Re:my scope probes almost melted i need help!!!

Hey guys, i have a bit of a situation here with my scope. i have never had this happen to me till now.

so i am currently useing a autel scope. i am trying to check for timeing on a 1998 ford f150 5.4L useing the crank posistion sensor and the cylinder number 1 injector as a sync. So with my injector hooked up to my scope and i have a good wave form i like, i tried to hook up my crank probe ground clip to a stud on an engine (stud off the timing cover) i got a small spark, some smoke and part of my clip melted. like if there was some kind of short going on. i have tried diffrent ground but it still sparks. has anyone run into this before?
i need to why this is happening and how i can fix it

Either your scope ground lead is carrying voltage, or your "stud off the timing cover" is carrying voltage. If you have another, independent, volt meter, Check for a difference in potential between the scope ground lead and the timing cover stud.  Also, check for a difference in potential between the battery negative post, and the scope ground lead. And, between the negative battery post, and the timing cover stud.

Thank you, i will do those checks, ill post what the results were after i do it.

By the way, an injector is NOT a good sync. You don't know, exactly, WHERE in the 4 stroke cycle that the injector fires. It is much better to use and ignition strike, coil control, or coil current. These events happen very close to TDC.  An injector event can take place at different times.

I'm with Chad I'm 99% sure your going to find voltage differential between battery and engine block (meaning you have voltage drop on your ground wire) this can cause all sorts of problems ... On a side note the mp408 scope only requires 1 lead to be grounded it is shared to all channels so just connect 1 to battery and not anywhere else

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so should i just dedicate one scope channel as a battery ground and use the rest of the channels as regular channels then to prevent this issue?

The "channels" are the POSITIVE leads. They are separate from each other, as I'm sure you know.

Depending on the scope, the GROUND leads may, also, be separate from each other. OR all the "channels" might share the same GROUND, internally to the scope. Meaning that if ONE channel is grounded, ALL channels are grounded. 

so should i just dedicate one scope channel as a battery ground and use the rest of the channels as regular channels then to prevent this issue?

You can't use a "channel" as a ground.


As Ben said, you are likely to find voltage on that timing cover stud. This will, likely, be due to a bad ground between the negative battery post and the engine block.
Fixing the bad block ground should fix the problem.[/quote]