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7.4 MPI, MEFI 3 odd timing problem

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7.4 MPI, MEFI 3 odd timing problem

Old 10-14-2021, 01:13 PM
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Had which problem ?
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Old 10-14-2021, 07:51 PM
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Originally Posted by SB
Had which problem ?
The no knock fault on start when using 91/93 octane vs 87.
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Old 10-14-2021, 07:55 PM
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Thanks for clarifying :thumbs
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Old 10-15-2021, 12:20 AM
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Originally Posted by AllDodge
Correct, the MEFi 3 tries to test the knock sensor on first throttle up after re-start. It advances the timing fully to make it knock. If it doesn't see it, it retards timing a bit. This can happen from using 93 octane instead of 87 gas. Mine was doing that running 89, so I went in a turned it off using MEFIBurn
My marina only has 89 octane. I will look up ways to test the knock sensor. I was considering getting my MEFI 3 reflashed to try to wring another 10 hp out of it, or perhaps if a MEFI 4 was cheaply available. Silly me for hoping !! I have a 454 - 380 hp in the garage that is supposed to go in as a swap when the L29 fails, and I recalled I had the complete ECM, harness and everything, but I just checked and its a MEFI 1.
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Old 10-15-2021, 07:14 AM
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OK with MEFI 1 the problem is probably in the EST distributor
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Old 10-15-2021, 01:36 PM
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dt21
Ive got twin 502's Mefi3, but had same issue, very low timing. I will attach the timing chart. But if you look at orig specs that is what it is supposed to be for your motor. I guess for engine safety - old gas, over-prop'd , etc. Anyway i attached a timing chart and sure enough your advance is exactly where the specs say it should be.
Around 16.9 deg advance in the 2nd column from the right which is about where you'd be running near WOT mid/upper rpm.

I used mefiburn and advanced mine 4/5 deg more than chart said where the timing was low at mid/upper rpm and lower MAP. Basically the mid/upper right section of chart. It felt like a different motor, peppier. Gained 3mph also.

But i have always run premium, occasionally 89, and fresh gas.
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Old 10-15-2021, 01:40 PM
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timing chart for 454mpimag
Attached Files
File Type: pdf
TIMING CHART FOR 454 MPIMAG.pdf (202.1 KB, 65 views)
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Old 10-15-2021, 08:28 PM
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With the orig timing i could only turn 26 Bravo one 4 blades, 5200rpm. 76mph. Now with more timing i can turn 28's, but just barely. 5050 rpm, 79mph.

FYI my motors are stock except for air filters, roller rockers only because the orig where worn out, and Eddie Marine standard log type exhaust - but they flow well over stock, gained another 3 mph with them also.
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Old 10-16-2021, 05:39 PM
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Originally Posted by Cap'm Kurt
With the orig timing i could only turn 26 Bravo one 4 blades, 5200rpm. 76mph. Now with more timing i can turn 28's, but just barely. 5050 rpm, 79mph.

FYI my motors are stock except for air filters, roller rockers only because the orig where worn out, and Eddie Marine standard log type exhaust - but they flow well over stock, gained another 3 mph with them also.
Thats some good info, thanks for posting, Ive never saw a unlocked stock 7.4 bin file, just 454 mag/502 mag mefi1 and 3. I thought a 502 mage at 28/29 dgrees was lame, wow. Im sure its because of the vortec style peanut port heads, I know when I tune a Vortec 350 L-31 in like a 98/99 chevy, they have similar timing tables, sub 20 or close to it, thanks for sharing, Smitty
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Old 10-26-2021, 01:18 PM
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stock cal id is FE28 for the 454 mag EBC4
stock cal for 500EFI is DA02
the table shown is even low timing for stock 454 MAGMPI
table looks like an L-29

Last edited by tunertech; 10-26-2021 at 01:22 PM.
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