I have a 1997 29 Fountain with procharged 454MPI Mag's, computers were tuned by Precision Marine. One engine runs really well and the other one is running really rich above idle. We put in o2 sensors to run a wideband and see what's going on. I took the boat to a local Marina to have them plug their scanner into it. The engine that runs rich was not reading as much data as the other one. It would not read RPM's, Timing, and a few other things. I had them plug it in because I thought it was in fuel enrichment mode, but the temp was a little higher on the side running rich. I'm trying to figure out why some of the data was missing and we were getting funny readings. Has anyone ran into anything like this?

You are going to have to methodically check sensors, grounds and inputs. Check TPS voltage sweep, check the MAP sensor, check all the ignition wiring etc.

What were the AFR readings for the good and bad motor at the same data point?

Yeah that's kinda what I was thinking, just didn't know if anyone had seen the same issue. I switched computers, map sensors and still the same issue. I will start checking wiring and grounds.

As far as the AFR's they both are right around 11-11.3 idling around in gear. The good engine stays around 11.3-11.5 from 2800-33800 RPM's then drops to 10.5-11 from 4000-5000RPMs. I think those numbers are pretty good for finding out I have an old bad set up. The rich engine pretty much pegs my gauge at 9.6 all the way up until 4000 rpms. From 4000-5000 its comes up to about the same as the other side. If the boat is really warm I can get it to come up off pegged to @ 9.8-10 at cruise speed. It does not seem to change at all no matter where I set the fuel pressure at. At idle with the vacuum line off they are both set at 35psi. We boat at the Ozarks and run 100+ miles every weekend so my cruise AF is pretty important.

Prominent inputs that determine your main fuel BPW are RPM and MAP. I'd start with looking at those input channels to the ECM. TPS voltage sweep is easy to do but is predominantly for transient response characteristics and not steady state.

On a separate note, the idle AFR are too rich. That is a no boost region and you are simply pouring gas out the tail pipe.

Thanks for the help. I will start checking wiring this weekend. We are going to print out the Wire Pin diagrams and start checking.

I need to make a spreadsheet this weekend on the AFR's.

Zack