Ok, so I have been fighting split BLM's on my fuel trims since I started tuning this thing...here is the situation.

At Idle my BLM's are split...by A LOT. It is Rich on the Left and Lean on the Right, so I started looking for reasons. I started with the right...if it is lean, that means that there is either a vacuum leak, Exhaust Leak, Bad O2, or Injector Missfire. I did an inspection and I have found NO vacuum leaks, NO exhaust leaks, and I switched the O2's and nothing changed. I pulled each injector plug and watched my AFR and listened to my idle and on all 4 plugs, the AFR went SUPER lean and the idle bogged which means all 4 injectors on that side are working. So I figured maybe it was the other side...

On the Left side it is Rich and that would be caused be a vacuum leak, bad O2 or an ignition missfire. I again found no vacuum leaks, and I had already switched the O2's so it wasnt that. I pulled each SP Boot (burning the crap out of myself while I was at it) and it bogged and y AFR went SUPER Rich for each plug...so all of my spark plugs are firing.

Now I went to GENERAL problems...IAC, TB, Timing, ETC. The IAC was wide open at 160 and having trouble idling, so I worked with it...now it sits at about 45-50 and the idle is good....NO change to BLM's. I have a Professional Products 58mm TB. I altered the idle a little bit to make the IAC around 60-70 to make sure the problem wasn't reversion...no change. I reduced my timing to 23-25* at idle and no change. At this point, I am SEVERELY lost and need to know if anyone else has had this issue and fixed it! The Split BLM's continue with throttle, but they are MUCH closer together.

Also, if it was a bad O2, they shouldn't be reading like they are should they? One would show WAY OFF on the MHz wouldn't it? Both of them seem to be responding the same as the other, and if I make an adjustment to my AFR or my Injectors, or my MAF Calibration, the BLM's change accordingly for BOTH sides and the O2's reflect that in their signal. WTF is going on???

Here is the video I recorded of my datalog with TunerPro RT. I give it a little throttle in the video too but does anyone see anything out of the ordinary here??? My cam is a 238/244, .592/.592 with a 111 LSA on a 106 ICL.

Thoughts?

 

OH, and for the record, this was done in Speed Density Mode. I switched it over in TunerCats when I uploaded the latest tune. This is also on an OBD1 PCM from a 94 Z28.

 

I had split BLM's untill I closed TB blades completely and enlarged the IAC passage and discussed here,
http://www.camaroz28.com/forums/lt1-...ameter-699051/

 

Ok, I will pull the TB and take a look to see if it is causing this problem. Thanks

 

Lean it out and see what it does. You MUST remember the O2s read OXYGEN left in the exhaust and not fuel. Many time I have played with this and got really close by just getting the tune dead on. To much Fuel can look like not enough

Once you get the tune dead on play with the cylinder to cylinder adjustments. They have one for idle and cruise but not WOT.

Last but not least remember they will never stay identical no matter how hard you try

BTW I am see alot of LS stuff that once dialed in likes ALOT less timing at idle. I keep getting in cars jack to over 30 degree's at idle and when it is all dialed in with fuel and air flow they seem to like 14-18 degree's the most

 

Ok, I set the timing at idle to 18* and the BLM's got MUCH closer...I need to lean her out and rework the tune tomorrow (didnt have time tonight) but the BLM's went from being almost 30 apart, down to 6 at most, and 4 at best, but it was pulling A LOT of fuel now...they were sitting at L 109, R 112. The max it will pull is 108. So I will go in and lean it out tomorrow and see what happens.

 

I think you are headed the right direction man good luck

 

Ok, so...I spent the whole night and morning modifying my Throttle Body. Yippee.

I took it off and drilled n 1/8" hole through the IAC passage, completely closed my TB Blades, and I am about to go buy a piece of copper tubing from ACE to block off the IAC passages that bleed into the main air passages during idle...Once I get this done and re-install the throttle body, I SHOULD be able to eliminate my split BLM's completely, or as much as is possible at least, and get this tune dialed in properly!

I will keep y'all posted on the results! We have a huge car show and races at the drag strip today and I am rolling out with a few friends so the SS gets to sit in the garage until the show ends, then I will try and finish this up and hopefully have an update by this evening! Thanks for the help everyone!

 

anybody know how lowering the timing helped the split BLMs get way closer? im just curious on the science behind it.

 

I remeber another thread where u said u had knock and split blms at idle and u lowered the timing down to the low 20s and it fixed the split. Did the split come back after u did that?

 

What happens is someone is usualy add's a bunch of timing because they read it is the cool thing to do so then they add a ton of fuel because they think it is lean...because it is actualy mis-firing

 

Lowering the timing did not SOLVE the Split BLM problem, it merely moved them a little closer together...the Split BLMs are still being a PITA

 

Ok, I just finished drilling a hole in my IAC Passage in my Throttle Body, and blocking off the IAC Bleeders so that I can close my TB Blades COMPLETELY and the idle runs completely off of the IAC Passages... I got it all finished up and nice and pretty and ****, and here are my results after re-installing everything!

I am starting to get a little pissed off...Got the IAC Valve down to 70-75 when warm, idling at 825 rpms and timing sits between 15 and 18*. BLMs are STILL split, sitting at L 122, R 147. I got pissed and said **** it and started dicking with my Individual Cylinder Fuel Trims again...I BARELY changed them and suddenly the car would not idle anymore. I could get it to start with gas, then as SOON as I let go, dead stop...no sputter, nothing...just stop. I realized I was still tuning in MAF mode so I switched to SD mode and changed the trims back...she fired right up...BLMs changed to L 133, R 157. I went back into fuel trims and made the EXACT same change that I made before switching to SD mode...started right up and BLMs changed to L 133, R 152 (I gave the right side more fuel...). I went in and made a slightly more drastic change to the fuel trims...started right up and BLMs went to L 132, R 147. Finally, this last run, I made another drastic change to the trims, and I changed the VE tables for my idle by 1%. The result was BLMs of L 133, R 148. I went the wrong way on my VE table... Still no exhaust leaks, no. vacuum leaks, kPa sits between 60 and 65 at idle, No misfires...What the hell am I missing???

Here are the videos of the very last idle I mentioned above...2 vids total, 1 of the dashboard in TunerPro, and one of the list view which has EVERYTHING. Don't mind the coolant temps, TunerPro is off, I wasnt at 214* lol, I was at 170*.

 

i had this problem for years and could never figure it out. i did all the bs you did above and nothing. then one day plug wire 8 was sparking and you could easily see it. so i was like ok time for new wires (they were msd). so i bought another new set of msd wires and installed them and the difference was night and day. the car felt way stronger. so i said this is crazy let me take a datalog. i did and the split was gone. so my problem seemed to have been the wires all along but i had checked them and they never showed signs of being faulty. but i swear to you as soon as the new wires went in my issues were solved.

im not saying this is your issue but it was mine and the weird thing was i checked the wires and they never showed any signs of being bad. its not until wire 8 was visibly messed up that i decided to change them and it was a miracle. a tuner i knew had always told me to ohm test the wires but like a stubborn *** i never did. i bet if i had ohm tested them i wouldve caught the problem years before.

 

Also check the plug wires to ensure they have good conductivity casue misfires will csue the BLMs to drop and believe it or not, do crazy things to the opposite bank. A while back I had nasty splits at idle and the MSD spiral conductor was broken from the plug side terminal resulting it misfires. I check the wires with an multimetter and after the repairs, splits were tons better.

As already mentioned, aftermarket throttle bodies casue nasty splits becasue idle is dumped into the plenum as opposed to the small hole on the front of the intake like GM originaly intended. Reroutinh the idle air makes a big difference too.

Make sure there are no header flange leaks or vacuum leak around the intake including hoses.

Lastly ultra tight LSA cams will frig up the idle BLMs too.

BTW I have near perfect idle BLMs but it took work to get there using the solutions mentioned above. IMO, fixing split BLMs is always mechanical and never anything to really do with the tune. The tune can be used to move the ranges of the BLMs up and down as needed but again, not to address splits.

 

Goes with what i said above.

use the mutlimeter to get readings of all the wires positive in one side negative in the other. and then divide that number by the length of the wire to get the average per inch. all wires should be pretty close probably within 10%. if one is way off or goes to infinity its messed up.

 

My wires with the issues were infinite resistance when the conductor broke from the plug end terminal. Due to the high voltage though, the spark is very able to jump the break and still fire the plug but not as well as it should. There will be combustion but not complete combustion and then sends the BLMs to Hell.

 

absolutely true. i think that was my case for the longest because i tested the wires using a inline spark plug tester and it looked fine which is why i never ohm tested them. once i changed the wires the car ran way harder than it ever did. im curious if i got a faulty set of wires from the start.

 

China.