Looking for a sensor to feed 1227747 ECM

[Six_Shooter]

That "special" filter is the same one used on every other fuel only Howell setup, in that it just triggers the ECM as the pulses come into it. Basically just takes the coil negative signal and buffers it to provide a ground pulse to the ECM.

That hall effect sensor should drive the GM ECM, since the output signal would be very similar to what the HEI module would provide (square wave pulled up to the pull up voltage). You'll want to make sure the pull up voltage or output positive voltage of the sensor is no more than 5V. That sensor can be powered by 5V which will take care of that.

I think you're on the right track with using a crank trigger with evenly spaced triggers, to get a more stable RPM input. You still will not have any spark control ability doing this.

Alternatively you could look at the Megasquirt line. The MS2 and Microsquirt (as well as other models) allow for odd fire engines and would allow spark timing control as well.

[RBob]

What six-shooter said. The ECM REF+ input is a 5V digital signal. Be sure to run a ground to the REF- input of the ECM (pin B3). This ground should originate at the same location as the Hall Effect sensor ground.

The reason for the varying RPM readings is that the ECM calculates the RPM via the time between distributor reference pulses (DRPs). With the odd fire setup this varies between the pole pieces.

RBob.

[1project2many]

GM chose to use oddly spaced trigger pulses to make effective use of an already designed ignition module. For most engines the module doesn't need to do anything more than control the coil current and dwell time based on the incoming pulse time. If the odd-fire engine were to use evenly spaced pulses there was an added requirement for a time delay after some of the reference pulses in addition to needing a detection strategy to indicate which pulses did or did not require a delay.

When computer control was introduced to GM engines the basic ignition module was altered to allow selection of internal or external coil control. When the coil is controlled by the ecm, spark advance is created by using the reference pulse to indicate start of a timer which, when combined with the amount of time and number of degrees between reference pulses, is used to generate spark at a desired crank angle. No cylinder detection strategy was included as most engines did not require it. It is around this time that odd-fire V6 engines were being switched to even-fire engines, possibly to eliminate the cost in designing and producing of an odd-fire electronic control system.

The problem you are fighting cannot be cured with a filter. The ecm code is written for engines with an even number of degrees between reference pulses. The ecm determines engine speed by measuring the time between reference pulses. RPM is calculated as degrees / time. With the odd-fire engine the time between reference pulses is always changing. So the ecm calculates engine speed as repeatedly increasing - decreasing - increasing - decreasing.

In theory it is possible to use a pair of sensors to allow an odd-fire configuration to work with hardware and code designed to be used with an even-fire engine. By introducing an additional signal similar to a cam signal, the ecm could be coded to recognize the start of a sequence of long/short/long pulses. The ecm could add time to (or subtract time from ) every other reference pulse based event. I believe this strategy of "evening out" an odd-fire signal would require a number of code modifications to make the system work as intended.

This same "dual sensor" approach could be used to make an odd fire engine work with evenly spaced pins. It may even save time and effort to code this into one of the ecm's used with sequential PFI. This could be extended to alter injection pulse timing to be consistent with individual cylinder events. I suspect that this may be easier than the above approach as you would be working primarily on the output for spark and fuel. This would be a neat experiment and cool "one of a kind" technical achievement.

Several years ago another member of this forum used two GM computers to attempt to control an odd-fire V6. By treating the engine as separate three cylinder engines the ecm hardware and software should be usable without substantial modification. Ultimately the poster abandoned the idea of spark control because he was using a common trigger and icm which didn't work. These two threads may help illustrate what was done.

http://www.gearhead-efi.com/Fuel-Inj...5267-Willys43&
http://www.gearhead-efi.com/Fuel-Inj...0-Odd-Fire-TBI

Of course MS or another aftermarket ecm which can be programmed for odd-fire engiens is also a good option.

If you decide to tackle spark control with a GM ecm it may be a challenging project. But I'm sure there are a few folks here who would be willing to help with the details.

[NorCal69]

That "special" filter is the same one used on every other fuel only Howell setup, in that it just triggers the ECM as the pulses come into it. Basically just takes the coil negative signal and buffers it to provide a ground pulse to the ECM.

That hall effect sensor should drive the GM ECM, since the output signal would be very similar to what the HEI module would provide (square wave pulled up to the pull up voltage). You'll want to make sure the pull up voltage or output positive voltage of the sensor is no more than 5V. That sensor can be powered by 5V which will take care of that.

I think you're on the right track with using a crank trigger with evenly spaced triggers, to get a more stable RPM input. You still will not have any spark control ability doing this.

Alternatively you could look at the Megasquirt line. The MS2 and Microsquirt (as well as other models) allow for odd fire engines and would allow spark timing control as well.

Here is what I have made up.
We have a LS2 cam sensor.
I removed the Howell tach filter and wired up the LS2 cam sensor as follows.

Sensor terminal A- 5v- connect to terminal C14 on ECM
Sensor terminal B- Low Rev- connect to terminal B3 on ECM
Sensor terminal C- Signal- connect to B5 on ECM

I wired up the sensor as described above but the engine did not fire, fuel pump did not run during cranking and injectors did not fire.
Monday afternoon I got my multimeter out and probed the sensor connector. When probing terminal A and B the meter did not produce a reading. When probing terminal A and C the meter read 5.05V, the fuel pump kicked on and the injectors fired. Next I probed terminal A and the other probe to a ground on the frame and the meter read 5.05V.
At the ECM I probed C14 and B3. The result was 0.02V. Next I probed C14 and B5. The result was 5.05V and the fuel pump kicked on/ injectors fired.
This lead me to believe that terminal B3 was not making the necessary ground connection. I pulled the pin from the ECM connector and touched it to the body of the ECM. The fuel pump came on and the injectors fired. I clamped the wire to the ECM body and turned the key.... the fuel pump ran, injectors fired and the engine started!
I sourced a second ECM and terminal B3 does not make a good enough ground on it either.
What am I doing wrong?
With the sensor grounded to the ecm body, the engine is reading lean and the idle is unstable.
Reading the computer with my snap on brick, the idle speed reading is now consistent with the actual engine rpm fluctuation.
I am nearing my end with this entire Howell setup....

Here are some pics of the install.