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Old 07-04-2016, 12:12 PM   #1
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Default AFRs drop when I lift slightly

Gents,

I was coming back from the track this morning. I'm in traffic at about 75mph. The temp was in the high 60s with about 100% humidity. Cooler than it has been since getting the current tune., IAT was hovering around 84 degrees, 4000 rpm in fifth gear on the highway, with AFRs in the low 14s. If I lift ever so slightly to maintain spacing, the AFR would drop down into the 13s, even though I can hear the recirc valve tittering . If I take out another RCH of power, AFR drops even more. I actually saw 11s with almost no load on the engine. If I lift a little more, the AFR shoots up into the high 16s then oscillates down and up with noticeable surging till I move the throttle again. That almost seemed like a misfire. No problems on track or in city traffic.

Anything to worry about? Is there anything I could/should do?

Thanks,
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Old 07-04-2016, 01:30 PM   #2
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tune AE, EAE, and that specific part of the VE table better.
but its really not a big problem
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Old 07-04-2016, 02:05 PM   #3
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Quote:
Originally Posted by 18psi View Post
tune AE, EAE, and that specific part of the VE table better.
but its really not a big problem
TS indicates it's using Time-based AE. Wall-wetting AE and TPSdot are both off. Attached is the Time-based Accel Enrichment pulldown.

I have zero idea what to do with it.

Thanks,
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AFRs drop when I lift slightly-ae.jpg  
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Old 07-04-2016, 02:16 PM   #4
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in that case what it's doing is exactly what's expected.
it's not pulling any fuel on throttle lift, and the afr dip is from that extra fuel being burned off
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Old 07-04-2016, 02:20 PM   #5
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Thanks for the quick replies. Any suggestions?
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Old 07-04-2016, 02:21 PM   #6
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suggestion would be to start reading up on the 3 things I posted above and learn how to tune them.

...then, tune them.

when you switch from time based to eae, you will have the ability to pull fuel on throttle lift, among many other things. it's a steep learning curve to get it just right tho.

make sure you save a copy of your current tune before you start. you'll likely have to start over a few times (I did when I was learning this)
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Old 07-04-2016, 02:30 PM   #7
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I figured that would be the answer. I read and write for a living. Reading for fun has lost it's shine.

Have a great rest of your Fourth!
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Old 07-04-2016, 04:49 PM   #8
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18psi,

Alrighty then. I went here Tuning Software for MS-II/v2.9 and read this:

Decel Fuel Amount (%)
When you let off the throttle rapidly (that is the closing rate exceeds TPSDOT Thresh) and the engine is turning faster than 1500 RPM, then deceleration fuel cutoff is performed by MS. Deceleration fuel amount is multiplied by the "normal" pulse width, that is, if the calculated pulse is 12.0 ms and you have 20% decel amount, then the resulting pulse width is 2.4 ms. A value of 100% causes the fuel to remain at its calculated value, and can cure bucking on deceleration in vehicles with manual transmissions; those with automatic transmissions may benefit in fuel economy by using values below 100%. The MegaSquirt® variable "TPSDQ" holds this value as a percentage.

The jpg I uploaded shows Decel Fuel Amount is 90. The way I read it as a complete noob, the MS is pulling 10% fuel on deceleration. OR, I REALLY don't understand. Please throw me a bone.

I'm searching the MS3 files now.

Thanks,
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Old 07-04-2016, 05:18 PM   #9
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I went here http://www.msextra.com/doc/pdf/html/...ence-1.4.html, and read this:

Decel Fuel Amount (ms)
Deceleration fuel cut amount in percent. 100% is no cut, 0% is complete cut of fuel.
100% is suggested for this setting.

It seems as though it's pulling 10%, unless I'm missing something, which is certainly possible. Do I need to pull a little more fuel because the Rotrex is requiring extra fuel to begin with?

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Old 07-04-2016, 05:24 PM   #10
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EAE? Not a chance I will understand it.
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Old 07-04-2016, 06:33 PM   #11
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Use Accel-pump and not timed based AE. At least with Accel-pump you can tune the decel amount better. Time-based is old legacy MS1 era code, Accel-pump was at least written in last 5 years.

turn on and tune EAE if you really want to tune AFRs for small throttle manipulations, and not rapid ones.
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Old 07-05-2016, 07:41 AM   #12
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Let me ask this. If my Accel Enrichment pulldown is setup as in the jpg I provided, can I play with Decel Fuel Amount, or is there something that needs to be turned on first?

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