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Old 04-16-2012, 07:34 PM   #1
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Default Car cuts at high boost.

Hey guys i'm having problems with my car when it comes into high boost. Normally around 10psi but higher if im easier on the throttle. The car was fine last year with the same set-up. My boost cut is at 230 kpa, plugs are gapped all the way down to 22. Also im running toyota cops so ive ruled spark strength out i would think. Could it be a bad ground? I can post a data log if someone tells me how
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Old 05-02-2012, 12:45 AM   #2
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I've been out of the game for a while, but cutting out at high boost means one of two things:
- AFR is waaay off
- Spark blowing out

If your AFR-meter reads OK, then you're not sparking. Combustible mixture + spark = explosion. One of those two missing means no power.

Did you check your AFR? I would assume so....

Of course on my turboed BMW535i I had a problem like that and couldn't figure it out for weeks. At WOT it would sometimes cut out and in and out and in....

Eventually I realized that the old style fuse for the fuel pump was not clamped properly any more. The holder was bent open slightly. Under strong acceleration the fuse moved back a bit and lost contact. That would stop the flow of fuel and the car to decelerate. That would cause the fuse to move forward again, closing the circuit. Fuel starts flowing again, the car accelerates and the whole thing starts over again.

So it MAY be something really weird, but it is likely just the spark or the AFR.
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Old 05-02-2012, 12:23 PM   #3
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Quote:
Originally Posted by stefanst View Post
If your AFR-meter reads OK, then you're not sparking.
Not true. If you are missing, your AFR will give you a false LEAN reading due to the presence of O2 (because you didn't burn it).

I'm assuming you pulled the plugs and they're not fouled? Still most likely a spark blowout issue. Ignition components don't last forever.
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Old 05-02-2012, 12:28 PM   #4
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Quote:
Originally Posted by hornetball View Post
Not true. If you are missing, your AFR will give you a false LEAN reading due to the presence of O2 (because you didn't burn it).
Right. I should have written: If your AFR reads OK up to the point when you lose power and then all the sudden goes lean you most likely have no spark.

If it leans out slowly and then you lose power, you're not getting enough fuel.
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Old 05-02-2012, 02:27 PM   #5
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I'm having the same problem - full boost at sub 6krpm or less than about 10psi above 6k rpm is fine. Get above 6k with over about 10psi and I start running into misfire problems. Planning on replacing my spark plugs, and if that doesn't work, I'm going to buy a new COP and start searching for the bad one.
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Old 05-02-2012, 02:51 PM   #6
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Or you could have made the noob error I made and forgot to check the Overboost protection in Megasquirt - the default maps cut spark at 155kpa I believe...
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Old 05-04-2012, 10:44 AM   #7
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I got my problem solved - new spark plugs did the trick.

I did find that one of my old plugs was gapped at about .045 while the other three were gapped between .038 and .040 - might have been the cause of the problem in the first place...
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Old 05-04-2012, 10:56 AM   #8
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without better coils, .045" is too much for higher boost.

on stock coils you need to be closer to 0.030"
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Old 05-04-2012, 11:02 AM   #9
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On Sav's COPs
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Old 05-04-2012, 11:08 AM   #10
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then you should be able to run at least 15psi at .040" -- i do at least.
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Old 05-05-2012, 05:28 PM   #11
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Hey guys sorry for no reply but im still having problems. It doesnt seem to be the amount of boost being a issue but more when the car is under heavy load. For example its bad if im cruising in 5th on the highway and lean into it hard it cuts out. I have switched coils, rewired the cops, re-did all the grounds and tried 2 sets of plugs. I'm currently running the non-resistor v power plugs on flyin miatas site. I had the same set-up last year with no issues. All i changed over the winter was a new clutch/flywheel and installed a resistor for the tach. Do i need a capacitor wired in if im running a resistor? Any help is appreciated i already bent a rod because of this.. :(
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Old 05-05-2012, 08:11 PM   #12
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Hi Brad,

A few suggestions / questions:

- What is your AFR immediately before it cuts out?
- Does it stutter or cut out completely?
- When you increase throttle slowly in 5th, does it still cut out, or can you get all the way to full boost?

When you go from cruise to WOT, (leaning into it hard) the manifold pressure increases rapidly. This causes vaporized fuel to deposit on the intake runners which in turn causes a short ultra-lean condition. That's why you need accel-enrichment.

Suggestions:
- To make sure it's not boost related, wire open your wastegate. If it goes away it's boost related
- If you see a significant change in AFR, compensate for it

Good luck!
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Old 05-05-2012, 08:36 PM   #13
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AFR stays right at 11.0's, The car just cuts hard like a spark blow out condition, If i lean into it i dont have a issue 90% of the time. Like i said its the same tune as last year and i never use to have the problem.
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Old 05-05-2012, 08:51 PM   #14
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Check battery voltage on your datalogs. Maybe a loose alternator wire from the clutch job. Also, how are your COPs wired? Specifically, where are your grounds going? This sounds like a bad/intermittent electrical connection to me. Also, what firmware are you running?

Spark cutting out alone shouldn't bend rods unless spark is coming in when its not supposed to. Now, if you lose a substantial amount of electrical power across the board and your injectors cut out intermittently, that will break things by causing a temporarily lean condition that might not even show up in AFR readings, especially at the log rate of the MS. Check that voltage through several logs. Maybe you'll catch a big dip in one of them. Then check your main wiring: alternator +, battery + and -, power connections on your MS board, injector harness to main harness plug, ECU plug, etc.
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Old 05-07-2012, 07:34 AM   #15
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My cops are wired just like the instructions in the how to thread with a ground to the head. As for firmware just whatever the early style mpnp came with. I'll go and do a log and check for voltage loss. How do i post up the log?
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Old 05-07-2012, 06:51 PM   #16
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Ok guys heres a log and my tune to help.
Attached Files
File Type: msq new map.msq (34.8 KB, 117 views)
File Type: xls missfire.xls (1.31 MB, 109 views)
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Old 05-07-2012, 06:59 PM   #17
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As i look at the map it seems when i am getting the cut its going crazy lean. also the fuel pressure goes from mid 20's to low 60's. Not sure how it reads the pressure

Last edited by whitemiata; 05-07-2012 at 07:09 PM.
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Old 05-07-2012, 07:23 PM   #18
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your accel enrichments are going crazy. Where is your MAP line spliced into?

you're running dangerously lean in boost...you're hitting 22psi.

what coils are you running, that's a lot of boost for stock coils/plugs.

your CAS is on the way out, you're getting crazy RPM spikes.
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Old 05-07-2012, 07:33 PM   #19
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Quote:
Originally Posted by Braineack View Post
your accel enrichments are going crazy. Where is your MAP line spliced into?

you're running dangerously lean in boost...you're hitting 22psi.

what coils are you running, that's a lot of boost for stock coils/plugs.

your CAS is on the way out, you're getting crazy RPM spikes.
My map is spliced into the vacum port on the back of the intake by the firewall, my boost gauge is pliced into the line.

Running toyota cops

I'm going to re-run the vac lines to the ecu, I never thought my boost was that high my gauge never went past 14.... fml
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Old 05-07-2012, 07:44 PM   #20
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That'sthe worst sppot for map. Slice off fpr.
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