Im glad it worked out for you. It hasn't for ALOT of people over the years.
Marine wet exhaust systems should >not< be modified to use an O2 sensor, and not just because of USCG and ABYC rules. The only reason O2 sensors were ever used in the first place is (a) vastly CHEAPER than other methods of determining proper air-fuel mix and (b) the need to monitor O2 in the exhaust stream for emissions control regulations and (c) to protect catalytic converters from being destroyed. All of these are primarily important in automotive and truck markets.This has been a great thread, lots of good thoughts and experience. My experience with efi is solely diagnosing and repairing existing systems primarily on OEMs.
When someone tunes / adjusts / sets up an efi system in the boat, with no o2 sensor, a/f meter or egts to provide a closed loop feedback, what are they using to measure or "prove out" their adjustments?
I imagine the efi software requires basic information like cubic inches, expected volumetric efficiency? Does it give you a theoretical window for proper air / fuel mix? I'd really love to learn and get some experience in it. Maybe when I get some free time
No...increasing fuel pressure would only be "adding fuel" if the injector pulse widths remained the same, but they do not, because injector pulse widths are controlled (and reduced as needed) based on the MAP (intake manifold vacuum) sensor.
You can read up on the principle here....
It's obvious you have never owned a 5.0 speed density mustang and then one with a mass air flow meter and done cam swaps. SD absolutely will not tolerate a cam swap without tuning it, a MAF adjusts instantly on it's own.
yeah but the raylar doc says the tune isnt modifed, so upping the fuel pressure would be a global enrichment. what they are really saying is ......the fancy parts we just sold you dont make any horsepower over stock so we leave the tune alone"
Owned plenty. Ran all the of the alphabet cams back when. MAF will idle is about it. Still needs to be the right size, correct injectors, pump(s), and tune.
Buttttt it looks so much cooler when the hatch is up!
If you run a B or an E cam you don't have to do anything as the 19lbshr injectors are only running at about 65% in stock form, as soon as you got to a bigger cam than that or go with aluminum heads and and better intake that's when you need to start dealing with injectors and tune.
Heads, upper/lower/TB, long tubes were a given. The stock E7 heads were the reason for only making 225hp haha.
No, upping the fuel pressure does absolutely nothing 'global', because in a Marine EFI system the injector pulse widths are automatically reduced to compensate based on MAP. I am guessing you are mostly familiar with older automitive 'base map' programming techniques. Advice...forget everything you know about how cars work. Marine EFI is a completely different animal. After you've worked on one, you'll pick up on this quickly.
I ran an E cam in a 97 explorer motor (GT40P heads) in my 91 notch with head work and the stock 19's and an AM MAF. That thing hit hard AF, burn through 2nd and scratch 3rd, I figure those injectors were running at 95-98% duty cycle
so what you are saying is .........take any speed density map, making no changes other then fuel pressure and it will not have any effect? LMAO.
Friend...you are talking about a primitive, 1987 automotive implementation of Speed/Density, four decades old technology and apparently (as you say) was well known to be a crappy implementation from day one. No, I've never owned a 1987 Mustang but what does that have to do with putting EFI on a boat engine here in 2024?
No, I am saying that the ancient concept of a "speed density map" does not exist any more in a MARINE EFI context. For about 30 years now, speed/density has been calculated in real time. There simply is no "map", nor would any pre-defined map even work in a marine context.
Wow, Dave H does EFI setups and programming for a living on high performance marine engines. You're in way over your head trying to tell him how things work. Everyone else is laughing because you don't know who you're talking too.
I think where you are confused is that you didn't read what I wrote. I didn't say "injector pulse width is "reduced" due to lower MAP values"
No, I'm afraid you are confused. There is no "lookup table" in MEFI. Injector pulse widths are calculated in REAL TIME, like this: Done laughing now?
I don't care who Dave H is or who is laughing. Dave H may know EFI systems in general, but doesn't understand how MEFI (Marine Electronic Fuel Injection) systems work, and why they don't use or need O2 sensors, don't use a 'lookup table' and that injector pulse widths x Fuel Pressure = Fuel Flow Rate.
Embarrassed?
No. Here is how MEFI works. No O2 sensor, no "lookup table", just simple inputs from tachometer, MAP (intake manifold vacuum) that give Engine Load plus coolant temp, Throttle Position Sensor and Intake Air Temp. The injector Pulse Width is calculated and adjusted in real time. The more the engine inhales air for combustion, the higher the pulse width and the more fuel flows to match. That's how fuel-air ratios are maintained in real time.
You are confusing a "lookup table" with the outputs of the computer. Try using the MEFI software system from Diacom and you'll see how it works.
Listen . . . this is me trying to be constructive -
It does not use a fuel pressure sensor. If you have not looked, you'll see how it works here.One more question, based on your reply above:
Your saying that the ECM will command additional pulse width (more fuel) to compensate for a drop in fuel rail pressure?
Theres no fuel pressure sensor on these motors . . .that absolutely does not happen.
But please - school me, i'm always open to learing!
Service Manual #33 - Mercuiser 8.1L
Open loop is a term that only applies to automotive systems or other systems that rely on an O2 sensor. MEFI (MARINE EFI) does not have, use or need an O2 sensor.
No, spark tables are NOT the same as injector pulse width. Spark does not even HAVE a pulse width! This kind of confusion happens when you try to use automotive engine software (and expertise) in a marine context.
No, it does not make sense for this reason - the engine has no way of knowing that it is starving for fuel. There is nothing monitoring the AFR.
maybe we have finally found super duper self learning ECU's.
Ok, so I can throw a set of AFR 220's and a 580 lift solid roller in a stroked 11:1 sbc and the stock mercruiser EFI will be fine as long as I increase the fuel pressure. Interesting
apparently you dont even have to change fuel pressure, the ecu will see the map values change and adjust accordinglyOk, so I can throw a set of AFR 220's and a 580 lift solid roller in a stroked 11:1 sbc and the stock mercruiser EFI will be fine as long as I increase the fuel pressure. Interesting
I guess Whipple has been ripping people off saying they are re-flashing peoples ECU's when I reality the ECU is still stock. Scumbagsapparently you dont even have to change fuel pressure, the ecu will see the map values change and adjust accordingly
Seriously though, I posted this awhile back and didn't get a response, now that this thread is current, anyone care to school me?This has been a great thread, lots of good thoughts and experience. My experience with efi is solely diagnosing and repairing existing systems primarily on OEMs.
When someone tunes / adjusts / sets up an efi system in the boat, with no o2 sensor, a/f meter or egts to provide a closed loop feedback, what are they using to measure or "prove out" their adjustments?
I imagine the efi software requires basic information like cubic inches, expected volumetric efficiency? Does it give you a theoretical window for proper air / fuel mix? I'd really love to learn and get some experience in it. Maybe when I get some free time
Chat GPT-MEFI 4.0 has all this covered, using a 6th sense algorithm.apparently you dont even have to change fuel pressure, the ecu will see the map values change and adjust accordingly
If the same combo has been built and tuned before, you can flash the ECM that same base tune to get it close, and then verify the fuel pressure is the same as the other combo. Run it on fresh plugs and do a plug check, see how the plugs read and where the timing mark is on the electrode. But if you don’t do that, or slip an O2 into the dry riser pipe to get some readings, your assuming it’s safe based on the last combo being “safe”….which is sort of what the factory EFI MEFI motors running around in boats are doing, except that tune is super safe and developed thru shitloads of factory testing under adverse conditions.
fixed it for you
