Surging
Thread Starter
Teching In
Joined: Feb 2004
Posts: 18
Likes: 0
From: South, South Texas
Surging Ok guys, got a question for you nitrous guru's. I have a 99 a4 ls1 NX wet kit. I currently have a 100 shot and it seems to make the car surge after 100mph. My pressure was about 950. The only thing I can think of is that I'm using a 52 jet for the nitrous and a 31 jet for the fuel instead of the 28 jet like it says on the NX chart. I did call NX and they said that using the 31 jet was acceptable. Hope I make sense. Any input?
Mods are LT'S, oryp, lid, NX 100 Shot.
Mods are LT'S, oryp, lid, NX 100 Shot.
Staging Lane
Joined: Jan 2004
Posts: 70
Likes: 0
From: Mckinney, Tx
Originally Posted by Sigma
Ok guys, got a question for you nitrous guru's. I have a 99 a4 ls1 NX wet kit. I currently have a 100 shot and it seems to make the car surge after 100mph. My pressure was about 950. The only thing I can think of is that I'm using a 52 jet for the nitrous and a 31 jet for the fuel instead of the 28 jet like it says on the NX chart. I did call NX and they said that using the 31 jet was acceptable. Hope I make sense. Any input?
Mods are LT'S, oryp, lid, NX 100 Shot.
Mods are LT'S, oryp, lid, NX 100 Shot.
TECH Apprentice
Joined: Oct 2002
Posts: 321
Likes: 0
From: Aurora IL
if your using the fuel pressure sensor take it out of the loop and see if it clears up... the hobbs switch has been the culprit in most cases... if your not using this switch and your still seeing pulsing have a FP gauge connected when you run the car to see if the FP is fluctuating.... if this is not it then the bottle can be getting empty even with the pressure if the liquid is not there you will see a surge as well... hope this helps.. keep us updated on the fix...
Thread Starter
Teching In
Joined: Feb 2004
Posts: 18
Likes: 0
From: South, South Texas
The bottle is full so that can't be it. And by fuel pressure sensor do you mean fuel pressure safety switch? I'm going to have my car tuned for nitrous in 2 weeks so hopefully that will fix the problem. But the bigger problem is that I can't stop using this stuff. 
Mine does this as well. Pulls hard from 3k-4kish, then looses momentum until ~5k, then picks up steam again until the window switch @ 5800. 
Did this last night with a totally full bottle and I know my siphon tube orientation is correct.
Did this last night with a totally full bottle and I know my siphon tube orientation is correct. 
Banned
Joined: Sep 2002
Posts: 1,298
Likes: 0
From: So Cal, CA
3 jet sizes on the fuel size is very rich. Especially when your not running the bottle pressure up to 1050-1100 like it should be. Factory NX jetting is already a little rich (and is fairly rich @ 950 psi bottle pres). Take that 31 jet out and put the correct jet in (28). Theres no safety reason to run it overly rich.
Trending Topics
Thread Starter
Teching In
Joined: Feb 2004
Posts: 18
Likes: 0
From: South, South Texas
Ok guys, had my car dyno'd today.
NA it made 323.13 hp and 335.08 torque.
On the spray it made 378.54 hp and 453.86 torque.
So yeah, something was wrong.
The guys said it might be the spark plugs. They told me to gap the plugs at 35 because from the looks of the graph they think the nitrous might be blowing out the spark. From what i've read most of the people on here have gapped theirs at at least 40 to 42. I'm changing the fuel filter tomorrow because it's been awhile since i've done it.
I'm hoping that it's either one of those things because if not then i'm stumped.
I don't have a scanner but i'm going to try to take a pic so i can post the graph up later tonight.
Any idea guys?
NA it made 323.13 hp and 335.08 torque.
On the spray it made 378.54 hp and 453.86 torque.
So yeah, something was wrong.
The guys said it might be the spark plugs. They told me to gap the plugs at 35 because from the looks of the graph they think the nitrous might be blowing out the spark. From what i've read most of the people on here have gapped theirs at at least 40 to 42. I'm changing the fuel filter tomorrow because it's been awhile since i've done it.
I'm hoping that it's either one of those things because if not then i'm stumped.
I don't have a scanner but i'm going to try to take a pic so i can post the graph up later tonight.
Any idea guys?
Last edited by Sigma; May 5, 2004 at 06:30 PM.
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I have seen several reasons for surge.
As said above...the #1 problem is usually the fuel pressure safety switch set on the edge. But it sounds like you dont have that.
Other items ive seen:
plugs gapped too loose
pulley tensioner allowing belt slippage under hard acceleration (seen that on two cars)
too rich or lean...check Af on the dyno with wideband
Blocked or collapsed lines
freezing maf on dry shot
As said above...the #1 problem is usually the fuel pressure safety switch set on the edge. But it sounds like you dont have that.
Other items ive seen:
plugs gapped too loose
pulley tensioner allowing belt slippage under hard acceleration (seen that on two cars)
too rich or lean...check Af on the dyno with wideband
Blocked or collapsed lines
freezing maf on dry shot
hehe!! Thread Starter
Teching In
Joined: Feb 2004
Posts: 18
Likes: 0
From: South, South Texas
Yeah no kinks in the line. The last thing I need to do is to check the gaps on the plugs again. Where do you guys have your spark plugs gapped at? Oh, and thanks for all the responses.
