'71 240z, MSD 6A Install, Tach Issues

[rbates]

careful with those violet/green wires - I got some unwanted pinging after i did this swop (E12-80 out). MSD & someone on this site suggested switching the pick up wires ..apparently getting them round the wrong way can cause unstable timing. Will let you know how I get on. Hope this is not another case of poor Quality control at MSD..

[Zed Head]

MSD most likely uses what's called a zero-crossing trigger, I think it's the basis to the variable reluctor electronic ignition. The variable reluctor produces an alternating current, from positive voltage to negative and back, voltage crosses zero twice. It's only consistent, timing-wise, going one way. The modules are designed to trigger one way, either going positive or going negative, so if they see the wrong direction of the crossing they are unstable. Swapping wires puts them back on the consistent zero-crossing direction. As I understand things, at this point in time. It's not a flaw, it's just the nature of the technology.

[Zed Head]

careful with those violet/green wires - I got some unwanted pinging after i did this swop (E12-80 out). MSD & someone on this site suggested switching the pick up wires ..apparently getting them round the wrong way can cause unstable timing. Will let you know how I get on. Hope this is not another case of poor Quality control at MSD..

Aside from the pinging, did your tach work? Maybe you could share the wiring scheme for ksbeta.

[rbates]

yeah - tach works above 3000rpm ! the Tach is a pain to get at but my intent is to go the 'resistor jump' route to get it working ..when i can find the time. I follwed the wiring diagram that came with the unit. I'm thinking I may have to go back to E12-80 if I can't get the pinging sorted. I know there are noticeable improvements in driveability going from 240Z points ignition to MSD..I'm now wondering how large the improvements (if any) I will see over the stock 280zx dizzy

[ksbeta]

Thanks All. Speaking with MSD, they're response to my 200-RPM Idle, and minimally responsive Tach was "Did you remember to cut a loop on the MSD box for a 6 cyl car?" (I did, yes).

I've heard of a few folks removing the E12-80, but I get the sense most people leave it on.

Did anyone follow the Chrysler instructions for this install? Someone told me that would work on our cars, but I haven't the foggiest idea what that would entail. He mentioned it uses the ballast resistor, etc.

[sklein239]

I too have similar problems, and gave up after many hours...anyone know of someone in FL who can work on tachs/electrical challenge for the early Z's?

[Zed Head]

I wonder if some of these problems aren't due to RF or inductive interference on the lines that run to the tach. I had a problem with my tach after installing a different coil, with my GM HEI module ignition. The coil tested fine and the engine ran great but the tach would just sit and quiver at about 500 RPM. I added a typical ignition system "condenser"/capacitor to the negative post of the coil and the problem went away.

The MSD generates multiple bursts of high voltage from its internal capacitors. Any wires in the vicinity are going to pick up some inductive current and/or some RF from the multiple powerful sparks.

This is on a 280Z which uses a different tach trigger but might be worth a look anyway. An extra capacitor or two won't hurt anything except an electrical engineer's sense of correctness.

[ksbeta]

It very well might, Zed Head. I wonder if the ballast resistor would change the same issues. Thanks for the input. Looking forward - well, kinda - to getting back in the garage to play with this.

[ksbeta]

Bobs is looking a lot more attractive. Anyone have a spare 71 tach I can send up there?