LT5 ECM Tuning thread

[ShawnZR-1]

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 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!

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

[tpepmeie]

Originally Posted by ShawnZR-1

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.

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

[ShawnZR-1]

Originally Posted by tpepmeie

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.


Todd
93 #411

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....

[tpepmeie]

Originally Posted by ShawnZR-1

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.

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

[-=Jeff=-]

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?

[ShawnZR-1]

Originally Posted by tpepmeie

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

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.

[tpepmeie]

Originally Posted by ShawnZR-1

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.

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

[XfireZ51]

Originally Posted by ShawnZR-1

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....

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?

[ShawnZR-1]

Originally Posted by XfireZ51

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?

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?

[XfireZ51]

Originally Posted by ShawnZR-1

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?

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