Controlling Fuel Only - $8D?

[Scott68B]

Would there be any issues with controlling fuel only, no spark, with code like $8D?

Scott

[Six_Shooter]

I'm not sure why you'd want to, that's throwing away 60% of what makes EFI great.

It has been done with 1227747 years and years ago. I believe the bin file and information for that project can be found in the moates repository on this site, and possibly the diy-efi.org mailing list.

If I were to do it, I would likely use the '7747 as well. Using a '7730 with $8D to run fuel only seems like such a waste.

The most difficult part is triggering the ECM to enable spark. In OEM form this is done through the dizzy and the ICM. There used to be an aftermarket supplier that sold small adapters to trigger the Delco ECM for fuel only mode, I just don't recall who it was. I thought it was Howell, but lst time I looked for it I couldn't find it. I know there were schematics floating around for it. IIRC it was a transistor, and a few resistors and couple caps, that made the circuit small enough to fit inside a wire harness loom, to be hidden. It was triggered off the primary side of the coil IIRC.

[dave w]

I've used the MSD 6A tachometer output to send the needed trigger for the ECM. http://www.msdignition.com/Products/...n_Control.aspx

dave w

[EagleMark]

We have pictures of an actual Tach Filter made by AFI, neither they or Howell sell them anymore. MSD works great.

[Scott68B]

I should have explained my situation a little better. I've got an old MGB with a 3.1 V6 in it now and I'm going to be upgrading to an LS4 in the not too distant future. I believe the best route for me longterm is an MS3 but I'm investigating getting a MSD 6LS to run the coils on the LS motor and using my existing 7727 for fuel to get up and running quickly. Would this be feasible?

[dave w]

Looks like your idea of using the MSD 6LS should work. The MSD 6LS tachometer signal can be used to trigger the '7727 computer. To be 100% positive, I would verify that the MSD 6LS tachometer output signal is a square wave signal. I really doubt the MSD technical support people would know if the MSD 6LS tachometer signal is square wave, but an oscilloscope would. Seems to me like the MSD 6LS tachometer output would be square wave, but I don't have any personal experience with the MSD 6LS to know.

dave w

[34blazer]

keep in mind that $8D uses spark timing to fine tune idle, might run into surging problems especially when ECM attempts to add/reduce timing in the event of an over/underspeed condition. id suggest removing IAC and zeroing out idle spark error tables.

[Scott68B]

Thanks for all the information! Really helpful here.

Regards

Scott

[Six_Shooter]

Why not add a reluctor wheel and use the Northstar ignition system?

Short of adding the N* ignition, MS3 would be the best alternative to the OEM PCM.