having an issue with my race car. we dyno tuned it a month or so ago and took it to the track and it ran good a couple passes. next time to the track after that it was breaking up really really bad. come to find out it was way to rich causing it. we threw it back on the dyno to check everything out and it was at low 11 high 10 afr's when we tuned it to 12-12.5 on the dyno (c16 fuel). took it back to the track that week and ran spotless all day. 10.0's @ 147mph. on the datalogs using the oem wideband (kpro) it seemed to be reading fine at 12-12.5 afr's across most of the rpm range. we had a dyno day yesterday so i threw it on and it was breaking up first pull. i datalogged the pulls and again it was way too rich like before.

what in the world could be changing to cause this? here's a quick rundown of my setup. let me know if you guys can give me some ideas/advice. never seen this happen before

built k20 prayoonto stg 2 cams
billet 6768 turbo
afi intake manifold
tuned on kpro with an aem 5bar map
weldon 2025,nrg tech fuel cell,-10an feed/return lines,aeromotive fpr,id2000 injectors

 

I have never seen such an issue. My advice:

1. Check for consistency in the vehicle's voltage. The battery voltage drastically changing can cause a tune to change.
2. Check to make sure the fuel pressure is exactly the same.

 

fuel psi is exactly the same i checked that as well. when i datalog batt voltage jumps pretty crazy IMO. i don't have anyone elses datalogs on my computer to compare to but mine jumps around a lot. want me to post one up for you to look or do you have one that I can compare mine to?

 

yeah let us see it,

 

Also look at ECT correction but I'm sure you would have noticed that.

 

Both ect correction columns were unchanged. It does it at any temps as well. Last time it happened I had it at an event and it broke up bad all day. Threw it on the dyno after checking a bunch of other things and it was way rich. Retune back where it shouldve been and to track the next day and ran great. Sat for a week then first pull on dyno breaking up and rich

I will post up a datalog tonight. Should the voltage when datalogging be pretty consistant? Mine jump up and Down very quicky from mid 13's to high 11's. Also what about fuel tank pressure? Our road race car had a problem running rich so we pulled the gas cap off and it went away. Put it back on and started rich again. I have the nrg tech cell vented like it would stock