LT5 ECM Tuning thread
 

Most of you saw my thread on the "other forum" about IAC counts. It started to turn into more of a general tuning thread. The best (or worst) thing I got out of it was that nobody really has a consolidated summary of the code for the LT5's ECM's.

In my free time :rolleyes: I'm going to start to delve deeper into the inner workings of the code for my '91. I don't expect this to take a weekend... it could quite possibly take a couple! :D

What I'd ask is if you have information, tips, tricks, trials, tribulations, or any advice, post up! I would love to gather as much information as the LT1 guys have wrung out of their ECMs :pray
:handshak:

Re: LT5 ECM Tuning thread
 

Really? I think at least a couple people have done this. As I have said before, I have the whole code commented in a working assembly file. I have this for each production year. The effort was in the hundreds of hours.

Having said that, I am more than happy to contribute to this thread and answer anybody's questions that I can. If I don't know the answer, I'll look it up in the code.

What I have seen a lot are questions like "...such and such isn't in TunerCat...where is it located so I can add it to my definition?..." I don't think it is productive to just give that stuff away. First of all, it's different in different model years, and second it can be dangerous if the person doesn't understand what "such and such" does.

Now if a person says, "I'd like to change this parameter to solve this problem, and I think it is located at 0x??. Is that right?" I'll definitely help confirm what you have found.

I'd love to get a four or five page thread going on this, so post away and I'll contribute what I can.

PS. Have you reviewed this? http://www.zr1netregistry.com/PromTuning.ppt

Todd
93 #411

Re: LT5 ECM Tuning thread
 

Shawn,

There's already definitions($8E, $AF, and $D0, along with the "A" versions for each) for the 90-92 ECMs that I have from Tunerpro. Some of the work has already been done. Unfortunately, they're pretty bare bones, nothing like what Todd has available. We might be able to pick up some additional items by going through the corresponding Tunercat .tdfs and merging the two into a single def file.

Re: LT5 ECM Tuning thread
 

I think the available Tunerpro definitions were made from .tdfs, so they will be very very similar, if not identical.

Re: LT5 ECM Tuning thread
 

Shawn good to see you post this over here :thumbsup: we need to hook up...

Steve

Re: LT5 ECM Tuning thread
 

shawn , dont mean to hijack the thread , did you like the results of taking the secondaries out . and did you have to redo your prom

Re: LT5 ECM Tuning thread
 

Yeah, I misspoke, I know that it had been done but I should have said it wasn't widely available as some of the other ECM code is.

In that you have the in depth knowledge, here is one of my dilemmas that has pushed me into the wonderful world of ECM programing:
I have a PIA surge when I'm coasting down in neutral or clutch in. As I come to a stop, the idle drops very low and sometimes actually stalls the engine. From what I have gathered, it may be related to the IAC follower portion of the code, however, there are no parameters for that in either TunerCat or TunerPro.

I played with the DFCO parameters but ultimately simply disabled it entirely to get rid of the popping in the exhaust (and a nasty surge on decel).

IIRC, it started happening sometime after installing my headers. I can't be absolutely sure though. I also have a Fidenza flywheel so the rotating inertia is obviously less than it was stock.

This is just the beginning of my unraveling of the inner workings of the code. I'm sure I will have even more questions....

Re: LT5 ECM Tuning thread
 

Yes, I'd remove them again in a heartbeat! A couple of things had to be ironed out in the prom but I think I'm about 90% of the way to optimization now. It's smooth as silk from idle all the way to 7200RPM!

My plan is to hit the dyno with a wideband in the next month and play. I am pretty sure I'm running rich but I don't want to pull fuel without making sure I'm staying safe.

Re: LT5 ECM Tuning thread
 

In my experience, this is not throttle follower related. What are the IAC counts doing during this surge? The throttle follower routine opens quickly as the throttle is opened, and decays slowly once the delta TPS stops increasing. It would almost certainly be decayed out in the coast down scenario you described.

I have found the consequence of getting too aggressive with the decay rates. What typically will happen is that on a very quick stop, when the clutch is dipped, the revs will drop too fast and the car can stall. IF the throttle blades are adjusted to high single digits at idle, that is usually enough airflow to avoid the stall.

curious, does this situation occur with the stock calibration, or just with a modified one?

Do you have a data recording of this event occurring?

Todd

Re: LT5 ECM Tuning thread
 

Does the LT5 ECM ( 1990 specifically for me) have any exrta inputs?

on my 89 with 1991 ECM and dash I use an extra input to feed my WBO2 voltage into the ECM and then using info from Craig Moates on Thirdgen I was able to send the data from that extra input to the ALDL stream in place of Battery voltage or such so I could correlate the WB with the ALDL Data

Can this be done with the LT5?

Re: LT5 ECM Tuning thread
 

Shawn,

Maybe Todd can tell us where the Prop Gain tables are for the $AFA, $AF Mask ID. If you're getting a surge, it may be due to too high a Prop Gain. That could also explain the popping exhaust on decel. You'll want to start by lowering the Prop Gain in the <16gm/sec cell.
I'd agree with Todd that you'll want to check the #of steps at DFCO and not drop the IAC steps too quickly. Had same issue with my old 84. At some rpm points in DFCO, I'd push in clutch and motor would go dead.

Whadya think Todd, would that help?

Re: LT5 ECM Tuning thread
 

This seems to occur with both the stock and modified. With the stock one however, it seems worse. I can't say for sure since I am unable to test back to back easily.

My IAC counts are well into the double digits at idle (15 or so). I honestly can't remember what they are during the surge. I'm assuming they run pretty low when it surges.

Question: Why does it only do it until the speed goes below a certain MPH? It seems to settle down around 5 MPH and if I blip the throttle when I'm not moving, the idle drops like a rock right to the set idle RPM and doesn't dip at all.

Re: LT5 ECM Tuning thread
 

I have the DFCO completely disabled.

I don't see any Prop Gain table, is it one of the ones that never made it into the masks?

Re: LT5 ECM Tuning thread
 

Right. That's why I asked. Is the exhaust popping with DFCO disabled? Is the motor dying with DFCO disabled?

Re: LT5 ECM Tuning thread
 

The idle air PID control takes over at 5 mph to control the idle speed.

While it is tempting to go in and start changing the calibration, such as has been suggested here, I honestly don't think that is the solution. GM didn't miss the tune on 6000 cars, and they all don't surge. Some things to check...

1) if the condition exists only with the modified cal, is the spark advance smooth in the region of low load, low rpm? Has the closed throttle advance been increased?

2) check the MAP hose for contamination. When I had this condition, the MAP reading at coast down was fluctuating wildly, and causing the surge.

3) if you still suspect the IAC movement is responsible, try to reset the IAC motor as outlined in the service manual.

Todd

Re: LT5 ECM Tuning thread
 

Hi todd,

I have a question, I had the secondaries removed and unfortunately VA has cut the HC standard down to 48. it's made it impossible to pass.

car does have cats (random ss, probably not nearly as good as stock) and I haven't yet had a wideband to see how rich the car is running but it seems WAY rich at light throttle.

I need some help to tune the car to pass emissions. marc is a bit too far away in chicago. I do have EASE, and I could install a wideband or take the car to a shop with a dyno.

the car is an LPE 390 and has the big 234 cams. do you think there is ANY way I can get this car to pass??? I tried doctoring the gas with alchy a few years back when I had the LPE chip in the car (open loop). it was even more rich and I could get the HC down to about 97 running 2/3 alchy, but I don't think that will work anymore, when I last tried the "cocktail" it still was up to 150 HC and I couldn't get the car to run with as much alchy in the gas. I love the ZR-1, but this is a problem

any ideas (besides moving) :mrgreen:

Re: LT5 ECM Tuning thread
 

Shawn,

I did a search on ThirdGen regarding surging decel. This was in a thread that deals with another ECM, the EBL. I won't go into what ot is but I used it for almost 2 years. Outstanding piece of work by RBob. That ECM in combination with Moates OStrich and Tunerpro RT really changed tuning.

So here's RBob's advice:

"'Option word 3 - bit 5 - OpDcl' is probably set. This will put the ECM in open loop fueling during decel. Once un-set, you may experience surging during decel. If so it may be either the proportional gain at the gms/sec airflow is too high. Or the ECM is switching in and out of async fuel mode.

DFCO, to enter this the vehicle speed needs to be above the MPH parameters, and the RPM above the RPM parameters. This is usually for highway speeds on a thottle lift. Keeps the CAT(s) from melting.

RBob."

Here's the link to that thread.
http://www.thirdgen.org/techboard/di...=surging+decel

Granted EBL code is not the same as our LT-5 stuff but I think you'll find that the controls do pretty much the same thing. Its just that RBob has provided an .xdf which makes all those paramters available to the tuner along with a bunch of tuning aids.
I agree with Todd that first and foremost you make sure everything is "mechanically" correct before turning to the tune.
As a side note, if any of you don't know RBob, he is one of the more highly knowledgeable sources over at 3rd Gen. Heck of a nice guy too. I keep begging him to build a version of EBL for our LT5s. :sign10:

Re: LT5 ECM Tuning thread
 

I wonder if corey could burn a couple of different tunes for you to try. he has alot of different tunes in his files. just a thought

Re: LT5 ECM Tuning thread
 

RK,

I would definitely put a WB on it. Is the issue you're having at idle or all through the rpm band?

Re: LT5 ECM Tuning thread
 

No, there's no popping with DFCO disabled. Well, there's kind of a burble on decel but with DFCO set to stock, there was a nasty surge and POP as it decelerated down the RPM band. VERY annoying to say the least! The car is almost undrivable with the stock chip.

Re: LT5 ECM Tuning thread
 

Well, to go along with the "Check Mechanical" before tune, I would pull the plugs and get a read on them. You'll be able to see if they are running rich.

High HC is usually a symptom of incomplete combustion. It's possible the spark is advanced too far or your plugs are fouled.

What kind of test does VA perform? Is it a two-speed, dual load or just an idle test?

Re: LT5 ECM Tuning thread
 

Ron, it'll never, ever pass. You'll have to get rid of it... just sell it to me, and that will solve your problem. :mrgreen:

Seriously, though, I'm not sure I have many good ideas in this case Especially from afar. you might have to bring somebody in to tune it in person. Is the VA test dynamic ie., on the rollers or just idle?

There are various tricks always mentioned, but I've never tried any of them (fortunately my state doesn't require testing). Dom is right, if it's been done, you'll find it on ThirdGen.Org DIY-PROM board. I just don't have any answers off the top of my head.

Good luck.

Todd

Re: LT5 ECM Tuning thread
 

Sort of sounds like what RBob was describing. Can you do a bin compare between stock and modified and see what if any difference there is?
Do you have a scan of the motor when its doing this?



RK,

As for your issue, my "suspicion" is the cam overlap. Particularly at low rpm. I am going to stress the word SUSPICION. I don't want to do a Bill Frist on your Z from hundreds of miles away.:sign10:
Again, is your problem primarily at lower rpm and idle? I'm guessing it probably is if its on one of those IM240 EPA Test dyno cycles.

Re: LT5 ECM Tuning thread
 

yes it's the IM240, they test at 15 and 25 mph

with the cam overlap it's going to be pretty tough at these standards

I need someone who can tune on the emissions machine which has proved hard to do.

I know the car is currently running rich, and hopefully leaning it out will help but I doubt I can get it down that low.

thanks for the advice

Re: LT5 ECM Tuning thread
 

rk,

Any idea what the O2 is reading at idle? Does it show lean? What about the BLMs?

Re: LT5 ECM Tuning thread
 

What are the numbers? Reading/limit ?

Re: LT5 ECM Tuning thread
 

Dom, Proportional Gains tables are below...Some of the formatting got messed when I pasted, but it should get you going.

Todd

Re: LT5 ECM Tuning thread
 

Thanks Todd. I was able to create items in the AFA and AF .xdf
For RK's issue, I'm wondering if we couldn't modify the O2 swing points because of his bigger cams, particularly at low airflow. Would you confirm for me that the addresses for these items in $D0A mask are the same or not?

Re: LT5 ECM Tuning thread
 

Ron, we had the same test here in Illinois what we would do on big cams install an air pump and pump fresh air in the exhaust lots of it and alchy.
Heck connect 2 leaf blowers if you have to :)

What i use to do with my Z i had Show Car insurance 2500 miles a year or less which was legal in IL got waiver from Emmisions.

Now Illinois is done testing OBD1 cars.

Pete

Re: LT5 ECM Tuning thread
 

Damn that looks familiar. He he.

Before tearing the calibration apart get a WB, log the O2s vs other perameters and post the log. That is the way we do it on the Megasquirt forum and it has proven to be the best way to get informative help. If I read the earlier part of this post its present in both stock and moded cal. That tells me its something else. From what i read I can't tell if its a too rich or lean.

Yes the calibration can be changed to allow O2 info to be reported in the ALDL stream and its simular to what was reported on the other forum.

Ron I am pretty sure you could get an emissions only calibration tha would pass. PM me later in the week for some thoughts, I am at the NCRS meet this weekend and am rather busy trying to make it happen

Tyler

Re: LT5 ECM Tuning thread
 

Look who's come out of lurker mode. How the heck are you Tyler? Figured you would join this thread eventually.

Dominic, what I posted was for the BFXB calibration. Ron has a '93 (?), so obviously the tables are not at the same address. Not hard to find, though.

Let's get some talk going about how or why things work in the LT5 calibration, rather than just table addresses.

Todd

Re: LT5 ECM Tuning thread
 

Been a little busy.

http://www.ncrsfl.org/Events/30thReg...thRegional.htm

OK. Something to think about. Just what do the spark tables do and how can manuliptating them solve Rons problem?

Off to the Lions Den for awhile.

Tyler

Re: LT5 ECM Tuning thread
 

Todd,

I thought the $D0A Mask was for the 92 which is what I was asking about. Are you saying that the code varies by broadcast code?
I was curious about the Prop Gains for Shawn's issue since he was complaining about a decl surge.
If Ron's problem isn't mechanical, I would look at lowering the O2 sensor R/L voltages. I'll be glad to discuss why I think this may help as an exercise for the members of this forum.
I would also suggest that if the members here are interested in reading material there are several good writeups available on 3rd Gen dealing with tuning in general, PID Controls, and the function of various IAC parameters.

Jeff,

I had previously asked Todd about inserting the WB data into the ALDL datastream. He brought up 2 very good points however for keeping it separate:

1. The ECM only sends data up to 6300rpm

2. My ZT-2 WB captures 35frames/sec, a data rate about 2x as much as the ECM. At WOT having that additional data makes tuning more accurate. The ECM data will "lose" significant portions of the scan even below 6300rpm.

So tapping into MAP and RPM outputs for the WB scantool would be the better way to go IMO.

Re: LT5 ECM Tuning thread
 

While I agree the ZT-2 datalogging would be better since thereis no RPM limit and the speed is faster, having it being able to connect to the ECm and show up in the ALDL datastream would be nice if you are using it to troubleshoot problems, it helps to keep the W data correlated witht he BLM / INT especially when doing part throttle tuning (where you typically are MOST of the time). Even though I have my Z now it does not mean I am going to do WOT blasts form everystop light.. just 1/2 of them :sign10:

Re: LT5 ECM Tuning thread
 

Yes, table addresses can vary by broadcast code (but are generally the same for a given Mask ID.).

I wasn't sure which problem we were trying to solve: 1) surging on decel w/ stock and modified chip, 2) passing emissions with highly modified LT5 w/ big cams.

$D0 is different than $AF in some areas, though I don't recall if these tables are in same place. Will have to check.

Todd

Re: LT5 ECM Tuning thread
 

Freaking computer geeks but still haven't answered this question.

Pete

Re: LT5 ECM Tuning thread
 

That is because we were waiting for you :-D

Re: LT5 ECM Tuning thread
 

Tyler,

The spark or SA tables are just that. Its 3D tables of the commanded
spark advance (SA). Based on the rpm and kPa at any given time, the ECM will command the stated timing. That's the simple explanation. However, there are several ancillary tables that are also used to modify the final SA depending on the parameters that are met (i.e. Idle, warmup, Decel, TPS, CTS etc.)With just what Ron has described I'm not convinced that the SA tables are the solution for Ron. Not sure that there is a solution for Ron. Getting some scantool and WB data would help in trying to narrow it down. But with big cams and more overlap, there's a tendency to overscavenge the chamber exposing the NB O2 to more air.
That causes the ECM to think the motor is running lean which in turn causes the ECM to try to "richen" the mixture which then increases the unburned HC. Lowering the O2 voltage swing points at lower airflow tells the ECM that the motor is not running lean. That's why the WB could be reading stoich but the BLMs show lean.
That's why I'm interested in the R/L O2 voltage tables. They're in the calibration just haven't been created in the .xdf or .tdf.
Make sense?

Re: LT5 ECM Tuning thread
 

So have we discussed everything that needs to be discussed for tuning our ZR-1s?

Re: LT5 ECM Tuning thread
 

Apparently, since nobody has a Decent definition file for them. I wish I knew how to decode them , if I had the know how and the means to do itmost any ZR-1 owner would be able to benefit fom them.

Unfortunately I don't know where to start on decoding a MEMCAL (Bin) file for our cars or any for that matter