2MCHPWR

iTrader: (10)

i had the car tuned a few months back, but there was a 1400 RPM stutter. i finally went back to tuner today to fix the stutter (which they did by adding fuel) but we also found fuel pressure dropping:



compared to last time it was dyno'd, it gained a like 10 hp and 10 tq:
http://207.127.219.37/images/rx7/rxdyno.jpg
the fuel system is from HINSON:

what i think is weird is the FPR is right in front of the tank; i would think it should be near the rails up front.
my tuner (cartek) wants to run AN8 going up fuel rail, using the existing #6 as a return, putting the FPR up front near rails, and using a booster pump or external pump.

a/f ratio was up to 13.8 on the dyno. this was only at 22.5 degrees timing. i want it closer to 27 but that will have to wait until i fix the pressure issue.

i wonder if they always nose off like that when they are set up near the tank...a friend mentioned to me that speed inc did some experimenting with adjustable FPR's near the tank for an easy swap on LS1's... didn't work.

Inspector12

iTrader: (29)

Well I have made well over that with the stock lines and rails. I do have presure drop, but we/MTI tuned around it. I am running a walbro 255 and a MSD BAP stock FPR.

slowpoke96z28

iTrader: (2)

what does the pressure drop to? i'be noticed as low as 52.5 psig @ WOT from 57.5~58 psig @ idle. i get a little detonation in the upper RPMs, too.

2MCHPWR

iTrader: (10)

48 . see graph above

jimmyblue

iTrader: (11)

The thing with a rail mounted regulator is, you
-know- what the pressure is. It stays pretty
constant regardless of pump head pressure or
injector demand (as long as you set it below
pump delivered pressure at max flow). With it
regulated at the back end of the car, you have
a flow*plumbing_resistance pressure drop that
the IFR table fails to model, you have to fake it
with inappropriate things like PE table tweaks
and so on.

I would like to eventually put on a rail mounted,
return regulator. Waiting for them to start showing
up used

slowpoke96z28

iTrader: (2)

sorry. i'm used to that being a/f ratio. do you run into any detonation?

2MCHPWR

iTrader: (10)

i just hooked up voltmeter right before pump; its reading 10.9 at 6000RPM and about 11.3 to 11.5 during normal cruising at 2000RPM.

Ojustracing

iTrader: (4)

Scott that doesn't sound right. That two low. Is the fuel filter New? Also in that info we were talking about the other day, they listed a Fuel Pump Balist resistor. Is that still working or been played with. Later John

2MCHPWR

iTrader: (10)

thanks, yeah its not good. that ballist resistor is bypassed (stock is puts 9v at idle, 12+ under load). so its the wiring. i'm gonna hardwire it from the battery using a relay to turn it on; its a common issue with the rx7's. Many of those guys have to rewire the pump.

Frost

iTrader: (45)

You get this voltage drop at the pump from not having 'enough' hot wire. The resistance of the wire becomes an issue at higher current levels, and to supply the current demand there is a voltage drop that will increase proportional to the increase in current consumption. (current) I = V(voltage) / R (resistance of yer wire) . You are right to use a relay and a heavier supply wire.

Here's a chart that shows the relationship of current, voltage, resistance, and power. Since we are dealing with DC it makes things nice and neat. :

2MCHPWR

iTrader: (10)

i just cutoff the connector and soldered the wires directly to each other (just bypassed the connector) and normal cruising was 11.9 to 12.2 which is better than above. i can't do 6000 reading because its raining and there ain't no traction. so at least i made an improvement. i ordered fuel pressure gauge and that will be real test.

Ojustracing

iTrader: (4)

Yeah it should be fairly simple to wire a hot lead form the alt/batt with a relay just like the racetronics kit. You need any info drop me a note. Later John

Frost

iTrader: (45)

That's a considerable loss through a connector, perhaps they were dirty or weak at the bend points where they go into the connector...

2MCHPWR

iTrader: (10)

thanks guys. i did WOT 6000 RPM reading and it dropped to 11.5 (improvement from 10.9 before i bypassed the connector). i'll run wire directly from battery tonight (fuse and relay) to pump directly which i'm sure will work nicely (battery making 12 to 12.1 off and 14.7 running). then i'll re-check fuel pressure.

2MCHPWR

iTrader: (10)

I rewired the fuel pump like I described.
after starting it cold, it was 14.4 volts at the pump. after car warmed up, it was steady 14.2. at WOT 6000 RPM, it went to 14.1 :yup: tomorrow night i'll hook up the fuel pressure gauge to verify its no longer dropping...

2MCHPWR

iTrader: (10)

Cartek retuned me now that i fixed the low voltage issue with the fuel pump. Fuel pressure was perfect at 56psi. HP is now at 398 (up from 386 last session) and 410 TQ (up from 397). Julio was great and spent a lot of time looking for the best settings and explained everything as he was doing it.

best pull:


comparison from last session:


this damn ricer should move with that power especially since it weighs 2730 with no driver.

Race Car Driver

My pressure starts at 56 and drops to 50 at WOT. Which fuel pressure regulator is most people using and where are they mounting it? Aeromotive, rail mounted?

2MCHPWR

iTrader: (10)

yeah aeromotive on rail would be good place for it. you'll have to run a return line though.