LFX E39 tip-in KR? It's not burst knock

Hi folks!
I swapped an LFX into my Exocet and have finally gotten around to tuning it. I've tuned my MAF and VVE and everything seems to run very well. However, there are two issues I'm having (with two corresponding threads in this forum) that I'm hoping someone might be able to help me fix. Here's the knock issue.

I seem to be experiencing knock on tip-in. I disabled burst knock to see if that was the cause, but the knock persisted. I can remove all the spark advance in the world, and I'm still reading knock on tip-in. There is no cylinder consistency - it appears in various cylinders depending on the event. The engine is mounted on stiff poly bushings, and I can't seem to find anything loose that would be triggering the knock sensors. Wideband EQ ratio looks good and narrowband O2 sensors don't seem to indicate a lean condition.

Attached is a tune and a log. Does any kind and wise soul out there have any ideas about this issue? Attachment 141579Attachment 141580

I'm just relay what I've read elsewhere, but it might be worth posting in the GM Gen V section. There doesn't seem to be much traffic here in the V6 section. I'm curious about what you find. I have an LFX in an RX8, but haven't yet noticed this issue.

Might try higher octane fuel/race gas and see if it is actually knocking.

Is it likely to be a fuel issue on a stock engine? I'm running 91 pump gas, where the application only calls for 87. Also, check this out - it's my spark table from my spark tuning session, before I realized that the timing changes weren't helping with the knock. Look at the trench I dug in the tip-in zone! :eek:
Attachment 141739

You really shouldn't try and post a different thread for different issues. They may be (probably?) related. If this is a stock engine moved into a different car, I would set pretty much everything back to stock and then tune air/fuel for any changes to intake/exhaust.

Doesn't change the suggestion to try higher octane to check for real knock. Higher octane and knock doesn't reduce, then you probably don't have knock.

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Originally Posted by gtstorey

You really shouldn't try and post a different thread for different issues. They may be (probably?) related. If this is a stock engine moved into a different car, I would set pretty much everything back to stock and then tune air/fuel for any changes to intake/exhaust.

Doesn't change the suggestion to try higher octane to check for real knock. Higher octane and knock doesn't reduce, then you probably don't have knock.

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Thank you for the help. It is indeed a stock engine moved into a different car, and air/fuel was tuned before moving on to spark.

So what happens with stock spark tables? How are you adjusting spark?

With the stock spark table, this is my logged KR:
Attachment 141767

To try to tune it out, I was subtracting those values from the Spark/Advance/Base High Octane table, then smoothing the area around the reduced values. That's how I ended up with the trench pictured in my last post. With the trench, the KR was better, but always that 1-2 degrees at tip-in persisted. Here's the logged KR with the trench in the base table:
Attachment 141768

When I realized that I couldn't lose the KR by reducing the base table, I did some searching and found out about burst knock. I disabled that (and confirmed with a log that it was truly off), but it didn't change the behavior at all. Even a slow throttle application tends to result in some KR as the engine loads up.

It's happening during PE. MAF table is wrong. This throws off cylinder airmass, so the spark map isn't tracking where it should be.

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Originally Posted by SiriusC1024

It's happening during PE. MAF table is wrong. This throws off cylinder airmass, so the spark map isn't tracking where it should be.

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Interesting. I assume you must have looked at my log and tune to figure that out, and I'm grateful for your taking the time to do so.

I'm curious how I might have screwed up my MAF tune. I mostly followed the MAF tuning guide on Youtube from Goat Rope Garage, which didn't involve touching any PE settings. From his guide, I disabled DFCO, open loop, LTFT, COT, CFCO, and dynamic airflow. However, I also followed HP Academy's MAF tuning video which suggested setting the entire gas PE table to a fixed value (I went with 1.195).

I switched all of those back to the factory settings when I was done with MAF and SD tuning. My final MAF tune showed an EQ error within 2-3% across the range, mostly on the rich side. EQ error in subsequent logs looked good.

Should I have done something different while MAF tuning? Should I have disabled PE entirely?

I should add that this is all road tuning, not on a dyno. I've been doing WOT runs and varying loads and rpms during my logging sessions. My only goal for spark tuning was to reduce KR, not to add any advance.

Try tuning closed loop with fuel trims. That seems to be preferred way on here vs open loop wide band.

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Originally Posted by fixbroke

Interesting. I assume you must have looked at my log and tune to figure that out, and I'm grateful for your taking the time to do so.

I'm curious how I might have screwed up my MAF tune. I mostly followed the MAF tuning guide on Youtube from Goat Rope Garage, which didn't involve touching any PE settings. From his guide, I disabled DFCO, open loop, LTFT, COT, CFCO, and dynamic airflow. However, I also followed HP Academy's MAF tuning video which suggested setting the entire gas PE table to a fixed value (I went with 1.195).

I switched all of those back to the factory settings when I was done with MAF and SD tuning. My final MAF tune showed an EQ error within 2-3% across the range, mostly on the rich side. EQ error in subsequent logs looked good.

Should I have done something different while MAF tuning? Should I have disabled PE entirely?

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Idk about the 2-3% error. It's a lot higher than that.
Attachment 141821

The MAF curve shouldn't have humps in it.
Attachment 141822

When MAF tuning did you set High RPM Disable to 200rpm? Don't worry about disabling PE. Use CL fuel trims off the narrowband. When PE kicks in switch corrections to wideband.

Is it a stock intake tube? Was there motivation to work the MAF cal that much? I would say the most noticeable thing here is that it only knocks in power enrichment. The fueling does look to be richer than target in PE...so maybe not the culprit. But if you look at PE spark adder, its definitely throwing a couple degrees at it, keeping it snugged up against that MBT surface. That'll keep it knock-prone, but that's where you want to be. But the cams are also moving in the background and are adding spark with RPM. I'd say definitely log intake and exhaust cam positions so you can see and correlate the symptoms with what they're doing. I'm betting they're heavy handed with spark.

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Originally Posted by smokeshow

Is it a stock intake tube? Was there motivation to work the MAF cal that much? I would say the most noticeable thing here is that it only knocks in power enrichment. The fueling does look to be richer than target in PE...so maybe not the culprit. But if you look at PE spark adder, its definitely throwing a couple degrees at it, keeping it snugged up against that MBT surface. That'll keep it knock-prone, but that's where you want to be. But the cams are also moving in the background and are adding spark with RPM. I'd say definitely log intake and exhaust cam positions so you can see and correlate the symptoms with what they're doing. I'm betting they're heavy handed with spark.

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Welcome back, smokeshow.

I believe he's having to redo MAF because it's a swap.

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Originally Posted by SiriusC1024

Idk about the 2-3% error. It's a lot higher than that.

The MAF curve shouldn't have humps in it.

When MAF tuning did you set High RPM Disable to 200rpm? Don't worry about disabling PE. Use CL fuel trims off the narrowband. When PE kicks in switch corrections to wideband.

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Thanks for looking at my log.

• The errors you're seeing are with everything re-enabled, but with tuned MAF and SD. Before re-enabling everything, MAF error was 2-3% (see attached log and tune, taken from when I had finished MAF tuning and was about to move on to SD tuning). I think the difference between the commanded and actual EQ in your screenshot is caused by something other than MAF tune.
• The reason for the hump in the MAF curve is that my MAF sensor seems to top out at 9900 Hz, so values above 9900 are just sort of arbitrarily scaled and smoothed, erring on the rich side.
• Dynamic Airflow/High RPM Disable was set at 100 while MAF tuning.

Attachment 141878 Attachment 141879

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Originally Posted by smokeshow

Is it a stock intake tube? Was there motivation to work the MAF cal that much? I would say the most noticeable thing here is that it only knocks in power enrichment. The fueling does look to be richer than target in PE...so maybe not the culprit. But if you look at PE spark adder, its definitely throwing a couple degrees at it, keeping it snugged up against that MBT surface. That'll keep it knock-prone, but that's where you want to be. But the cams are also moving in the background and are adding spark with RPM. I'd say definitely log intake and exhaust cam positions so you can see and correlate the symptoms with what they're doing. I'm betting they're heavy handed with spark.

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Thank you for the info!

Not a stock intake tube, due to the swap. I was getting a very bad hunting and occasional stalling at idle with the stock MAF calibration, but it's smooth now.

I didn't know about the PE spark adder table till I read your comment. I'm inclined to zero it out, as some other cat-less folks have done, but you say that it's where I want it to be?

It's been rainy and nasty here lately, but I'll try to get the car out soon for a logging session to see what the cams are doing.

In the first log the error is above the High RPM Disable threshold, so it's all MAF. Latest log looks better. This points to inconsistency in MAF readings. I'm just now remembering someone had a weird issue with MAF on those kind of cars. Idk if it was Alvin or who. Is there a MAF screen in the intake?

However, MAF fueling is tracking in your recent log. Your idea of zeroing out the PE spark adders might be what it takes.

Cam angle spark tables are called VCP. Log the cam angles.

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Originally Posted by SiriusC1024

In the first log the error is above the High RPM Disable threshold, so it's all MAF. Latest log looks better. This points to inconsistency in MAF readings. I'm just now remembering someone had a weird issue with MAF on those kind of cars. Idk if it was Alvin or who. Is there a MAF screen in the intake?

However, MAF fueling is tracking in your recent log. Your idea of zeroing out the PE spark adders might be what it takes.

Cam angle spark tables are called VCP. Log the cam angles.

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Now that I think about it, the reason it's running rich in that log is likely due to the restrictive Laguna pipe exhaust setup that gives that log its name (if you're not familiar with Laguna pipes, it's a ridiculous exhaust tip that is designed to beat sound restrictions at Laguna Seca). I don't think I have a good log that includes EQ AND a normal exhaust setup.

I'll try the PE spark adders route soon and report back.

Thank you for your help, SiriusC1024. I've seen your name attached to a lot of helpful information on this forum. It's very kind of you to help out those (like me) seeking tuning answers.

No I'm not familiar with them, but that makes sense. If changing airflow compared to when it was tuned that would explain why fueling is rich during OL. Maybe have a separate tune for when running those pipes.

Idk how useful I've been for this one, but thank you. Hope you get it solved.

Haha come on those pipes look ridiculous.