Car Won't Hold Idle
 

Just Installed 42 SVO green tops, and reprogrammed the CPU with the Crane Power Max tuner. No SES codes but car will not always hold an idle. The 42# are like 49# at 58psi so I figuerd they where 70% larger than stock. There where no Idle issues before changing the injectors and programming the CPU. I really don't want to change the injectors back to stock to verify this. Alot of people are running the SVO, could it be a problem with the Crane Powermax Tuner? is 70% the right size increase? the problem is mostly when the engine is not all the way up to temp, but even when it is hot it sometimes has this problem.

nope, flow doesn't increase linearly with sizing, the formula to use is
sqrt(newrating/oldrating)
so in your case it's sqrt(48.5/28.8)=1.2977 ~ 30% extra flow.

Your best bet is to get in touch with Joe Vinci, I finally gave up on my crane tuner and got a RWTD custom dyno tune.

Well I just returned the tune to stock, but left the 42#'s in the car. The car idled fine I slowly drove around the block and what do you know, no problem. So i reinstalled the tune but this time just for the injectors. No fuel added, no fan settings, nothing but injector size. The instructions say if your going from 24# to 32# to increase 30%
so I assume there math is 24 x 1.3 = 32 1.3=30% My numbers 28.8 x 1.7 = 48.96
and the idle problem returned. I'll be calling crane to see what their tech line thinks, I just thimk its funny the large injectors run better with the stock tune

www.stealthram.com/vhptuner.htm

new size divided by old size gives percent change. 49/29 (rounding) = 1.68 or 68% change. have you tried 60% rather than 70%?? it may have went somewhat lean.

for giggles, do a 30% change and tell us what happens. when i use another formula, it comes up with 30% as well. 28.8# / .7 (30% increase) = 41.4#

ok, got pointed out where my math is off on the first formula. 28.8/48.5 = .59 then subtract that from 100. 100-59 = 41% change.

I tried 40% more and so far so good. :) Engine was warm though. I'll try again in the morning and she how she does. I data logged the A/f and it was around 10.9 at 85% throttle and 5psi. Thanks for the suggestions and I'll let ya know later if it all works out I"d like to buy you a :chug: mrr23

no problem. i have to change it on my webpage. my mistake on it.