Engine falls flat after ~6,800, can't figure this out! - Miata Turbo Forum - Boost cars, acquire cats.

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Old 05-21-2015, 10:35 PM   #1
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Default Engine falls flat after ~6,800, can't figure this out!

Ok so I've been having this issue for a while, since I got the MS3 installed. Basically I'll be driving, and when I run it to redline in any gear, it pulls pretty good till about 6,800 , then it just feels like it hits a wall. It keeps going, but power goes from ripping to bam, flat/lazy. It feels like the boost just dropped 10 pounds instantly if you can imagine what that feels like. Or it all of a sudden pulled a bunch of timing. It seem sudden enough that I think it's a tuning issue not a hardware issue but I do not know that. It really feels like it just looses the timing it needs.

Today I datalogged this event and even made a video of it. I will post a pic of datalog and link to video below.

Car specs:

'99 miata, Built bottom end, built head with stock cams but ported, heavy double valve springs, flat top intake manifold, 20x12x3 core Bar/Plate IC,

Whipple running 21 PSI boost with no belt slip (finally!), ID 1,000's set at 60 PSI (so flow 1,175 cc/min), 1:1 Fuel pressure regulator/return style 6AN fuel system, 255HP Fuel Pump, 3 stage water injection pure water no meth. Running 93 Octane Gasoline.

01 OEM Header with collector cut and 3" pipe welded to it, 3" 300 cell catalytic converter, DynoMax baffled muffler (no more glasspacks). Car has a cold air intake that works decent but not great.

IGN1A Race coils. Dwell set to 4.5ms in boost as per DIY Autotune. Plugs are BKR6's gapped to .040".

If I'm forgetting anything important just ask and I shall provide!

So basically I've tried to tune this spot out. I tried adding fuel, didn't' help. Pulling fuel, seems to help power but not too much difference in this spot. Turned off WI, no difference. Pull timing, this hurts power and seemingly makes it worse.

ADD Timing- I THINK this helped, but the last time I did this I thought it was helping, ended up around 20 degrees of timing when I broke a piston in half. So I'm a bit hesitant to throw timing at it. Though I may very well need to do so. I'm currently running 14 Degrees of timing at 20 PSI and 12:1 AFRs with 30-40% water by volume for detonation suppression.

Pics/Links

3rd Gear
Vid:
Datalog
Name:  Datalog%203rd%20Gear_zpsxywoonlq.png
Views: 11
Size:  113.6 KB

4th Gear I lifted early in this vid as I felt power drop, datalog shows timing dropped as W.I. Pump pressure dropped around 5,500 RPM, I was low on water and pump sucked air. Failsafe FTW!
Vid:
Datalog
Name:  Datalog%204th%20Gear_zpsvqmjtkyl.png
Views: 12
Size:  107.3 KB

6th Gear
Vid:
Datalog
Name:  Datalog%206th%20Gear_zpsj2l5zbaz.png
Views: 11
Size:  90.7 KB
Attached Thumbnails
Engine falls flat after ~6,800, can't figure this out!-datalog%25203rd%2520gear_zpsxywoonlq.png   Engine falls flat after ~6,800, can't figure this out!-datalog%25204th%2520gear_zpsvqmjtkyl.png   Engine falls flat after ~6,800, can't figure this out!-datalog%25206th%2520gear_zpsj2l5zbaz.png  
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Old 05-21-2015, 10:37 PM   #2
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Spark retard rev limiter
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Old 05-21-2015, 10:47 PM   #3
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That's what it feels like. I only have a fuel cut limiter enabled, it's set at 8K. I have also turned it off completely and that didn't help.
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Old 05-21-2015, 10:57 PM   #4
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<p>Knock sensor pulling timing? &nbsp;It was doing it on mine N/A until I turned the threshold down.</p>
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Old 05-21-2015, 10:59 PM   #5
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I don't have a knock sensor installed, Knock sensor is disabled in TunerStudio.

Also, MS Logs show timing is holding constant/as expected during this event, look at the logs it's pretty steady around 14 Degrees advance. The reason it's flat is boost keeps building so as I make a pull I keep moving up and to the right in the map.
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Old 05-21-2015, 11:21 PM   #6
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Also! I just decided to again turn off the rev limiter and retest, and now TunerStudio will NOT let me set the limiter over 7,500 !!! No idea why, it gives me an error message that says "RevLimNormal2 value of 8000 is too high!. Must be less than: 7500.0

In the past I just set it to 8,000 but today when I opened it it was at 7500 and won't let me change it.... Any ideas? Maybe there IS something screwey going on with the MS3 rev limiter causing issues!

EDIT: Fixed this part, the rev limiter apparently is affected by some setting in TunerStudio, when you click Basic Load/Settings, go down to bottom to "gauge limits" and apparently changing the gauge limits actually stops you from adjusting the rev limiter!

This doesn't explain why my motor falls flat up top though...
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Old 05-21-2015, 11:47 PM   #7
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valve float?
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Old 05-22-2015, 12:01 AM   #8
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6800 is weird, but BPs don't make power past 7000-7500, even CNC'd.
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Old 05-22-2015, 12:27 AM   #9
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Quote:
Originally Posted by JasonC SBB View Post
valve float?
Possible, but I have the heavy double Supertech springs, and I've reved this head to 8,800 before. I wouldn't think the intakes would float with 20 PSI boost at 6,800, but it's possible.

Curly- this feels to abrupt to be the engine just choking, see the vid in 3rd gear, it's pulling very well from 6-6.5, and just past 6.5, it's like it hits a wall and power feels like its cuts in half in the driver seat. Like it instantly lost 10lbs of boost or something, it's sudden, not gradual.

Also torque should not fall off too hard given all the mods to the head, intake, and a supercharger that keeps stuffing more and more boost in it. I know it's not a honda but this is too sudden, something has to be wrong. I'd hate to waste money dynoing it just to see how bad something is wrong up top! Would realy like to get this fixed as I'm fairly sure there's something going on up top.
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Old 05-22-2015, 12:42 AM   #10
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Also I just tried adjusting the dwell. I was previously running 4.5ms in boost.

3.0ms- stumbles, misfires, black smokes. Blowing out the spark.
3.4ms- same, not quite as bad
4.0ms- clean up till about 5,500, then begins misfiring
skipped 4.5
5.0ms- clean, feels like 4.5ms I thought, but something odd happened!!!!!!

So I hit it in 2nd gear, and the car kept pulling past the 6,800 spot! It went to 7,400 and I lifted just because that hasn't happened. So then I said screw it and grabbed 3rd. And it was lazy! Misfiring, RPMs going wacky while WOT in boost.

Datalog shows it pulled clean to 7,000 in 2nd, then began to level off SOME, but not as bad. But then 3rd was really lazy/not right at the lower 6,000 Revs. I datalogged it so I can post this in a bit.

6.0ms- Same as 5ms, not any better that I can tell.

So now, I'm going to try gapping down the plugs and redo the dwell test. Maybe these coils don't want to run a lot of dwell, but the plugs need it because of the .040" gap. So perhaps less gap + less dwell will be the winning combo?
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Old 05-22-2015, 12:43 AM   #11
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Quote:
Originally Posted by curly View Post
6800 is weird, but BPs don't make power past 7000-7500, even CNC'd.
Also, I have to.... This BP will make power up top! I won't stop till it does!
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Old 05-22-2015, 01:26 AM   #12
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From memory dynos show the Flat top suffer up top. Also the only change i see in your (1st) map is it going rich at 6800. Not sure how rich but richer than 11.7.
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Old 05-22-2015, 01:30 AM   #13
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Is it breaking up at all? Could be loosing pickup, check your crank sensor gap lately? Or is your latency correct if you're running something besides the stock 4 tooth?
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Old 05-22-2015, 01:33 AM   #14
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I'm running the stock 4 tooth wheel. Stock ECU driving it, MS3 PRO is piggy backed off the stock cam/crank sensors. Not loosing sync as far as I can tell. It's not breaking up as long as the dwell is 4.5 or more, it's clean, just looses power around 6,800.

This is going to sound terrible, but I possibly found the problem. Going to test and will report back. Hope I'm wrong as it's bad, but will know soon enough.
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Old 05-22-2015, 01:36 AM   #15
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You are using this coil?

IGN-1A Race Coil DIYAutoTune.com

Did you see this here at the bottom of the page?

Nominal dwell: 3.0 ms
These are very solid, robust coils that will do well for you if dwell is set up correctly. However, they can be killed by excessive dwell or duty cycle.

Here's another page that supposedly calculates blowout voltage at the very bottom, voltage for that coil is given on the first link.

Megasquirt Sequencer Coils

With random numbers put in (240kpa) I see around 34kv which is pretty close.

Bigger coils?
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Old 05-22-2015, 03:38 AM   #16
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Quote:
Originally Posted by patsmx5 View Post
I'm running the stock 4 tooth wheel. Stock ECU driving it, MS3 PRO is piggy backed off the stock cam/crank sensors. Not loosing sync as far as I can tell. It's not breaking up as long as the dwell is 4.5 or more, it's clean, just looses power around 6,800.

This is going to sound terrible, but I possibly found the problem. Going to test and will report back. Hope I'm wrong as it's bad, but will know soon enough.
Ok well I had the original plugs (BKR6's) from the last motor still in the head and they were gapped at .040" I checked and they were really more like .044... So thought that might be the issue. Installed new 7's, gapped to .030" and tried again. Didn't fix it, but I can now run 3.0ms dwell no problem.

Quote:
Originally Posted by deezums View Post
You are using this coil?

IGN-1A Race Coil DIYAutoTune.com

Did you see this here at the bottom of the page?

Nominal dwell: 3.0 ms
These are very solid, robust coils that will do well for you if dwell is set up correctly. However, they can be killed by excessive dwell or duty cycle.

Here's another page that supposedly calculates blowout voltage at the very bottom, voltage for that coil is given on the first link.

Megasquirt Sequencer Coils

With random numbers put in (240kpa) I see around 34kv which is pretty close.

Bigger coils?
Yes those are the coils I'm running, the IGN1A Race coils. I have them now at 3ms dwell and they are working ok with the gap down to .030".

I made 1 pull without changing a thing, just put new plugs in at .030 and drove it with 4.5ms dwell. Drove the same more or less. Then dropped dwell to 3.0 and made another pull, ran fine, no misfires with .030 Gap. So this is an improvement, now I can run normal dwell.

Then I pulled over and pulled the plugs out to inspect. They look perfect. No signs of detonation. Insulator look perfect.

So then I decided to try adding a bit of fuel to see what that would do. I added +5VE to the table in boost over 150kPa and made a couple pulls. Tonight isn't a great night for tuning so couldn't get much in but it didn't hurt, can't say it helped for sure though. 2nd gear isn't terrible but 3rd it still shows up as power falling off up top. Here's a datalog pic of 2nd gear.




You'll have to zoom in to see the slope of the RPM line very well.

You can see how the slope of the RPM line is pretty flat from 4,000 to ~6,400 but after 6,400 it's definitely dropping (so torque is falling off after 6,400) and at 6,800 it begins dropping noticeably harder.

I think tomorrow I'm going to try adding a bit of fuel, and then try to dial in some timing and see if that helps. I've never tuned a SC motor before so I don't really know what it wants....
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Engine falls flat after ~6,800, can't figure this out!-datalog%25202nd%2520gear_zps7pat3hxo.png  
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Old 05-22-2015, 03:49 AM   #17
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Your TS error message is most likely due to your gauge configuration having a max revs of 7500 on the tachometer.

Tuner Studio won't allow you to have a value higher than the max rpm for the tach.

Edited to say... I see you already discovered this back in post number six. That's what I get for foruming late at night on my tiny phone.
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Old 05-22-2015, 09:07 AM   #18
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<p>where's the virtual dyno plots to see what's actually happening to TQ?</p><p>&nbsp;</p><p>logs look clean to me, nothing obviously. &nbsp;I'd rework your spark map though--14&deg; flat to redline seems odd.</p>
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Old 05-22-2015, 02:04 PM   #19
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Here's the timing map I was running during those logs, this is the WI timing map.



Timing is not flat in the map. It's just that boost keeps going up as I rev it.

I'm wondering I need to add more timing up top, 14 degrees at 7K+ seems low, right? Even at 20 PSI?

I'll see about the virtual dyno and try to do something.
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Engine falls flat after ~6,800, can't figure this out!-timing%2520table%2520with%2520water%2520injection_zps5xselkks.png  
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Old 05-22-2015, 02:22 PM   #20
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<p>that's like 10&deg; less timing than I'd run if i had WI. &nbsp;That's less timing than I ran on my 1.6L.</p>
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