Someone did an experiment with Idle Spark Advance vs BLM Split, and they found the more they advanced, the more Split they became... I'll post the link tonite, I think I've got it at home.

Possibly you could try lowering/raising your idle advance?

 

Please post the link! I haven't heard about that one before....I thought folks were increasing timing to get rid of the split if anything.

I found that this setup pulled more idle vacuum with more advance (28 degrees) as compared to stock (20 degrees) in the 400/800 rpm areas. 1200 rpm is at the stock 30 degrees.

Rob
95Z28

 

Jason, were you maybe thinking about this site:

http://www.carprogrammer.com/Z28/PCM...k%20tuning.htm

I read that a while back and have recently pointed folks that way. Guess I had to go read it again for myself......maybe I have to do some more tinkering with the closed TPS advance.

Rob

 

Yes, that's the one I was thinking of. Right now I'm having the same problem, split BLM's at idle. I'm running 24* at 400-800 and 30 at 1200, I'm going to drop mine down to stock and see what happens, but I've got to wait until it's not Raining/Snowing outside.

For the webpage above, the guy 'could' have had a leak, and the advancement makes things worse off...


A week ago my MAF was dirty and I was running 118 on both sides, cleaned that up and I get split blm's <sigh>.

 

I "blindly" used the closed TPS advance I was using in my previous set up (26* at 400/800 and 30* at 1200). Now I've got 33 more cu-in, a bigger cam, more compression, and better quench. Maybe that wasn't the place to start.

What are your mods?

 

My mods? Nothing much... only thing I have that should drastically affect my tune is a CC305 (220/230 .544/.544 [1.6rr's] 114LSA). Stock bottom end and stock heads.

 

What TB are you using? Did you do the TB MOD? If not thats a great place to start, last is jack the car up, turn it on, put your hands around the collectors where the o2's are, you probably have an exhaust leak you can't hear, I couldn't hear my exhaust leak & I had very bad split, as I would tighten the collector my blm would get better it was funny to watch, finally after fully being tightened my BLM are identical, this is from 120/160, the 160 kept going down with every turn of the wrench.

Also, raise the idle if you want, basicly by raising the idle you direct more air through the IAC/idle discharge ports in the intake, this will also bring your blms closer together. As for drivability rpms (if you get that) the IAC follower table has a huge affect on that, depending on where your IAC is while driving will work the same, have more/less going through the iac, basicly you want as much air groing through the iac as possible.

so start at the exhaust leak area, like I said jack the car up, start it up & feel with your hand, don't worry the ehxuast is acctually kinda colt when it comes out of an exhaust leak area.

Don't worry about vacume leak like some people tell you, that will lean out both sides not just one, trust me.

If nothing works you can do a leak down test, set an air compressor to 80psi & push that plus the fititng into the spark plug hole, with the valves closed & the piston at TDC not BDC, this is acctually kinda hard to do, you have to make sure its at TDC or your rockers off will prolly work fine aswell put your ear to the headers/intake with TB blades open & see if you hear anything.

But I doubt it, I've tried unhooking an injector while the car is running & it makes barely a difference.

 

I feel your pain!! Heres a bump for ya!

 

heres an interesting solution. try it out and see if you get the same results.