I've been tuning now for about 2 months, using numerous bypass jets (from .038-.120). I can't seem to stabalize my fuel pressure.

What I'm seeing is that when my nitrous kicks on, my Fuel Pressure shots way up (for about 2 seconds), and then backs off about 20psi, and then stays stable (for the remainder of the run). So you can see my delima...

while I'm spraying I have about 20psi of variability. So, I'm either way lean or way rich on 1 end of the curve.

Why would the system kick on and run such a high psi at first and then back off that much.

Is that normal? Any advice or similar experiences?

(FYI: I'm running a ZEX kit w/ a 44 nitrous jet, a walbro 255lph hp pump, and a SARD adjustable fpr. My n/a a/f curve is near flat at 13.1, with no fuel pressure spikes and drops)

 

how's your bottle pressure? make sure you've got enough nitrous in there to begin with. also, if you don't have a bottle heater you might want to invest in one to keep bottle pressure consistent. how much the fuel pressure is bumped up is controlled via the bypass jet, but bottle pressure affects the amount of nitrous going through that bypass jet.

 

It also sounds like you may have a vacuum leak as well. Have you zip-tied/clamped all the vacuum lines in the system? Even one missed vacuum line can cause the fuel pressure to be sparatic somewhat like that. I had forgotten to zip-tie one of the vacuum lines going to my T-fitting and my fuel pressure would shoot to 85 psi, then it would drop to 60 psi and stay there for the remainder of the run. Once I zip-tied that line, all was well.....

 

[QUOTE]Originally posted by sx7r
bottle pressure affects the amount of nitrous going through that bypass jet. [QUOTE]

Yea, I originally had this problem too. But, I now have a heater, and I was at 1000psi for each run.


[QUOTE] Originally posted by Ramius
It also sounds like you may have a vacuum leak as well. [QUOTE]

I wondered if i might be leaking. I didn't know zip ties were suggested. I'll zip all my pressure lines and see where it gets me.

Thanks.

 

Checked my lines and all are clamped at the connections; but I'm going to replace all the hoses (since it's so cheap and easy) and reclamp them, just in case there is a leak somewhere.

If that doesn't work... any other suggestions? Anyone?

 

It's ok for the pressure to spike for a second, then drop and stay steady. What's your final reading? It should be no less than 60-65 psi. on the juice. If it stays there, then you have plenty of pressure. I have a dry kit in my Stang, and it spikes to 90 psi, and level's off at 75-80 psi. I'm running a 150 shot tho'.

 

Well on the Max. we should run around 90psi for a 100 shot (according to other members). Which poses a problem, if I spike 20psi higher.

Because to run 90psi stable, I have to spike around 110, which I have found locks up my injectors (causing me to go lean-real lean) until my psi drops down and evens out.

So, I'm wondering if this is how everyones max is, and how the other 100 shot guys get around it.

Has anyone even watched their FP gauge (on the max) and noticed what it does when they shoot?

 

For a 100 shot, 90 psi is a little too much. You should be running about 80-85 psi to get the optimum performance out of your car, also so your plugs don't foul up early. Have you checked all your vacuum lines????? Spikes are NOT normal and should not happen with any nitrous kit......

 

Dude, call NOS tech support, and get the answers you need. That is the only way you will find out for sure, 90psi is way to much for a 100 shot, 65-70 is plenty.

 

He has a ZEX kit. I am going to agree with Ramius, probably some kind of vaccum leak is causing your spikes. Maybe a cloged fuel filter could cause it as well. More likely a bad vaccum hose/connection/leak.

 

One thing you may want to consider is that the computer turns off the stock fuel pump when it is getting rich readings (when booster kicks in). Therefore you get a hill like effect on a a/f graph...at least that is what mine does and i have a 125 shot, walboro 255, and a regulator. When it hits my pressure goes up to around 90..

 

Yeah, a clog in the fuel system will definately cause a spike like you're talking about. Change your fuel filter for starters.

 

Hmmm the only thing I dont have clamped or ziptied is the vac line that connects where the once from the fpr went too.......not sure if i can get my hands in that area to put one on. I pushed the hose about 1 1/2 back onto it tho. I'll spray when it gets warm.....or the roads clear to find out if i have the same prob. Im running the Zex as well.

 

Just put the new fuel system in about 2 months ago, and the filter was cleaned at that point. I'm sure it couldn't be that. But, when I have my next oil change, I'll tell them to open up the tank and check it.

 

So, what do you do to overcome it. You can't run it like that, do you?

How do you keep a stable A/F?

I was hitting a/f readings well into the 20:1 region when I spike-that ain't healthy.

 

I called Zex and they want the kit back to look at it. I'm going to send it, once I exhaust all these other options.

And i'm not trying to nitpick but I do believe on the 2k and 2k1, 70psi is not enough to run a 100 shot (w/ a bottle heater). Even at 80psi I am still running an a/f well in the 13's. I believe mid-upper 12's is suggested-to have a safety margin.

 

Yes, 12.1-1 is ideal, but what I'm saying is it shouldn't take 80-90 psi to get you at 12-1. Something else is wrong.

 

Mine flows from about 11.8 to 12.5, maybe spiking at around 12.8 to 1 (i don't have the chart in front of me however to say for sure)