502 mag mpi running lean
08-04-2020, 10:06 PM
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502 mag mpi running lean
Hey guys I got a friend with a 1997 fountain 27 fever with a 502 mag mpi. He just upgraded from stock manifolds to Gil headers. Since he's put the headers on he has been running lean. He got a tune from Arizona speed for headers and still running dangerously lean (plugs white). Was wondering what is making it lean even after the new tune from Arizona speed. He's checked everything in the fuel system.
Thanks
Thanks
08-04-2020, 10:34 PM
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What are you using for plugs ? Some are real hard to read.
i worked on a 96 502mpi , from brand new that added gils after a few years otherwise stock motor that did not ‘go lean.’
i worked on a 96 502mpi , from brand new that added gils after a few years otherwise stock motor that did not ‘go lean.’
Last edited by SB; 08-05-2020 at 06:01 AM.
08-05-2020, 04:14 AM
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Not doubting you, but wouldn’t vac hose being off regulator make engine rich all times except under load and then be in range?
08-05-2020, 06:00 AM
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What plugs are you trying to read and how old are they ?
Last edited by SB; 08-05-2020 at 06:06 AM.
08-05-2020, 07:22 AM
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tune from Arizona speed
Without AFR readings would be good to see some data from the sensors.
Happen to know if the fuel pressure is at 37 psi for VST?
Is MAP (Pin-J1-9) voltage at 4.9V with ignition ON, and what is it running (around 1.5V)?
08-05-2020, 08:01 AM
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After adding Gil's you didn't need a tune?
08-05-2020, 08:39 AM
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08-05-2020, 09:17 AM
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The BPR6ES have a .750 reach and are gasketed, which many aftermarket heads use.
The factory 502mpi uses .460 reach plugs with tapered seat (no gasket)
Fsctory plug MR43T. Many people use R43TS. Which is projected tip version. Not available in Marine (M).
The Gills are far from a tuned header. Ther are not a header either. They are just slightly better than stock manifolds on a NA engine. Much less weight though. 80+lbs lighter.
Last edited by SB; 08-05-2020 at 09:22 AM.
