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Mpi afr not consistant under boost


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#1 boostinmini

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Posted 09 May 2019 - 09:36 AM

Hey guys

A little backstory I used to have my truck running megasquirt ms1 with the Ford edis ignition turbocharged it's the 2.6.  I had throttle body injection,  drove it for years fairly decent tune with the megasquirt. I recently upgraded to multi-port injection with a magna intake and now it seems like under boost my air fuel ratio is always different depending on the time of day. I thought i had the afrs dialed in, nice ve table, but for example this morning it was about four degrees Celsius outside. My air fuel ratio under boost was reading approximately 9.5 and then this evening it was maybe 10 above Celsius outside and my air fuel ratio was about 12.5 to 13 underboost.  usually my intake air temperature is only about four degrees above ambient I have a fairly large intercooler.  So just wondering how my afrs can be so different for say the same kpa and rpm every time i drive it.

My afrs say to about 100kpa stay consistent .... Just under load i have inconsistent afrs



I know one thing I'm a little confused about is the Target air fuel ratio table and it seems to never remotely follow it. which I'm not quite sure why that is,  also i set up mat correction thinking it was the changing temperature swings changing the afrs depending on outside temperature but it does not seem to be solving my problems.

I can e mail a msq and i will try and get some logs.

To summarize, tbi seemed to have constant afr for given load and rpm, now with mpi it's different every time i drive it... With out adjusting ve table.

Edited by boostinmini, 09 May 2019 - 01:33 PM.






#2 speedyquest

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Posted 09 May 2019 - 12:32 PM

Your post was a little hard to follow without punctuation or any sentence structure but I think what your saying is that at some time in the past your truck was tuned decently and running TBI. But after switching it over to multiport it doesn't run as well? Is that what you mean?

As for differences in AFR depending on outside temp, really that all depends on how you tuned it. There isn't a simple fix for "My truck doesn't run great". Your going to need to datalog and then make changes to your fuel map to correct the rich/lean conditions you see. You could also take it to a tuner in your area and have them look it over.

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#3 boostinmini

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Posted 09 May 2019 - 01:25 PM

Hey sorry, that was pretty late...i read it this morning and it was pretty bad lol.


I edited it today so maybe re read it

#4 speedyquest

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Posted 09 May 2019 - 01:38 PM

No worries at all man. I'll take a bit of time later to read it over and respond.

1987 Flatty Starion -- Widebody Conversion -- V-Mount Setup --  JDL Tubular Manifold  --  MX-6 Intake -- MS3-Pro -- AEM FPR  --  ARP head studs -- 3" hood exit exhaust -- Hahn Racecraft 16g --  Tial F38 Wastegate -- Tial Q Bov -- Short route piping -- 5 lug & LSD conversion -- Tubular Front End -- Manual Steering Rack Conversion -- Manual Brake Conversion -- Stack Digital Dash -- AEM UEGO -- D2 coilovers -- full GNT poly bushings & mounts -- four 8" rears -- car lightened significantly...  More to come!


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#5 scott87star

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Posted 09 May 2019 - 02:12 PM

Post up a datalog and the tune file responsible for the log.  Never touch your MAT air density table, that is the law (PV=nRT).
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#6 boostinmini

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Posted 09 May 2019 - 02:56 PM

wont let me add tune or datalog, says file is not supported

Edited by boostinmini, 09 May 2019 - 02:58 PM.


#7 boostinmini

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Posted 09 May 2019 - 03:02 PM

hey scott, this is the link for the mat correction i was trying.


seemed to help, but i am a little nervous to get to crazy with trying it to aggressively.

http://www.mez.co.uk/ms15-new.html

My Iat temp sensor is located in the upper intercooler pipe about 10 inces before the throttle body. I also have water meth, but the sensor is before the water meth, was not to sure how it would like being sprayed, its a gm open element sensor.

#8 kev

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Posted 10 May 2019 - 09:42 AM

How is your fuel pressure?

#9 Turbo Cary

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Posted 20 May 2019 - 08:06 PM

If your IAT sensor is calibrated correctly then it's initial reading when the car has fully cold soaked should match or be within 2 degrees of whatever ambient temperature is.




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