davek9

Short Story, took the 86.5 on a 500 mi trip (w/ some heave rain) three weekends ago, on the way back noticed idle was low and engine was off song.
I also knew it was time to rebuild the TT, so I did that and afterword proceeded to track down the miss fire / dead cylinder, here is what I found.

Pulled all the plugs to see which one(s) were having an issue, discovered #5 was really sick, so while plugs were out figured good time to re-check compression, went to pull the Ignition Driver wires and saw this:

One of the two main Black (power) wires had melted, not all the way through but almost and the Boots Outer and inner were both split (I did not cut these).

Does anyone have any Ideas what could have caused this?

Thank you,

Dave

Mrmerlin

I would guess that water got into these parts while you were driving and shorted them,
creating extra heat the heat then split the boot .

NOTE these igniters need to have a smear of heat past to assist them in dissipation of the heat they make,
radio shack should have this,
it might be a good time to clean off the old and put on new paste

davek9

Thanks Stan for the reply, do you think a failing Coil and or Transistor under load (3.5 hr drive) could have been drawing too much current over heating the wire?
This was my thinking and when the water got in the steam split the boot.

Dave

WallyP

I agree with Stan - normal module operation generates quite a bit of internal heat, and having the proper heat transfer paste on the bottom of the heat sink is critical.

davek9

Thanks Wally for joining in; Yes I'll re-do the Heat past as that protects the Transistors for over heating.

But that doesn't explain why one wire would get hot enough to melt, something drew too much current, not know exactly how this circuit works I'm not sure if a bad coil would/could cause this or is it just a failing Transistor?

I don't want to melt anymore wire harnesses.

Dave

PorKen

Note the paste turns to glue with age. When you try to remove the amps, they will likely fall apart.

If you have to replace and are running non-resistor plugs (with large gap), then get Bosch amps (with a steel back plate).

davek9

Hi Ken, right now I have the Amps and Coils moved over from the Blue '85, did this in order to make Tech for the DE Day last Thurs, and I found this issue on that weeks Tuesday night. I also replaced all the plugs w/ NKG's version of stock Bosch w/ stock gaps.

My "end to end" wires ohm out at ~ 4200 ohms each, did not see any Ignition Wire or Cap/Rotor issues (all less than 3k miles) w/ clean connections.

I realize I could and did ohm out the two windings of the coils and both coils are the same, however that's not under load, something is drawing too much current, if I shotgun this and replace both coils and Amps, well... ouch!

Thanks, Dave