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Old 09-01-2013, 06:12 PM   #1
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Default My Miata occasionally goes lean under boost

Hey everyone, Im new to the whole forum thing and I need some help with my car. I have a 99 1.8l miata with a Jr supercharger running 5psi on a stock ecu. From the looks of things under the hood, this install was done by an amateur at home.
Now for my issues; about six months after I bought it, it would occasionally fall flat on its face under boost even when it only hits 3psi or less. I originally thought the fuel pump was going bad so I replaced it with a new high flow pump and I still had the issue, so then came a new fuel filter, still with no result. It has also been throwing a code for the IAT sensor but I'm not sure if that would cause the issues that Im having. Any help would be very appreciated
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Old 09-01-2013, 06:26 PM   #2
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IAT could very well be the problem.

But running boost on the stock ECU is bad and you should feel bad.
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Old 09-01-2013, 06:29 PM   #3
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Bad IAT sensor could cause a lean condition.
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Old 09-01-2013, 06:33 PM   #4
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Have you ever heard of an O2 clamp? Search for it on this forum and see if it matches your symptoms.

But for your sake, get an MS3 Basic from Reverent.
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Old 09-01-2013, 10:39 PM   #5
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Have you ever heard of an O2 clamp? Search for it on this forum and see if it matches your symptoms.

But for your sake, get an MS3 Basic from Reverent.
Okay thanks for the info. As for the MS3, I cant find the price on one or a place to buy it any info there would be appreciated. And about the o2 clamp, I cant find it ether.
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Old 09-02-2013, 01:43 AM   #6
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You do realize that running 5psi on a stock ECU with no added fuel is a great way to blow up the motor, right?
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Old 09-02-2013, 07:40 AM   #7
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Okay thanks for the info. As for the MS3, I cant find the price on one or a place to buy it any info there would be appreciated. And about the o2 clamp, I cant find it ether.
MS Labs is in the vendor section.

O2 clamp is in a sticky at the top of the parts for sale section.
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Old 09-03-2013, 09:10 PM   #8
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You do realize that running 5psi on a stock ECU with no added fuel is a great way to blow up the motor, right?
Its a stock ecu yes, but it is the old style jr supercharger kit so pre power card. It gets plenty of fuel whenever my weird issue isn't hindering it. And whenever that happens I don't let it go into boost.
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Old 09-03-2013, 10:09 PM   #9
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Pooooowwwweeeeerrrrrrrrcardddddddddd.


What happens to the afrs when it "falls flat on its face"?
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Old 09-05-2013, 10:20 AM   #10
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how do you even know it's going lean?
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Old 09-05-2013, 10:45 AM   #11
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Obviously "falls flat on it's face" = "lean" duh.
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Old 09-05-2013, 11:02 AM   #12
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oh. I thought that was just what a JR45 felt like.
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Old 09-05-2013, 11:24 AM   #13
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Superchargers are a drag.
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Old 09-05-2013, 12:15 PM   #14
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Just a shot in the dark here but i betcha the OP has no wideband :P
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Old 09-05-2013, 12:41 PM   #15
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Old 09-06-2013, 11:24 PM   #16
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Yup, Correct. No wide band, yet. I do have the "red, yellow, green" waving led type AFR gage(cant think of what it is called at the moment) I have a new IAT sensor coming to me tomorrow. Really hoping that solves my issue.
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Old 09-06-2013, 11:28 PM   #17
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Superchargers are a drag.
No joke there, in more ways than one. A turbo is what I really want, but sadly, it isn't in the budget.
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Old 09-06-2013, 11:40 PM   #18
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Where does the red yellow and green waving gauge take its signal from if you dont have a wideband?
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Old 09-06-2013, 11:45 PM   #19
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Yup, Correct. No wide band, yet. I do have the "red, yellow, green" waving led type AFR gage(cant think of what it is called at the moment)
It's called garbage. It would benefit you more to pipe the exhaust gas into the cabin and try to sniff it to determine if you were rich or lean and by how much. Be sure to do this with all of the windows rolled up or it won't be as accurate.
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Old 09-07-2013, 12:56 AM   #20
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It's called garbage. It would benefit you more to pipe the exhaust gas into the cabin and try to sniff it to determine if you were rich or lean and by how much. Be sure to do this with all of the windows rolled up or it won't be as accurate.
Definitely legit method. I also use a vice grip on my fuel line to adjust my afrs.
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