5.0L TBI running rich.

I have never seen EGR on a marine engine, and my manuals don't mention EGR systems. Unless Merc made them just for export, that's probably not your problem. I think you'll find the injectors defective.
 
Chris: I don’t know how much if any I can help out here in the MEFI department with my automotive knowledge. Perhaps just cycling your post may bring us more input and we all can learn.

GM ECM strategies are some what of a hobby of mine. I’ve got some bootlegged tooling for reprogramming/reflashing OBDII systems and an LS1 with 8,250 miles on it to practice on.

After studying my “82”-“01” fuel injection manual this AM, sounds like your working with a L83 TBI early OBDI system. It uses a MAP, TP, IAC, ECT and RPM to control ms to fuel injectors. GM engineers call it speed-density tuning.

With an L83; the fuel pressure regulator is in the throttle body group. It needs engine vacuum. Otherwise the system will stay in a high fuel pressure state for engine starting. Might be worth swapping the TB group with sister engine!

Also the L83 ECM has a “Fuel Backup” (Limp Home) strategy. If voltage is below 9vdc as read by the voltage monitor pin or if the ECM PROM went south. The ECM will deliver a set ms on time for the injectors. Delivery rich fuel at low rpms and lean fuel at high rpms If you throttled a engine up in this mode, you would find an rpm where it runs good. Won't give a code for this.

TTT… for you.
 
First up a bit of history. This is a new boat to our marina, a 2005 Champion 925 with twin 5.0L TBI Mercs driving B1’s Raw water cooled, and it’s the owners first “big” boat. .
Sorry But I'm a little bit confused, Going off of memory, Mercruiser didn't use a TBI (throttle body injection) engine in 2005, They where using MPI (multi port injection) by then.

Are you sure it's a 2005?:huh:

Do you have the engine serial number?:smt024
 
Unfortunately, I didn't get to look at the boat today, the owner has been delayed in Brisbane, so it looks like things will happen tomorrow.

I was in doubt about the year, as the TBI's finished in 2001. It may have been the boat came to Australia in 2005. Like I said in my initial post, "History is lacking".

Never the less, it has TB injection and it definately has EGR and PCV. I'll get some pictures tomorrow and post them up.
 
Does anyone know how this came out and what the end result was? I have this exact situation going on. Thanks Al Schmitt
 
We did and thanks for the info. The starboard side head gasket is blown between #4 & #6. When I checked the compression in July it was at 149 psi. It must have been the very beginning of the failure. It's good to find the answer and thanks again.
 

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