1999 270 DA, Accidentally switched battery selector to "off" while running. Mistake!

[brando76]

Hey all,
Any advice would be much appreciated if you have any suggestions.

We made a mistake on our 1999 270 DA 7.4 MPI (single engine) & the battery selector was accidentally switched to "off" while running. Seems to have been a big mistake & the selector & manual read never to do this. Kind of obvious now but i am trying to determine what needs replaced.

Upon switching the battery selector it immediately killed the engine. From what i've read & discussed, i've replaced the alternator & checked the fuses & relays. New alternator, fuses, & relays all seem to be in order but when key switch is turned on there is no "beep" & the fuel pump does not engage (fuel pressure is at zero & relay does not pop). Moved relay to different location & relay seems to pop in different location, so i assume relay is okay.

Any advice? Would this have toasted the ECM & how can i tell? Any other items i am missing & can check?

Any help would be much appreciated.

Thanks,

Brandon

 

[gerryb]

Re: 1999 270 DA, Accidentally switched battery selector to "off" while running. Mist

I don't think you did any damage to the ecm. when you engage the switch, do you get a crank? Wha tis the voltage at the battery terminals?

 

[480ces]

Re: 1999 270 DA, Accidentally switched battery selector to "off" while running. Mist

Did you reset thr ecm's breaker? It's somewhere on the top of the engine.

 

[fc3]

Re: 1999 270 DA, Accidentally switched battery selector to "off" while running. Mist

My manuals are on the boat, but other than the three fuses near the top of the engine, I don't believe that there's anything else other than the ECM that could cause that problem.

What happens when you turn the battery switch off is that the load on the alternator drops significantly. Without the battery's load and without the battery acting like a giant capacitor, the output voltage from the alternator will spike. Depending on what the field current was at the time of the switch being opened, a spike of 70-100 volts is easily possible. That much voltage could damage the MEFI-E and short of having a scan tool, I don't know of an easy way to determine if the MEFI-3 module has failed.

Try to get your hand on a scan tool. You'll instantly know the status of MEFI-3 once you connect to the DLC.

That said, the MEFI-3 module might not be your only problem. You may also have a bad ignition module inside the distributor and some of the sensors, such as the MAP sensor, may have also failed. You won't know without some extensive testing.

The 1999 7.4 MPI was pretty much "stock" GM. So you might find this document handy if you don't have the Mercury manuals as it should be exactly the same procedure.
http://www.pleasurecraft.com/manuals/L510004.pdf

 

[brando76]

Re: 1999 270 DA, Accidentally switched battery selector to "off" while running. Mist

All,
Thanks for the responses. This is helpful info. I have to travel to get to the boat, so i will check out this weekend. I did try & reset the breaker on the engine. It doesn't seem to have popped. To answer "gerryb", i engage the switch & it does crank. Voltage appears to be correct. One of the items i am being pointed to is the 90 amp fuse on the back of the starter. Told it has 3 wires from it serving the ECM, EFI, & Ignition, & that the starter will crank with it blown. Anyone know if there is any truth to that?

Thanks again for any advice.

Brando76

 

[brando76]

Re: 1999 270 DA, Accidentally switched battery selector to "off" while running. Mist

All,
Thanks for all the advice & help. Discovered the ECM was the problem. Unfortunately, for the 1999 7.4 MPI Merc, it is a part that is no longer available. Was fortunate enough to find a used one & it did work. Glad to be boating again. Thanks again.

Brando76