who has split idle BLMs b/c of a cam?

i am currently running the XE 224/230 110LSA and cannot get it to idle for crap. my BLMs have been recorded as bad as 108/160 but usually more like 115/140 and its driving me crazy! i have done almost everything i can think of to correct the problem like cleaning the tb, messing with the idle screw, cleaned the IAC passages, increased and decreased closed throttle timing and tried even increasing my idle rpm. nothing is working here! im now trying to think of a way to disable closed loop in cell 16 so they cannot adjust from 128/128.. no proven solution yet however.

now i have a theory here about cell 16. it is both an open loop and closed loop cell so it seems like there could be a way to keep it in open loop at all times maybe with a basic program. does anybody want to donate some time to see if this is possible. id do it myself but i have a very limited knowledge when it comes to programming.

Have u tried loading someone elses bin? I have one for the 224/230 if you want it emailed to ya. At least you can compare it with what u got and maybe find something.

Jeff D/

Brad are you still OBDII?

Originally posted by Dan K
Brad are you still OBDII?

no way man. whys that matter? i could spend some cash reverting back to OBD2 if that made a difference.

Originally posted by turbo_Z
i am currently running the XE 224/230 110LSA and cannot get it to idle for crap. my BLMs have been recorded as bad as 108/160 but usually more like 115/140 and its driving me crazy! i have done almost everything i can think of to correct the problem like cleaning the tb, messing with the idle screw, cleaned the IAC passages, increased and decreased closed throttle timing and tried even increasing my idle rpm. nothing is working here! im now trying to think of a way to disable closed loop in cell 16 so they cannot adjust from 128/128.. no proven solution yet however.

now i have a theory here about cell 16. it is both an open loop and closed loop cell so it seems like there could be a way to keep it in open loop at all times maybe with a basic program. does anybody want to donate some time to see if this is possible. id do it myself but i have a very limited knowledge when it comes to programming.

set your "ENABLE CLOSED LOOP TEMP" both to 150C, the car will stay in Open loop mode all the time. I had the same problem you do with mine where it would split the BLMs to hell at an idle and run real rich. I tried to set WOT % to zero for RPMs below 1600 and decrease fuel in the PE table, however that only disabled the long term fuel trims in cell 16 at idle while in closed loop. the BLMs still split and the ST fuel trims loaded it with gas.

To solve this problem my car is set it open loop mode all the time, and the WOT% is setto zero below 2000 RPMS and I use the PE table to tune my idle A/F ratio. Now my BLMs are fine and no more running rich at an idle.

Originally posted by TriPinTaZ
set your "ENABLE CLOSED LOOP TEMP" both to 150C, the car will stay in Open loop mode all the time. I had the same problem you do with mine where it would split the BLMs to hell at an idle and run real rich. I tried to set WOT % to zero for RPMs below 1600 and decrease fuel in the PE table, however that only disabled the long term fuel trims in cell 16 at idle while in closed loop. the BLMs still split and the ST fuel trims loaded it with gas.

To solve this problem my car is set it open loop mode all the time, and the WOT% is setto zero below 2000 RPMS and I use the PE table to tune my idle A/F ratio. Now my BLMs are fine and no more running rich at an idle.

dont you get horrible gas mileage b/c of the full time open loop?

i am starting to wonder if putting in a switch to turn off the O2 sensors at idle and then flipping it back on off idle would be the only solution to this madness!

Originally posted by turbo_Z
dont you get horrible gas mileage b/c of the full time open loop?

i am starting to wonder if putting in a switch to turn off the O2 sensors at idle and then flipping it back on off idle would be the only solution to this madness!

actually no, I get much better gas mileage. Howver you nneed to adjust your open loop vs temp AFR table so its not so rich. Its set rich because its usually used for warm up. I set my AFR in all operating ranges in that table to 14.5 and 100 KPA I set to 12.9. Car runs great. Then what you do is tell teh PCM that WOT is at 0% TPS below 2000 RPMs so you can use teh PE table to tune your idle A/F ratio. I currently have my idle PE settings to -14 car idles great and not rich and doesnt stumble anymore. SCrew Closed Loop, the O2s are a PITA !

I used the cylinder fuel trim at idle to get the left and right BLM close to 128. If you are 115/140 make a 3% adj to each cylinder and see where you are ...add to the right subtract from the left or visa versa. Just make sure you have no exhaust leaks that are effecting the numbers. Always save you base file for a reference.

Originally posted by turbo_Z
no way man. whys that matter?

Just wondering. :)

I've got the 224/230 on a 112 in my 383. I'm having split issues but I've been fiddling with things since February and KNOCK ON WOOD, things are looking better.

I've played with the TPS, IAC, checked for any leaks (exhaust AND vacuum) all over, been through several sets of O2 sensors, new IAC (broke my stock one). Anyway, now my BLMs are pretty consistent across the board except for cells 6&7, using the stock boundaries. Idle is 119/122 or so and cells 6&7 are ~ 108/110 at their worst.

I still have some tweaking to do since the car is not responding as I'd like it to. Once I get my part throttle/idle stuff figured out I'd really like to hit the dyno for some WOT tuning.

Originally posted by ryaskovic
Idle is 119/122 or so and cells 6&7 are ~ 108/110 at their worst.



Might wanna try the MAF tables for cells 6&7.

Originally posted by gb95zconv
Might wanna try the MAF tables for cells 6&7.

Yeah, I've considered that. I think I'd like to gather some more data and do some more thinking before tweaking the MAF tables.

Rob

What kind of throttle body is on the car?.

Originally posted by radik
What kind of throttle body is on the car?.

It's a stock unit ported to 52mm.

i'm fighting the same issue with a blown cc306, it got better when i drilled out the bbk 'throttle body' iac circuit a bit.

Of course you tried opening your tb stop a half turn or so right?.

Once you do that you should disconnect the battery terminal, start the car for 10 seconds, shut it of and restart it.

I've gone through all SORTS of things! Upon tweaking the throttle plates, I wasn't getting any response.....BLMs were still split. Since this didn't jive with what other folks had seen, I started looking elsewhere. I had ruled out everything but the Optispark was still a question in my mind. I changed that out with a new GM unit and then started to see some affect!

I have plugged the IAC bypass hole and have tapped in a seperate route for the IAC bypass air (tapped into the intake tubing, after the MAF, ran it througha valve to the PCV intake - this passage feeds the IAC passage). So now, I can tweak the throttle plates as well as the IAC bypass hole size. This got me close but things still weren't how I wanted them. Trying to remove all variables, I removed the Ford SVO 30# injectors and re-installed the stock injectors/constant/offsets. The car is running much better and showing the data I posted earlier. What confuses me though.....previously I had swapped the Ford SVOs from side to side and did not see a change in my split.

So now, the car runs pretty good at part throttle but I'm RPM limited at WOT 'cuz the stock injectors just can't keep up! I haven't had the time to play with things lately.

Rob
95Z28

Let me make sure I have this straight:

With a big cam, the BLMs will often be split because the PCM thinks one bank is running lean. But in reality, the bank isn’t running lean? Intake air is going into the exhaust on that bank so the O2 reads a lean condition, but the actual combustion in the cylinders is not lean? Is that correct?

I’m contemplating going with a PE idle and this would get rid of all the extra fuel that’s being dumped in that bank so I want to make sure that those cylinders don’t really need that fuel before I do so.

Split BLMs, or How do you adjust the IAC and why?

This split BLM that the Big Cam guys complain about - so what? Suppose you're idling in the staging lanes at the drag strip, and your engine has split BLMs at idle. When it's your turn to run and you hammer the gas, one side of your engine might be fueled with a 118 BLM, but the other side may be fueled by a BLM of up to 160. Why do we care? Because max power is obtained only with correct air/fuel mixture. There's no way to get max power in this scenario, because all of the PCM fuel control tables are applied to both sides of the engine. Lean out the rich side and the lean side gets leaner. Fatten up the lean side and the rich side gets richer. You can't win..

What can you do to fix it? If the problem is not something that can cause false O2 numbers, or something that can really cause one side of the engine to be different than the other (check out the first paragraph for a list of suggestions), what can it be? It's been a puzzle! Split BLMs suck big time, but read on for a possible bandaid.

Recall that IAC is what the PCM uses to control idle speed. Zero is closed (no air gets in, really slow idle!), and 160 is wide open (faster idle). Generally speaking, you want to set it to a fairly low value (40 seems like a popular setting for a warmed-up engine) so that the PCM can raise the idle when you switch on the a/c, or when it's way cold outside first thing in the morning and the engine doesn't want to idle.

I wondered if my split BLMs were caused by my long duration cam disrupting the contents of the intake manifold, which is essentially just one big cavern (plenum) with 2 holes in front for air to get in and 8 holes spread out along the sides for air to get out. Ordinarily, the plenum only contains air, but the extra valve overlap (both intake and exhaust valves open at the same time) caused by longer-than-stock duration cams can create reversion, which means that some of the air/ fuel mixture from the combustion chamber flows backwards through the intake port in the head and ends up in the manifold plenum. If fuel is in the plenum, the cylinder that draws it in will be too rich (because the PCM thinks all the fuel is coming from the injector).

But idle air coming through the IAC has its own small passageways in the manifold - it doesn't use the plenum (unless you have an aftermarket throttle body, at least some of which have a big "leak" between the IAC outlet and the main plenum - see below). I figured if I could get all, or almost all, of the idle air to go through the IAC and those small passage ways, big cam reversion would have less effect. You can't "adjust" the IAC, but you can trick the PCM into adjusting it for you by messing with the throttle body stop screw. This screw holds the throttle body blades slightly open when you're not touching the gas pedal.

If you close the throttle blades almost completely by adjusting the stop screw, the PCM will compensate by opening the IAC (remember that the PCM has a programmed idle speed that it tries to hit). I started the engine and connected my scan tool (Diacom back then) to the PCM. The IAC was probably in the 40s or 50s, and the split BLMs were something like 125 and 155. As I closed the throttle blades, the IAC climbed and the BLMs got closer together. By the time the IAC got above 140, the BLMs had actually reversed, meaning that the went from 125/155 to 125/120 (or something like that - I've forgotten the exact numbers). Try out this trick to see if it solves your split BLMs.

OK, now for the aftermarket throttle bodies. My AS&M 58mm throttle body had a major "short circuit" between the IAC outlet and the main plenum as shown in the pic below left. Even if I close the throttle blades completely, this will allow idle air into the main plenum. What to do?

Fortunately the IAC outlet is exactly 1/2" in diameter, and it turned out that a piece of 1/2" brass tubing from the local hardware store fit perfectly. Some careful work with a carbide burr in a die grinder was needed to create an opening in the wall of the tube that matched up with the IAC port. The pic below right shows the new tube completely inserted. The IAC opening in the intake manifold is a bit larger than 1/2", but once again the hardware store came through, this time with an o-ring from the plumbing department that seals the gap between the tube and the intake pretty well.


would attatch pictures of how I did it but don't know how??? someone help me so I can show you how to deal with this problem.


here are the pics I attatched them on my home message board
scroll to the bottom of the page....
http://www.ksfba.org/forums/showthread.php?s=&postid=57875#post57875

I have never figured this out... now I hardly drive my car enough to care and I dont check out my scanmaster 24/7 so out of sight and out of mind is my only solution. It could very well be an exhaust leak causing all my stress but driving on the highway the drivers side is always 10 pts higher than the pass side so actually that is reverse of what im seeing at idle. So even if i have a leak.. its not affecting my idle fuel trims.

I have already read all that information about the IAC on the web page of the original author... it did nothing for me.