Swapped intake, high knock control and check engine light after drive

[bay_hatch]

The race MAF is too large to have a perfect MAF scale at all levels of flow. The flow dynamics simply don't allow it. STFT will swing both directions because of it. LTFT and the mean trend should be close to 0.

So if i'm understanding this correctly, STFT will fluctuate greatly (but should it shoot up to 25%?), but because i'm using the RACE MAF without a custom tune for the intake it's normal? But if LTFT isn't greatly increasing then i'm ok?

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[hobby-man]

FWIW I'm still working with DRob sending datalogs back and forth to re-scale my TSP1 tune with the 27WON Race MAF. My STFT is very jumpy under certain conditions (-24% to +21%) but the LTFT never drifts further than about +3%. There are definitely some physical limits with an oversized MAF where STFT will swing hard.

 

[gtman]

So if i'm understanding this correctly, STFT will fluctuate greatly (but should it shoot up to 25%?), but because i'm using the RACE MAF without a custom tune for the intake it's normal? But if LTFT isn't greatly increasing then i'm ok?

That's the same question I have for JR. It may have only been for a few seconds here and there but seeing STFT's off by over 30% isn't something I see often on logs. And the short term swings were like watching a roller coaster at times.

I understand short term is constantly compensating and they are very active but isn't the goal to be within + or - 10? If Derek and JR say 25% off for a short time is OK, than I learned something today. I was always tought the 10% rule.

And what are the long term effects (if any) of the + or - 25% STFT swings?

 

[KTuner]

We're both saying it's a necessity for STFT to correct when you go with a much larger than factory housing. How much will vary. As you increase the size the resolution is actually reduced. Flow dynamics play a much larger role, too.

 

[gtman]

We're both saying it's a necessity for STFT to correct when you go with a much larger than factory housing. How much will vary. As you increase the size the resolution is actually reduced. Flow dynamics play a much larger role, too.

Got it.

I guess I need to learn more about the race maf and reading datalogs.

My apologies for giving any incorrect info to the OP. I'll stick to reading my own datalogs from now on.

I thought for sure when I saw +46% on one of the datalogs there was an issue.

JR do you have any idea what sort of emissions CEL the OP might have had or do you feel it's irrelevant?

 

[hobby-man]

Got it.

I guess I need to learn more about the race maf and reading datalogs.

My apologies for giving any incorrect info to the OP. I'll stick to reading my own datalogs from now on.

I thought for sure when I saw +46% on one of the datalogs there was an issue.

JR do you have any idea what sort of emissions CEL the OP might have had or do you feel it's irrelevant?

I think the Race MAF is just a special case in regard to STFT. The basics of knock control, boost targets vs MAP, LTFT, etc. Still apply. I'd prefer if you didn't retire from helping out with datalog reading just yet

 

[bay_hatch]

Got it.

I guess I need to learn more about the race maf and reading datalogs.

My apologies for giving any incorrect info to the OP. I'll stick to reading my own datalogs from now on.

I thought for sure when I saw +46% on one of the datalogs there was an issue.

JR do you have any idea what sort of emissions CEL the OP might have had or do you feel it's irrelevant?

No I greatly greatly appreciate the help! It's great to know at least the basics for whats "normal" for these engines.

I'm very curious to know what that CEL code now too. Wished I hadn't tried to rush things and pulled the code first.

 

[gtman]

Thanks for the support guys. I do try to help.

I have a general question for JR that would be a big help to me. Say I'm reading a datalog of 30 minutes and I see many instances of short term trims hitting in the + or - 30% range. Maybe for a few seconds here and there but in one case staying elevated for a full minute (basically what I saw on the OP's log) ...

As long as LTFT's are normal, should I disregard the crazy STFT numbers?

 

[KTuner]

You're not wrong. No, don't disregard, but it's what you get with a larger MAF and general MAF scale.

I don't particularly like when the ECU has to correct that far, but the scale is a general starting point that produced a fairly even trend line with the swings in testing on multiple vehicles. I'm sure with a custom tune it could be more tailored to his setup specifically.

 

[gtman]

So basically with the race maf, there's your included maf scale that will produce decent numbers for most vehicles. But, it might produce some crooked STFT numbers in certain situations.

And ideally, to keep short term fuel trims in an even better place with less drastic corrections, a custom tune would be the best bet.

That about right?

 

[bay_hatch]

I'm very curious to see how this plays out when I revert to the stock intake later today. I'll be sure to perform another data log and will post here.

 

[bay_hatch]

Swapped back to the stock intake and flashed back to stock.

Did a data log driving to target

 

[gtman]

I looked at the datalog and everything looks pretty much perfect. No crazy +46% STFT corrections, that's for sure. Take a look at the center of the graph. See the green and purple lines? See how nice and flat and linear they are? Those are your excellent fuel trims.

What's interesting is that knock control starts out at .89 on the factory tune. The good news is your k.c. dropped down to .49 at the end of the drive. A+ datalog results. Next, I would recommend doing another datalog after you upload a KTuner tune (keeping the intake stock).

Just for $hits and giggles, I added one of your datalog graphs with the PRL Race SRI. See the top blue line that looks like the Swiss Alps? Those were your STFTs.

 

[bay_hatch]

I looked at the datalog and everything looks pretty much perfect. No crazy +46% STFT corrections, that's for sure. Take a look at the center of the graph. See the green and purple lines? See how nice and flat and linear they are? Those are your excellent fuel trims.

What's interesting is that knock control starts out at .89 on the factory tune. The good news is your k.c. dropped down to .49 at the end of the drive. A+ datalog results. Next, I would recommend doing another datalog after you upload a KTuner tune (keeping the intake stock).

Just for $hits and giggles, I added one of your datalog graphs with the PRL Race SRI. See the top blue line that looks like the Swiss Alps? Those were your STFTs.

I was so relieved when I was monitoring that too!


I also noticed knock control at .90 after flashing back to stock which raised concerns. Checked out some other member's post and they saw the same thing when going back to stock. After driving conservatively on the highway, it steadily dropped back down which was great to see.

That's crazy how much bigger airflow throws off STFT by so much. I'll probably end up getting the street maf housing, since I don't have intentions on going full race, only a peppier fun to drive daily

Thanks again @gtman and everyone else who helped me sort out my rookie mistake. I've learned a great deal about this platform and things to look out for!

 

[KTuner]

So basically with the race maf, there's your included maf scale that will produce decent numbers for most vehicles. But, it might produce some crooked STFT numbers in certain situations.

And ideally, to keep short term fuel trims in an even better place with less drastic corrections, a custom tune would be the best bet.

That about right?

If you're running a large MAF housing you're going to see STFT spike in certain situations, even with a custom tune. A custom tune will likely get you closer to a "perfect" trend line for your specific setup.

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