Idle BLM

[BLG355]

I have a question about BLM at idle. I've ran several logs and corrected the fuel table numerous times, but it seems at the end of every log when I let the truck idle, it goes crazy rich and the BLM drops down to 110-112. Here is a example of a log I just ran. The other day I got everything down to with +/- 4 blm, then today I ran another log and adjusted some more, most were from 127-131. So I ran a second log today and the idle is just horrible with the BLM. Also, is there a way to smooth out the idle? My cam should idle silk smooth but it feels like its a 230@.050 duration cam. It literally shakes the whole truck at an idle, open and closed loop, the idle is crap. One thing I didn't do is lower the timing at an idle, its close to 30, but when it was at 25 and even 20, it wasn't a whole lot better, if at all.

From what I've understood, perhaps this is incorrect, the idle VE table needs to be blended in the with off idle VE table...right? If anyone has any free time and gets a chance to look and could offer some advice, I greatly appreciate it.

BLG

[steveo]

you have to experiment with idle timing and idle speed. try to get high vacuum without any 'roughness'. too little timing is rough, and so is too much.

your cam is very small, i would expect no more than 20 degrees timing would be required for a smooth idle. 30 degrees is for a big cam. imo, of course.

have you forced open loop to see if the blm trims are why it's rough? is it rough while warming up? if it's rough before it even hits closed loop, it's probably not an AFR problem. it's timing or something else.

your trims will be screwy if your timing is out to lunch, or if there's some other problem...

are you sure it's running evenly on all cylinders? perhaps there's some other reason it's idling rough?

[Roadknee]

Hot idle is still around 46 IAC counts. Open up the throttle blades. The increased airflow around the butterflies mixing with fuel may improve fuel distribution and idle quality. It might not, but at least you can rule it out.

[BLG355]

Hot idle is still around 46 IAC counts. Open up the throttle blades. The increased airflow around the butterflies mixing with fuel may improve fuel distribution and idle quality. It might not, but at least you can rule it out.

I did want to lower it some more. I remember Mark telling me, ideally you want it close to zero on the hottest day of the year with the engine warmed up. I'll get it closer.

BLG

[BLG355]

you have to experiment with idle timing and idle speed. try to get high vacuum without any 'roughness'. too little timing is rough, and so is too much.

your cam is very small, i would expect no more than 20 degrees timing would be required for a smooth idle. 30 degrees is for a big cam. imo, of course.

have you forced open loop to see if the blm trims are why it's rough? is it rough while warming up? if it's rough before it even hits closed loop, it's probably not an AFR problem. it's timing or something else.

your trims will be screwy if your timing is out to lunch, or if there's some other problem...

are you sure it's running evenly on all cylinders? perhaps there's some other reason it's idling rough?

I seen in another post your mentioned setting idle timing from vacuum and I am going to try that next. I was messing with it from 16 to 22, i did have some good results but i was messing with a bunch of other things and the idle never seemed to bad until recently. I figured i'm overlooking something simple. I want to get a bung welded in to move my O2 front and i'm going to use the stock O2 bunch for WBo2.

BLG

[Roadknee]

Take a look at this. I've come to respect Danny a lot over the years.

http://www.chevytalk.org/fusionbb/showtopic.php?tid/253395/

This information was written for Holley C950 and HP aftermarket fuel injection. The principles work for GM injection too. Pay particular attention to his instructions on the base fuel table.

[brian617]

Ive noticed with my truck that idling for 1 minute at idle vs idling for 5 mins or better that the BLMs will come back around. The way I understand it, the reason to keep the idle VE and Off Idle VE close is for transition.

[brian617]

Take a look at this. I've come to respect Danny a lot over the years.

http://www.chevytalk.org/fusionbb/showtopic.php?tid/253395/

This information was written for Holley C950 and HP aftermarket fuel injection. The principles work for GM injection too. Pay particular attention to his instructions on the base fuel table.

As he mentions Cell Boundaries, I often wondered if increasing idle speed too much would have a bad affect on idle. Getting too close to the cell boundary given the stock TBI engines will idle hot at 525rpm. I recently lowered mine and it seemed like it made a difference. Of course I have no idea where to find the cell boundary table for reference.

[Roadknee]

Barry - what valve springs you running and what are your open and closed pressures?

[Fast355]

you have to experiment with idle timing and idle speed. try to get high vacuum without any 'roughness'. too little timing is rough, and so is too much.

your cam is very small, i would expect no more than 20 degrees timing would be required for a smooth idle. 30 degrees is for a big cam. imo, of course.

have you forced open loop to see if the blm trims are why it's rough? is it rough while warming up? if it's rough before it even hits closed loop, it's probably not an AFR problem. it's timing or something else.

your trims will be screwy if your timing is out to lunch, or if there's some other problem...

are you sure it's running evenly on all cylinders? perhaps there's some other reason it's idling rough?

I have found 26-32 seem to work best for me on even a stock cam vortec engine.

[BLG355]

Barry - what valve springs you running and what are your open and closed pressures?

I have Howards 98213 springs, they are 120# on the seat and 300# open.

[BLG355]

I'm still messing around with this, slowly. So I figured I'd give an update. I've been able to the BLM at idle down to +/- 1 or 2 from each other. I've messed around with the timing from 22 to as high as 32 at idle, just trying to see how it changes everything. My next step is to try it at lower settings. I'm also messing with the idle speed. It doesn't seem to like to idle really good below 650rpm with higher timing, and I am going to mess with it more when I try a bunch of lower timing values and see how it does. The smoothest it runs is right after it fires off, it's silk smooth for a few seconds then starts to roughen up...but I'm thinking a lot of it is in my head...I'm comparing it to a 2002 6.0 LQ4...which is smooth as silk from idle to redline. But the whole reason for this thread was the BLM's @ idle and I did get them in line after much effort in messing with the tables again. Now I just have to mess with idle speeds and timing some more and I think I got it nailed. Thanks to everyone for their input.

BLG

[Rocko350]

I have always tuned idle for the lowest, leanest , stable idle possible with the least amount of timing. This is of course modified slightly with the cam and combination being used. I have to get more creative with tuning a build that someone else put together. I know it sounds cryptive, but the method i've reverted back to is just what we used for older carbed cars. Points, timing, then carb. It has served me well going in that order. Usually set to open loop and have a vacuum gauge hooked up and drop timing back until it starts to get thready. Then start leaning it out until is stumbles a little and then add that fuel back. Drop it in gear and feel the transition. Hopefully no surge or stumble. Quick, small throttle move in gear, foot on the brake and it should settle down slowly to idle, and not drop like a rock. Give it what it wants. That's the trick.

As far as idle fuel trims, Idle should be one of the last subroutines fleshed out after the rest of the tune is in order. SO if there is some learning out at 5 minutes, maybe increase the prop gain a little and see if the trims come back into line quicker.

[BLG355]

maybe increase the prop gain a little and see if the trims come back into line quicker.

Is this what you are referring to? I haven't messed with this at all but I could always give it a shot and see what happens.

9082

Thanks,

BLG

[Rocko350]

Yes. The values in the 800 rpm line. Set those to the cells around them in the 30,40, and 50 kpa lines. Look at your over speed and under speed tables. Are they stock? How does the vehicle react during the transiotns from closed hrottle in gear to c/t in park. Any surge or stall?

Chris

[Roadknee]

$0D has specific proportional gain values for idle in Scalars. I think that table if for off-idle only. If your engine has larger capacity injectors and larger cam, and experiences a surge during O2 swings, reducing the values in that table where the surge is occurring can help get rid of it.

[BLG355]

Yes. The values in the 800 rpm line. Set those to the cells around them in the 30,40, and 50 kpa lines. Look at your over speed and under speed tables. Are they stock? How does the vehicle react during the transiotns from closed hrottle in gear to c/t in park. Any surge or stall?

Chris

It is pretty smooth. Sometimes it will surge a little and then settle out after going drive to neutral. Going into gear it always seems good.

BLG

[BLG355]

$0D has specific proportional gain values for idle in Scalars. I think that table if for off-idle only. If your engine has larger capacity injectors and larger cam, and experiences a surge during O2 swings, reducing the values in that table where the surge is occurring can help get rid of it.

I am trying to figure out where this surge I have is coming from. It seems anything below 2000 rpm at light throttle it surges. Cruising down the highway with the TCC I notice it pretty good. If I get the the throttle it goes away, it seems to be the worst 50KPA-20KPA. I tried lowing timing to get rid of it but it made no difference. It was around 34-36 in the higher vacuum lower rpm ranges and I slowly lowered it down to the mid twenties with the same results. I was assuming it was from O2 latency but no matter what I try there I cannot clear the surging. My last resort is to move the O2 sensor to the header and out of the Y-pipe but I was hoping to be able to get it out with the tune. Perhaps I will give this a try.

BLG

[BLG355]

I'm still messing with this. I read some from this thread http://www.gearhead-efi.com/Fuel-Injection/showthread.php?4601-Rolling-idle-o2-problem(long) and tried some of these settings with horrible results, I wanted to share. I was amazed I could actually see the surging on the log it was so bad. I thought the sub 2000rpm surging was bad before, this is really bad. So I'm thinking the o2 settings may be ok. I copied all the settings from the posted bin into mine, and I noticed the cross counts were going like crazy...perhaps too fast and causing the surging? I just can't seems to get anything I plug into this thing to work.

This is one hard thing to get straightened out. I really don't want to move the O2 from the stock location, but I guess I am going to have to and give it a try. It's really going to suck if I move it and it isn't any better. It seems the smoothest with the BIN I attached. I lowered the prop gain settings, I'm not 100 percent sure it did too much, it did throw the BLMs out of whack which I am working on getting those straightened out again. over all it isn't bad, but it definitely isn't right. what sucks is I had zero surging before the headers, after the headers install it started. Anyone have any other ideas or perhaps see something I am overlooking or didn't do?

Thanks.

BLG

[Roadknee]

The surge is caused by the O2 swings. It's interesting to note that installing headers on my stock engine did not create a surge. But I have helped 355Chev tune most of the surge out of his. He runs a 10:1 Vortec headed 355 with a bigger cam than yours and the Flowtech version of your headers with the O2 sensor in the stock location.

I've loaded the fuel trim parameters from his current BIN into yours (with slightly lower O2 thresholds) and attached below. They are a lot different than what you are running. Although I can't make any promises, I'm optimistic you'll see some improvement.

[BLG355]

I tried this bin on my way home from work and ran a log with it. It feels pretty good overall but I will run another log out on the highway and such to see how it feels. In the log you can still see some pulsing that looks like it goes in coordination with the o2 sensor. I think it's getting closer though. Is it the frequency of the o2 swings or is it more of a balancing act or both? what would be the first thing to try changing?

BLG

[Roadknee]

I'm on the road so can't view the log. Try bumping up the values in the rich O2 voltage vs airflow table by 100

[brian617]

Some good info here on closed loop fuel control, about halfway down under Process Control. There are many more pages of good info also on this site.

http://www.masterenginetuner.com/efi-tuning-3.3--theory---operation2.html

[Roadknee]

I took a look at your log. I really don't see any surge and it's definitely better than what 355chev is experiencing with his bigger cam. I don't know how much more I can help.

I wish I was smart enough to read code and understand how those fuel trim parameters are used to influence pulse width. I have a general idea, but to advance my understanding will take a lot more trial and error. Another reason to get the new engine finished and in my truck.

You've done a great job with your VE table. I've never seen one with as many cells that close to 128.

I noticed the initial advance in your BIN is set to 1.4 degrees. Is this where you have initial advance set with the timing light? It's important these two match because the ECM subtracts the initial advance from the values in the main timing tables.

I think your engine could benefit from more light throttle low RPM advance. I recommend setting the 2,000 rpm 30, 35 and 40 MAP cells to 40 degrees and blend into the surrounding cells. If you have any mild surge in these areas more advance might help.

[BLG355]

I ran a two logs today to see how it looked. I did notice one thing, during open loop it stuttered pretty bad off idle, looking at the log I see it appeared to be very lean. But the confusing part is on the second log I ran once it was all warmed up, it is removing fuel from all the cells. This will lean out he open loop startup even more correct?

Overall it feels really good, and it may not be surging I am feeling. But I noticed in the log, steady throttle and speed and timing, the rpms change. I'll attach a screen shot. It may be totally unrelated. Can changing the fuel trim parameters change the BLM's this much? I noticed they are all much lower. I changed the STOICH AFR from 14.7 to 14.1 too, which I though would go the other way, perhaps this could be why the BLMs are all lower now?
9187


On the timing, I did have it right between 1 and 2 degrees but I did just get it back to zero and fix the initial advance in the BIN. I've been slowly modifying the timing table. I like to make a change and drive it a few days to see how it feels overall. I've been slowly adding more in that range, I'll keep going and see how it works.

Once warmed up, it feels good with the exception of very light throttle I think I am feeling pulsing of sorts below 2,000rpms but it's hard to tell with the aggressive tires. I've been driving it a lot more lately and I'm sure 99.99% of people that would drive it and never notice it.

BLG

[Roadknee]

Well, I'm pleased those fuel trim parameters seem to be working. It took a lot of trial and error with 355chev to get there.

With the warmer weather we're having, perhaps the lean condition in open loop was due to the coolant temp being warmer, and the ecm was in a leaner part of the open loop afr vs temp vs vacuum table. The AFR the ECM was targeting during the lean condition was in the 15.3 to 16 range. You could try setting all the values above 14.5 to 14.5 in that table.

It's normal to see up to 50 rpm change in the log even when the true rpm is steady. It's just noise.

In all the work with 355chev, changing fuel trim parameters never changed BLM's significantly. Your BLM's went down because you reduced the stoich AFR from 14.7 to 14.1, about a 4% change. I imagine your BLM's were about 4% lower too, and you would need to reduce the VE table values by about 4% to bring them back in line. Or just put the stoich AFR back to 14.7.

[BLG355]

I will give that a shot. I was wondering if perhaps the large throttle body could be causing perhaps what I am feeling? The throttle is extremely sensitive and I was starting to wonder if at such light throttle with all the air coming in it isn't flowing consistent? I am seriously considering going back to the 350 one because I will probably hardly every go over 5000rpm anyways. I will have to drive it some more to see if I can get used to the touchy throttle. In the past year I only put 3000 miles on it...I will have to start driving it more.

BLG

[BLG355]

I think your engine could benefit from more light throttle low RPM advance. I recommend setting the 2,000 rpm 30, 35 and 40 MAP cells to 40 degrees and blend into the surrounding cells. If you have any mild surge in these areas more advance might help.

Is the upper rpm stuff ok at 40 too? Like 2000+ rpms in the 30,35 and 40 all to 40 degrees? I attached pics of what I did. I have surging about the 2000rpm though. less than 50kpa and 2000-2500 rpm I get some. So I think I will try changing the tables a little bit and see how it responds. Anyone ever go over 40 degrees in any of those cells?

BLG

[Roadknee]

I've run as high as 50 degrees in those cells, but that's usually for a larger cam with more overlap. The maximum advance the ECU will add is just under 42 degrees. If you want to add more, you'll need to bump up the initial timing. Personally, I like your spark map and would leave it where it is.

I don't see surging in the log. Not saying it's not there; just I don't see it. Try reducing the Upper Limit for Slow Filtered O2 (scalar) from 903 mV to 850 mV and give it a try. You can also multiply the values in the Proportional Duration Offset vs Airflow table by 0.5. I'd try these changes one at a time and together to see if they help any.

[BLG355]

I'll give that a try. I hope to have time this weekend to run a few logs and make some small changes to see if I can eliminate or at least move the surging again to perhaps figured out what I am changing to remove it from certain spots and hopefully eliminate all together. When it does it now, it almost feels like a manual transmission when you go on and off the throttle. About every second or so I can feel on-off-on-off-on feeling. The lower rpm stuff seems to be really good now, but the 2000-2500rpm when gently cruising seems to really buck now. Bucking is a better word for it lol!. Thanks again.

BLG

[Roadknee]

I'll give that a try. I hope to have time this weekend to run a few logs and make some small changes to see if I can eliminate or at least move the surging again to perhaps figured out what I am changing to remove it from certain spots and hopefully eliminate all together. When it does it now, it almost feels like a manual transmission when you go on and off the throttle. About every second or so I can feel on-off-on-off-on feeling. The lower rpm stuff seems to be really good now, but the 2000-2500rpm when gently cruising seems to really buck now. Bucking is a better word for it lol!. Thanks again.

BLG

I took another look and saw the surge or bucking your refer to. I think reducing the proportional gains some more in those areas is also worth a try. See attached. This, together with reducing the upper limit for low filtered O2 should do it. Try these before reducing the prop duration offset vs airflow table.

[brian617]

Out of curiosity Roadknee, what is happening when you reduce the values in that table? Lower values = ? Higher values = ?

[Roadknee]

Out of curiosity Roadknee, what is happening when you reduce the values in that table? Lower values = ? Higher values = ?

The fuel trim parameters together influence the ecm base pulse width calculation. When the O2 is rich, the ECM reduces the BPW to swing it lean. When the O2 is lean the ECM increases the BPW to swing it rich. Reducing the proportional gains reduces the amount the ECM alters the BPW and increasing the proportional gains increases the amount the ECM alters the BPW to swing the O2.

[BLG355]

I lowered the upper limit for low filtered O2 from .903 to .851, I will give this a try and see how it works. I will also try the prop gain as well(a few days later), I'm curious how it will respond even if it feels ok after changing the upper limit for low filtered O2. I'm curious, I noticed in several different similar tunes that the o2 mv is different. Is there a reason these get changed? Sometimes they are all the same, sometimes they are like these where 0 airflow is higher mv and sometimes its opposite.

9250

I changed my bin and I'll swap the chips tomorrow and run it for a few days. it is definitely pretty good. But it seems like it gets better in one spot and falls off somewhere else. I need to stop changing so many things at once! lol.

Thanks again for all your help. Everyone has been extremely helpful and I appreciate it all.

BLG

[brian617]

The fuel trim parameters together influence the ecm base pulse width calculation. When the O2 is rich, the ECM reduces the BPW to swing it lean. When the O2 is lean the ECM increases the BPW to swing it rich. Reducing the proportional gains reduces the amount the ECM alters the BPW and increasing the proportional gains increases the amount the ECM alters the BPW to swing the O2.

Reducing the number would decrease the amount of PW correction to switch from rich to lean or lean to rich correct? I can see where having a substantial increase of fuel pressure over stock like Barry and I are running, would make for a larger correction than needed.

[BLG355]

I ran a few days after changing the upper limit for low filtered O2 from .903 to .851. I still have some surging so I am currently changing the prop gain to how roadknee recommended. it's definitely going better and feels very close, I just have to keep trying these little things until I find the sweet spot. Thanks again for everyone's input and help.

BLG

[Roadknee]

Thanks for checking back in, Barry. If the prop gains don't do it, we'll probably try richening the O2 voltage threshold tables. I'd like to see a standing start 0-60 mph WOT datalog on a straight flat road if you get a change. Ideally with decent traction.

[BLG355]

I'd like to see a standing start 0-60 mph WOT datalog on a straight flat road if you get a change. Ideally with decent traction.

Still hasn't happened! :yikes: I thought I found a decent spot tonight, the traction was way better but it was slightly uphill. I spent last Sunday at the race track, I am thinking about taking the truck there this Sunday. If I do I will log every run. But here is my log for tonight I ran to check the BLM's and feel the surge difference, which I usually feel when filling in all the hard to fill cells out on the highway. I am also messing around with the timing at an idle as well which I will post a question or two about later. Here is the log from tonight with much less wheel spin, and a tad uphill. I think it pulled pretty hard the whole time, it felt good.

BLG

[Roadknee]

Still hasn't happened! :yikes: I thought I found a decent spot tonight, the traction was way better but it was slightly uphill. I spent last Sunday at the race track, I am thinking about taking the truck there this Sunday. If I do I will log every run. But here is my log for tonight I ran to check the BLM's and feel the surge difference, which I usually feel when filling in all the hard to fill cells out on the highway. I am also messing around with the timing at an idle as well which I will post a question or two about later. Here is the log from tonight with much less wheel spin, and a tad uphill. I think it pulled pretty hard the whole time, it felt good.

BLG

Overall I think that log looks really good. You ran 0-60 at 7.5 seconds a tad uphill... damn good for a heavy truck. Your converter flashes to 2,800 which probably helps. It's interesting that the BLM's in the areas where you reduced the proportional gains are a little low now. I hope you make it to the track. About all I'd suggest is to add some TPS AE in the bottom cells of the table. When you mashed the throttle the O2 went lean in the log.