand Master

scotty nm35

Posted
Posted

Of course you get the same figures, it is the reg that controls the pressure, not the pump.

You must have a very high idle, with a low idle there is much more vacuum which will drop the pressure even more. If you are still worried, swap the reg. More than likely the gauge is out by a bit though.

89CAL Grand Master

89CAL

Posted
Posted

Of course you get the same figures, it is the reg that controls the pressure, not the pump.

You must have a very high idle, with a low idle there is much more vacuum which will drop the pressure even more. If you are still worried, swap the reg. More than likely the gauge is out by a bit though.

This

Pressure is restriction to flow, the Pump creates the flow, the regulator restricts the flow on the exit of the fuel rail.

It is possible your gauge is out as above or the FPR is a bit dodgy. But it isn't really that big a deal. I know its not the cheapest option but you can just go and get it retuned (It looks like you have a Power FC) and the car will run fine.

Having said that, if you drop the base pressure, you'll have to get a re-tune anyway as the fuel pressure under load will be a tad lower and thats a bit more dangerous then it being a bit rich

I'd just take it for a retune, I dont think your Dangerously above the standard base pressure but if your that worried about it, replace the FPR (Maybe borrow a stock FPR if you know someone) and see if that fixes it and get a re-tune then

  • 2 weeks later...
_x_FiReStOrM_x_ Community Regular

_x_FiReStOrM_x_

Posted
Posted (edited)

Possible causes: slight blockage in return line, either gunk in hardline or internal swelling of a rubber hose. Blockage or fault in fuel pressure reg itself. Aftermarket fuel pump delivering a high volume of fuel, which the regulator can not return quick enough.

For a start i'd try get a hold of a good quality or known accurate fuel pressure gauge and then go from there. You can also do a simple fuel flow test to determine the actual flow rate of the pump if it's unknown.

Edited by _x_FiReStOrM_x_

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
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • Duncan
      Mistakes were made, my R34 Story

      By Duncan · Posted

      jeebus. glad you weren't under it while performing the stunt. Also thanks for the link to the wheel measurer, exactly what I needed
    • Duncan
      Who has a Infiniti Q60, Q50 (V37)?

      By Duncan · Posted

      In the older stuff there were very significant differences 2wd to 4wd, for example Stagea had strut front end for 2wd and double wishbone for 4wd so it was not minor to swap. From poking around the 2wd v37, it *looks* like it might be more possible; some of the parts specifically have "2wd" stamped on them which suggests the platforms are more similar. You'd still want to start with a 4wd half cut to swap stuff from though. I'd suggest if you don't have a tune on the ECU you don't really need one on the trans either. Throttle mapping is in the ECU side (and you can always use a Roar Pedal if you want the throttle to actually respond to your foot), and really if you are happy with the stock power you probably accept the stock trans behaviour too....its all made to be "sporty" not racey.
    • Kinkstaah
      Mistakes were made, my R34 Story

      By Kinkstaah · Posted

      So, updates. I have not washed the car since it came back from Tassie. I've driven it around a bit but not got around to actually sorting it out. I DID raise it because I cracked the rear bar leaving a hotel which was very distressing. Interestingly, the car drives more compliant now that it's raised a fair bit (5mm front, 15mm rear). Also noticed that my FR height was 10mm lower than FL. So that's now sorted out, too. I also bought this and had it printed: https://www.etsy.com/au/listing/1576422240/wheel-and-tire-fitment-tool-universal?ref=shop_home_feat_1&dd=1&logging_key=08f604d9fa4cc383550ba985e6ac85cd5cac7fbb%3A1576422240 Now, if I was smart I would have taken my brake calipers off to actually use this correctly but it was evident enough to me that in the region where the caliper was... there was nothing to hit suspension/guard/arm wise. So I'm going with "it'll be fine" after using the tool to hopefully very precisely measure the wheel clearance. Also while doing this, I had the very VERY bad idea of jacking one of the wheels/suspension arms up while the rest of the car was on jack stands. I did this to see how the arm would travel. This all was well and good until the car slid off the stands and went through a fence. So don't do that. Incredibly nobody was hurt and there was only minor damage to the rear bumper as the car didn't have far to slide, and had 3-4 wheels on it. The only damage turned out to be the fence itself which was easy to fix, and a little bit of damage to the fibreglass rear bumper trim. I had already planned to try a touch up paint kit to fix the time I drove into my garage door to see if it'd help in the interim before I get it fixed properly. I used the Dr Colorchip kit after looking online and seeing everyone talking about it. Yes it's made for chips and not huge broken missing pieces and I'll be 500% recommending it for stone chips after using it for stupid things like me. This took about ... 10 minutes and looking at the half assed photo the 30 second job I did on the bumper corner was almost perfect just by using the tiny little brush and painting it in. The sealact stuff to remove over-painting is really useful, so if/when I do it again I'll likely slather the touch up paint well over it and then clean it up with the cleaning solution. The wheels should arrive in a couple of weeks. I am still kinda confident after doing a stupid amount of measuring (and borrowing a set of 18x10.5+15) that they will not fit because I overlooked something, somehow and flew too close to the sun. ALSO R34 GTR guard liners do not fit on a GTT. I bought the undertray brake duct guides and had the wonderful problem of them not fitting my intake, my oil cooler and the liners themselves were even worse. Attempting to fit them won't work in general - You would have to cut them up as another poster mentioned as the bodywork is different on the GTT. At least I can try to resell them. So instead of cutting those up, I cut up my old already-cut-up GTT liners and extended them by using some PP plastic and drilling some 8mm holes for some nissan clips for the 'extra' bit. Because I was happy to cut them I was able to mount them pretty damn forward so I now have some semblance of guard liners, and the brake vents seal the bumper from the bottom. It sort-of-looks like this, to give some idea - If you look at the GTR and then the GTT this is when I realised that I needed to seriously measure as the inside of the rim area is entirely, entirely, entirely different and could not take any internet measurements for granted.   
    • wizlb
      Who has a Infiniti Q60, Q50 (V37)?

      By wizlb · Posted

      If you are Ecutek tuned then these TCU tunes are anywhere from $550 to $700 usd. If you are not ECUTEK tuned, then it gets costly!    
    • brillo
      Leak from Tokico BM50 Brake Master Cylinder

      By brillo · Posted

      Sorry to hear your HFM BM57 was faulty,  did you contact HFM I would hope they would be at least grateful for the information if there was some sort of manufacturing fault, you would hope they would be sympathetic even if your item was 2 years old if it had never been fitted. May I ask where it leaked from ?
×
×
  • Create New...