Mad-MAX_SE

iTrader: (2)

So I installed my Synapse FPR/FMU and the car idles and even drives fine, but its not working like i would have thought so i have a couple questions.

When my roommate had his nitrous the fuel pressure gauge would climb from about 33-34 psi to 40-42 at WOT (non-nitrous). On my car at idle, I adjusted it to about 35 psi at idle. The issue I'm having is that when I rev the car in nuetral, the gauge will go up 1-2psi but when the car is under load, the fuel pressure drops 4-5psi then starts going back up. My first thought is that I might have a vacuum leak somewhere cause the idle fuel pressure as of this morning was at 40 psi then drops down to 34ish under load then back up to about 40 at WOT. It seems to make sense that would be the case as this regulator is really really responsive versus the stock one (it's a non-diaphragm / piston FPR).

My first question is should i set the FPR to 42 with the vacuum off the nipple and go from there? That is to say check and see if I have a vacuum leak in a very rudimentary way? My wideband doesn't come in for a few more days but I don't think the car is running lean at all (if anything it might still be a bit rich), but should I just cruise around at low rpm/throttle to keep the computer in closed loop?

Thanks for the help!

Mad-MAX_SE

iTrader: (2)

anyone have any ideas?

I changed the bypass fitting and was able to have more room for adjustment in the main screw. The pressure still drops, though, under load.

streetzlegend

iTrader: (8)

Well, your supposed to have mid/high 30's psi with vacuum off, with vacuum on it should be around 42-46psi'ish, more or less. So yea what I would do is disconnect the vac, and set it to low 40's, once you hook it back up it shoudnt drop more than low 30's.

Do you have your o2's hooked up an working properly. if yes then I dont see a problem driving around and keeping rpm's below 3k. (since the ecu will be compensating and trying to keep a/f at 14.7 unless you have huge injectors or pressure is WAY off)

question: what exactly do you mean it drops when in load? you referring to WOT? Remember that when driving around sometimes you go into situations where there is more vacuum than idle (when engine breaking, or cruising sometimes) in those cases you might see less pressure.

t6378tp

iTrader: (69)

With the vac off the afpr set it to 43psi then when you connect it, it should read around 35psi if you do not have a vac leak and the vac is around 21-22 with the car in netrual. Streetz had it in reverse, as the vac from the engine sucks on the diaphram this is what lowers fuel psi. As the vac goes away fuel psi goes up till it goes into boost than it will raise at a rate or 1-1

As for vac it should be around 22 and like street say on de-acel and cruisin it will go up around 26-30

Hope this helps

streetzlegend

iTrader: (8)

crap my bad! I knew what I was writing but my hands wanted to type in reverse, a little slip there lol. Yeah more vacuum = less pressure(leaner)

Mad-MAX_SE

iTrader: (2)

My boost gauge came in today, and the readings t6378tp gave are pretty spot on, but I'm still having the pressure drop. Might be a sign of my fuel pump going bad. I mean the thing is almost 15 years old, so it's probably getting pretty tired at this point. I have a Walbro 255 I'm going to be installing sometime next week so that should really let me know if I do in fact have a problem with the FPR/FMU.

Just to give you guys an idea of how big this FPR/FMU combo is, here's a couple pictures:



The other nipple on the FPR is for the FMU functions (it only gets a boost signal - check valve on line to it) to give it a rising rate of 2:1-12:1 depending on what you dial in to the little knurled **** beside it. Pretty nice compact setup

Also just installed a universal dash pod to the steering column. It's going to have the boost gauge and my Wideband when it comes in next week; the fuel pressure will go on the pillar with my tranny temp gauge once I get my cooler installed:

t6378tp

iTrader: (69)

nice setup how much for the fmu/afpr, small one unit, please tell me it rebuildable

also the stock pump is only good for around 225-250hp so my guess is you maxed it out

Mad-MAX_SE

iTrader: (2)

The regulator was $140 shipped off eBay. Normally they run $200 + shipping, but I got lucky. The regulator is rebuild-able, but since it uses a piston versus a diaphragm, the service intervals are much fewer and farther between. The booklet that came with the FPR even says the unit should be completely maintenance free; only requiring periodic re-lubrication of seals and o-rings.

As far as the stock fuel pump, Unless I gave it a stroke a couple years ago playing with laughing gas and race gas, my car has never made that much continual horsepower.... Yet... I think age is playing a big role and the new fuel 300z fuel filter. It's like an old man who's used the same walker (representing fuel pressure) every day for 15years without ever hitting the wheels with WD-40, then suddenly putting in brand new wheels and bearings onto the walker and taking off the skids and replacing them with wheels. Now expecting him to be able to keep the walker under him is nigh impossible...

t6378tp

iTrader: (69)

Or better yet a fat old man with asthema fuking young freak chick with a.d.d

He only got a few minutes before he's out of breath

streetzlegend

iTrader: (8)

Something to think about, some of our cars have a "drop resistor" for the fuel pump, basically varies voltage depending on certain conditions, I bypassed this and hardwired my pump. Before that it didnt let me get higher pressure since it wasnt putting out actual 12v, was less.

Mad-MAX_SE

iTrader: (2)

Haha I like your analogy a bit more Tp

Streetz, how did you go about the wiring for that, and where is the resistor at?

streetzlegend

iTrader: (8)

Its in the trunk, facing the trunk on your left hand, remove the plastic covers and it should be there. What I did was run my own ground wire to the pump and cut the one coming from that resistor/device.

Mad-MAX_SE

iTrader: (2)

In the trunk near what exactly?

streetzlegend

iTrader: (8)

On the left side, you know where the antenna motor is located on the right side of the trunk? well same thing but on the left side(driver).

Mad-MAX_SE

iTrader: (2)

Well, my car apparently doesn't have a drop resistor for the fuel pump (atleast not at that location). According to the '95 FSM, that was only on the Cali cars, and mine is fed spec... I think I'm just going to hard-wire in the pump and use the stock wiring to run a relay if need be. Just going to wait and see what the A/F looks like when the blower goes in.

Installed my wideband today, and even with the pressure dropping at the higher RPM's, the A/F is still fine (13.3-13.6; highest was 13.9 at the top of second).

streetzlegend

iTrader: (8)

Ya some max's didnt have the resistor. Mine did, you should still def hardwire the pump. I used the power from the stock harness to trigger a relay and ran a 12v from the battery.