260 ecm ground question

[MidnightCarving]

I just picked up an stv euro with a 96 260 a63 ecu, it would run for about a minute then sputter and die. I've traced it down to a bad ground in the ECM. Let me elaborate.

At the top of the ECM there is a 4 pin plug that connects to the DDT (though i couldnt get the DDT to actually read through it), so in messing around with the plug and ddt i found that it ran perfectly with the DDT harness connected supplying power through the leads on the harness. So I was checking voltage, used a test harness, all the usual tests, and finally found that the resistance to ground from the ECM was no good, unless the DDT harness was hooked up (which has a ground and pos lead)

So, i took the ecm connector apart and tested resistance from the plug to ground, 0 ohms, good connection. So i tried the ECM side of the pin to somewhere farther up the wire. also good. It must be within the ECM?!

having said all of that, if i get desperate and just ground it through the other black lead going to the DDT connector is it going to cause me problems? i've taken the back off of the ecm to find that it's buried in potting rubber.... so now I think my only solution is to ground through the DDT connector.

I'm pretty new to the 260 so i'm not sure if that will cause problems for me, or just splice the wire and run it!

[MidnightCarving]

also there seems to be a hole in the potting material with what looks like a small screw slot, what is this thing? It lines up with a hole in the back of the ecm box too...

[h2oskiier30]

A) It sounds like you have an A6 instead of an A63...assuming your box is a Merc box and not a CDI box.
B) The "hole in the potting material with what looks like a small screw slot" is your fuel % adjustment knob.

Wish I had an answer for your other questions, but I don't. Hopefully, someone will come by soon and be able to help you.

[MidnightCarving]

A) It sounds like you have an A6 instead of an A63...assuming your box is a Merc box and not a CDI box.
B) The "hole in the potting material with what looks like a small screw slot" is your fuel % adjustment knob.

Wish I had an answer for your other questions, but I don't. Hopefully, someone will come by soon and be able to help you.

It may be a CDI box, it says on the chip inside "CDI a63 w/FMS"

Whats the difference between the CDI and merc box?

[stokernick]

44 days, so get crankin'!!

[MidnightCarving]

well i spliced the wires and so far so good... ran it for a good hour or so today with no problems.

This is my first 260, and i must say they are NASTY but tempermental sob's. ran 103 at 7200rpm in the STV tonight and the only reason i backed off was because i don't have the balls to push it farther yet. They are a totally different ride from the V bottoms i'm used to, but the learning curve doesn't seem too bad. just a different trim attitude and a little trickier to feel when it's just right.

The 260 is another story all in itself. it seems to barely hang on to an idle, runs rough in the mid range, but man once you touch about 4500 rpm it starts to SING. I've heard them from the shore, but its like nothing else hearing that thing come into the powerband when it's directly behind you.

overall it was a successful evening.