Long story short, the engine builder was not able to communicate with the ecm (MEFI 1)and they never tuned it. The entire build process had taken so long that I became frustrated and picked up the boat to complete the rigging in a more timely fashion. I chalked the ecm issue up to inexperience and went on my way, completed engine install and it started right up. The only wiring I did was put the plug into the socket on the engine harness.

Having lost faith in my original tuner, I found another reputable tuner in my vicinity (distance being a relative concept I suppose) and leave it with him. He called monday and says hey "I can't communicate with this ecm, did you know about this?" Sheeeeet. Yup, I sure did. Two independent tuners having the same issue is confirmation that the ecm is bad, or at least unwilling to cooperate.

So we reviewed my options and given the circumstances decide to upgrade to a MEFI 2. He has a known good one on the shelf, it matches the existing harness, it offers a little better mapping and so that's the plan.

Parts fail, I get that. I just want to male damn sure the MEFI 1 was an organic failure, if you will, not one induced by something else. Unfortunately, too many changes happened simultaneously to do any logical proving.

However, the run-on was never an issue before the engine was disassembled for rebuild. :(

i fix copiers for a living. if an external problem causes a board failure, it usually causes it instantly and will kill the replacement instantly also. boards don't wear out. they are just like new till they decide to quit FOR THE MOST PART. now, obviously i don't run copy machines where a bilge pump is a necessity. but these ECM's are sealed up pretty good.

Followup, in case any one cares. The ECM was working properly, just not communicating with the tuning software. It was replaced with the MEFI 2.

Engine still runs on, back to needing a diode in the alternator.

Who is doing this checking and trying to reprogram your MEFI 1. in which came out in 1993. Also U have a 1997 boat and MEFI 1 - MEFI 2 came out in sometime in 1996.and MEFI 3 came out in late 1998 for the marine side of things. Why MEFI 1 on your app.

You reported no shut off ability for a running engine and then a faulty MEFI 1 and now say its good. The person checking your MEFI 1 - did they do a diagnostic scan ?? Code 51 showing up on a scan is Calibration checksum error - means faulty ECM so do you have this code ?

Just saying MEFI 2 not much better for capabilities compared to MEFI. MEFI 2 offers some refinement in fault codes as to voltage hi or low and added code 41 OPEN IC circuit, added code 44 Can not detect knock, and a added Code 52 EEPROM
failure.

The deal with MEFI 2 is if GM part # is any # other than 16210729 it is STILL MEFI 1 software in a MEFI 2 case. A true MEFI 2 part # from GM is 16210729.

The L29 454 MPI and the 350 Mag MPI had true MEFI 2 software GM part # 16210729 everything else during that timeframe was MEFI 1 software in a MEFI 2 case. .

Also if I remember correctly for L29 454 MPI injector banks were 1-3-5-7 and 2-4-6-8 all other were 1-4-6-7 and 2-3-5-8

Mefituning.com has it, tunertech here, and I trust his input.

The boat is a 1997, the engine is a 1996 (ser. 0K021096). So many changes in such a short period, and not knowing how far in advance certain components were procured, I can't speculate.

The engine still runs on, something is backfeeding a circuit, we're thinking in the alternator.

Why a MEFI 2? Because he had it on the shelf and I want to go boating damnit. :) I really don't care if it's a 1 or 2, as long as the damn thing runs either will serve my purpose.