Sandro

iTrader: (1)

I am installing an aux battery in the rear.

I was thinking sending additional power to the fuel pump from it - through a relay activated by the existing power wire to the pump.

Potential problem I see with this configuration is that it would bypass the resistor. Full 13 V would then be applied all the time.

Could that indeed be a problem?

Thanks.

- Sandro

arghx

iTrader: (3)

cut the resistor out in the first place, and forget the extra battery. you've got an aftermarket ECU anyway right? removing the resistor relay if you have a PFC or something like that is not going to affect your gas mileage. The tuning is what matters for that. Use a separate relay triggered by the stock pump wire to get straight voltage from the battery through heavier gauge wire.

Railgun

Sounds like you said the same thing the OP did.

Yes...this is the same thing I did. I have original power wire feeding a relay. Pretty simple work around.

gracer7-rx7

iTrader: (16)

stock FD fuel pump?

If so, I'd probably check the FSM to verify if there is an acceptable voltage level specified and you aren't giving it too much current.

Dale Clark and Chuck Westbrook both have write ups for doing this if you didn't know already.

arghx

iTrader: (3)

you're not going to give a fuel pump "too much" voltage. The highest it will receive is battery voltage. Devices such as the Kenne Belle Boost-a-Pump ramps voltage to like 16+ which in theory may reduce pump life or cause some heat issues, but that's not on issue if you are at battery voltage.

The resistor relay is to help gas mileage and driveability on a completely stock car. It's a feature that has since been rendered useless on modern returnless fuel systems like on the Rx-8, which have a duty-cycle controlled fuel pump instead of a mechanical FPR connected to a return line. If you have an aftermarket ECU any potential side effects from removing the resistor relay can be essentially bypassed through tuning, which needs to be done on an aftermarket ECU anyway.

Sandro

iTrader: (1)

Thank you all for your replies.

I remember reading Dale's notes in the past but his server must be down right now and I wasn't able to access it and refresh my memory. But I read Chuck's notes and he actually mentioned that "some racers...place the battery in the trunk..with a relay..and use original power wire to trigger new relay"

I asked because i wondered if there might have been other any other hindered problems like at the pressure regualator or other components.

But I guess no based upon arghx and Railgun. I gathered, if any, fuel flow could be cut back with the PFC. I guess the only reason for the resistor is to avoid excessive fuel pump duty while cruising. Not my case because my car is a dedicated autoxer.

I am still newby on this matters. Car has been substantially in its stock form until today. I am going to install the PFC in a few days but still have the stock pump, that's why I was looking at this first. I am planning on staging up mods and will monitor injectors duty cycle and AFR monitor carefully.

FSM does not specify - or at least I couldn't find - voltage limits but I don't think there are any (obviously within the battery voltage). Section TD-5 only mentions hydraulic data.

Thank you again for the useful information.

- Sandro

arghx

iTrader: (3)

^ I have my battery in the trunk triggering my fuel pump as I described, with no resistor relay but an extra relay that I wired in, engine management is PFC. But it's not an extra battery, it's just an Optima red top relocated. There's no need for an extra battery unless you are running crazy audio.

Sandro

iTrader: (1)

Yes I hear you. I have been using a PC680 in the stock location under the hood for years. Which is OK but some times only marginally. I am now planning on installing a WI pump in the rear (and maybe water/ice IC with a reservoir/pump also in the rear - questionable yet if legal in SP) and I will likely need a larger fuel pump too if I step up the boost. As I was looking at the options, I considered a full relocation but then I though of a second PC680 in the rear. I realize it may not be the smartest choice. My perceived benefits are that I will still have a power supply close to the starter and will be easier to place a PC680 in the rear rather than a larger unit.

- Sandro

grimple1

iTrader: (1)

if you got chuck's notes he's got a good fuel pump rewire setup. includes double negatives and constant power sources.

gracer7-rx7

iTrader: (16)

Sandro,

Rich (Goodfella) had an old thread entitled "fuel system ramblings" or some such title that had a lot of good info in it. Might want to search for it.

Personally, I'd sooner do a larger single battery in the bins or trunk rather than have two. The distance between the bin or trunk mounted batter over a 2 gauge or 0 gauge cable has no effect on the starter's ability to do its job. I also had a PC680 battery and the car starts much better with the full sized Optima red top in the passenger side bin than it ever did with the PC680. FWIW, both my Mini and my old e36 BMW had trunk mounted batteries with 2 gauge wiring to the starter. I think moconnor had an excellent write up on battery relocation.

FD3S2005

iTrader: (11)

I want to do my pump but to scared if I mess anything up. I need lots of pics if I were to do it my myself. Anyone want to contribute?

Sandro

iTrader: (1)

Thanks Grimple. Yes, I read Chuck's notes. What I am planning doing is more straightforward and direct, as Railgun said: "Pretty simple work around" But I will give up part feeding the pump through the resistor when cruising.

- Sandro

Sandro

iTrader: (1)

Thanks for the tip. I will certainly look into Rich's thread.

As for the single battery in the rear, I don't disagree of course. There must be good reasons why everyone does it and I admit my "short distance to the starter" argument is quite weak. Still, it's much easier placing and securing an extra PC680 rather than an Optima, which would require hatching the storage bin and drilling the floor to properly secure it.

- Sandro

gracer7-rx7

iTrader: (16)

That is true. It is a good thing I did that on mine though. That is the only way to pass NASA HPDE tech - with it secured to the floor from 4 sides and terminals covered.

Good luck! Give Scott a run for his money!

Sandro

iTrader: (1)

I completed this project and wanted to share feedback.

I cut the power wire to the fuel pump and connected the two ends to the common poles of a DPDT switch. I looped the two poles of the first throw (so, in this position the fuel pump is powered through the OE wiring, including the resistor). I connected one of the second pair of poles (second throw) to the trigger of a new pump relay powered directly from the battery, and the second pole to the relay "output" power wire.

I disconnected the air pump, and at idle switched positions back and forth between the two throws and watched the AFR monitor for changes. On average, AFR was 0.3 richer with the direct wiring, like 12.0 instead of 12.3. I don't drive the car on the street and could not make comparison under load. But I will try to make similar back to back logging and comparison at my next autox event.

- Sandro