Toying with the idea of building a TPI 350 for my boat. Unfortunately you can't have an O2 sensore on an inboard motor. Buying a new MPFI marine engine costs $8000. Thinking I could set one up for half that and use a 7730 ECM. Anyone here have experience tuning a boat motor?

 

Just curious. Why can't you have an o2 sensor in a inboard engine? Its got exhaust pipes.

Are you worried about water coming back up the pipes and hitting the o2 sensor?

 

I don't have any experience as of yet but I can think of a few things you might want to do if you DIY. First, what kind of water is your boat going to be in, secondly, what type of exhaust system? If the exhaust is high enough and you aren't running water cooled manifolds then you could probably use an o2 sensor.
No matter what, you'll want a marine intake that has brass cooling jackets.
The 7730 should work great. Tuning a marine engine shouldn't be hard, it's not like you've got to worry too much about AE, just keep out of the lean backfire and rich bog area . Good luck.

 

Tuning's tuning.
Yep, done a boat.
No gears, and with the prop at full load from idle on up they can be a real pain.

Use a 727, it's the water resistant version of the 730 used in underhood applics.

EFI doesn't mean having to have an O2. You can tune an engine to run open loop.

Part of the added expense for Marine Appcs is for spark supression, any spark under deck can be catastrophic.

I've seen used MEFI's on ebay.

 

Yeah, like some export vehicles that need to run leaded gas (middle east I think). Still, open loop SD for the life of the vehicle scares me...assuming recalibrations aren't done every 50k (normal people, to say the least, wouldn't be doing that).

 

All the new MPFI boat motors are 100% open loop but they are MEFI-4 which isn't as easy to tie into a computer and adjust like a 730 you are dependent on the dealer too much. I like the idea of setting up a system based on a 730 but without an 02 sensor or dyno I am afraid the tuning might be very difficult.

 

I have thought about this a bunch too. I have a 4.3L in my boat, with the water jacket manifolds, hence no way to put in a O2 sensor. I guess I could just start with a 4.3 bin, make it run open loop, and watch knock counts, but that doesn't seem like a good way to tune. I wonder if you could tap a O2 sensor into the exhaust crossover in the intake manifold. Would there be enough flow to be accurate?

 

No expert here, but I think you could probably come pretty close based on performance. A boat is going to see a much more consistent load range than a car. So here's the idea:

First you have to get it close enough to run..

set it so it stays in PE all the time, and set the PE tables to command a 12.5-1 AFR.

start logging runs. set it at 10% TPS, let the speed stabilize, and read RPM's. Do this at different throttle settings.

Now do the same runs 2 more times with chips that have 5% more and 5% less fuel. BY watching which way improves RPM's, and repeating a few times, you should be able to get pretty close. max performance should be somewhere around 12.5 to one, so when you turn off PE, you should be close to 14.7-1

Now do the same thing for timing. If you change timing much, you will need to go back and do the fuel again.

This might get you pretty close at cruise. fuel still might be off when you are accelerating, but you could probably tune those areas by a combination of Butt Dyno and data logging.

You would need to watch out for wind, and make sure all runs are done with the same load in the same spots, and with the trim set the same.

 

Dry stacks?.
Just tape the sensor into the end of the pipe.
If you have 4" of pipe past a WB you can get by with that, ugh, least I have.

Is there an exhaust cross over on the intake?.
EGR?.
You just need to sample it.

Tuning for knock limit on a boat aint the way to go, unless an all out race boat. And the situation gets worse for between deck installations, lots of heat build up.