I am hoping that someone might me able to shed some light on the problem I had last night at the track... I got to the track with too much fuel... around half a tank of 94 octane... I did a couple a couple of motor passes and the car ran champ aside from being a little slower due to the extra weight... I planned on spraying a 100HP shot later in the evening and was going to add some 110 octane but because I had so much 94 in the tank I decided to go with 5 gallons of 114 octance... all the fuels I run are unleaded. My car is 98 Firebird with a Walbro 340, with the 114 added the gauge read about 3/4 full... I never tried racing with this much fuel in the tank!

Here's where my problems started... I did about 5 passes and the car would sputter just after launching... the car leaves pretty hard in the 1.5x range... I noticed when it did this the fuel gauge would shoot up the full mark and stay there till I restarted the car... it seemed like after 5 passes the sputtering went away, I tried spraying a 100HP shot just before the track closed and it sputtered In case anyone is wondering... here's what I ran, it's my new best on the motor...


10:49PM 800FT DA
60ft 1.531
1/8 7.0 @ 95.9
1/4 11.1 @ 121.2

Not the 10 second I was hoping for but a new PB on the motor... it's hard building a car to run well on the motor and the spray... my converter is a 3 disk type that is designed for nitrous and I am on a VERY tall tire to make sure I don't run out of gear when spraying... the car works much better with a 27" tall tire on the motor... I guess all these hurdles could be overcome with more motor

At this point I decide if I don't spray it on the next pass I will not get to spray it all I tried to bring up the bottle pressure, but the heater and alternator under drive pulley don't work well together and I had to make sure I did not kill the battery... I could not get the pressure much higher than 800lbs (not enough!). Here's my only spray pass of the night, another PB by a couple 1/100th's...

10:58PM
60ft 1.595
1/8 6.9 @ 103.3
1/4 10.70 @ 130.6

 

sounds like you got a fouled plug.

 

Keep in mind it only did 1 sputer just when launching... after it ran perfect... it seemed like it stopped sputering once the tank got down to about half...

 

hmm clogged fuel filter? regulator? bad fuel?

its probably something easy and very obvious.

 

Do the other gauges max out also?
The reason I ask is because I had the same problem and it was the battery tilting forward and arcing out against the A/C bracket because it was not secured. Stand in front of the battery, grab it with both hands to check if it's secured and not tilting toward the A/C bracket. I'm almost positive this is your problem. I bought a black metal battery strap and that fixed the problem. Hope this helps.

 

Interesting idea... my battery is in the back of the car... I will double check the connectors to make sure it's not shorting out on the box...

 

honestly to me it sounds like you have something grounding out somewhere..not fully but close enough that it hits on the launch. unfortunatly you will know for sure when the wire wears through further and you blow a fuse, and if its making the car stutter it's prolly gonna blow a fuse that will kill fuel/spark like pcm bat fuse or soemthing similar.

you do any harness relocation or anything like that where something could be rubbing?

reason i'm saying this is this exact thing happened to me. i'd get on the car and it would cut fuel out for quick sec..couple days later ground got bad and blew fuses. it was part of my harness rubbing in the engine bay creating a ground.

 

A quick way to verify is check the metal terminals that connect to the battery and look for signs of arcing/melting. Mine would kill right at the peak of launch (1.57 60-fts), the dash entire dash would light up (like the key is in the ON position), and the car would slam down very hard. My friend (non f-body) had the battery relocated in the back and the battery was sliding into the bracket causing the same problem.

 

I double checked the battery box and everything is tight back there... I did notice some signs of arcing on the metal, so I put electrical tape on the box where it could touch just to be safe... the arcing must have occured with the previous owner...

It's weird that the car never acted up, until I tried racing with 3/4 tank of fuel... as it got down to 1/2 tank it seemed to be fine, but it did stutter on my final nitrous pass (more violent launch)... I will go back this weekend with a 1/4 tank and see what happens! I was also running a NO2 tune with a couple degrees of timing pulled and had the equivalent of 105-110 octane in the tank...

 

it could be coincedental and it really has nothing to do with fuel at all.. the arcing sounds like it was the cause of your problem.