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Old 07-26-2012, 03:09 AM   #1
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Exclamation Stutter/misfire under load/boost

MY miata is turbo'd and built up.
I'm running a megasquirt PNP ecu with what seems to be a fairly decent tune.
I don't run lean or excessively rich.

I AM running a VTPS on the car, because i was told it would fix this issue but it hasn't.

At about 4k RPM and higher, when i MAT the throttle (push it all the way to the floor) under acceleration, it will get like a stutter, and jump the rpm back about 300 for a second on the gauge, its very fast but it will occur lots.

Like ill punch it and it will go good then . .. . ... . . . sort of pattern of stuttering.

If i just give it about 75-80% it will still haul and i won't have this issue, but it would be nice to have a full range of throttle motion..

Any suggestions?

I have gapped the spark plugs smaller and it didn't fix it. I was thinking spark might be getting blown out, but I'm only running 7/8 psi.
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Old 07-26-2012, 11:05 AM   #2
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That's almost ALWAYS spark blowing out. Do you have a WBO2? If so, does the AFR stay solid before the stutter and then go very lean all the sudden during stutter? That's the excess unburned air.
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Old 07-26-2012, 11:34 AM   #3
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1)what is your boost cut set to
2)what plugs are you running
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Old 07-26-2012, 02:47 PM   #4
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edit: nm i'm dumb.
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Old 07-26-2012, 06:57 PM   #5
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Quote:
Originally Posted by stefanst View Post
That's almost ALWAYS spark blowing out. Do you have a WBO2? If so, does the AFR stay solid before the stutter and then go very lean all the sudden during stutter? That's the excess unburned air.
No it doesn't, I've looked at my mega log and i can kinda see on my rpm line where it stutters a bit, but by like 100-200 rpm at the most, but the AFRs only fluctuate by about .2-.4....

Quote:
Originally Posted by 18psi View Post
1)what is your boost cut set to
2)what plugs are you running
It doesn't have the boost cut set and the plugs are NGK something.. a 7 heat range gapped to .25"
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Old 07-26-2012, 08:41 PM   #6
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Wait, the tach flutters by about 300rpm too?
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Old 07-26-2012, 09:39 PM   #7
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How's the plug wires?, even though you are only running 7-8 psi, you could have a bad coil.
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Old 07-27-2012, 02:35 AM   #8
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I solved the problem, not sure what it was but i reloaded a base tune and adjusted all my setting to how i had it before and it went away..

Either way, its all good now!
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Old 08-03-2012, 08:03 AM   #9
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So i m kinda having the same problem as OP did.
My car is a 2001 eu spec 1.6 with built motor, rev ms2 ecu, toyota cops.
Plugs are NGK BKR7, 0.32 gap.
When i floor it(wot) the car sometimes will jump 300-400 rpm back,usually around 6K Rpm and under load,like in 4th gear lets say.Tach jumps back also!
I have logs ,i will post them afterwards.
Any ideas?
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Old 08-03-2012, 07:30 PM   #10
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What is your overboost protection set at?
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Old 08-04-2012, 05:31 AM   #11
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Overboost protection is set at 17 psi, i use wastegate's spring boost atm, roughly 10 psi.
Here's the log
Download 2012-07-18_02.45.56.msl for free on uploading.com

Check what happens when i 'm at 100%tps, when the rpms start clmbing.
Btw i am in 4th gear.
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Old 08-04-2012, 06:08 AM   #12
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Which firmware are you on? If you are on 3.1.6, then there is a known bug that causes a random misfire. I can help with the upgrade once I am back from vacation on the 10th.
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Old 08-04-2012, 08:31 AM   #13
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Hey Dimitri, I know you're on vacation thats why i didn't call you to tell you about this prob. Did you check my log?
Firmware is 3.1.6!
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Old 08-04-2012, 08:41 AM   #14
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Definitely the firmware then. Keep out of boost for a few days.
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Old 12-13-2012, 12:59 AM   #15
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Just thought i'd help out anyone else who had this issue.

I had forgotten it and It was recently brought to my attention.

But the issue was:

In megatune there is an overboost protection, mine was set to just below 8.
After i re loaded the base map, i went through each and every setting and found out that it turned off the overboost protection which is why i wasnt experiencing the problem after the re-load.

Once i got it tuned, i had to overboost set to somewhere around 15 i believe, and havent had the problem since!

So FYI to all those who experience this, CHECK YOUR OVERBOOST PROTECTION!
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Old 01-23-2013, 04:11 PM   #16
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My log suggests I'm hitting overboost protection at 150kpa but I have a standard t25 actuator and the dashboard mounted boost gauge showed just under 10ps which was Tee'd off the same line.

I have the map line tee'd off the FPR then through the firewall then to the ecu with a T in that line to the boost gauge.

At or close to WOT it does it just a fraction under 4k rpm but if I use less throttle it will go above that.

Is this a bad map signal or a genuine reading? Can someone have a look at my log and see?
Attached Files
File Type: msl run after removing boost controller.msl (1.27 MB, 107 views)
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Old 01-25-2013, 03:39 PM   #17
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I'm surprised nobody mentioned knock retard, though it's a MS so maybe he doesn't run a sensor? My hydra cuts timing and feels like I go NA for a few seconds after a knock retard.

Edit: Just re-read the date and the last few posts. Nevermind
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