I finally got a couple dyno pulls today to try to narrow down my remaining issues with my new 383 daily driver.

Dyno Sheet

The dyno guy said the part throttle and WOT A/F ratios look good, but when I'm sitting still in gear, my A/F is in the low 14's and when I'm in neutral, it's high 17's which is very lean. I also have an annoying stumble coming in and out of gear. Since I have a madz28 tune, the dyno guy suggested getting a revised tune that adds more fuel down low and see what happens. i have some access to a scanner and have noticed that the LT fuel trims are pegged at 160 when sitting still in neutral, but start leveling out a little better (between 140-150) when I get out on the road under some load.

Based on the looks of the dyno, does it seem logical as a next step to try adding some more fuel down low in the tune and see if it helps. If anybody sees it differently or has other ideas, I'm all ears. The only other strange thing about the two dyno pulls is that the second pull ran richer than the first. The only difference between the two is that the car sat turned off for another 20 minutes between the two pulls. I have no idea why it would run richer the second time.

Thanks in advance guys...

Robert

 

Call Ion and discuss it with him. 15-1 is normal for idle,but 17-1 is a little on the lean side. That stumble may be the tip in fuel needs to be richer and all of this may be because it is idled to slow.

 

1racerdude,

one of the first things ion and i tried to do early on is up my idle by 100 to 850/825 but i remember ion saying that i should be able to idle in the 700's with no problem as mild as my cam is. do you think i should try idling even higher than 850's ?

 

As a follow-up, I have spoken with a local guy that's done quite a bit of LT1/LS1 tuning, and he seems to think that it's not that uncommon to be idling in neutral in the high 17's A/F ratio and that I probably shouldn't be focusing on this. Is this true??

 

TRUE

Idle it up and see if it runs better.

 

Why is that? CL stoich is ~14.7. I don't think your cam specs are that aggressive for a 383 to cause overlap false lean, are they?

Gary

 

A/G,

Your post echoes what I've heard from a number of people. My cam specs are certainly mild for a 383 so I'm stumped as to why I am running that lean in neutral and have a stumble when I go in and out of gear. My dyno guy suggested that I add more fuel down low in the PCM tune, but my tuner does not believe that should be necessary and that I must have some other issue because the same tune has worked perfectly for others with the same specs as mine.