Fuel Pressure gauge and setting

[Tony Martyr]

This may be one for Alex, who I know has fitted a dual reading VDO? gauge that measures fuel pressure and something else.

I would like to know if the standard transducer or sender bought with the gauge screws directly into the second plugged tapping on the high pressure side of the regulator.

If I fitted a dual fuel and oil pressure gauge does the original caterham oil pressure signal work on the VDO gauge or does it need its own device?

After fitting TBs ECU etc I never got round to checking the fuel pressure at the injectors. I simply fitted the regulator, as supplied by QED. As the engine runs well it has not been a priority but now I can't find any recommended pressure setting for a K series with the original injectors in TBs.

Any advice based on empirical data gratefully received.

[EFA]

Tony,

 

The fuel pressure sender is ideally situated mid way along the fule rail. If this is not possible it is best to locate it (using Goodrich or Earls type fittings) on the pump side of the fuel rail.

 

You will not be suprised to know that the regulator is only god for the pump and fuel line installation against which it was calibrated.

 

Moving it to another car (or out of the box - I strongly doubt QED set these up pre-sale) means your fule pressure is out of calibration.

 

In a fully mapped setup it is generally not the case that you get pinking if the fuel pressure is too low, more the case the car simply does not produce the power.

 

When I changed from a external tank facet pump to the JPE internal tank pump I found my fuel pressure dropped from 60psi to around 32psi!!!

 

Generally accepted norm pressure for injectors is 45psi (3bar) although some engines are mapped to run the injectors ar higher pressure to get more from the duty cycle. (Like mine - although its not particularly good practice!)

 

 

 

 

 

Fat Arn

The NOW PROVEN R500 Eaterid=red>

See the Lotus Seven Club 4 Counties Area Website hereid=green>

 

[Jason Plato]

Oily would be able to provide far more info than me , but - I know several people run the std 3 bar regulator on the K with either std injectors at upto 200bhp or alternative injectors - calibra turbo / saab at upto 230bhp .

I dont think the fuel pressure is the key but the injector pulse and duration should be altered/remapped if the regulator pressure is altered at any time .

If you are running the regulator upon which the engine was mapped then there shouldnt be any cause for concern as to what the "exact" pressure is - assuming it remains constant .

 

Dave

[EFA]

Dave, the pressure remains constant if the pump flow rate is constant. Any difference in the system will give a fuel pressure discrepancy, even battery voltage!

 

Fat Arn

The NOW PROVEN R500 Eaterid=red>

See the Lotus Seven Club 4 Counties Area Website hereid=green>

 

[Jason]

Arnie

 

a regulator will regulate the flow to be a constant pressure on the output assuming the flow is within the range of the regulator and there is enough supply to the regulator, what you describe sounds like a simple restriction valve or a regulator working outside it's designed peramators.

 

Jason

R500FUN

 

 

Edited by - Jason on 28 Dec 2001 22:08:27

[Alex Wong1697456877]

My SPA gauge uses a sender screwed into the other side of the regulator. The regulator QED supplied me only had the one input for the fuel line. DaveK sorted me out with a regulator with two inlets on the high pressure side. Once calibrated to atmospheric pressure, the guage has been very accurate when compared to a mechanical guage plumbed into the fuel rail (which has provision for a guage)

 

See http://freespace.virgin.net/alex.wong/liegephotos/spadials2.jpg

 

If I remember right, the sender uses a 1/8 BSP fitting. The guage measures water temp and fuel pressure. I did have problems with the temp sender but SPA have fixed this with their new senders. Since then, the gauge has been faultless.

 

I like having on-dash fuel pressure readings as I have had problems with pinking and misfires due to low pressure before. If I'd have had the guage then, it would have saved days of investigating for the cause.

 

They also do one that displayes fuel and oil pressure. They all have provision for external warning lights which can be set to light up at a pressure that is appropriate to your engine.

 

See Demon Tweeks 2002 catalogue page 154

 

These gauges need their own senders which come with the gauges. The temp senders are 1/8 NPT. DaveK supplied me with a 1/8NPT to M10 converter to bolt directly to the temp sender port of my Vx engine.

 

Alex

 

 

 

Edited by - Alex Wong on 29 Dec 2001 01:01:08

 

Edited by - Alex Wong on 29 Dec 2001 01:03:50

[Harry Flatters]

Short of fitting Alex's digital guages into my dash, is there a standalone fuel pressure guage that will attach to the outlet (can't remember the name of this valve, looks like a tyre valve)in the centre of my fuel rail for periodic pressure checking?

 

Steve Mell

PTM 88

[Chelspeed]

The tyre pressure valve is a schrader valve. I've got a small glycerine filled oil pressure gauge from a custom bike shop, it's designed to be plumbed into the oil gallery on a bike engine. With a replacement plastic footpump pipe from Halfords, already fitted with the schrader fitting, you have the gauge you need for checking fuel pressure. Fit and remove it with the engine not running or you'll spray fuel everywhere, remember how some air always leaks when you fit the air hose to your tyres.

 

As others have said a fuel pressure regulator regulates pressure, it doesn't know what is upstream of it, so if the regulator is set for 3 bar then it'll maintain 3 bar whatever fuel rail, filter or pipes are upstream. Provided of course that the pump is man enough to deliver more than 3 bar under all coditions.

 

It doesn't matter what pressure you have provided that it is the same pressure as was used when your engine was mapped. If it was designed to be 3 bar but was mapped with 3.3 bar then you need to keep 3.3 bar, resetting back to 3 bar will leave you running lean. I would hope that QED would supply the regulator set to give the pressure that they used to generate the map for the set of bits they've sold you. But I would also ask QED what this pressure is to double check it's set right and to check over time that the regulator hasn't drifted too much, springs will take a set, heat soak might change a regulators action etc etc.

 

I use my manual gauge to read the fuel pressure before and after it's mapped then check reguarly that the pressure is being maintained. I use the dash mounted gauge only to check that I don't suffer total lack of fuel pressure during an event due to surge or a pump shortfall.

[EFA]

This posting is written Without Prejudice.

 

QED don't supply a map that works with their engines. Mike Culmers map would not even allow his engine to idle. QED supply the same map independent of type of TB's and pistons/compression ratios - any wonder it diodn't work?? How "expert" are they.

 

They call this an engine kit.

 

With respect to QED checking/claibrating what they ship leaves me in hysetrics! Remember they do not even open bearing boxes to check the material! (To the extent that they claim that prior to Feb 2001 they were unaware more than one bearing material existed for the VX engine!)

 

Jason,

 

You are correct as to what a regulators function is, but it is completely screwed up by variation in the flow rate of the fuel pump hence requires initial calibration in each installation. Things like power supply to the pump also make a big variation to fuel pressure. Look at the pressure readings on your car with the engine off and then running. (i.e charging, not charging - 12v/13.8v)

Remnember I built what was probably the first common rail fuel injected Caterham Seven so I have felt most of the pain in getting these things working properly!

 

Fat Arn

The NOW PROVEN R500 Eaterid=red>

See the Lotus Seven Club 4 Counties Area Website hereid=green>

 

[Alex Wong1697456877]

I know Arnie's prior experiences but I must say that I'm very happy with my QED engine. They mapped it on their dyno for me and the map was excellent, especially as it was obvious from driving the car that they'd payed attention to the lower revs and partial throttle openings.

 

I also checked the fuel regulator they sold me and it registered 43psi just as they told me it would.

 

Alex

[CHRIS CLARK]

...........by the way, if you buy Q.E.D. parts via Alex you'll probably get a good discount (due to the advertising)!!

 

Only Joking!

 

[Alex Wong1697456877]

I've never got a discount off them.....

[Chelspeed]

3 bar is a knadgers under 43.5 psi. Spot on then.

 

I run 50psi on my SBD kit with yellow Peco injectors. To get 250bhp out of standard cream injectors this was pushed to 60 psi on the previous spec. Before this it was back to 50 psi for the standard engine on creams. So just goes to show you need to know the design point for your kit or your fuelling will be all over the place.