Fuel Pump Resistor

[BlitzBoy]

The 044 pump is capable of delivering >200l/h so I am quite surprised that there is a need to run two pumps.

Its been show on many Rx7s on many dynos around the world as soon as you get near 550bhp + fly and beyond a single stock 044 just cant supply enough fuel to the injectors when on high boost and fuel pressure falls away.

The original Reworx rx7 stripey ran a modified 044 pump to get to 650 bhp, I was going to go this route of the modfied version when I hit the fuel flow problem myself but the cost of the modified 044 was more then two stock 044s put together.

So I have went two stock 044s instead running one per fuel rail on braided fuel lines forgot the size but bigger then stock anways.

There are quite a few high horsepower rx7s running twin pumps in this country at the moment.

I suppose your surprise is due that your car has to run to a certain hp in your class you are competing so is not near these HP levels maybe and will not encounter this problem I suppose.

[Prof]

Also found this, which was what I was eluding to in the earlier post:
 
http://www.rx7club.com/showthread.php?t=626724
 
Basically the stock FPR can\'t flow that well and struggles with the flow rate of the pump running at full 12V - hence the series resistor.

[bnaellis]

You measure voltage at the fuel pump with voltage going via the resistor. you will see a max of 9v, bypass the resistor and you will see a max of 12v.
I don\'t have a stock fuel pressure regulator so whatever the limitation of a stock one is doesn\'t affect my setup. But what I am perfectly sure of is the electrical setup of an fd\'s fuel pump circuitry.
On a stock fd pump they will fail sooner rather than later running constant 12volts, plus it does heat up the fuel more than necessary at idle and low load if it was to see 12 volts at all times, hence the reason why Mazda as do many other car manufacturers have fuel pump resistors.
My concern with my setup is not that I will burn out the 044 pumps, but that the 044\'s are best run with atleast 45 psi and I did not want to be running too rich at idle & low load, it would be preferred if during idle and low load I could run less voltage to the pumps, as the apexi pfc does not have the same granularity as Blitzboys motec for trimming fuel etc.
The second reason was I did not want my fuel to be preheated by two intank 044\'s running at 12 volts at all times.


rgds

Brian

[bnaellis]

Also found this, which was what I was eluding to in the earlier post:
 
http://www.rx7club.com/showthread.php?t=626724
 
Basically the stock FPR can\'t flow that well and struggles with the flow rate of the pump running at full 12V - hence the series resistor.

I think you misread the thread. a stock fpr my struggle with an uprated fuel pump and cause excessive fuel line pressure at low load and idle. But that\'s nothing to do with runninga  resistor.


rgds

Brian

[bnaellis]

I\'m with Sparticus on this one. Ive not seen so far in any race application anyone regulating the voltage of the fuel pump. They are designed, and manufactured to be used at 12v and so should be run accordingly.
 
I am all for pushing the envelop but usually the race fraternity is a good indication about what works and what doesn\'t.  This is something that is evidential with Brakes...you never see a GT car with a 16 pot calliper, most are running 4, 6 and starting to run 8\'s.
 
As above, the fuel pump is meant to deliver the fuel, any regulating of pressure should be done via the FPR.
 
With regards to running two pumps...what size fuel lines do people run?
 
The 044 pump is capable of delivering >200l/h so I am quite surprised that there is a need to run two pumps.

My car won\'t be used for race only hence the requirement to to have variable voltage as a stock fd would.
I have not made up my mind yet on fuel line size but I am thinking 2 x -8 lines from pump to a y connector with single -8 onwards, and -6 back to fuel tank.


rgds

Brian

[Spartacus]

Still learning here but I would have thought that the ecu would be able to control the fuel flow via the injectors at idle and slow running via its map? Then with an aftermarket fpr bleed off any access pressure back to the tank.

Also just a thought but for those who are running high flow pumps or twin pumps how about using 2 of the 3 FD\'s hard lines for increased capacity and some Y connectors and do away with the emissions line?

[BlitzBoy]

Also just a thought but for those who are running high flow pumps or twin pumps how about using 2 of the 3 FD\'s hard lines for increased capacity and some Y connectors and do away with the emissions line?

In my original config we did use this idea of using the the 2 hardlines to feed the primary and secondary rail individually (no Y connectors) and using the emissions line as the return, but decided to get rid of this in favor of bigger bore braided lines.

[Prof]

One thing to note then.  If you are going ahead with retaining the resistor, it will be the wrong value, as you have 2 pumps instead of the one, and they are also different and draw different current to the stock FD / FC ones.  This means the resistor value needs to be changed so that the same voltage conditions / fuel flow exist with the twin pump arrangement.
 
Having said that, why not switch one of the pumps off using a relay in parallel with the resistor relay, as you don\'t need 2 fuel pumps on at idle / low load crusing ? :driving

[Spartacus]

One thing to note then.  If you are going ahead with retaining the resistor, it will be the wrong value, as you have 2 pumps instead of the one, and they are also different and draw different current to the stock FD / FC ones.  This means the resistor value needs to be changed so that the same voltage conditions / fuel flow exist with the twin pump arrangement.
 
Having said that, why not switch one of the pumps off using a relay in parallel with the resistor relay, as you don\'t need 2 fuel pumps on at idle / low load crusing ? :driving

Or 2 stock resistors?

[antnicuk]

having resisters in the wiring is just something else to wrong Brian.  Not worth IMO,  play with the pressures, injectors and tuning to get it right, it can be done.

[Spartacus]

What he said:yes

[bnaellis]

Fair point guy\'s about something else to go wrong but then on the other hand if the resistor did go wrong that would (i think) only mean the pumps would always see full voltage rather than see no voltage which could mean bye bye engine. If I had a better ecu it would make life easier but I can\'t be bothered now, just want to get the car back up and running after so longa time.


rgds

Brian

[chris]

`Hi Brian,
I am running an additional 044 with an additional fd resistor, to help reduce airating the fuel and unnecassary heating as you said.
I am running a stock in tank pump, feeding a swirl pot with an 044.
I used a pair of new 40A 12volt relays topower the new 044, both relays wired in parallel, the first wired with the resistor in series which is switched on from the oem fuel pump relay, the second switched by the power fc using the same speed signal used in the oem system,it also helps quieten down the pump while cruising. I agree peoples comments about one more thing to go wrong though.