7747 tbi 5.7 into my boat

**bigbillyboy** · 09-21-2015

first off, thank you for all the great info. i was able to convert my 5.7 mercruiser to tbi this spring. it runs pretty well, definitely better than the quadrajet that came off. I pulled the ecu/harness/sensors out of a truck with a manual transmission. i do not have a vss or o2. i have not attempted to tune at all. I was just wondering if anyone has a tune available for the 7747 that eliminates the o2 and vss and optimizes for high rpm (3500+).

the symptoms i would like to get rid of are:

1. slight bog when rapidly going from idle to WOT.
2. seems to run out of top end about 4,000 under a load.

thanks!
jason

**dave w** · 09-22-2015

You can "Ground" the Park wire, which tells the computer the engine is in "PARK" all the time eliminating the need for a VSS.

You can set the closed loop coolant temperature to maximum to keep the engine in "Open Loop", which should eliminate the need for an O2 sensor.

dave w

**96lt4c4** · 09-22-2015

This gets tricky because you will need a way to tune fueling. You would need to put it on an engine dyno, or be really good at reading plugs. What year truck?

**Fast355** · 09-22-2015

Originally Posted by 96lt4c4

This gets tricky because you will need a way to tune fueling. You would need to put it on an engine dyno, or be really good at reading plugs. What year truck?

You can get adapters for 02 sensors for some ehaust manifold/riser designs. Plan to use them when my L31 from my Express ends up in my boat with the 0411 running it.

**bigbillyboy** · 09-22-2015

the tbi setup came out of a 1989 1500 with a 5.7 and manual trans. would i still need to ground the park wire if the computer came from a manual trans truck?

**fastacton** · 09-25-2015

The harness from a manual truck won't even have the Park wire and I don't believe the manual trans tune will look for it. I don't have any experience with boats, so i don't know if the manual tune is better than one for an automatic for your application.

**96lt4c4** · 09-28-2015

Originally Posted by Fast355

You can get adapters for 02 sensors for some ehaust manifold/riser designs. Plan to use them when my L31 from my Express ends up in my boat with the 0411 running it.

I have seen those, don't remember them being around when I did mine years ago.

My new boat has a TBI 350 in it stock, will do 55 MPH, and pulls anything I want behind it. I am leaving it alone...LOL

**96lt4c4** · 09-28-2015

Originally Posted by 96lt4c4

I have seen those, don't remember them being around when I did mine years ago.

My new boat has a TBI 350 in it stock, will do 55 MPH, and pulls anything I want behind it. I am leaving it alone...LOL

**walter** · 09-28-2015

I like your conversion. I did a conversion carb to TBI a couple of years ago (7747 ECM). I fabricated my own O2 adapter to install in one riser. I then tuned the engine with a wideband. When I was done, I installed a 3 wire NB O2. It really ran great and had improved fuel economy with the CL. I just installed the ECU in a weather box from an Audi I had here at the shop.