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Old 12-30-2012, 04:34 PM   #1
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Default Engine goes lean under boost,

somethings broken and I can't figure it out. Engine fuel mixture goes lean after 5000 rpm but it was good under same calibration before, it is worse as engine warms up, 10 minutes or so. Finally was able to get a screen capture of a PC log showing problem. I have increased fuel map by 50% the fuel to try solve problem but engine is continuing to miss. Turbo, AEM EMS-4, 2001 VVT engine. My GoPro shows fuel pump pressure is good, running 14 lbs boost on a built motor with no knocks recorded, limiters set at 7200rpm. Returned to original calibrations and no improvements.
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Old 12-30-2012, 05:48 PM   #2
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Are you getting you 1:1 rise in FP to boost?
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Old 12-30-2012, 06:17 PM   #3
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A good question. best answer is this video of my dash. center upper is boost and right below is fuel pressure guage. video at Buttonwillow Trackday - 11.18.2012 on Vimeo go to 34 seconds. I'm using a aeromotive 13105 regulator which is connected to intake and is designed to rise 1 to 1.

Last edited by twpipe; 12-30-2012 at 06:24 PM. Reason: regulator model #
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Old 12-31-2012, 11:30 AM   #4
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I could not see on the vid,

The other thing is to make sure you are getting 12v to the fuel pump.
You may have pressure but not flow.

If it is a relay set up, I have seen a relay on the way out cause a voltage drop, and cuse the FP to lower its flow.

SOrry I am no help on the tune...
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Old 12-31-2012, 11:35 AM   #5
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retune, after you build new motor.
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Old 12-31-2012, 11:38 AM   #6
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Quote:
Originally Posted by BogusSVO View Post
The other thing is to make sure you are getting 12v to the fuel pump.
You may have pressure but not flow.
Huh? If you dont have enough flow pressure will drop.
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Old 12-31-2012, 12:59 PM   #7
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Braineack - please explain what you are seeing and I'm not getting. thanks.
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Old 12-31-2012, 03:11 PM   #8
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Huh? If you dont have enough flow pressure will drop.
Moron comment made, due to not enough caffine in system for brain to engage in proper though process......
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Old 12-31-2012, 03:54 PM   #9
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Unless the outflow ( injectors) was restricted, then of course you were correct.
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Old 12-31-2012, 04:00 PM   #10
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That is always possiable, trash in the filter buckets in the back of the injector.

My first TC drove me nuts with a miss from that.
Found 4 cups of red clay/sand in the tank....

Have you checked the vac line from mani to AFPR for a leak?

Where are you tap into to read fuel pressure?
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Old 12-31-2012, 04:14 PM   #11
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I'd say fuel filter.
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Old 01-03-2013, 11:15 PM   #12
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I did compression check and engine is even, leak down shows 4% for 1,2,4 cylinders and # 3 at 10%.
Ran the car today with slowly building to redline in 3rd and it runs. 1st and 2nd usually pulls well to redline of 7200.
My fuel pressure reads from fuel rail and then runs antifreeze to my guage on dash. I run an external fuel pump with filter ahead of pump. I will check filter again tomorrow, outside of the garage.
Is it possible my fuel line leading to fuel pump is collapsing at 60 psi. vacuum when it adjusts from 26 psi at no boost and then builds to 60 psi plus? I'm picturing a sudden collapse and then of course releasing as vacuum drops.
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Old 01-04-2013, 01:37 AM   #13
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Red line on top is engine speed, peaking thru 6400 rpm. middle lines, green is 02 reading and blue is 02 target, low is rich, high is lean. lower pink line is throttle. One show gradual throttle and it works, the other shows punching it and it stuttering so lower line shows throttle line shows big drop off. Fuel filter looked fine, so thinking vacuum is collapsing line or ?
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Old 01-04-2013, 12:31 PM   #14
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Wait, what is your base pressure? Aka the pressure at your fuel rail when you have the fuel pump running but the car off? And what is your fuel pressure at idle and full boost?
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Old 01-06-2013, 05:28 PM   #15
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BogusSVO, Faeflora, and Leafy - looks like you were all right. I am too old to be embarrassed but fuel filter in day light examination was restricted. Some of the black fuel tank foam and some crap was reducing the flow and increasing the vacuum which did collapse my intake line to fuel pump, leading to the sudden lean condition. I cleaned filter and changed out to teflon/ss fuel line and car will now rev out. Also external Fuel pump is much quieter and pressure across the range has increased which brings the mixtures back in. Low speed pressure was 26 now 31 so the pressure regulator is affected also. thanks all, time to renew my support to miataturbo forum
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