Hello everyone I am so new to this form that infact this is only my first hour as a member. I have a 95 miata with a built motor, supertech forged pistons 8.6 to 1 Compression, manley forged rods, ported and polished head and ported intake manifold, flying miata fmII turbo kit with a gt3071r turbo, MSPNP2 ecu, 255 fuel pump, 700cc injectors but I increased rail pressure to 70 psi with no vacuum so they are closer to 850-900cc injectors "will be changed out for 1000cc soon" long story short I cracked the old cylinder head hand it pourd coolant into the oil "not much as i caught it immediatly." now I have Built a new head and installed it took the car out for a drive and due some fine tuning with the new head. the car ran and drove perfect and did not miss a beat, came home sat for a few hours as i re checked all the fluids, did an extra oil change and went over to make sure nothing was leaking. go out and drive it again and it runs perfect, go to work the next day and again perfect runs great onder boost makes a ton of power and no misfire. on the way home from work I jumped on it and it ran great again but when i let off it backfired " didnt seem unusual as i had it running a bit rich" still drove under normal conditions fine, BUTTTT!!!!after that when i go under boost "only happens under boost and is not in anyway rpm related" the car missfires and will not accelerate, like i said it drives completly normal unless i go under boost, i do not see any vacuum leaks. So i got home and checked compression C1 140 C2 135 C3 140 C4 130 now i personally thought those numbers were low and yes that is with the engine at about 100 Fahrenheit but i am running low comp pistons, old cracked head "before it was cracked" had comp test of C1 150 C2 145 C3 145 C4 140. and in my attempt to solve the miss fire i changed the plug gap in my NGK R5671A-7 from 30 to 25 and i also replaced the plug wires " all snapped on correctly as i double checked like 20 friggen times" which it still misfired. so i bought new plugs and nothing changed. so i took my old set of ignition coils and still changed nothing. not sure where to go next, CAM Position sensor? Fuel Filter? Clean Injectors? The car was driving perfectly fine under full throttle and all of a sudden it happpened. So hopefully one of you guys can shed some light on the situation i appologize for the long post but id rather you have all the information than not enough.
Thanks for any help!!!
Donald Jackson

 

Wow that's a wall of text. Take care writing your posts, you just lost half your readers with all that. It's very wordy with no spaces. Breath...

Have you checked all your charge pipes after the misfire for leaks?

Attach your msq so we can see if we see anything wrong.

Did you sync your timing when you initially installed it?

What's your over boost protection set at?

 

I was going to say the coils until you said you changed them.

Post a datalog from your Megasquirt that shows it breaking up. Maybe there is something that it can tell us.

 

Yeah, wall of text is hard to follow on the mobile application, too!

 

Sorry about that wall i just wanted to give you all the info that I had, i have not checked my charge pipes i will have to do that.
Here I did attach the file and yes I did sync the timing
Please excuse the file name.... haha

 

Maybe this makes things easier to read.

How much boost?
What does the wideband say when you do this?
Can you repeat the problem while datalogging and post the outcome?

 

15 psi of boost, wide band reads lean and here are two data logs.. im not sure how the data logger works as i have never used it.

 

Update Changed CAM Position sensor and timed it with still no change. here are two videos i made showing what is happening.

 

Quit buying and or replacing parts.

Edit*nvm

In your tune i noticed that you have "use cam signal if available"; it is checked "off".

Also, to record a log you hit Ctrl-L. Then just hit spacebar when you're about to go into boost as it makes it easier to find when going back through the log.

It sounds spark related as i've had spark related issues before. You said it went lean though, doesn't make much sense.

 

I had my dad drive it while I looked at the guages and it appears that it doesnt really go lean. i will try to see where that use cam signal is and check it

 

Update. I changed that ignition setting to use the cam and it didn't change anything. Do you guys think resetting the megasquirt would help?

 

Try and take a proper log. I don't know about anyone else but I can't see anything in it.

 

Tried my best to take a proper log and here is what I got not sure if they all worked but at least one of them should have something. i know the afr was jumping around like crazy and not sure if a data log should make the tach jump when you click stop but it did.

 

Try leaning it out. Right before it hits the wall, you're choking it with 10:1 afrs. Lean it out closer to 11:1 or 11.5:1. Although I see your target is 12.3:1 there, so it really just needs to be auto tuned.

But with the RPMs bouncing like that, it does look like a software rev limit, not a symptom of richness.

 

I will try leaning it out there but it should be going to that 12.3:1 because I was running auto tune or atleast going close to it. do you think it could be a problem with my software? it sure feels like an electric problem with the way it cuts out and comes back on, it sounds like the flat shift which i have disabled and never worked on my car anyways. i am wondering if possibly reloading the firmware on the ecu will fix the problem?

 

Swap out those plugs for ones with resistors. BKR7E is the defacto standard for a reason.

 

I didn't read your post, or watch any video, but your problem is spark.

edit: now that i've read, you absolutely have to replace your spark plugs!!!!!

I reccomend BKR6E-11.

 

I had a very similar problem, pretty much exactly like your car when I saw the video. It was my spark plugs as others are saying, changed them out to BKR7E and never had another issue.

 

Brain, why do you recommend heat range 6 rather than heat range 7? TSE recommends 6 for NA, 7 for forced induction.

 

because 1.8Ls have a heat range of 5 stock, and there's no reason to jump 2 heat ranges.

I'd run the hottest plug you can get away with.