NOS 5175 running lean

[malice10985]

I used a nos 5175 this weekend with a narrow band A/F ratio gauge. The gauge showed me a dangerously lean condintion throughout the entire quarter mile. Fuel pressure gauge showed a constant 74#'s of pressure. anyone got any cheap solutions? I am a little too poor to be buying new injectiors or fuel pump. [img]graemlins/omg.gif[/img]

[runmy6]

I heard that stock O2 sensors connected to A/F gauges never give a truely accurate reading. I think the only way to get a true A/F ratio reading is by a wideband O2 sensor, so maybe you are not as lean as the gauge said you were, but that all depends on how big of a shot you ran too.

[John_D.]

What size shot?

Are you spraying before the maf sensor?

74psi is a lot. Should be plenty for an 85 shot.

Is your car running rich at idle or part-throttle? That could throw the ltrims off enough to make the pcm try to take fuel away at wot.

[malice10985]

I spray 2 inches before the MAF sensor. I don't increase the fuel pressure until the pre-stage lights come on, so I don't think the computer has enough time to lean it at idle.

[malice10985]

It's an 85 shot too.

[John_D.]

I couldn't get mine tuned at all when I was spraying close to the maf sensor. After I backed it up into the lid, it worked much better.

Also, 74psi could be too much pressure. At some point the injector operation becomes erratic with too much fuel pressure. On the kenne-bell site they say mustang injectors go off above 60psi (I think that's the number anyway, just going by memory). If you could bring it back down to the 65psi range, that would probably be safer. Mine runs ok on 60-65psi.

You may be ok on the timing of when you bump the presure. I played with my bap setting while sitting in staging though, and saw my ltrims were changing in the autotap log when I did that... If you could tie the fuel pressure bump, to the activation of the nitrous, that would be the ideal solution.

[malice10985]

I will try moving the jet into my airlid, but I am not too sure how to decrease the fuel pressure. RIght now I have the fuel press. reg. hooked directly too the blue thingy on the n20 solenoids. Should I have a vac line running to the intake manifold as well? I don't have that right now.

[John_D.]

<blockquote>quote:</font><hr>Originally posted by malice10985:
I am not too sure how to decrease the fuel pressure. RIght now I have the fuel press. reg. hooked directly too the blue thingy on the n20 solenoids. Should I have a vac line running to the intake manifold as well? I don't have that right now.<hr></blockquote>

That would be the problem.

You need to have that other tee, with the bypass jet in it, bleeding off some of the pressure from that vacuum line. That's also what lets the pressure off your fuel pressure regulator when you're done spraying and both the solenoids close up again. Otherwise it's a sealed system and that pressure is going to stay on the fpr vacuum port until it slowly drains off overnight...

Also the vacuum line is normally supposed to supply vacuum at idle, to reduce the fuel pressure some. The vacuum tapers off as you give it more gas, to kick the fuel pressure up some. (that's from factory, before the nitrous came into the equation). That's the way the pcm expects the fuel delivery to be working anyway... That could throw your ltrims off too, which would affect wot operation somewhat.

[ June 02, 2003: Message edited by: John_D. ]</p>

[malice10985]

I guess that is my problem. When I finish using the n2o, I pop the hood, disconnect the vac line to the fuel press. reg., and suck on it to get the fuel press back down. I will put in the Tee and see how it does. I didn't put one in when I first installed the kit because I thought it would not send enough pressure to the fuel press. reg.

[John_D.]

<blockquote>quote:</font><hr>Originally posted by malice10985:
I will put in the Tee and see how it does. I didn't put one in when I first installed the kit because I thought it would not send enough pressure to the fuel press. reg.<hr></blockquote>

That should be ok. Just make sure you have a bypass jet to go in it, and it should be fine.

Oh yeah, and I would still move the nitrous nozzle to the lid too. I saw a big difference with mine.

[ June 03, 2003: Message edited by: John_D. ]</p>

[12secondv6]

Dry kits should have their nozzles mounted as far away as possible from the maf

74 psi..... seems a bit high.... but better to have more psi, than not enough


You mentioned you increase the fuel psi when the pre stage lights come on.... how?

[malice10985]

I gave each solenoid a separate switch. I open the bottle in the staging lane, then toggle the first switch at the prestage lights which opens the first solenoid and ups the pressure. The second button is on the shifter, so I hit that to start spraying when I am ready.