Jump to content
SAU Community

Radical Changes In Fuel Pressure With Malpassi.

DennisRB30

By DennisRB30,
in Engines & Forced Induction

 Share

Recommended Posts

DennisRB30 Community Regular

DennisRB30

Posted
Posted

So I set my malpassi to 50psi base (referenced to atmospheric) Then had a look a week later and its at 30psi. My car was going VERY hard at that fuel pressure with wheelspin through first and second with 0.7bar. So I put it back to 50psi as I think it was at 50 when we tuned it. (I say THINK because I set it a few days before we tuned it and it may well have went down before we tuned it).

After I put it back to 50 I went for a drive and the car ran like crap and was misfiring. So I checked it again and it was at 75psi base! I put it back to 50 again and it seems to be staying there now.

WTF is going on?

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

I've heard the Malpassi have been known to have problems such as what you've described where by the pressure is all over the place.

Not sure if its a product or installation thing... but then... its not hard to install one so i think i'd go with product

TurboX Mentor

TurboX

Posted
Posted

I would be checking the reference air lines as it only can work with what it sees from your manifold unless it has a diaphram problem or similar.

Aside, I thought the base ref was 43 PSI?

Though I seem to have killed four gauges till I figured the one way valve that was removed from on the in tank Bosch 044 may be needed in the line to stabilise the gauge from high speed fuel pump pulsations.

Have not fitted new gauge yet to see if putting in line has solved problem.

dangerous_daveo Grand Master

dangerous_daveo

Posted
Posted

50psi!!! Mines on 30psi at 800rpm idle. I also have the standard dr drift rb20det chip and its a flat 12afr, and I do mean flat. So Im guessing try going back down a few psi first.

Where the problem might be is in what model malpassi you have and where its located.

#1 if its ratio is wrong its going to pump in way too much fuel. I had a black top one on mine a while ago and had the same problems you have. I then replaced it with a silver top and all was good.

#2, if its near excessive heat this apparently CAN have an affect on its performance. That said mines bolted to a bracket on the side of my plenum and is spot on perfect in winter and after sitting in 1hour of summer traffic...

Beer Baron Grand Master

Beer Baron

Posted
Posted

I've said it before and I'll say it again. I wouldn't put a malpassi regulator even near my car. They should call them de-regulators. cheap pieces of crap. through it in the bin before you lunch your motor. :)

DennisRB30 Community Regular

DennisRB30

Posted
  • Author
Posted (edited)

Its a black top 1.7:1.

It is installed on my strut tower away from heat and vibration. I can't see how my installation could be causing the probs. Its fairly straight forward to install.

I also have a intank 044 with the valve removed. I have noticed my gauge reads 5 psi with the pump off, which is wrong as it should read zero with no valve in the system.

I always set the base pressure in reference to atmospheric pressure, IE with the vacuum line off (so the lines are not a factor, plus they are all OK anyway). So 50psi is only a bit above standard. At idle its 25psi.

Edited by DennisRB30
DennisRB30 Community Regular

DennisRB30

Posted
  • Author
Posted
I've said it before and I'll say it again. I wouldn't put a malpassi regulator even near my car. They should call them de-regulators. cheap pieces of crap. through it in the bin before you lunch your motor. :)

That is what I have been hearing. What actual experience do you have with them? I would like to here some first hand info as opposed to regurgitated hearsay.

Tex Willer Apprentice

Tex Willer

Posted
Posted
I've said it before and I'll say it again. I wouldn't put a malpassi regulator even near my car. They should call them de-regulators. cheap pieces of crap. through it in the bin before you lunch your motor. :)

Agreed. 1 of 2 fails. IMO

Guilt-Toy Grand Master

Guilt-Toy

Posted
Posted
I've said it before and I'll say it again. I wouldn't put a malpassi regulator even near my car. They should call them de-regulators. cheap pieces of crap. through it in the bin before you lunch your motor. :)

AGREED.. they hardly ever work properly. get a sard for the min. many people have lost engines because of malpassi's dont be another victim. replace it asap. dont hit boost untill thats done.

DennisRB30 Community Regular

DennisRB30

Posted
  • Author
Posted
AGREED.. they hardly ever work properly. get a sard for the min. many people have lost engines because of malpassi's dont be another victim. replace it asap. dont hit boost untill thats done.

f**k this. I have been hearing this all to often. It scared the shit out of me when I saw it was running 25psi less than what I set it to.

Will a this Sard be OK? http://cgi.ebay.com.au/SARD-Fuel-Pressure-...1QQcmdZViewItem

I have heard from someone that they are not the all that good either. But my mate has one on his Aristo with a 044 fuel pump and it seems to be OK. It says its rated for max 450 HP? I will be running a lot more than that. Does anyone else use a Sard with 500+ RWHP?

DennisRB30 Community Regular

DennisRB30

Posted
  • Author
Posted (edited)

I finally figured the Sard FPR's out.

http://www.upgrademotoring.com/performance/sard_reg.htm

The Ebay ones appear to be the 450hp ones. The bigger one costs a lot more. So what would happen with a 450 one? My guess is that if you use more than 450hp worth of fuel the pressure starts to drop since it can't handle such a large variation in flow.

My mate with the Aristo with the Sard changed from a stock fuel pump to a 044 and base pressure shot up by like 20psi. Some people might say, well DUH there is more fuel flow. But to me that is a sign off poor regulation with varying fuel flow. What happens when the engine is using most of the fuel flow from the pump at high load? My guess is the pressure will drop. If pressure goes up by 20psi with more X amount fuel flow, its going to go down by like 20psi when the engine uses X amount of fuel flow up. Does that make sense?

His sard does seem to be stable though. Its always the same when you check it unlike the malshitty.

Edited by DennisRB30
R31Nismoid Grand Master

R31Nismoid

Posted
Posted

The sard wouldnt "increase" unless it was set to do this.

Just changing pump wont increase the fuel pressure if the pump is on good order

UNLESS the pump that was in there was dying and wasnt keeping up the pressure, and hence the reg was bumped to compensate without realising.

DennisRB30 Community Regular

DennisRB30

Posted
  • Author
Posted (edited)
The sard wouldnt "increase" unless it was set to do this.

Just changing pump wont increase the fuel pressure if the pump is on good order

UNLESS the pump that was in there was dying and wasnt keeping up the pressure, and hence the reg was bumped to compensate without realising.

There was nothing wrong with the old fuel pump. We were running 0.9 bar with a T04Z on a 2JZ with 11.8 AFR's at 50psi base pressure, you can't ask for more out of a stock pump! But we changed it to an 044 so we could wind the boost up to be safe.

So I would say that changing the pump DOES increase fuel pressure if the FPR is being overwhelmed with fuel flow. That is my theory. It leads me to believe that the 450hp Sard is too small to regulate pressure effectively with a 044 pump.

Edited by DennisRB30
Guilt-Toy Grand Master

Guilt-Toy

Posted
Posted

I turned my rb25 into macaroni and cheese with a malpassi. I now run a sard - might be upgrading it because im past the 450hp mark so make a offer :)

f**k this. I have been hearing this all to often. It scared the shit out of me when I saw it was running 25psi less than what I set it to.

Will a this Sard be OK? http://cgi.ebay.com.au/SARD-Fuel-Pressure-...1QQcmdZViewItem

I have heard from someone that they are not the all that good either. But my mate has one on his Aristo with a 044 fuel pump and it seems to be OK. It says its rated for max 450 HP? I will be running a lot more than that. Does anyone else use a Sard with 500+ RWHP?

Abo Bob Grand Master

Abo Bob

Posted
Posted

I think you need to look back to the start here.

You set it to 50 psi, then you checked it and it was 30 psi, so you increased it to 50 psi, then you checked it and it was 75 psi.

It seems to me that the malpassi didn't change it's pressure at all. Either you stuffed up the reading of the pressure when you thought it was 30 psi or your gauge read it wrong.

It looks like you got an incorrect reading, increased the pressure, got a correct reading, reduced the pressure back to where it should have been.

That said I also am not a Malpassi fan. I had one and had erratic fuel pressure so I ditched it.

DennisRB30 Community Regular

DennisRB30

Posted
  • Author
Posted
50psi base once, 50psi base another time... you guys all gambling with stock injectors?

Yeah stock ATM, but to be upgraded very soon. In fact I am doing mine Today :D BTW its only 7psi more than standard.

A FPR that is the same ratio as the one you replaced, will not alter fuel pressure

In relevance to the increase in fuel pressure on the Aristo, this statement is wrong on so many levels.

Firstly, when the prob occurred we didn't change the reg, we changed the PUMP.

Secondly, all pressure references we made are to atmospheric. So if its rising rate it wouldn't matter.

Thirdly the Sard reg is a 1:1 reg anyway and it DID alter fuel pressure with the bigger pump.

Fourthly, or course if you change the reg the fuel pressure will change, its not like they automatically come set to exactly what ever fuel pressure you were running previously!

As you say the pressure shouldn't change. But it if does something is not right! Seems pretty obvious that the Sard reg is too small and can't flow enough fuel to keep pressure down with a 044 pump. This shouldn't be surprising since the Sard FPR is rated at like 250 horsepower less than the 044 pump! Thats probably why they make the bigger one.

Guilt toy, what happend with the Malpassi, are you sure it was at fault? No thanks for the offer on the Sard. It will be too small since I already have over 450hp.

Bob, I didn't stuff the readings up. Its pretty hard to stuff it up.

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

    • JC71
      new 1.5 LSD issues/concerns

      By JC71 · Posted

      sold listed as a Tomei LSD 1.5 Way For 1998+ Nissan Skyline ER34 25GT RB25DE w/Open R200 https://www.ebay.com/itm/174006114594?campid=5338967980&mkevt=1&mkcid=1&toolid=10050&customid=&mkrid=711-53200-19255-0&loc_physical_ms=108689&loc_interest_ms=&campid=5338967980&mkevt=1&mkcid=1&toolid=10050&customid=71883f2ccc571356e0a757bc7adfdde2&mkrid=710-53481-19255-0&loc_physical_ms=108689&loc_interest_ms= it went in like butter all gears, alignment, back lash etc, rotation and clearances correct, and if rolling all rotates smooth and free when coasting down road , clutch in or out over 10 mph smooth... its the binding, clunking and jerking from a stop that is most concerning, also seems like its going to tear the tires off in 10 miles of normal road driving. 
    • Kinkstaah
      new 1.5 LSD issues/concerns

      By Kinkstaah · Posted

      What 1.5 way? There's no such thing really as a 1.5 way, just different ways of explaining 2 ways with different ramp rates. HOWEVER. In any driving in a straight line your 1.5 or 2 or 1.7 way should have no clunking at all. With the clutch fully depressed the diff should be silent (unless it's welded but I'm assuming it's not). Something aint right here.
    • JC71
      new 1.5 LSD issues/concerns

      By JC71 · Posted

      Clutch is a spec brand, new clutch system,( PP, flywheel, friction disc, etc. pull type) installed 100 miles ago, with no problems.
    • JC71
      new 1.5 LSD issues/concerns

      By JC71 · Posted

      looking for some help and maybe some insight on others experience with a new LSD. R34 GT ran and drove beautifully, but always alot of grip loss due to the open R200 rear end, so I just installed a new 1.5 LSD way into the stock open R200 for a ER34. Simple. Everything seemed right. I test drove for the first time this weekend. as I started to back out the garage the first time slowly with tires straight it sounded and felt like I had a loose or half disconnected drive shaft...that was clucking around loose and shaking entire vehicle, and making it feel like the trans clutch was spontaneously slipping then grabbing very roughly while just letting out pedal slowly. I backed it out went to pull forward with the same noise, shake and slip grab feeling with hesitation, I turned the tires to back out more and then pulled ahead some same thing but worst because of added wheel resistance (which that I expected) puzzled … pulling it back in checking everything over and finding nothing wrong, I tried it the next day. same thing, couldn’t believe how it shook everything again making a terrible noise and making it feel like the trans clutch was slipping and grabbing, but I got it out of garage into the driveway, got it straight, drove forward and then reveres a few times in a straight line everything shaking , causing what felt like clutch slip and grab every time, sounded like right behind front driver tire and I could feel it in the floor board with my feet,... worst right when beginning to let clutch pedal out to engage slightly, shuttering and sounding terrible along the way…I managed to slowly get down the road, babying it the whole way, once I was rolling (out of 1st) seemed to be better and between shifts, then clutch felt closer to normal…not slip/ grab etc., but back down to any stop, straight road or turning, same thing. Made no difference if all tires were straight or if I was turning. All other gauge read out correct. with in 2 miles as planned I reached the empty parking lot and performed the break in procedure that came with lsd, essentially to drive in a figure 8 a bunch.  Did this, binding chattering, and shaking the car the whole way. I drove it back home seemed somewhat normal once I was in straight line and past 10 mph or so, and I know it will “bind” on corners and cause some tires squeal when turning especially from a stop, but when I begin to move it still causes what feels like the trans clutch to slip and jerk badly as well as shaking the entire car, and sounds terrible, that I didn’t expect. I used the fluid they supplied with LSD kit and did the breaking, planning to change fluid as they suggest after breaking, but wondering will it get smoother or less aggressive with use? maybe a 1.5 is just too aggressive for normal road driving?   I have a LSD that I put in my 71 cuda when I restored it, with amazing smooth , quite yet effective results. Different style LSD but that ones a joy to drive. maybe expecting too much from this R200?
    • Matt Z
      SAU NSW - Archies Flame Grille Meet & Cruise to Kurnell

      By Matt Z · Posted

      Join SAU NSW for a flame-grilled feed & flame-spitting cruise! Sunday 17th August 2025 3:30PM Meeting Archies Flame Grille Sylvania Waters 4:45PM Cruise Departure 5:15PM Arrival at Cape Solander Kurnell Meet Location: Archies Flame Grille Final Destination: Cape Solander Kurnell *Disclaimer* There will be a lead and follow car so no one should get lost. If you would like to attend or bring others along please put your name down and a +1 as numbers will be needed prior! This is NOT a race and we will all be adhering to all road rules. If this is what you want please come to one of our many track days. This is an official SAU:NSW event and will be run under a CAMS permit. One of the things that really sets our club apart is our commitment to being true enthusiasts. When on normal roads we strive to maintain good relations with the authorities as well as the public in general. When attending one of Skylines Australia NSW events please try to: • Be aware of surrounding environment and act accordingly. • Drive courteously on the state’s roads as a true enthusiast should. • Understand how important it is to maintain the good name of SAU NSW and thus, treat others accordingly. • Any misbehavior will not be tolerated and you will be asked to leave.
×
×
  • Create New...