MEFI Burn Tuning for idle.
08-25-2015, 02:57 PM
#21
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Agreed. From post #8 "Bravo 1 running 5 blade labbed Maximus. " big diameter prop and an extra blade = stall. What pitch is the prop?
08-25-2015, 03:02 PM
#22
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In the car world, we would be discussing stall converters right now. But, it is the i/o boat world. We have direct drive with props. So, only thing that slips is the prop.
Edit in: I hope to god these motors don't have MPI intakes as they crash at an early rpm and thus cut down on hp.
The cams sweet spot should be 3500 or so to 6000-6400rpm or so, depending on rest of engine build. Again, a 502MPI intake will start biting it low to mid 5k's.
Anyway - just being an internet jockey giving you a different perspective on the engine build.
Last edited by SB; 08-25-2015 at 03:21 PM.
08-25-2015, 09:50 PM
#23
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question - what's the compression ratio and heads? You're going to need a lot of timing at idle and probably fuel to keep it from dying due to the lack of velocity with that cam.
08-27-2015, 02:08 PM
#24
One theory I am mulling over is that due to the load the prop applies when going into gear the large kPa transient causes the ECM to go into one of the rarely used low rpm / high kPa cells. It is highly likely this cell doesn't have enough timing (in the ignition table) or fuel (in the BPW table). These are very difficult to tune because the motor doesn't stay in that regime very long. You will likely not even see the wide band react fast enough for this situation too. Just a theory at this point.
08-27-2015, 05:30 PM
#25
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One theory I am mulling over is that due to the load the prop applies when going into gear the large kPa transient causes the ECM to go into one of the rarely used low rpm / high kPa cells. It is highly likely this cell doesn't have enough timing (in the ignition table) or fuel (in the BPW table). These are very difficult to tune because the motor doesn't stay in that regime very long. You will likely not even see the wide band react fast enough for this situation too. Just a theory at this point.
I had a fast system and was was able to log the in gear and out of gear to find what cells were being accessed. I then was able to increase and decrease timing and got the motor to idle perfect out of gear, going in gear, in gear, and the same going out of gear I had tried to do it with the IAC but could not get it to move fast enough where the motor would not flash up in idle going in neutral and same in reverse.
08-27-2015, 06:16 PM
#26
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I recently had a similar problem. What I did was set my timing at 17 btdc in the cells my motor idles in. Then the cells immediately to the left of the idle cells (lower rpm) I set the timing at 26 btdc. That solved my problem.
As soon as my rpm drops going into gear my timing bumps up and saves the stall. I believe the timing can react quicker than the IAC. I am still fine tuning my timing but this is what has worked for me so far.
As soon as my rpm drops going into gear my timing bumps up and saves the stall. I believe the timing can react quicker than the IAC. I am still fine tuning my timing but this is what has worked for me so far.
08-30-2015, 08:47 PM
#27
I would add that he likely has EST in his stock ignition and this will automatically compensate for desired idle characteristics assuming base timing is sufficient. If this is the case it may likely be fuel related.
09-03-2015, 12:46 PM
#28
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One theory I am mulling over is that due to the load the prop applies when going into gear the large kPa transient causes the ECM to go into one of the rarely used low rpm / high kPa cells. It is highly likely this cell doesn't have enough timing (in the ignition table) or fuel (in the BPW table). These are very difficult to tune because the motor doesn't stay in that regime very long. You will likely not even see the wide band react fast enough for this situation too. Just a theory at this point.
Also, as SB stated, the MPI Mag intake will give up the ghost in the mid-5000 rpm range, so your cam may not ultimately be a good match for it... assuming you can get this Idle issue worked out.
09-03-2015, 04:00 PM
#29
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Go to page 11 it looks like you may be able to rewrite from mefi 1 to 2 which i presume does have timing table's. It depends on which module you have...hmm i believe 2 has timing table's
https://www.mdmotors.ru/netcat_files...MPI__alb_3.pdf
https://www.mdmotors.ru/netcat_files...MPI__alb_3.pdf
09-04-2015, 12:54 AM
#30
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The cam was spec'd out by Erson, I would assume they would know more about cams and motors than all of us, he just said use dry exhaust. Right now, I have seen 75mph in a 02 38 Powerquest that has every single option(AC, Bathroom, shower, full stereo, generator, ETC) with 5 blades at only 5100rpm, so it can't be that far off for that heavy of a boat, and I haven't even adjusted the timing at the top end yet, still only 32 degrees I beleive and somewhat rich(12.0:1).
No load, 60ish KPa, load jumps to 80 then back. I would have to screenshot the values, but I dump fuel in it when it jumps to 80 and then around 60, its significantly less fuel. Never tried a different prop.
Either way, this weekend, I kicked out the mechanical pump, starboard motor quit running but I hear the electric, will only pop every now and then, so I have to fix this now and move from there.
No load, 60ish KPa, load jumps to 80 then back. I would have to screenshot the values, but I dump fuel in it when it jumps to 80 and then around 60, its significantly less fuel. Never tried a different prop.
Either way, this weekend, I kicked out the mechanical pump, starboard motor quit running but I hear the electric, will only pop every now and then, so I have to fix this now and move from there.
Sorry but they are way off and the cam has too much duration.
