Newbie Wanting to Install a TBI on Marine 4.3 - Looking for Advice

**Ski** · 11-21-2020

Got to get this disclaimer up front, I'm a babe in the woods when it comes to EFI, grew up with Carburetors, however I love the reliability of my fuel injected vehicles. I have a little bow rider with a 4.3 that I would like to add a TBI to, I'm tired of wrestling with the old carburetor each year. I know I can just buy a kit, however it's a bit more than I would like to spend and I also enjoy the DIY challenge. I'm off looking for a donor 4.3 vehicle with a TBI system to harvest as many parts as possible. From my reading I think I want to use a 1227747 ECM. I have tried to read as much as possible to use this system on a marine engine but could use some help. I'm sure changes need to be made to the software, is it worth investing in all the required gear to burn chips and tune, or should I just have someone perform that task (Any takers?. Like to understand the advantages and disadvantages of open versus closed loop, I know there are ways to do it, but will it make a large difference? I just want a good running stock motor, nothing crazy that will be reliable and have improved idling and staring over what I currently have. Apologize if this has been gone over before, I didn't find a lot in my search. Thanks in advance and anxious to get some expert advice on the best way to get started.

**dave w** · 11-21-2020

Budget is usually a factor, a link to a "Google" Marine 4.3 TBI system: https://store5603150.ecwid.com/TBI-F...ION-p166155202

dave w

**1project2many** · 11-29-2020

I've watched as a few different people worked through similar conversions. They seem to work out ok although there's rarely any reports about the swap after the first year. Tuning your own has the potential for tune that better suits your needs although judging by the marine calibrations I've seen it would be easy for someone else to produce an acceptable calibration.

Most factory marine calibrations I've seen are open loop. I'm sure this due to practical considerations. O2 sensors don't work well in cold exhaust and my understanding is that water dumped exhaust must be cooled before it exits the engine. I knew of one individual who tried putting an O2 sensor in the crossover passage in the intake manifold. He said that worked well enough but I probably wouldn't do the extra work these days.

You should learn about the rules around the fuel supply. I've read that people worrying about an inspection work hard not to violate their coast guard approved fuel tank. Mercruiser V6 / V8 used to use a mechanical pump to a separate fuel reservoir which contained an electric pump to supply the EFI system. This way their efi could be used on any craft.

The 7747 ecm is not water tight by any means. It may stand the weather OK or it may not. You may be able to find an older MEFI I or II system which uses flash memory and can be programmed like an OBDII car. Mefiburn is one bit of software that I believe will reprogram the older MEFI.

For years there was a company called CustomEFIS that was supplying parts for "marine conversions." He started with used parts but over time the kits included more new parts than used. I believe that spoke to the reliability and trustworthiness of using used parts in a marine application. You may be able to find one of the old CustomEFIS manuals floating around the web if you'd like to see what they offered.

If you can design a system that's reliable then I believe you'll be much happier with EFI. If you have a relatively stock engine it may not be too difficult to create a calibration. But the farther your powertrain is from a stock vehicle, the more tuning you're likely to need.

Good luck.