Did my dyno pulls last night, not gonna say my numbers until I know what the problem is (gain of 36hp and 107tq )The dyno graph from 3000 to about 3500 was smooth but after that the graph gets squiggly, The tuner said it might be the main line not being enough or my noid may have some issue (clogging, not big enough), but another friend said he has seen the line squiggly thing when a NOS FPSS is not working right. My A/F was perfect and I have a 255 walbro pump so fuel shoudn't be an issue. I hit it twice on the way home and didn't feel any surging, just a moderate more pull (was expecting more of a hit feeling with a 150 shot) I'd like to see a graph of a bad FPSS. Also like to know your thoughts on what else may cause a 150 shot to turn in a 36 shot?!?!?!

 

Mine did the exact same thing - bypassed the FPSS and no more surge. I tried adjusting it way down, but still wouldn't work - I don't use one now. I've heard plenty of others say they are flaky as well. I figure with the Racetronix 255 I am fine on fuel for any shot I'll be spraying.

 

I also had that problem. It made my A/F ratio look all crazy because it kept bumping the system on and off. No matter how I adjusted it, it wouldn't work right. I threw it in the trash. I run a fuel pressure gauge so I just keep an eye on it myself.

 

I'm new, can someone explain what an FPSS is?

 

It's a fuel pressure saftey switch. If your fuel pressure drops below the set level (usually 45psi or so) it will shut the system down. It our cases it was bumping the system on and off for some reason.

 

Fuel Pressure Safety Switch - it is supposed to cut the system off if the fuel pressure drops below the setpoint.

 

thanks GM Muscle!

I have a post with some questions about nitrous below this post. could you answer there? should I consider a FPSS? have any info on it, like where to buy and price?

 

Well thats what is so strange, my A/F according the tuner was perfect, I watched the dyno run and during the run it was running in the low 11-12 area, once it did hit a high 10 but on my dyno sheet the A/F doesnt look like its going crazy.

 

here's RavenousT/A's graph:

 

Your air fuel may have been ok but the fuel pressure safety switch may need tobe adjusted.The easest way to tell is to by pass it.Since your air fuel is safe it should be ok to do so.

Alot of people mis understand how to adjust these units and feel that they are "junk"
Almost every set up we install has one.
They work fine.
Dave

 

Darren make sure you dont have the 150 jets in when u unplug that FPS switch. i don't think those 295' Eagle F1's will hold 550rwhp

 

Well I have to get a bottle refill, damn purge happy fingers. Sean didn't think the FPSS was the problem, wouldn't my A/F jump up and down if the FPSS was kicking on and off? What would it look like if the line was clogged?

 

Mine didn't - mine stayed pretty flat. It is shutting off both the fuel and nitrous solenoids, so it shouldn't really jump too much - there isn't really time for it to go to the N/A AFR and back to the nitrous AFR. Just hook both wires together for one pull and see if it doesn't cure the surge.

Dave,
I tried every which way to adjust my NX FPSS and couldn't get the surge to go away - even when it was set at 35# and my memory on my fuel pressure gage says I never go below 64# - any tips for me?