I notice that when I have my Aux pump running inline on my system that FP is at 40 at idle.

When unplugging the Aux pump and running only off the in-tank, it drops to 35.

I've had major fuel pump issues in the past - and the one in my tank now is questionable.

It had issues before but because I don't think it was installed properly (Under 1/4 tank it would start to lose pressure) - then I installed a new one and it blew the very next day on the Dyno when messing with my Cartech FMU and running 100PSI at Redline. - so I put the "old" one back in and removed the Cartech completely since I think it's bad anyway

(Cartech wouldn't allow me to adjust no matter what setting I put it on - suspect it is broken....and I'd rather not use it anyway if I can get the Z32 MAF working.)

Under throttle, the Walbro I have now <the one that I don't think was installed correctly originally> doesn't seem to be missing a beat, but I'm not sure if it's flowing properly due to the drop without the Aux Pump. It's also only hitting 50-55PSI at redline while with the Aux Pump plugged in, it hits 59-63.

I do notice backfire when downshifting with the Aux Pump plugged in - so I'm sure I'm rich down low. However, I'm leaning out up top - so I'm worried if unplugging the Aux pump and redlining too much might lean me out to the point of destruction.

What do you guys pull base FP with either the A32 MAF/JWT ECU or Z32 MAF/JWT ECU?

<Without an adjustable FPR adjusting, obviously>

I know a Dyno is the only way to really tell me anything about my specific car - but getting ideas from comparing to others may help.

Thanks!
IanS

 

i have an adjustable FPR, but i set mine at the stock FP (34psi) like JWT recommends for their ECU.

 

I told them, per Mardi's suggestion, to raise the FP to "3 bar" - when they programmed my chip.

I guess maybe I don't understand the implications of that. Does that mean I should be at 40PSI at idle with this ECU or not?

 

1 bar = 15

 

Yes - I am aware of that - 3 bar = 40. Which is what my FP is at now.

What I was asking is if the idle pressure is what Mardi was talking about or if telling JWT "3 bar" means something else.

 

his language has been turbofied. i thought 3 bar would be 45.

 

Good point - it would be 45....I forgot to account for the fact that I suck at math.

I'll call JWT and find out for sure...maybe run some tests at low RPM this weekend and see how it runs at the lower pressure.

I'm not going to got to redline unless I'm 100% sure my engine won't pop..(still haven't gotten the Z32 MAF to work)...so I'll need a Dyno to find out.

 

I have the paxton adj FPR set b/t 33-34psi at idle...

 

Interesting...

Here's the backstory:

When I first installed the SC, I had the stock fuel pump and T-Rex Aux Pump with a Cartech FMU and a "disconnected" Hobbes switch. Car ran fine.

After going to smaller pulley sizes, I went with the Walbro 255LPH Pump. When installing we lost the clip that holds the pump to the strainer and had to use zip-ties to hold it on. The way that worked, the pump sat a little high in the tank and under 1/4 tank of gas, I would start losing FP. If I had the Aux pump plugged in, it wouldn't do this....so I had both the Walbro and Aux Pump running until I could find a new clip.

One day, I finally got a hold of another clip. I also came upon a brand new Walbro so I installed that one (for no other reason than it was newer) at the same time I put the clip in. Car no longer dropped FP without the Aux pump, so I left the Aux unplugged. Drove around all day boosting happily with no issues.

The VERY next day, I went and Dynoed, trying to use the Cartech FMU again to solve some lean issues I had up top. Cartech wasn't working right, and under any adjustment was causing me to hit 110PSI at full boost and be VERY rich up top. Otherwise - Dynoing went fine, but as I drove down the road 1/4 mile away from the shop, I floored it and the car bucked BADLY. I did another run - keeping a close tab on when to let off by feel and watching the gauges. At 5000+ RPM the FP would drop DRASTICALLY. So I plugged the Aux pump back in - ran fine again.

2 week later I replaced the bad pump with my older, but fully functioning one I originally had. Just because the sudden loss in FP freaked me out last time, I kept the Aux plugged in. FP was at 40 I noticed plugged in, and at 34-35 when the Aux was not plugged in. <Thus why I posted this thread>, I never did any hard runs without the Aux because of safety and not wanting that to happen again.

SO tonight I decided since everyone else seems OK at 34PSI, I should be too - and I unplugged the Aux pump. Did a hard run, watching the FP Gauge. sure enough - at 5000RPM, pressure dropped to 20. Pulled over VERY quickly, plugged Aux back in - runs fine now.

Why the hell do I keep blowing Walbros!?!?

 

3bar is 43.5psi last I checked. Stock fuel pressure at idle is 34psi and with the stock 1:1 fpr it will raise to ~43psi at WOT until boost sets in with the stock fuel pump. Both will be higher with a Walbro HP or aux pump running at idle.

Anyways, why do you keep blowing walbros?

"it blew the very next day on the Dyno when messing with my Cartech FMU and running 100PSI at Redline."

You can't run that high of fuel pressure.

 

Granted - I didn't think much of it that day at the Dyno because it was somewhat obvious why it blew.

But I don't think the Walbro should have any problem with 100PSI at all, especially for only 3 runs on a Dyno. That's cr@p.

And why this 2nd one blew when I've never taken it over about 65PSI - that pizzes me off.



I guess I'll ask my question again - short and sweet:

Hey everyone out there with a SC - what is your idle FP?

Thanks,
IanS

 

Maybe you should try hard wiring the fuel pump. Blowing walbro's is not uncommon and many other Nissan guys have found that after hardwiring they stop going through fuel pumps.

 

How does one go about hardwiring it?

 

34psi at idle, Walbro with no problems and an AEM FPR + Cartech FMU

matt

 

Maybe some of my problems are caused by that FP being at 40.

So I just bought a SARD FPR from sx7r.

Even if it doesn't help my cold start issues with the Z32 MAF - it will likely fix the fact that in the upshift from 1st-2nd gear I usually backfire with the 3" exhaust.

So 34PSI is what I want - correct?

Thanks!
IanS

 

Im at 37 PSI at idle.

 

yes 34psi is what you should be looking for at idle.

 

I stopped into my local speed shop today to inquire if they had any used FMU's or SFMU's. No luck but he asked me why I needed the S. I said I'd like to incorporate the AFPR and FMU into one in order to unclutter the engine bay as per Slimer's advice. He was confused as to why I need an AFPR with stock injectors. I told him that many people that run the Walbro's see higher base FP. I told him I wanted to be able to control this. He says hes never seen a Walbro bump the FP. Keep in mind that this is a shop that specializes in Ford stuff; specifically Mustang. But he has tons of experience with SC'ing(This is the place I bought my blower.) He proposed that the base FP is bumping because the return line is too small and causing restriction. So I ask you all, Why does the base FP rise from the Walbro?

 

From what I have been told it is simply because the walbro over powers the stock FPR.

 

sounds like you may have answered your own question! The fuel pressure regulator can't open up anymore than wide open.

The fuel pump will build pressure continuously, it cannot regulate itself (that is what the fpr is for). If the walbro pumps more fuel than is being bled off, pressure will rise until an equllibrium is acheived. Under driving conditions, your injectors bleed off some of the pressure. But at idle, your injectors are only open for a couple milliseconds and therefore don't bleed off any of the pressure. This is why you see an increase of fuel pressure at idle but not under driving conditions.

Now, how do you explain the lower fuel pressure under heavy load? If the maxima fpr is like other nissan regulators (ka24de and sr20det) it is a 1:1 regulator that should be able to compensate for increased manifold pressure (aka boost). BUT under heavy load, the injector pulses are MUCH longer and therefore bleed off more pressure. This makes your pump work harder to keep up. To keep up, the pump simple draws more amperage from the 12 source. Although our beloved nissans engineers made our engines stout enough to handle high hp, they dropped the ball when it came to wiring the fuel pump. The poor fuel pump is only being fed with a tiny 18g wire that runs the length of the chassis. Most of you probably know that long small diameter wires create a lot of resistance. In this case, inhibiting the transfer of amperage from your battery to your fuel pump. Crappy fuel pump wiring has led to the death of many an engine, and even more fuel pumps. Hardwire it through a bosch 12v auto relay with 10-12ga wire and you should see a significant decrese in high load afr's and increase in fuel pressure and fuel pump longevity.

 

Case in point, this is what I've been seeing:

 

Cool, now go hardwire your pump and do another session with the LM-1 so we can put the theory to the test.

 

Good info.

So am I to assume that if I lower my base FP, it will not affect my FP under full boost (i.e.: I'll ahve the same A/F ratio at high RPM and under load in general)

Or am I way off base?

 

It will at WOT because ecus are programmed based on a certain pressure drop across the injectors when calculating duty cycle for the injectors. In your case, JWT assumes a 43 psi injector pressure. That means that at zero manifold pressure your fuel pressure should be at 43 psi, and the fuel pressure should rise at a 1:1 rate with manifold pressure during boosting. That also means that at idle, when manifold vacuum is around -9 psig, your fuel pressure should be set at 34 psi.

If your fuel pressure at idle is 40 psi, then at zero manifold pressure your fuel pressure will be 49 psi, and so on. So your injectors will be seeing higher fuel pressure, fuel flow will be higher and afr will be lower. How much lower depends on how large your injectors are.

 

I'd like to know too.

 

Interesting - because my FP was 43 when I disconnected the vacuum line from it last month, and 40 when connected with 20Hg of vacuum.

So what does that mean?

 

the follwoing should apply to pretty much any car. I don't know the colors for the maxima fuel pump wires though so you will need to find a diagram or check it out with a multimeter...

Disconnect battery

cut 12v wire and ground wire at the fuel pump betwen the pump and chassis harness connector

30 – 10-12ga wire - 30a in-line fuse (within 2 feet of battery) – battery [12 volt power source]
87a – open [not used]
87 – 12v wire (pump side of connector) [12v power to pump]
86 – to chasis [ground]
85 – 12v wire (harness side of connector) [on signal to relay]

Grounding your fuel pump
Cut the ground wire between the pump and connector.
Leave connector side open
Ground pump side to chasis


That is it. Your fuel pump may sound louder/stronger after you do finish (mine did)

 

Hmmm. I was trying to explain that to Ben at JWT yesterday when talking about my ROM tune. He seemed to think it did not matter...or we were not understanding each other.

 

Here is a very detailed write up for hard wiring the fuel pump in a 3000gt/stealth. It is the same principle.

http://www.team3s.com/~egross/3S/Mods/TT/FPRewire/

I can't tell from the haynes or the FSM if we have a resistor set up to lower voltage at idle like the 3000gt has. If you have an adjustable FPR then I don't think it would even matter and if you don't then the walbro will raise the FP anyway.

I know h2kfrosty had a lot of problems with running lean when low on gas with his walbro. The guy who is trying to put his new turbo setup I think is going to try to put a bosch pump in there or something. I told frosty he should just hard wire the Walbro and get a FP gauge.

 

So the question remains.

With 0 vacuum I am at 43PSI
With full vacuum (18-20Hg on my boost gauge) I am at 40PSI.

That's only 3PSI difference, not 9 as suggested above.

Also, I used to notice on cold start that my FP would go up to 43-44 at start, then 30 seconds later drop back down. Is that normal? If it is normal - then it's not doing it anymore - it's always 40 no matter what.

 

Good find on the write up h2kSPIG.

I wouldn't worry about small changes of 3psi at start-up, idle, etc. The big concern is the pressure drop under high load.

 

Actually, my big concern is that the car seems to run way more rich than it should at cold start, backfire when I go into Nuetral and rolling, etc....

Which is why I'm looking into this.

 

Its programmed to run rich on cold start. I don't understand while you're so worried about it. Just let it idle for a minute before you drive. Either way backfiring is not bad for anything except your gas fund.

 

I am fully aware that on cold start a car runs rich....

Backfiring is also bad for your Catalytic Converter.....not to mention annoying, attractive to cops and pisses off neighbors......

But I know my car and I know at cold start it's way too rich. So much so that sometimes the engine floods and the car stalls immediately and barely starts up again. With the Z32 MAF and JWT Program installed the car does not run AT ALL it's so rich on cold start. It runs like the MAF is disconnected - lunges forward, have to feather the gas to keep it running, etc.

This may or may not help that specific problem - and I'm willing to spend the money and try it to see if it helps.

Not to mention if my car doesn't run 100% reliably and perfect it bothers me to no end.

I have to rev the gas to keep it running on especially cold mornings and get severe hesitation at 2000-3000RPM along with nice clouds of black smoke - this is not by any means "normal".

If it's above 60 degrees out and/or the car is warmed up - it still feels too rich at idle, but is at least bearable.

 

..........

 

Don't we have systems like that already? I thought thats what the IACV and coolant pluger/thermoresistor on the TB do.

 

The problem is that the IACV is ecu controlled and it seems that Ian's JWT ecu isn't doing a good job of controlling idle air when cold. I don't remember having any problems with my JWT ecu in that regard, though.

 

Nevermind. Doesn't work with supercharger constant pressure.

 

You shouldn't need both the Walbro and the inline. What you need is a hardwired walbro, and an aFPR set to ~34psi at idle.

With the FPR unplugged it is getting 43psi at idle but the stock FPR can't release enough fuel with a working high flow fuel pump so you need an adjustible one to compensate.

 

Stephen...

But remember these things:
1) A32 MAF + A32 JWT 370cc ECU runs fairly well - just slightly rich when cold and backfires occasionally on downshift - probalby caused by 40PSI FP.
2) Z32 MAF w/JWT Z32 MAF ECU works great at idle - as long as the SC piping isn't plugged into the SC....runs mildly rich when cold. When SC is plugged in, it runs like A**, bogs heavily, black smoke, etc.....
3) Z32 MAF w/Stock ECU and no SC runs beautifully - passed emmissions this way....(again, slightly rich at idle)

I really think the whole Z32 MAF thing is mostly turbulence from the blower - why it doesn't affect you or delio, I have no idea.

This FP thing I've decided won't completely solve my problems with the Z32 MAF, but it may help some....and at least lean out idle with the A32 MAF....which works well enough but is somewhat rich sown low (and lean up top)...

I'm betting not enough to "fix" my issue however.

SO what I'm saying is:
I don't think this FPR will fix any issues I have with the Z32 MAF whatsoever, but it may help some with richness I already have with the A32 MAF down low.

I still need to find a solution to the Z32 MAF, and after everything I've tested - I'm sure I'm going to have to go to the non-charged side to make it work.

Non-charged side piping will be created when I get the time.