Need help understanding installation and function of the HEI system on a TPI being installed on my ZZ4 engine. I bought the TPI, supposedly complete, but it is missing the dist cap, rotor, and coil. I have an HEI with vac adv right now. My questions are:

- How does the TPI system actually control the timing advance. I see the dist has a magnetic pickup, but no physical way to adjust timing. right? Is the coil somehow triggered by the ESC? If so , the rotor would not be lined up with the dist cap contacts to send the current to the proper plug. HMMM

-I see mention of aftermarket coils being used. The ones listed don't appear to have connections for a factory harness. Is there a factory harness connection at the coil from the ESC.

- Anyone have pics of how this is supposed to look?

Thanks in advance

 

Welcome to thirdgen.org.

No pic's, sorry...but...

Assume you have the wiring harness and ECM as well?

Inside the ECM is a EPROM, in the EPROM the advance (among other things) is controlled.

You don't want/need to use your vac advance HEI. I'm sure someone has kluged it together before, but may as well let the ECM control things

Just to clarify, base timing is still set the "old fashioned way" in a sense, by adjusting dis. position, but total timing and rate of advance is controlled via EPROM adjustments. Info available on the DYI_EPROM board.

 

Thanks for the welcome! I do have the ECM and harness, and I do plan to allow the system to operate as much like stock as possible including letting the computer decide on timing advance. But, I am confused on how the computer can physically adjust the timing. What is the mechanism. In standard distributors the rotor itself is advanced via the centrifugal force on the weights/cam and vac adv. This TPI dist appears only to have the magnetic pickup (unless mine is missing parts). The info I have completely skips the "how" it operates, and I need to know since I must get this thing running and seem to be missing unknown parts.
Thanks,
JT

 

The distributor pulses are fed back through to the ECM and interpeted, at the same time the ECM is telling the ICM (referred to as "The Module",) located in the distributor, when and how often to fire the coil.

If this kinda is like a "Wow, how do they do that?" type of thing, you probably don't want to hear that this technology is obsolete on most engines these days, as most manufatcures go with distributor-less ignitions.

Going by my faded memory, on the base plate of the distributor, you should have an "electrical" looking device (The Module), with 2 wire going into one side, then either 3 or 4 coming out the other side.

There shold be a "star" shaped device (reluctor) sitting on top of it all, underneath the reluctor is the PickUp Coil.

All should be fairly visable without the cap and rotor on, especially if it's in your hand, and not installed on the engine.


If you have all the above, you should be good to go with a new cap, rotor and coil.


What type/year system are you using? What's it going on to? there may be simpler ways to set you up.

 

Thanks for the info. I do have the reluctor/pickup and module with connectors on the dist. What still confuses me is how triggering the coil to fire can alter the timing unless the spark is expected to jump varying distances inside the cap.

Usually with a new dist, you would cut a hole in the top of a spare cap, and with the timing light, adjust the pickup to fire the coil when the rotor is at the number 1 contact. After that the rotor/reluctor are advanced via the mechanical or vac adv and the coil fires only when the rotor is at a contact.

With the TPI just advancing the coil , it would make sense that the spark is expected to jump inside the cap to the nearest terminal?? Can it be so?

I have a MAF TPI from an 87 IROC 350 which is going into a 1971 GMC Truck with the ZZ4.

JT

 

Yep, it just jumps the gap when it is told to fire. Remember though, at that point is where the most energy is and a relativly small change in rotor position translates to larger degrees of advance/retard especially when the engine is turning faster.