sustained misfire @ high boost - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


MEGAsquirt A place to collectively sort out this megasquirt gizmo

Reply
 
 
 
LinkBack Thread Tools
Old 12-21-2008, 07:21 AM   #1
Elite Member
Thread Starter
iTrader: (24)
 
kotomile's Avatar
 
Join Date: Oct 2006
Location: Monterey, CA
Posts: 7,578
Total Cats: 40
Default sustained misfire @ high boost

So I'm reunited with my Miata over the holiday break, and the damn thing keeps wanting to idle around 2k and has a repeatable, sustained misfire at WOT and full boost (around 14 psi) with an accompanying difficult to describe braaaaaaappp when the misfire's occurring. Kinda like F1 traction control used to sound only muffled a bit. I've been running MLV the last few times I drove trying to iron it out to no avail really. I'm using the AFR targets outlined by Joe Perez in another thread. I just had the injectors reinspected by Witchhunter, and brother-in-law switched to platinum plugs for some reason. I also tried disconnecting the WI and that made no difference.

Setup is roughly MSPNP, Greddy 1.6, 460s.
kotomile is offline   Reply With Quote
Old 12-21-2008, 09:16 AM   #2
Boost Pope
iTrader: (8)
 
Joe Perez's Avatar
 
Join Date: Sep 2005
Location: Delicious and Moist.
Posts: 26,326
Total Cats: 1,925
Default

Overboost protection?
Joe Perez is offline   Reply With Quote
Old 12-21-2008, 09:24 AM   #3
Elite Member
Thread Starter
iTrader: (24)
 
kotomile's Avatar
 
Join Date: Oct 2006
Location: Monterey, CA
Posts: 7,578
Total Cats: 40
Default

I have that set at 220, and according to the logs I'm only getting to 207 at most.
kotomile is offline   Reply With Quote
Old 12-21-2008, 10:40 AM   #4
Elite Member
iTrader: (15)
 
patsmx5's Avatar
 
Join Date: Aug 2007
Location: Houston, TX
Posts: 8,797
Total Cats: 248
Default

New plugs gapped to .020".
patsmx5 is offline   Reply With Quote
Old 12-21-2008, 11:58 AM   #5
Elite Member
Thread Starter
iTrader: (24)
 
kotomile's Avatar
 
Join Date: Oct 2006
Location: Monterey, CA
Posts: 7,578
Total Cats: 40
Default

You're on the money Pat!

I just switched out the platinums he'd installed for a new set of 7s and that did the trick! I'm stoked. No more misfire at all, it sang straight to redline. I'm glad it was just plugs because I was ready to move the logs from computer to computer to post them, take videos, etc. to try to remedy the problem.

It would be icing on the cake though if I could get this damn thing to idle lower than 2100 rpm...
kotomile is offline   Reply With Quote
Old 12-21-2008, 12:03 PM   #6
Elite Member
iTrader: (5)
 
akaryrye's Avatar
 
Join Date: Jul 2006
Location: Central California
Posts: 2,526
Total Cats: 0
Default

Are you using the stock ecu for idle or MS?
akaryrye is offline   Reply With Quote
Old 12-21-2008, 12:15 PM   #7
Elite Member
Thread Starter
iTrader: (24)
 
kotomile's Avatar
 
Join Date: Oct 2006
Location: Monterey, CA
Posts: 7,578
Total Cats: 40
Default

MSPNP

Is it possible for the idle valve to be stuck?
kotomile is offline   Reply With Quote
Old 12-21-2008, 12:26 PM   #8
Elite Member
iTrader: (5)
 
akaryrye's Avatar
 
Join Date: Jul 2006
Location: Central California
Posts: 2,526
Total Cats: 0
Default

i guess it could be stuck, you might try spraying a little throttle body cleaner in the idle valve intake. Also check the TPS threshold (and that you have it set properly). You want the threshold to be activated just before the plate is closed so check and see what the ADC is at that point. I cant really think of anything else unless you messed with the closed loop settings. It really sounds like the idle is just not turning ON
akaryrye is offline   Reply With Quote
Old 12-21-2008, 01:17 PM   #9
I'm Miserable!
iTrader: (5)
 
bryantaylor's Avatar
 
Join Date: Dec 2006
Location: jacksonville, fl
Posts: 1,720
Total Cats: 0
Default

we dont need IACs in florida, i havent had one for over a year.
bryantaylor is offline   Reply With Quote
Old 12-21-2008, 04:45 PM   #10
Elite Member
iTrader: (15)
 
patsmx5's Avatar
 
Join Date: Aug 2007
Location: Houston, TX
Posts: 8,797
Total Cats: 248
Default

Quote:
Originally Posted by kotomile View Post
You're on the money Pat!

I just switched out the platinums he'd installed for a new set of 7s and that did the trick! I'm stoked. No more misfire at all, it sang straight to redline. I'm glad it was just plugs because I was ready to move the logs from computer to computer to post them, take videos, etc. to try to remedy the problem.

It would be icing on the cake though if I could get this damn thing to idle lower than 2100 rpm...
Likely blew a vacuum line off the manifold from having it backfire due to the miss. Look around.
patsmx5 is offline   Reply With Quote
Old 12-21-2008, 04:53 PM   #11
Ben
Supporting Vendor
iTrader: (33)
 
Ben's Avatar
 
Join Date: Jul 2006
Location: atlanta-ish
Posts: 12,689
Total Cats: 99
Default

Also, overboost is a predictive function. It can cut fuel before the limit.

The idle issue should be able to be corrected with standard troubleshooting. I'd start by looking at how much vac it's pulling and looking for a leak.
Ben is offline   Reply With Quote
Old 12-22-2008, 11:33 AM   #12
Elite Member
Thread Starter
iTrader: (24)
 
kotomile's Avatar
 
Join Date: Oct 2006
Location: Monterey, CA
Posts: 7,578
Total Cats: 40
Default

No vacuum lines gone, everything looks to be in place. Logs show (since there's surging) MAP going from 26-39 kpa. I need to get a zip utility on the other laptop so I can post logs.
kotomile is offline   Reply With Quote
Old 12-22-2008, 12:51 PM   #13
Supporting Vendor
 
Matt Cramer's Avatar
 
Join Date: Sep 2006
Posts: 2,266
Total Cats: 51
Default

I would check for vacuum leaks, might want to try the starting fluid test trick.
Matt Cramer is offline   Reply With Quote
Old 12-22-2008, 01:01 PM   #14
Elite Member
Thread Starter
iTrader: (24)
 
kotomile's Avatar
 
Join Date: Oct 2006
Location: Monterey, CA
Posts: 7,578
Total Cats: 40
Default

I changed the idle over to warmup only and copied compuatic's idle settings, so now it's down to 1600 rpm and doesn't surge.

I'm pretty sure there're no leaks, but what's this starting fluid trick?
kotomile is offline   Reply With Quote
Old 12-22-2008, 01:59 PM   #15
Elite Member
iTrader: (5)
 
akaryrye's Avatar
 
Join Date: Jul 2006
Location: Central California
Posts: 2,526
Total Cats: 0
Default

you spray starter fluid over areas you suspect might have a vac leak and listen to the engine. If there is a surge, you have found a leak
akaryrye is offline   Reply With Quote
Old 12-22-2008, 02:37 PM   #16
Elite Member
Thread Starter
iTrader: (24)
 
kotomile's Avatar
 
Join Date: Oct 2006
Location: Monterey, CA
Posts: 7,578
Total Cats: 40
Default

ahh, thanks.
kotomile is offline   Reply With Quote
Old 12-22-2008, 07:17 PM   #17
Elite Member
Thread Starter
iTrader: (24)
 
kotomile's Avatar
 
Join Date: Oct 2006
Location: Monterey, CA
Posts: 7,578
Total Cats: 40
Default

Ok, time to eat another slice of humble pie. Bought a can of starter fluid and every time I spray near injectors 3&4 the idle droops. Seeing as the injectors were out just a few months ago it's likely them, although I suspect it could be the intake manifold gasket but I've never heard of anyone here blowing one of those that I can remember. So, tomorrow it'll be time to yank the rail and check the seals.

Last edited by kotomile; 12-22-2008 at 09:23 PM.
kotomile is offline   Reply With Quote
Old 12-23-2008, 08:10 PM   #18
Elite Member
Thread Starter
iTrader: (24)
 
kotomile's Avatar
 
Join Date: Oct 2006
Location: Monterey, CA
Posts: 7,578
Total Cats: 40
Default

Either I suck at installing injectors, or that wasn't the problem... I'm banking on the latter. Time to take a serious look at the IM gasket I guess, still getting a droop when starter fluid is sprayed by #4.
kotomile is offline   Reply With Quote
Old 12-25-2008, 12:19 AM   #19
Senior Member
iTrader: (13)
 
Join Date: Jul 2008
Location: Macon, Ga
Posts: 826
Total Cats: 0
Default

same thing is happening with my car right now and it happens when i spray it on injector #4. i was thinking it might be my intake manifold gasket but i dont wanna take it off just yet. i have supra 305s and they dont flush near as good as the stocks. i was planning on putting sealant around them and seeing what happens
Sam Amporful is offline   Reply With Quote
Old 12-25-2008, 12:22 AM   #20
Elite Member
iTrader: (15)
 
patsmx5's Avatar
 
Join Date: Aug 2007
Location: Houston, TX
Posts: 8,797
Total Cats: 248
Default

FWIW, my 3&4 RC 550's leaked forever.... I just redid them today. I 'think' they're fixed now, or god I hope so.
patsmx5 is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 58 12-13-2017 10:04 PM
LucaCarMods's Boosted Dutch Miata Build! LucaCarMods Build Threads 11 02-14-2016 07:13 AM
Going back to stock. Need some 1.6 parts. Trent WTB 2 10-01-2015 01:15 PM
Bad head gasket or ? shooterschmidty Engine Performance 8 09-30-2015 11:28 PM
01-05 Fab9 PNP COPs (used) FrankB Miata parts for sale/trade 6 09-30-2015 12:48 PM


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 07:49 PM.