Megaboat RPM's won't break over 2000

[usagoal]

I finally got the boat I MS'ed into the water, starting and idling well. I created an initial map and took it out for a test drive. I couldn't get the rpm's over 2000 (though our first test run got it to 2800...but the water was calm and the boat moved easier in the water). There was a point that the engine would backfire slightly and I would have to back off the throttle. I guess I'm looking for some guidance in the area of what kind of numbers I should be expecting regarding pulse widths, duty cycles and what a VE map looks like for this project.

I've been going over the tuning manual and taking notes on what I "think" I should tuning when I'm out there. Weather has been a major factor here in NJ and I don't get too many chances for a nice afternoon of tuning. So I have to make the best of each visit. Thanks again for the support.

[usagoal]

I revisited my datalog file and noticed that the o2 sensor readings were lean during much of the driving, roughly were the rpm's maxed out. The manual states that a lean condition could occur if the ve table is too rich. This could explain the backfire/misfire we hear at the top end. Pw's are high during the lean condition and return to a normal reading when the pw is lower. I may have to go leaner instead of richer on the ve table. Does my theory sound correct?

[Bernard Fife]

The manual states that a lean condition could occur if the ve table is too rich

usagoal,

I don't think the manual says quite that. It does say that a O2 sensor that is too cold, or otherwise malfunctioning can send a lean signal, and if EGO feedback is enabled then the engine will run very rich.

Conversely, if the VE table is so rich that the engine is misfiring, then you could get a lean O2 sensor reading (but the engine is rich, not lean). If you have EGO feedback enabled, this will drive the engine even leaner. So perhaps that's what you are referring to.

So take your O2 sensor reading with a big grain of salt, and use common sense at all times - don't just blindly follow the sensor.

Backfires in the intake usually mean the mix is too lean. Black smoke from the exhaust usually means too rich.

Your VE table is screwed up. You have a 134 value in the middle (at 55 kPa and 1500 rpm), but the 100 kPa values top out at 106. The value below that 134 entry is 66 (at 50 kPa and 1500 rpm). I suspect you were between 50 and 55 kPa, and the correct value for both cells was closer to 75 or so.

In initial tuning, if you increase a value at a given rpm and load, then you should increase all of the table's cells at higher rpms and loads so that the table values are always smoothly increasing as rpm and load increase (at least up to the peak torque rpm - and even then it should only decrease slightly at most above that).

Once you have the VE table 'roughed-in' you can fine tune the individual values.

Finally, I see you are using 'Separate VE and AFR table w/ NB EGO'. I tried this on my car last week, and wasn't able to make it run properly or, or even make much sense of it. It might still need a bit of code work, I think. If this was mine, I would switch to 'Combined VE/AFR Table' - it will make tuning much easier, I think.

Lance.

[usagoal]

Lance,

Conversely, if the VE table is so rich that the engine is misfiring, then you could get a lean O2 sensor reading (but the engine is rich, not lean). If you have EGO feedback enabled, this will drive the engine even leaner. So perhaps that's what you are referring to.

Yes, that is what I'm refering to. My verbage is not as thorough as I would like it to be and I end up rushing through my posting while trying to avoid writing a book.

And for the VE table, some of those numbers were a last ditch effort to see which way I should go (lean or rich) for that RPM bin. I probably should have waited to post my questions until I had a second chance to get out on the water and retune. We literally got into the bay, attempted to tune for 10 minutes, then had to turn back because of lighting storms. Ugh. I ended up doing too much of the wrong thing too fast.

Good point about the o2 readings vs. common sense. It was only when I was reviewing the datalog that I noticed the 02 sensor readings were not quite right. While on the boat (or in my car), seat of the pants tuning usually works best for me. I appreciate the advice and will try to plan my tuning strategy according to your advice and the manual. I know I will get good results, I just need more time on the water....without the lightning and rain next time. Thanks again!
Dean

[usagoal]

I took a step back and decided to re-test and check all of my hardware. I tested everything from power & ignition wires to the fuel filter. I found that the fuel pump was not pumping enough gas to the TBI. This is what caused the engine to run "lean" (starving the engine of fuel). It all makes sense. From stalling in the driveway, only reaching a max of 2800 rpm the first trial run, 1500 rpm on the second run a week later and finally not even starting and idling correctly. I found a large amount of debris in the fuel pump inlet and also in the fuel filter. Along with alot of water too.

Are there any alternatives for a "prefilter" other than the typical mesh sock that is clamped to the inlet of the fuel line inside the tank? I currently have a replacable filter (17 micron) with water blocker in a clear housing to monitor the amount of water/debris so we can change it when needed. This is AFTER the fuel pump however. I'm thinking of a large clear plastic inline filter as a prefilter to catch debris before it enters the pump. A mesh sock would be a bit difficult to add since the access hole in the tank is too small for a hand to fit through. Suggestions are more than welcome.

[drholl]

Yes. Use the waterblocker as the pre-filter.And I hope that filter is a big one.
And as to the fuel pump, see my post of "8 pin HEI Dwell settings". I want to pull
my hair out after that. Put a pressure gauge in the pressure line somewhere.
Here's an msq of my TBI, don't use my reqd fuel though. It's for a 454.
But the VE scaling should be about right although mine is in a car. But mine is
setup for mileage. Lean at cruise. you'l want to go a tad richer.
WBO2 is pretty useful for about $200.

Oh yeah, since it's a boat which will probably be have a lot of full throttle
usage, go big on the fuel line, maybe 1/2 inch like from a 1984 motorhome with a 454.
The 1/2 inch fuel filters can be bought at most auto parts places, special order maybe.

Good Luck and let us know how it comes out.
Holl

[drholl]

You can have a look at mine in Success stories.
"16 MPG around town, 502 powered '59 Cadillac"

And "8 pin HEI Dwell settings" for fuel pump related stuff.
Holl