I can't figure out why. I really don't know where to start. The motor has almost 3,000 on it now. And no matter what I do the BLM's are split... bad. Bad as in one end is on a boundry marker (160/108) at pretty much all times.

In Cell 17 it's split and bouncing off the lean end of things, in the rest of the cells it's split and bouncing off the rich end of things. (aka 160 left in cell 17 with the right around 130, and the left somewhere around 120 (when driving, 135 when idle) with the right at 108 in most other cells).

The Optispark is new, the Coil has already been replaced, the plugs were new, the FPR was replaced, the motor has been replaced, the injectors have been replaced (switched to SVO's from stock). The O2 sensors were new when the motor went in (I still had this problem on my old motor with the old O2 sensors, so I don't think it's the O2 sensors). I've tried LJ's offsets, the stock offsets (neither makes a diff), I've tried stock injector size, and the correct injector size (25.4).

I don't have any exhaust leaks. The heads were replaced with the new motor, can't blame a bad valve or anything like that. I doubt it's something to do with the valve settings since it has happened on both motors...

Any suggestions?

 

Might be IAC follower tables, bump them up higher first then try bumping them down & see hwere it likes it, also back the idle stop screw far back.

 

But it's not only idle that's the problem. ie: in cell 6 (somewhere around 2000 rpm doing 35mph I'm split 120/108) the IAC/follower isn't going to affect the split BLM then. At idle yes, but since it's in every cell that can't be it. I'm wondering if it's something mechanically wrong, but what could it be?

The car doesn't misfire, or at least it doesn't seem to.

Since it's not an exhaust leak, could a vaccum leak only affect one bank? I would imagine that since a vaccum leak would be on the intake, that would mean it would affect both sides.

 

I see you have LT4 ported heads, I noticed on every car I've worked on that there will always be a big split if the heads were ported, I had a real nice port job from Lloyd Elliot, he did his best on my set & I got a 5 angle serdi valve job etc.. I also have upwards of 112/123 split in sertain areas. I think that with a cam you obviously get some reversion back up through the intake which will cause a split, but that coupled with a ported set of heads which BTW non of the ports are going to be 100% identical & because you loose a lot of mid RPM port velocity even though you might have efficient heads with good port velocity that might only be the case at higher RPM, but any time you increase port volume you decrease port velocity at low RPM, there are a few things you could do but not much, I know it kind of sucks, but ohh well. I've seen this a lot, & mostly being on every ported head car coupled with a cam.

I've gone through 5 setups with my car & never had a NO SPLIT situation at cruise, NEVER, on one of my setup when I had a bunch of mods & SLP shortie headers, I figured I'd weld an o2 bung the driver's side header in the exact same spot as the passenger side, well that helped nothing, even with a perfect valve train ZERO lash done while car is running, changed lifters since then etc.. you name it I've done it, nothing really helps.


Here is something to make you feel better, on my last setup I had a lifter that had the pluger retaining clip break off & the lifter pumped up (COMP R') & when I found this after installing my Joe overton cam I figured I'll help some, well guess what, the split is the same more less even after fixing that, no header leaks nothing, I stopped paying attention at cruise. If you really want to make sure your injectors pulse more less the same, find out the highest reading whether it be the left or right bank for BLM say 123 & lock your BLMs, I did that at one point & the car ran better & gas milage didn't suffer, I'm still tunning this setup so its back to 108 min. again.


What you will notice that is really interesting is if you had left side 108, right side 123 & you lock your BLMs to 123 for both, drive around a bit & check your SHORT TERM BLM's, you'll notice the one side that was 108 & is now 123 lock will still hang around 125 blm range for short term & flicker to 115 or so every once in a while like either a misfire or REVERSION, reversion being the case cuz I changed plugs, converterter to LS1 coils LTCC. etc... so you haven't really sacrificied fuel economy either because that flickering is what caused your LONG TERM to go to 108 & then you stay at 125 steady flickering to 140 at times when its correcting, I'd rather have it flicker to 115 & hang around 125 for short term so try locking the BLMs.

Also when I say lock to 123 blm I mean it won't go below 123 long term to correct but still go 123 & up for a lean correction.

Hope this makes sense.

ANyways headed to bed now.

 

I had the same situation on my old motor also, which had stock heads and intake. I understand what you're saying about ported heads, but in this case I don't think that is the complete cause of the problem.

I guess what I really need to know is what mechanically can cause one bank to run that much different than the other? Leaking EGR? Screwed up EVAP system?

 

Jason, here is what fixed my split BLM's. In Tunercat, I opened up both tables that said "individual cylinder fuel trim". Ones for idle and the other for "off" idle. Anyway, say you have high(lean) blms at idle on the left bank. Open that table and increase the multiplier for those cylinders. 1, 3, 5, and 7 by about .03 or 3%. The BLM's will decrease only on that bank. You should be able to get them reallly close by doing this.

 

Yeah but thats not really fixing it, your basicly doing the same thing o2s will do anyways.

what you can do is use a laser heat gun on each primary, at one point I did that while reving at 2500, if it was colder I took fuel out, hotter primary I put fuel in, got it pretty well within but then if its reversion you could sometimes get fuel into a different cylinder if your accelerating etc... so I left it as is.

 

If that's true, then split blm's would be only temporary. The O2's aren't fixing it, that's the problem. I don't know how adding/subtracting fuel globally will solve spilt blms. Are you saying it will? Please explain.

 

I dont' understand your question either, but what it seems to me is your saying subtract 3% from say left side bank & it fixes your BLM problems, well all that does is make the BLM's look pretty, but what the o2s would be doing is the same thing, they take out fuel from the left side if its rich & put fuel in the right side if its lean, get it? When you do your cylinder balance your BLMs just tell you what is having to correct for your set fueling, so if the BLM is spliting its just saying : OK, the way your tune is setup your running leaner on one side, here is what I'm going to do to fix it.

Now when you do your cylinder balance what your doing to the blms is this: I'm Mr. BLM, your fueling is perfect, I will not make any corrections because you seemed to of taken care of everything in your tune.


But essentially both will do the same, until the O2s are satisfied you will be removing/adding fuel using your o2s or using your settings inside the tune. & if there was a mechanical problem you are just covering it up.

Hope that makes sense.

& if its just reversion from the cam then the ultimate fix would be to identify exactly which cylinder is running lean & which one is running rich, & trim that one cylinder instead of doing that whole side, now what is happenig you might of had #2 cylinder lean, so that o2 saw this & you'll be adding fuel to the rest of the cylinders & #2 just to satisfy the end result, but now you didn't make anything better because you just made every other cylinder too rich just to fix up that one #2 cylinder & yet it still isn't optimal.


The best thing to do would be to add fuel to #2 if it needed more fuel.

See the picture now?

 

I see what your saying. It sounds great but it also doesn't sound like you have every had split blms or monitored them much.

If you have a split then the lt blm's never correct themselves. This ties up the INT to do a constant correction on top of others. It's strange since the O2's are suppose to act independant from one another but somehow they are tied together.
If I had a 115/130 split then I will always have it if I tried to let the O2's fix it. The O2's subtract/add fuel in INT but the BLMs never change by more than 1 or 2 in that cell no matter how much driving you do. That's the big problem with splits. It's not setting a long term correction. Both the O2's must be linked in someway and the rich/lean is cancelling itself out somehow and preventing a new BLM to be set.

If I set the fuel trim to get the BLMs closer together then I have done the job that the O2's cann't seem to do. Once you get the BLMs close enough together then they start to make the long term correction factor again.

As long as the INT doesn't get maxed (rare) then the split really doesn't matter I suppose. Its just math that adds up to the same pw in the long run.

 

Umm.. don't know what you mean but I have been looking at this stuff forever & still do, the long term blms do correct from 108 to 160, if you want to get the numbers within there say your constantly at 108 you should look at either your PE tables, MAF tables or bump up the injector size, or you could even bring the wall down from 108 to say 100 & from 160 you can go 180 or whatever you wish but not recommended, other then that, o2s do correct in long terms, maybe what your seeing is lack of cells avaliable, if you do a cam swap you should look at your Cell boundries aswell, I belive we have 16 cells avaliable, upon installing a cam you might only be using 4 cells which can cause your long terms to never settle.

matt.

 

Maybe I read over this but if you havent tried replacing the PCM or at the very least borrowing one from a friend then you might give the swap a try.. could be a bad board in the computer or wiring problems.

Another thing since you have scanner.. make sure the O2s start out at 445mV both left and right at start up and that they fluctuate from 0-999mV in closed loop.

 

This discussion is very interesting.

Just yesterday I noticed that my LTFT readings show a split. I don't know how long I have had this condition. I don't have a data logger but just a scanner with some readings. I was getting 128 on B1 and 145 on B2.,WHile they vary, they still reflect the need to make corrections on B2. My short term readings don't show as much variation as the LT readings, but generally indicate their some need to correct the B2 side. Is the B2 side, is the passenger side?

I was wondering if this is related to my occasionally appearing DTC P300 that I have experience for years. I assumed it was due to my cam and perhaps the lightweight FW fooling the CPS into believing I had a random miss, but now I am (still) puzzled. My heads were CNC and was surprised to learn that head work can create split side readings.

Any more advice for those of us with the split BLMs or LTFTs?

 

If you are split within 108-160 on the LT readings you will not have much if any split on the short terms because the long terms have already corrected for the condition & the short term readings are the result of the correction, if you reset your computer you'll notice the first time you go into closed loop that the short term on one B2 will be at 145 or so & B1 at 128 short term, it takes a few seconds but watch the long term on B2, it will start to go up to 145 & the short term on that side will start comming down to 128, this means long term had to increase fuel by 17 BLM to get the short term at 128, SHORT TERM is what your engine is seeing now, Long term is the correction for the short term.

 

Bunker, thanks. Ididn't know that. But I am still puzzled as to what is casuing the split on the LTFT and why B2 is so out of line.