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VVT Miata very lean idle at cold start

 
Old 09-24-2018, 08:37 PM
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Default VVT Miata very lean idle at cold start

Hey guys! I hate to join a forum just to ask a question, but i needed an account here anyways and cant find any info on what i am experiencing.
Anyways, i have a 2003 vvt miata with the bottom end from a 99, and mostly this car has been great.
I just put a turbo on it however, with an fmu. I know its a bandaid, im just trying to fix a megasquirt someone gave me (he couldnt solder and half the joints were cold) and this is temporary so i can drive it.
Somewhere in the mods i made to it, something happened where if i start it cold it goes very very lean (17+) and you have to help it idle for about 10 seconds, then it settles back to 15-16 and can idle on its own.
I did put a walbro 190 hp in it, and possibly as a clue, it runs about 13.5 and is leaning out at WOT at about 5 psi, despite how from what I've read, those pumps can take like 8 psi on an fmu.
Although at part throttle in 6th gear under boost it runs PERFECTLY 12 afr, all the way up to maybe 7 psi. So it seems to only be in open loop.
**But forget the boost, i just want it to run right.**
My first thought was an intake leak but i did the propane trick and the engine didnt rev at all no matter where i sprayed propane. I did fix numerous exhaust leaks around the turbo. I havent found any more but that doesnt mean there aren't any.
Anyways, i figured some advice from the extensive wisdom here couldnt hurt. Thanks! *Eats my 6th Warhead tonight, despite the fact that my mouth is burning*

Last edited by Melody; 09-24-2018 at 10:14 PM.
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Old 09-24-2018, 09:09 PM
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1. Remove turbo.
2. Fix megasquirt.
3. Install and learn to tune megasquirt.
4. Reinstall turbo.

These are the steps for success. All other paths lead to sadness and tears.
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Old 09-24-2018, 09:47 PM
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How are you retarding timing with your fmu setup?
Stock midrange timing is around 35 degrees in midrange. Should be around 20 in boost. Bad things happen with boost and lots of timing.....boom.....
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Old 09-24-2018, 10:12 PM
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Originally Posted by borka View Post
How are you retarding timing with your fmu setup?
Stock midrange timing is around 35 degrees in midrange. Should be around 20 in boost. Bad things happen with boost and lots of timing.....boom.....
This problem exists, boost or not. I just did a static timing retard for the moment. Its retarded 5 degrees from stock and i ofc am running 93 octane gas. Remember too this is only like 7 psi.
EDIT: Actually its 6 degrees. Fm says 6* static retard is good for 8 psi on NBs. I trust them.
However...... None of this matters cause my wastegate is unhooked.

My question was about cold starts, not boost.

Last edited by Melody; 09-24-2018 at 10:35 PM.
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Old 09-24-2018, 10:31 PM
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Originally Posted by Melody View Post
This problem exists, boost or not. I just did a static timing retard for the moment. Its retarded 5 degrees from stock and i ofc am running 93 octane gas. Remember too this is only like 7 psi.
However...... None of this matters cause my wastegate is unhooked.

My question was about cold starts, not boost.
im not sure how you managed to advance or retard mechanical timing on a 2003, its not adjustable like an NA, there is no CAS to turn.

MAF might be getting confused by the turbo and making the car run lean at idle. how close is the MAF to the turbo?
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Old 09-24-2018, 10:42 PM
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Originally Posted by borka View Post
im not sure how you managed to advance or retard mechanical timing on a 2003, its not adjustable like an NA, there is no CAS to turn.

MAF might be getting confused by the turbo and making the car run lean at idle. how close is the MAF to the turbo?
Thank you for being kind and actually helping me! Lol. I got an adjustable timing wheel from flyin miata.
Thats a good point, i can show you the setup when its light tomorrow. It goes filter-maf-90-90-turbo so it could be pretty turbulent in there. But like i said, its just starts. It drives just fine, if a little lean.
And as far as the actual start, i wanna mention it starts up no problem, never hesitates never takes more than 2 or 3 turns to fire up. After about a few seconds its fine. The fuel pump starts quiet then gets louder around the time it settles out.
EDIT: Small crucial detail, problem still happens with my old intake hooked up.

Last edited by Melody; 09-24-2018 at 10:58 PM.
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Old 09-24-2018, 11:40 PM
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is your idle high or normal?

any check engine codes?
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Old 09-25-2018, 10:55 AM
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Originally Posted by borka View Post
is your idle high or normal?

any check engine codes?
when it settles out it idles perfectly, starts at 1100 for a few seconds then drops to 800 and sticks there with stable 15-16 afr.
no codes at all.

Last edited by Melody; 09-25-2018 at 10:57 AM. Reason: Forgot to answer other Q.
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Old 09-25-2018, 11:10 AM
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you answered your own stupid question in your original post
you either have a vac leak, or exh leak, or both
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Old 09-25-2018, 11:47 AM
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Originally Posted by 18psi View Post
you answered your own stupid question in your original post
you either have a vac leak, or exh leak, or both
I swear i couldnt find any more, but i may have to smoke test it. I would have thought those affect it all the time not just at startup Thanks anyways
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Old 09-25-2018, 11:56 AM
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on oem ecu, the car runs open loop at start up, and goes into closed loop fuel correction after a little while. so it's not adjusting to whatever is causing the lean condition
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Old 10-01-2018, 07:17 PM
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Originally Posted by 18psi View Post
on oem ecu, the car runs open loop at start up, and goes into closed loop fuel correction after a little while. so it's not adjusting to whatever is causing the lean condition
So it actually had a post-turbo leak, i deleted the pcv and vent to be safe and checked it and there was an intake gasket leak. This caused the lean at idle. I however also found out that i got a fake walbro pump lmao! Thats Thats why it leaned out up top.
I got supra injectors though and it runs great up to 5 psi, finally went into some real boost with perfect 11-12 afrs and i i am just in love with it. Its the fastest thing ive ever really driven, at least. It probably only makes like 130 but i am addicted andi cannot wait to get megasquirt and do 8+ psi.
Thanks for your help 18psi, despite the snark which i really deserved, you helped me out by putting me back on the track for leak checks.
I seriously love my car so much omg. Im driving it every day when i get home.
Now i just need new engine mounts so it doesnt lift the whole engine up in first gear....
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