Marginal coils flipping the PCM the bird

[Telco]

Got to thinking about this, and was wondering. Does the RF interference ride up the wiring to the PCM via the trigger or is it actual emitted RF? If it's actual emitted RF, I wonder how a grounded metal shield between the PCM and the engine might prevent this little problem. Thoughts, anyone? May be barking up a tree with no leaves, but if it helps stop the problem it might be worth a little effort. If not, then perhaps a power filter on the PCM trigger lines like one might use on a stereo? 8 capacitors and 8 resistors would be a cheap solution to getting the PCM rebuilt.

 

[joegr]

It's most likely to be RF radiating from the coils into all of the wiring going into the PCM. I wouldn't put any caps on the lines between the coils and the PCM. That would drastically reduce the firing energy of the coils, since it is the rapid collapse of the primary current that causes the high voltage discharge from the secondary. Caps would slow down that collapse. Some low capacitance 12V MOVs on those lines might help as far as reducing damage to the PCM goes. Shielding all the wiring would probably help with the ETC and other issues from noise from the coils.

 

[Telco]

Hang on, so the primary voltage on the coils actually passes through the PCM? Did not know that. Is that a standard method or an LS only method? I thought the PCM just triggered the spark, didn't know it actually sent primary voltage to it.

 

[RigsLS]

It has a fuse for it also, did you know that?

 

[joegr]

Hang on, so the primary voltage on the coils actually passes through the PCM? Did not know that. Is that a standard method or an LS only method? I thought the PCM just triggered the spark, didn't know it actually sent primary voltage to it.

Standard for all the Ford/Lincoln/Mercury that I have played with since they went to COPs. (My Ranger has a coil pack, but it is also PCM fired. However, I think that when Ford first switched to distributorless ignition using coil packs, they used an ignition module separate from the PCM.) Of course, I can't speak for the 2010 and up.
It's also more or less the way my 325i works. (PCM fired COPs)

 

[elephantrider]

joe, i love when you talk like that.

 

[FDR]

The PCM is the new distributor

 

[Telco]

Hmm, so there's not a lot to be done to protect the PCM from interference from marginal COPS when they are directly connected. Nice. Wonder if twisting a grounded wire around the PCM wires would absorb enough RF energy to protect the PCM might do the trick then, kinda like how a twisted wire pair reduces RF interference on phone lines.

 

[joegr]

I can't say if that would or wouldn't work.