E38 Spark Table Operation

Hi.

After performing some logging on the E38 used in the Holden VE SS (Pontiac G8 GT), I have determined what is causing some of the poor throttle response issues on the factory tune.

Mainly under light throttle applications, I have noticed that the spark advance when going between Idle Base Spark, Main Spark and Idle Coastdown Spark, is slowly ramped up/down between these tables. For example, when cruising at light load (Main spark table being used), if the throttle is closed, the advance slowly ramps down to the coastdown table value for that rev/load. When the throttle is opened slightly again, the advance does not immediately return to values in the main spark table, but instead are ramped back up very slowly over a period of 1-2 seconds. This also happens when at idle and then opening the throttle - the spark is ramped slowly from the idle table to the main spark table.

This causes a noticeable flat spot in response until the advance reaches the correct value in the main table. I understand that the factory tune may be intended to smooth out things like throttle transitions, however I personally find it annoying and would like to change this operation for a faster response.

Is there a parameter that can be changed to remove this spark ramp up/down between tables? I have already disabled Tip-in limiting and burst knock, which have had no effect. Is there an engine torque management parameter which may be causing this?

Any suggestions would be appreciated.

Thanks.

Have you tried disabling spark smoothing? If the car is a stick shift it might be enabled.

I'm still battling asinine behavior at light throttle in my car...the spark advance won't stay on the main table...which causes a surge. Drives me insane. It's not a cam surge as the engine is smooth as glass when the spark stays where it should, but when the E38 plays with the spark advance, the whole car surges like crazy. Drives me nuts.

Hi Mike, I forgot to mention that I have the A6 trans, so spark smoothing is disabled by default.

It's interesting however that what I am experiencing is exactly what spark smoothing would cause.. I just hope it's not part of the inherent design of the ECU.

I may have experienced a similar issue to yours in the past, but not sure what I changed to fix it. Does the timing actually drop as low as the idle table? Any big changes in MAP or MAF values at the time it happens?

Thanks.

No changes I can see in MAP or MAF...but dynamic air drops...and when it does, timing drops a TON...and you really really feel it in the car. I really truly hate my car sometimes because of it. If I could just figure out how to make the dam PCM give me the right spark when I want it, I'd be so much happier with it.

Hmm, Since Dynamic Air, and only Dynamic Air, drops and timing drops too (opposite of what one would expect) it must be switching tables as you suggest.

Have you tried running the car in MAF-only mode, with Dynamic Airflow disabled? Maybe it won't switch tables??

Also, why would the Dynamic Air and MAF Air values be that different? Have you dialed in the Speed Density coefficients with the BlueCat GMVE calculator?

Quote:

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Originally Posted by bradyzq

Hmm, Since Dynamic Air, and only Dynamic Air, drops and timing drops too (opposite of what one would expect) it must be switching tables as you suggest.

Have you tried running the car in MAF-only mode, with Dynamic Airflow disabled? Maybe it won't switch tables??

Also, why would the Dynamic Air and MAF Air values be that different? Have you dialed in the Speed Density coefficients with the BlueCat GMVE calculator?

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Yeah, that's exactly why I don't understand it. I've tried it in MAF only (set to disable VE at 4 rpm instead of 4000), I've tried it in SD mode only with the MAF failed, and I've tried it in blending...always happens. I've got the VE coefficients dialed in up to ~3500 RPM...so when I have it blending, I set it to go pure MAF at 3000. It's too hard for me to collect data at higher RPM and every load point as I don't have a load bearing dyno.

Did you try lowering your main spark tables a bit and raising your idle/coasdown tables in the areas you are experiencing this? I did this in the first 2 rows of the tables and it helped solve a bog I was getting at off idle cruise as the tables transitioned.

This is what's in my car now. The VE coefficients are stock again (figured I'd try that with them disabled to see if it made any difference...it didn't).

I know the MAF table isn't really smooth at higher airflow...but it's what the wideband wants. Every time I try to smooth it out, the AFR at full throttle is all over the place again and the wideband data makes it look like this again.

Attachment 44181

Anything in your intake setup that is disrupting smooth airflow? If so check out the abaco MAF. It has the ability to smooth the airflow signal which may cause variations in your curve. I had a similar problem due a slight ramp in my air intake feed where airflow was merged between my intercoolers. The Abaco worked to smooth the signal and curve.

My 2011 sierra with a maggie has the same issue! When coming to a rolling stop and then tipping back into throttle, its like a 1-2second lag, or dead spot! Ive tried making my idle and main tables match, with no help.

Interested in this subject also.