I Have a 1991 Z28 with a TPI 305. I have recently installed some engine improvements. Accell SuperRam intake, Trick Flow Super 23 175cc Aluminum heads with 1.940 in intake valves, 56cc combustion chambers, 1.6:1 roller rockers, a mild cam and headers. No ignition improvement but the distributer and plugs are new.

I am very new to EFI tuning and I am trying to learn using TunerPro RT. I have noticed that during idle the spark advance spikes from about 17deg to about 32deg ever 3-4 seconds during both open loop and closed loop. RPM and MAP are steady. Does anybody know what might cause this or what items in the XDF I can isolate or manipulate to try to mitigate it?



Thanks for any assistance.

 

It is idle stabilization SA. It is these four tables:

RBob.

 

Thank you so much for your reply! ' any idea where I should start with these tables? i.e. what should I try to do with which one first, or do I just need to play with each and all of them?

Thanks

 

Not sure how to say/put this. But you stated that the RPM & MAP are steady:

Does this really need to be changed? It is something that you can play with, increasing or decreasing the idle stabilization SA. Be sure to keep decent notes and give plenty of time/driving to be sure of the affects of the changes.

One thing that is too easy to do is to give just a short amount of time/driving to evaluate calibration/BIN changes.

RBob.

 

What is your spark advance indicating for the first 1 - 2 seconds?

That is just my way of asking you what your spark advance is supposed be set at. Not sure if you're saying you have it set at 17* degrees, and it is momentarily jumping up to 32* degrees every 3 - 4 seconds, or if you have it set normally at 20* degrees (which is stock for an LB9), and every 3 - 4 seconds it drops from 20* degrees to 17* degrees, up to 32* degrees, then back down to 20* degrees. How did you setup the timing of the engine after your goodies were installed? What bin are you using? Did you set the timing with a timing light after you put the distributor back in, or just marked the way it was facing beforehand?

- Rob

 

If you can post an exported log from TPro (.csv file preferred), we can take a look at it.

 

RBob,
These little spikes probably are not that important in the grand scheme of things. I'm mostly just trying to learn how to tune EFI and use TPro at this point.

Street Lethal,
The timing was set with a light @ about 6*deg per the Catalyst. The .bin is a copy of the original .bin. At this point all ignition scalers and tables are stock. On the TPro engine data monitor the spark advance line is fairly steady with these little spikes about every 3-4 seconds. The whole event only lasts about a quarter of a second. The top of the spike is a point - not smooth or rounded. Then the spark advance returns to about where it was before. Then a straight line until the next spike.

 

Log would be helpful?

 

I've tried to upload files before with no success. Let me try again.

Hey, I think it worked.

 

When you start adding aftermarket parts, the kpa idle location in the VE table will of course soon deviate from its' stock location because it is affecting vacuum, so you will need to look at the surrounding cells in that new location in the spark table which works hand in hand with the VE. You more than likely seen an increase in kpa at idle by adding better parts (obviously) so being closer to the higher kpa cells, it will essentially want to "tug" the timing upward because of the average it is commanding, despite having and seeing a smooth RPM and MAP throughout...

- Rob

 

Several observations (see attached .xlsx file):
- An Error 51=non-specific MEMCAL Error is reported. Should not exist. Bad connection somewhere? Perhaps bad code-checked checksum.
- Spark seems strange. Don't understand the spark peaks (up to 40 deg+) right after startup. Spark thereafter looks normal up to approx log sample 350, where spark begins to decline significantly and remains at what seems low until engine into Closed Loop (CL) at sample 993. But later also seems low. hard to tell without BIN.
- Sample 1040 and beyond. Not related to your problem, but o2 sensor cycling in and out of "Ready". Indicates need for heated NBo2 sensor if want to maintain CL at idle.

Based on tables RBob showed, you can expect spark to fluctuate approx. +/-5 degrees when spark RPM is respectively below/above Desired Idle RPM.

Would ask that you post BIN, XDF and XDL files for analysis. Something does not seem right.
HTH, Elky

 

Rob,
I looked at the spark advance table. It doesn't seem to vary that much around the RPM range and MAP that it is idling at. Keep in mind that I am very new at this and probably don't know what I am Looking at.

Elky,
I included the .bin and the .XDF, .ADX that I have been using along with two logs for analysis. Both logs are from a dead start up. Everything seems to surge at first then suddenly even out in both logs. I'm not sure why it surges and or what happens to suddenly cause every thing to sort of smooth out.

After I finished the recordings I fooled around with those tables that RBob mentioned. Yes, I was able to change the amount of the spark advance peaks by changing the numbers in those tables. Those little spikes seem to be from small changes in the RPM. Maybe that is built into the .bin to help smooth the out the RPMs. They would seem normal then unless something else is going on to cause the errors in the RPM. In other words, are those spark advance peaks happening more than they should?

I want to thank everyone for your help so far. You don't know how stoked I was when I was able to change the numbers in those tables and make the engine react in the direction that I wanted it to.

 

Below is your Main Table w/SA Closed Throttle position (for others to see).

Give me a second to look at the log because I am in the garage flushing a sticky lifter...

- Rob

 

Can't get the log to open, might be my laptop, not your upload. Where is your VE at idle in the table? What RPM and what kPa? You appear to be set for 850-RPM in Park/Neutral, with 750-RPM as your base when fully warmed up. You seem to have a very low spark advance setting at idle, why not bump it up some from 15*/17* to 21*/22*? Your engine would love that...

- Rob

 

Rob,
After about a minute it is at 1000rpm and 50kpa. At bout two minutes it's about 900rpm and about 53kpa. After three minutes it's in closed loop and 850rpm and 53kpa.

Help me out...where do you see "850-RPM in Park/Neutral, with 750-RPM as your base when fully warmed up."? I will try bumping spark advance up by about 6*deg. Spark Advance Closed Throttle Vs. RPM table...Right?

 

You're Idle target in Open Loop is 1000-RPM, so this is what you will see during cold start. As the engine gets closer to operating temperature, the Closed Loop parameters are soon met, then it switches to the Closed Loop idle settings. Look at the picture below. Your Closed Loop idle speed settings (left), and the RPM adder when in Park/Neutral (right) embellishes 100-RPM. So your base is 750-RPM in Closed Loop during operating temperature, but 850-RPM in Park/Neutral because of the RPM adder...

Now look at the SA Main Table again, the area that shows your idle RPM and kPa specifically. What average do you see?

- Rob

 

Yes, just change the 800-RPM and 1000-RPM to 23*, leave the 400-RPM cell alone...

- Rob

 

Rob,
You asked; "Now look at the SA Main Table again, the area that shows your idle RPM and kPa specifically. What average do you see?"

Is 26.02 the answer your looking for ??

 

Each cell in the Main Table uses the surrounding cells to calculate an average. Your Initial timing is set for 17*, yet you stated that you occasionally seen 32* every three to four seconds. So your Initial timing is your 17*, while Open Loop at 1000-RPM and 50-kPa shows 31.99* as part of its' average in the SA Main Table, which is the 32* you are seeing (it's being tugged). It will happen in Closed Loop as well, despite targeting a tad lower of an RPM at 850-RPM. The spark advance needs to be smoothed out by either raising your Initial, or lowering the surrounding cells in your SA Main Table...

- Rob

 

Looked at your BIN, logs, etc. Some comments about the 4/18 log (see attached .xlsx):
- Immediately after startup, have major surging fluctuations in RPM approx every 2 seconds until sample 264 where it finally settles down. Don't know why, but making some changes below may help.
- Because you are $8d, looked at your log with S_AUJP ADX. it's clear there is something causing the ECM to believe the car is moving when it's not. This can be proven by looking at your Commanded Idle RPM .vs. Coolant in the attached log. At 133*F, your table shows idle should be commanded at 750 RPM. You are at 850 (see sample 837+). This can only happen if the car is determined to be moving where 100 RPM is added by the code to Commanded Idle RPM ("Desired Idle PM" in Log). Something is telling the ECM the car is in 4th gear regardless of whether it is in P/N or in any Gear. Don't know why this is happening, but if your VSS is not correctly connected, this can be the issue. Very important that VSS be properly connected to the ECM as it affects many idle, o2, etc. parameters.
- Best to have your Spark table at idle all at the same advance. Look at yours below and compare it to something that works very well. Look only at main spark idle (<=800 RPM). All spark is the same.
- Little known, but until coolant temp is > a certain coolant temp the 100 kPa column of the main spark table is used. Looks like your mask is 123*F. At sample 664, spark changes from 100 kPa column of main spark table to closed throttle spark table.
- The main spark table at idle should generally be set to agree with desired spark at idle (approx 21-22* for your setup). Yours may be different. Note your tables differences (11.85 deg .vs. 15.47 deg). Both too low IMO.

The pics below show your tables compared to those where an engine with mods similar to yours is very stable, without startup RPM flare or fluctuations.

And BTY, the values you changed in the idle fluctuation tables generally have no effect unless a really radical engine. Generally OK to leave as is.

Yours


What works well

 

Rob,
I bumped the Idle up 6*deg. It did seem to run a little smother. It didn't seem to vibrate as much and it actually seemed a little quieter.

Elky,
Thanks. That's going to be quite a bit for a newb like me to sort through. I'll be looking at it for the next little while. After reading through it a couple of times though...I seemed to remember seeing something about idle speed adding. I have gone through each item in the XDF several times to try to figure out what everything does. ( haven't figured much out yet. ) Any way, there is a Scalar for "Engine idle speed added to base when in Park/Neut ". With the description of "This is the amount that the RPM will increase by when in park/neutral. The value is 100. Wouldn't that explain the 850rpm at sample 837+?

Again, thanks one and all for your help

Bailey

 

That is what you are after. If you learned how to tune over the years from RBob, he would constantly pound that into your head that an engine that runs smooth, and runs quiet, is what you are after. Anything else feels fast because of the vibration and noise, but you're not running efficient that way, and actually running a lot slower. If the engine is quieter with less vibration after bumping the spark advance up six more degrees, then it is telling you that it is happy. Give it what it wants, always...

Good job Bailey.

- Rob

 

Bailey - First, forget my earlier comments about the VSS for now. Yes, the 100 RPM added to Commanded idle RPM in P/N is what you are referring to. But don't change it unless you know what you are doing. It's there for a reason.

But this is important to understand. Explaining the spark issue another way -- Until a certain coolant temperature is reached, the SPARK ADV, Closed Throttle .vs. RPM Table is NOT USED when idling. Rather the spark used is that in the 100 kPa column of the Main Spark Table, based solely on RPM. MAP kPa does not matter. There is nothing you can do about this for now. The Scalar in your XDF that determines the temperature at which the table change is made is: "Spark Advance Cold Disable Temp", which is =50*C or 122*F in your BIN. DON'T CHANGE THIS unless you know what you are doing.

Looking at your Main Spark Table, this means your TDC spark will be 11.95 deg at 800 RPM and below until 122*F coolant. You can see that in the logs. Then at 122*F and above, the SPARK ADV, Closed Throttle .vs. RPM Table begins to be used for idle spark based on the current RPM and MAP kPa. That's why in the logs you see the spark change to the higher RPM/MAP-based values in your Main Spark Table. You can also see IAC position drop by 10 counts. This is called IAC kickdown -- the IAC setting is kicked-down by 10 steps.

I understand your situation of not grasping all this now. We were all there at one time. So just trust the fact there is a spark TDC at idle at which your engine is happiest. What you need to do is trust that the following will work as a starting point, as shown in the tables previously provided:
- In the Main spark table at 400, 600 and 800 RPM at every MAP, set spark all to the same value. IMO, start with 20 degrees. Then at 1000 RPM between 30 and 60 kPa enter 20 degrees. You now have a constant spark at idle, whether in gear or P/N. Not initially required, but later you may want to smooth values so there is not a quick spike up in spark.
- Next, in the Closed Throttle table, enter 20 deg for 0, 400 and 800 RPM. Then at higher RPMs, as shown in the above table, set the spark to slightly less than 20 deg, say 16 deg. This will have the effect of mildly braking on deceleration in gear. Higher spark in the factory table (yours) can have the effect of feeling like the car wants to keep going when you are trying to gradually stop. If you detect a hesitation when accelerating after coasting in gear (unlikely), you can increase the values above 800 RPM.

Now with 20 deg at idle, you can see how it feels. Can even try higher values, but 22 deg is likely max. A vacuum gauge providing the highest vacuum at operating temp will reveal the optimal idle spark. But a 2-3 degree difference between 20 degrees and optimal will be hard to detect.

I would also suggest returning the values in the tables RBob mentioned to factory values. They are there for a reason, again unless a radical engine. It's OK if spark oscillates at idle with RPM slightly changing +/-25, unless it's causing engine surging. It's by design.

HTH, Elky

 

Bailey, the above is correct regarding data swing/oscillation. Meaning that you cannot be dead set on 23* of timing at idle and expect it to remain there as a constant until the throttle is suddenly increased. Example, mine is set for 24*, but will swing up to 26*, then down to 23* as the engine is idling. The intake charge is not predetermined and fixed, Closed Loop O2 correction is constantly correcting for what it is reading, regardless whether using a narrowband or a wideband, the air/fuel will fluctuate as will everything else that works in tandem with it, thus the term "Closed Loop". When we tune we are tuning for the greatest reduction of that range...

- Rob

 

I found the “Spark Advance Cold Disable Temp” scalar and put a description in the box so now I know what it does. What causes the IAC to kick down? I’d like to be able to put a description on that one too.

Can the MAP gauge in the .ADX gauges be used instead of vacuum gauge? I put a vacuum gauge on it just to see how it would work. It mostly stayed pretty close to 19 in Hg. It didn’t really vary by much until I went way off from 20*deg.

The engine seems to idle good at 19*deg spark advance. It runs smooth and quiet. (Not bad for Headers and a 3”straight pipe out of the cut outs.) The only thing is that it does get some knock counts just as it is turning over but not once it is running on its own.



I think I am happy with it unless the knock counts need to be addressed. I think we answered my original question; “I have noticed that during idle the spark advance spikes from about 17deg to about 32deg ever 3-4 seconds during both open loop and closed loop. RPM and MAP are steady. Does anybody know what might cause this or what items in the XDF I can isolate or manipulate to try to mitigate it?” Those little spikes appear to be part of the whole system that operates the engine. And above all, I learned a lot along the way.



Thank you everyone!



Where to next?


Bailey

 

GM engineers determined it was needed and wrote it into the $8d and other code. It's an indication the engine is warm enough to transition from the main spark table 100 kPa spark column to the closed throttle table, and engine does not need as much air to run so IAC is closed 10 steps.
While you cannot see it with your XDF, open the TPro hex editor and look at the byte at 0x62D. It's 05. Twice that value is used to kickdown the IAC (0x05 * 0x02 = 0x0a = 10 dec).

Yes MAP can be used. Same as vacuum, just different units of measure. Highest value at idle = optimal spark.

​​​​​​Knocks: Will always get knocks at startup. Not to worry.
Spark spike: Again normal and nothing to worry about if it settles down in a couple of seconds. The Table in your XDF (Spark Advance Startup vs. Temp.) adds 15.12 degrees to TDC spark from 100kPa column (12 deg), between coolant of 68-132*F. That's 27 deg right there, plus 5 deg for any underspeed (RPM < Desired Idle RPM) = 32 deg at a minimum. The startup spark adder should be decayed out over a couple of seconds so it disappears.

However, there is something strange with yours. Injector PW is all over the place and MAP and RPM are not steady, all for many seconds after startup. This is not normal. All should be relatively steady a few seconds after startup. Any chance there is a small vacuum leak or the MAP sensor possibly bad?

 

Elky
Yes, I'm sure it could have a vacuum leak. Or the MAP sensor could be going bad. It is the original one.
I'm wondering... could I send you a log ( .csv file ) of the way it is set up now and would you mind taking a quick look at it and telling me what you think? If the answer is no, I would understand.

Bailey

 

Glad to look at a log and have looked at yours previously, but a log won't directly show vacuum leaks, etc. -- just their possible symptoms as indicated in my prior post. All this while, you've only been idling. Does the engine surge in closed loop in P/N if held at steady RPM (2000-2500)? Could log that if so.

 

I haven’t posted in a while, but are you sure your timing chain isn’t having slack-issues?

Regarding timing assessment, how is the condition of your harmonic damper?

The former is going to give you erratic valve timing, especially at idle, or at “coasting” speeds.

The latter, if the elastomer joining the inner ring to the outer ring has failed, you will never get a timing light to give you a useful assessment of the timing.

 

W.E.G.
Thanks for your input. The timing chain is new. The harmonic damper looked to be in good shape when it went back on.

Here are some CSV files. One is from a cold start to closed loop then dropped in gear and pulled out of the garage. The other is at 55mph with cruse control on.

 

Quote:

Here are some CSV files. One is from a cold start to closed loop then dropped in gear and pulled out of the garage. The other is at 55mph with cruse control on.

Finally looked at 55 MPH log. TPS% and MAP are all over the place at a steady 1425 RPM and 56 MPH. Were you on a level road? If not, data is not meaningful.

What about this from earlier post: Does the engine surge in closed loop in P/N if held at steady RPM (2000-2500)? Could log that if so.
Note in Park, not moving. Do you hear a change in engine sound at a steady RPM?

 

Question: When does the spark timing use the Closed Throttle Spark Timing, vs. the main table? Is that determined by TPS sensor?

Case in point ... tuning a car ... when adjusting the idle set screw out (trying to reduce IAC at idle) ... once TPS voltage went from 0.54 to 0.55 the timing jumped ... well it changed from the closed throttle timing, to something the main table.

I could not find where the 0.54 volts was set in the BIN.

Mark.

 

It is by TPS%:

L8647: FCB 2 ; ENAB IF TPS > 1.2%

As you opened the throttle blades the ECM thought it was no longer in the idle state. Need to key-off for about 10 seconds, restart, let settle, then continue.

RBob.

 

I was able to turn the idle down restoring the 0.54 volts and the timing came back to close throttle timing. I was reading the hac and seeing address $647 is where it's stored. When I look at my BIN, I get a "2" there. Guess i was expecting 1.2 or a mv setting for the TPS. Im more curious than anything with how it's setup.

Mark.

 

I am looking at ANHT_Hac ... FYI. Looking up "647" references. I can see where it loads it and compares it, thus it would be the base to compare to for the 1.2%. I can't convert the stored number "2" into what 1.2% is. Idea?

 

The HACs aren't always correct. I use N * 0.392157 to convert from the BIN value to the TPS% value.

RBob.

 

Hmm. I didn't do any conversion on the data ... that would explain it.

I was working on another engine yesterday trying to get base tune done (HUGE cam), and the idle was crazy. Discovered the TPS was sticking!!! Same issue ... as soon as TPS was up, the spark switched to main table.

- Startup spark is the 0 RPM row and typically in the 90-100KPa cell.
- Closed throttle (below 1.2%) is a separate table which comes in after startup.
- Main spark table is used when above 1.2% throttle.

-

 

The $8d code considers anything < 0.78% (Scalar 0x647=0x02) with MPH=0 to be an idling state.This is why it's important to have TPS properly set at idle.Many code considerations made using this value. When moving, <= 2.3% and MPH <= 15 are used for similar considerations. I use a TPS% conversion formula of 1/256 = 0.390625. RBob's formula is 1/255 (0.392157). Either way is close enough.