i just realised that when i turn my car off my fuel pressure drops to virtually nothing straight away. shouldnt it hold pressure for like a minute after its turned off?

No.

short and sweet

from my gregories manual "(8) Switch the engine off and note the pressure gauge reading. If the pressure does not decrease appreciably in 60 seconds, the fuel system may be considered to in a serviceable condition."

Quote: Originally Posted by dr00 i just realised that when i turn my car off my fuel pressure drops to virtually nothing straight away. shouldnt it hold pressure for like a minute after its turned off? If the non-return valve in the high pressure pump is working properly then the pressure should stay near its operating point. If not it means that either the non-return valve in the fuel pump has failed or the recirculating ball mechanism in the standard pump is very worn - if thats the case then it will tend to lean out and/or operate erratically on high load. Its also possible your fuel pressure regulator is duff in that it has a flakey spring or seat, it is possible for it to fail so fuel dribbles from the regulator back into the manifold and you'd notice this by smelling a lot of fuel when you next start the car and/or your oil would be diluted with fuel. So do this a few times and check your oil level and startup smells :cry: I have a 450hp pump which has an extra nonreturn valve after the standard recirculating ball mechanism, its a bit bigger than the standard pump and has larger pipes and delivers higher pressure... So the short answer is, the system *Should* retain pressure after the ignition is off and the longer it does the better condition is your pump and your fuel pressure regulator.

well i have a 600hp pump sitting here waiting to go on so maybe ill stick that on and see if it makes any difference. hope its not the reg coz its a malpassi i bought off dragya Some original photos have not been recovered yet.

Quote: Originally Posted by dr00 well i have a 600hp pump sitting here waiting to go on so maybe ill stick that on and see if it makes any difference. hope its not the reg coz its a malpassi i bought off dragya Nice ! Where did yah get it, the pump that is ? did you get my PM re Wed ? Some original photos have not been recovered yet.

yeah just got it then. i got the malpassi and pump off dragya from these forums. now the cars not going at all though! the fuel pump doesnt make any noise when i turn the car on. but its weird theres a strange red led flashing that im sure doesnt normally flash. the only thing i can think of is the standard alarm has triggered somehow and cut the fuel pump... (i have a laserline btw)

fixed! i was getting no spark, no injectors and no fuel pump. turned out one of the alarms/immobilisers had triggered and one of my weird keys that lurks in the bottom of my drawer fitted the keyhole in the glovebox and turned it all on again. very strange.

I have had a fuel pressure gauge on my car for years, the pressure has always dropped within 2 - 3 seconds of shut down, with the std pump and 2 600hp bosch pumps. happened with the std reg and my adjustable one. Has anyone else got a gauge on their car?

im about to get a little gauge that mounts of the side of my malpassi , will let u know when it arrives and/or is fitted. sorry - im not much help

I used to have a differential gauge I made from a standard gauge, pressurised the housing etc, so I could watch the pressure between manifold and fuel (which in theory should stay the same even when on boost as a way to check your fuel pressure regulator and pump capacity on load), it used to 'droop' a little. The basic (standard) fuel pump from Bosch for the VL/VLT is a recirculating ball type which by virtue of its design has nonreturn valve function and this is an indcation of how worn the balls and races are in the pump. Putting a nonreturn on the end of a VL/VLT pump wont improve its flow though, because if its lossy internally then a nonreturn valve wont help. For the larger higher capacity pumps it seems that they need a larger clearance or are made with a larger clearance, some dont run off any lower pressure pump either. So I guess some leak back with those might be common but I think for different reason. I tend to follow what Holden says in their service manual - since I took apart a VL pump some years ago and *yes* if it doesnt hold pressure when off then it wont be able to flow as much when its on high load...

Mine gradually drops off within a two minute time period

Ive had a fuel pressure gauge for years and during that time ive had a standard pump and standard reg and the pressure dropped within about 3 seconds of switching the engine off. Then i got a 500hp Bosch pump and the same result and then i got another 500hp pump and an aftermarket reg and the fuel pressure reg and the pressure did the same thing. In my view thats what the fuel pressure should be doing because thats what the fuel pressure reg does. Basically what a fuel pressure regulator does is reduce fuel flow from the fuel rail back to the petrol tank. This reduction in flow creates the fuel pressure you get at your injectors.On turbo cars they use riseing rate fuel pressure regulators which means that the fuel pressure rises with the boost usually at a rate of 1:1 ie 1psi boost = 1psi more fuel pressure above what it would be at zero vacuum. The opposite also happens when you back off the throttle and go onto heavy vacuum the fuel pressure drops also. So what im saying is that when you switch your engine off, the fuel pump goes off and so it is no longer making pressure in the rail because the remaining pressure is flowing through the reg and back to the tank. So the pressure will drop pretty quick once the engine is swithed off. Sorry i probably crapped on for a bit long there and no one will read it but anyway thats thats why your pressure drops when you switch your engine off.

No, sorry to contradict you The fuel pressure regulator on the VL and VLT is the same. It is *not* a rising rate regulator. If you are using a fuel pressure gauge referenced to atmospheric then it will show an increase as you put the engine on boost, *because* the fuel pressure is actually referenced to manifold *not* atmospheric. To do a proper examination of fuel pressure across _The Injectors_ you need a differential gauge which measures between manifold and rail. If it wasnt this way then the pressure across the injectors would change and upset fuel metering, a slight rise is OK to compensate for wanting enrichment on boost but any fall would lean out, this is why the fuel pressure regulator reference pipe goes to Manifold after the TB ! When the engine turns off and the fuel pump turns off the fuel pressure regulator is referenced to manifold which is now at atmospheric pressure (within a few of seconds) and that apparent drop is what you see. If the pressure continues to drop to zero over a few minutes then there is a leak back through your fuel pressure regulator or your pump, either of these indicate a problem if you want maximum performance, most people can live with a little leak back. Some original photos have not been recovered yet.

Mike M: can u explain the mechanical difference between a std VLT reg and a Malpassi rising rate reg (1:1) please

Quote: Originally Posted by HSVSUX Mike M: can u explain the mechanical difference between a std VLT reg and a Malpassi rising rate reg (1:1) please I dont know the Malpassi but, from what I have heard, the fuel regulation is nonlinear, ie. It seems that the Malpassi allows more fuel pressure from the pump for higher manifold pressure - this is fine as an alternative method of enrichment for higher boost for some systems as a poor mans way of adding enrichment without having to reset the maps in the ECU. The VLT ( and VL ) fuel pressure regulators provide the same injector fuel pressure regardles of manifold pressure - this is ideal if you are retuning your maps in your ECU because thats the place you control the fuel metering. If I was setting up a system and had access to the ECU for remapping then I'd want only one set of variables to change at a time, so the standard VL/VLT regulator would be adequate but, if I couldnt get access to the maps in the ECU and just wanted more enrichment for higher boost (higher fuel pressures) then I'd use a rising rate regulator. The only possible negative is that the pump has to be able to deliver the higher pressure, if you have acces to the ECU maps then you dont necessarily need higher pressure as the pulse width can be made wider to get more fuel into the cylinders. I got around all of this by making a staged gain amplifier which hangs off my air flow meter, so when the air flow gets much higher due to higher boost the amp sends a higher signal to the ECU to make it think its using more air - this effectively increases fuel flow and provides enrichment. The amp is shown in this picture, I can adust the rate of enrichment with a simple 22turn trim pot, http://members.iinet.net.au/~erazmus/Twin_tyre_vehicle/Airbox_hole.jpg

Sorry Mike but your wrong about the rising rate regulator, all turbo cars need a rising rate regulator. The reason for this is that say for example my engine which runs 22psi, im at full boost with a manifold pressure of 22psi now if you go with what your saying and your fuel pressure doesnt change then the fuel pressure should be at say 38psi. Now your injectors are spraying into the inlet with a fuel pressure of 38psi behind them but there fighting a manifold pressure of 22psi which means the actual pressure of the spray coming out the injector is (38psi fuel pressure minus the boost pressure 22psi) = 16psi. As we all know this pressure isnt sufficient to give an injector a good spray pattern so how is it solved, you use a rising rate reg so the injectors will maintain a constant pressure as the boost rises. So what your saying is wrong because if you didnt have a rising rate reg then as you came on boost your fuel pressure at the injector would drop and you would leen out. So a rising rate reg isnt a poor mans way of enrichment its the way you overcome the manifold pressure to maintain a constant pressure. One more thing if VL regulators wernt rising rate why would they have a vacuum hose going to them, if they were to just keep a constant pressure they would just be like a carby fuel pressure reg ie no vac line.

You are using the wrong terminology and reading from the wrong perspective but what you say is correct if and this is handled by standard VL/VLT regulators, notice the reference line for the regulator goes to manifold - not atmospheric. The standard VL/VLT regulators might 'look' like rising rate regulators if you measure fuel pressure between rail and atmospheric - but that is *not* where anyone should measure fuel pressure - except as a quick test that some pressure is being generated when engine is off and ignition on. Trouble is differential fuel pressure gauges cost heaps and I had to make my own to check my fuel pressure under boost. If you measure in the correct place which is _differential_ between manifold and fuel rail then the VL/VLT standard regulators are *not* rising rate but they 'look' like rising rate because they regulate from manifold to fuel rail. Please note this important distinction:- The VL/VLT standard fuel pressure regulators maintain a constant pressure across the injector regardless of manifold absolute pressure and regardless of atmospheric pressure. This makes them look like rising rate if you measure with respect to atmospheric. Please understand the difference between "Differential" and where you are currently measuring fuel pressure with respect to what reference. You can also get fuel pressure regulators that go even further and that is a small proportional rise *across the injector* follows a proportional rise of absolute manifold - these are *true* rising rate regulators and I would only use these if I want high boost pressure and cant get to the ECU fuel maps. I had a differential pressure gauge made to verify this very situation, and this scenario also follows the detailled description in the GMH service manuals (the blue books), take a look at the gauge I made which measure between manifold (post TB) to fuel rail:- http://members.iinet.net.au/~erazmus/Twin_tyre_vehicle/Diff_Gauge_side.jpg And here also:- http://members.iinet.net.au/~erazmus/Twin_tyre_vehicle/Diff_Gauge_Face.jpg In other words, VL/VLT fuel pressure regulators maintain a _constant_ pressure between manifold and fuel rail. A true rising rate regulator maintains an slightly increasing pressure across manifold and fuel rail as absolute manifold pressure rises. The term 'rising rate' has often been used incorrectly by some mechanics because they havent specified where the point of measurement reference is.

Of cause the vacuum hose from the regulator goes to the manifold and not the atmosphere cause if it didnt the fuel pressure in the rail would stay the same but at the injector you would get a drop in pressure as boost came on. If this is not the definition of a rising rate regulator can you please tell me what a rising rate regulator does different to a VL one? If you want to know the actual pressure at the injector its easy take the fuel pressure at the rail and minus the boost pressure and that gives you your true pressure reading at the injector. Its simple your fuel pressure in the rail rises with boost and decreases with vacuum. To me that is a rising rate regulator but i think we may have to agree to disagree.