Images for DIS crank trigger bracket (Page 2/2)
pmbrunelle JUL 29, 08:24 PM

quote
Originally posted by Joseph Upson:

I wonder if you could accomplish the same with a modified distributor to spin a 12 + 2 trigger wheel since it turns half the speed of the crank and accomplish the same. I'm not sure cranking speed would be fast enough for a sufficient hall effect signal to trigger ignition. I don't recall if there was a design produced for the multi belt system of the Fiero and I remain apprehensive of the few arrangements where signal notches were placed in the outer ring of the harmonic balancer.



Hall works at near zero-speed (limitation is due to establishing a stable crossing threshold, not the Hall effect itself), and the signal is not speed-sensitive. It's the coil-based transducers that have a signal which is proportional to RPM.

A trigger wheel in the distributor could work, but then the wheel could be affected by slack in the timing chain and helical gears. I don't think the timing would be as stable as with a crank trigger.

It might be possible to do the 12 + 2 by replacing the stock star wheel with a 12 + 2 wheel, and by using a pair of fixed fingers to return the flux to the shaft, all while keeping the stock pickup coil, which could interface with the DIS brick. There may be also something to gain by replacing the stock magnets with stronger more modern magnets.

GM already put notches on the OD of the harmonic balancer of stock Fieros, and they didn't blow up, so I don't see the problem with adding more.

[This message has been edited by pmbrunelle (edited 07-29-2021).]

ericjon262 JUL 29, 09:03 PM

quote
Originally posted by pmbrunelle:


Hall works at near zero-speed (limitation is due to establishing a stable crossing threshold, not the Hall effect itself), and the signal is not speed-sensitive. It's the coil-based transducers that have a signal which is proportional to RPM.

A trigger wheel in the distributor could work, but then the wheel could be affected by slack in the timing chain and helical gears. I don't think the timing would be as stable as with a crank trigger.

It might be possible to do the 12 + 2 by replacing the stock star wheel with a 12 + 2 wheel, and by using a pair of fixed fingers to return the flux to the shaft, all while keeping the stock pickup coil, which could interface with the DIS brick. There may be also something to gain by replacing the stock magnets with stronger more modern magnets.

GM already put notches on the OD of the harmonic balancer of stock Fieros, and they didn't blow up, so I don't see the problem with adding more.




The bigger issue I see with adding notches to the stock balancer ring, is that they are known to slip over time and affect timing. I definitely wouldn't do this with an OE Fiero balancer, a new balancer would probably be ok though.

Crash_out JUL 30, 03:06 PM
I picked up a NOS Fiero balancer, along with the Ford Escort sensor. Have a '7730 ECU, and the replacement distributor/oil pump drive, and coil pack. I was hoping I could find the CAD files so I could CNC cut the bracket. I can probably take the original timing bracket and extrapolate the sensor mount from that, but would be much easier to just find the CAD file.
fierofool JUL 30, 04:39 PM
f85gtron did this conversion. I believe he first did it on a 2.8 before dropping in a 3.4. He's out of Fieros now, but I'll contact him to see if he might be able to advise you.
flimbob AUG 02, 11:42 AM
I have several files related to 85-88 fiero DIS conversion


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fierofool AUG 03, 07:26 PM

quote
Originally posted by fierofool:

f85gtron did this conversion. I believe he first did it on a 2.8 before dropping in a 3.4. He's out of Fieros now, but I'll contact him to see if he might be able to advise you.



I checked with 85gtron and when he did the conversion, he kept the distributor instead of going DIS. No sensor was needed. He used the signal from the distributor. He later went to a 3.4 and used the crankshaft sensor in the block.