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Self tune mefi burn, am I crazy?

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Self tune mefi burn, am I crazy?

Old 03-11-2013, 09:43 AM
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Default Self tune mefi burn, am I crazy?

After talking with few well known guys about selling me a proven flash for my upgraded 575scis I was told by all 3 of them to install 02 bungs and get AFR readings AFTER the burn and send back for adjustments, mainly because of my cam choice.

So I started thinking- I still need to buy a scan tool, invest in the AFR, weld the bungs, and then I need to pay any shipping to send a LOCKED ecm back and forth to fine tune, if needed. Or fly a guy out to sit on my boat and tune, which is the only way to get the most accurate tune

OR.....purchase mefiburn software, and sit down to do my own tune? How hard can it be? I decided to go with this option, which also doubles as a scan tool and leaves my ecu open for adjustments and diag.

Bob at mefiburn seemed very friendly and helpful, the support at this point appears to be above average.

As much as I love this site, it seems to lack knowledge in two key areas, hydrodynamics and efi self tuning. Not knocking the guys on here, cause the site is extremely strong in most boating areas of discussion, in fact the best. Some of th smartest engine, glass, prop, drive, diag, and electrical DIY'rs on the planet hang here, wonder why they hide from these areas?

I am going to document my tuning journey, win lose or fail, for two reasons. One is for guidance from anyone on this site that has experience, and two is to help others that are considering doing the same.

I am not looking to spend the rest of the summer tuning my boat, in fact I am hoping to get a tune relatively quickly.

Key areas that need to be addressed

-cold start way too rich
-rev limit raised to 6000 rpm and custom table for fuel cutoff
-calibrate to run on 120 degree stat
-calibrate to compensate for increased boost and cam change


Wish me luck! The fun should start next month
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Old 03-11-2013, 10:17 AM
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A friend of mine runs HP tuners, http://www.hptuners.com... I have no idea why this is not more common on boats.. I use to tune my 99LS1 back early 2000... go out record or monitor a run , then change what I needed to. I have no doubt you`re gonna love having the ability to tune your own stuff.

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Old 03-11-2013, 10:27 AM
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This was the main reason I went to a carb setup because I don't want to send out ECM for tunes while I sit, wait and hope for the best.

I tune motorcycles on my dyno all the time and its not bad once you understand what the motor is needing. With the afr installed you should be good to go.

Good luck.
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Old 03-11-2013, 12:52 PM
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I did basically what you are going to be doing. I'd be happy to share my experiences with you. Just PM me.

What MEFI unit? I presume a MEFI 4.

What ignition system?

If at all possible get a copy or download the baseline tune off your ECM and save it. Make multiple copies. If the tune is locked and you can't get the password then your job is harder.

You would need to do extensive data logging to gather all the fuel and timing parameters and reconstruct the data on a new unlocked base tune. You can't have too much data logging in this case! Log from a cold start idle through warm up. Log everything at steady state rpms through out the rpm band. Log slow and heavy acceleration from idle to WOT and everything in between. Log decel both heavy and slow (monitors what ignition and fuel does under heavy vacuum).

Once you modify the tune save it as a new file. When another change is made save it again as another new file. This way you have sequential copies of changes and can go back should you need to.

Make small changes and limit your changes to one variable at a time!

The rich cold start you wish to address is fairly easy to fix. There is a specific table labelled "Coolant Temp vs BPW". In essence and electronic version of a choke. Cool motor gets more fuel, warm motor needs less fuel.
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Old 03-11-2013, 01:56 PM
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Originally Posted by Trash
I did basically what you are going to be doing. I'd be happy to share my experiences with you. Just PM me.

What MEFI unit? I presume a MEFI 4.

What ignition system?

If at all possible get a copy or download the baseline tune off your ECM and save it. Make multiple copies. If the tune is locked and you can't get the password then your job is harder.

You would need to do extensive data logging to gather all the fuel and timing parameters and reconstruct the data on a new unlocked base tune. You can't have too much data logging in this case! Log from a cold start idle through warm up. Log everything at steady state rpms through out the rpm band. Log slow and heavy acceleration from idle to WOT and everything in between. Log decel both heavy and slow (monitors what ignition and fuel does under heavy vacuum).

Once you modify the tune save it as a new file. When another change is made save it again as another new file. This way you have sequential copies of changes and can go back should you need to.

Make small changes and limit your changes to one variable at a time!

The rich cold start you wish to address is fairly easy to fix. There is a specific table labelled "Coolant Temp vs BPW". In essence and electronic version of a choke. Cool motor gets more fuel, warm motor needs less fuel.
Hey thanks for the tips.

I have a stock mefi3 system, and stock merc HEI ignition....no plans to change.

The ECU is stock, and I will save the files as you noted. Finding someone to provide a "close" tune to adjust is near impossible, mainly because they will lock it so that their hard work can not be pirated.

The hardest part that I see ahead of me is aligning the ARF readings with the ecu data log. From what I can tell with the stuff I planned to purchase so far it would be manual, I need to do more research because I would like the two to work in the same log.
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Old 03-11-2013, 01:57 PM
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Originally Posted by cp5899
This was the main reason I went to a carb setup because I don't want to send out ECM for tunes while I sit, wait and hope for the best.

I tune motorcycles on my dyno all the time and its not bad once you understand what the motor is needing. With the afr installed you should be good to go.

Good luck.
Thank you! Good luck with all your winter improvements as well
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Old 03-11-2013, 04:26 PM
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If it were me would can all the merc crap, run a laptop programable on your boat and be done with all this sending back and forth B/S...its a short in the dark and usually not very close to where it should be....I run megasquirt with my own EFI setup with a procharger....
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Old 03-12-2013, 12:49 AM
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Originally Posted by 4bus
Hey thanks for the tips.

I have a stock mefi3 system, and stock merc HEI ignition....no plans to change.

The ECU is stock, and I will save the files as you noted. Finding someone to provide a "close" tune to adjust is near impossible, mainly because they will lock it so that their hard work can not be pirated.

The hardest part that I see ahead of me is aligning the ARF readings with the ecu data log. From what I can tell with the stuff I planned to purchase so far it would be manual, I need to do more research because I would like the two to work in the same log.
Ok, you have a MEFI 3 with a stock tune but a modified 575 correct?

I believe, but am not sure but the MEFI 3 ECMs were locked by Merc with a password. I can't confirm this but you will know when and if you try to download the file using MEFIBURN. I have a MEFI 1 and it was not locked. I was able to download and save the stock tune and go from there. Made my job much easier.

It is true that the AFR readings would be logged separately from what Scanner Pro logs. However you can wire and set up Scanner Pro to log AFRs as well. It takes a little extra wiring and some tweaks on ScannerPro. Not insurmountable but extra work. To date I've simply logged them separately and taken time hacks on the recording to along with a series of throttle inputs to align the playback. I also do some steady state simple paper/pen notes and that has worked well.

Much of the idle and warm up can be done on the trailer with a hose attached. This is good for cold start to warm idle no load tuning.

Do you know the stock motor cam specs and boost?

What modifications did you do to the motor? Cam? Heads? Both? Injector mods?


PM me for more details. I wish you the best of luck.
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Old 03-12-2013, 07:59 AM
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Here are a couple links to add a gauge. There's another I remember seeing that details the process fairly well but I can't seem to find it.

http://tunerpro.net/forum/viewtopic.php?t=518

http://www.carols62.com/ramjet/cruise_control.html
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Old 03-12-2013, 09:50 AM
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Originally Posted by Griswald
Here are a couple links to add a gauge. There's another I remember seeing that details the process fairly well but I can't seem to find it.

http://tunerpro.net/forum/viewtopic.php?t=518

http://www.carols62.com/ramjet/cruise_control.html
This might be the other link.http://www.carols62.com/ramjet/wideband.html

I've wanted to wire it up but have been too lazy.
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