Odd Fire TBI

[Willys43]

I wonder about the IAC controls? I'm thinking only one ECM needs to control the IAC.

I wonder about reference voltages, like the 5 volts to the TPS. I wonder what each computer sees for a TPS voltage when the ECM's are tied together?

Do you plan to bench test this setup?

For the bench testing I've done with a 7747, I use an electric drill for spinning the distributor to send a reference pulse to the ECM. When bench testing, I use TunerPro RT to data log so I can play-back the test.


dave w

The bench testing worked slick, Both ECMs "see" the same voltage from the 5v reference and the sensors provided the same out put with one or two ECMs hooked up, except for the ECT which required two sensors.

[Six_Shooter]

There's no real documentation for dual ECMs like you're trying to do. The only dual ECM engines I know of run each half of the engine COMPLETELY independent of one another. The ONLY common part is the crack, which each half of the engine just happens to share. Those ECMs are also designed with this setup in mind. The ECMs you are using are not.

On the bench is one thing, where signals and conditions are perfect, it's a very different thing on a running engine where syncing of each set of cylinders will a nightmare.

What you're trying to do is just over complicating the situation simply for the sake of over complicating it.

I ask again; Why have you not tried to use a single ECM? I think you'll be pleasantly surprised that it will likely work right with the right ignition module that takes into account the odd fire.

As I have already said the ECMs will not be in sync and when one ECM, sees an out of spec condition it will throw a code, our worse go into LHM. It won't take much for this to happen, a simple command in idle RPM change that it's not seen will cause the ECM to start doing other things, like changing spark timing to further compensate, which will then make the engine fight itself.

I just think you're over complicating what needs to Hadrian and there are far better ways to put EFI on an odd fire engine.

[lionelhutz]

The only way a singe even fire ECM could work on an odd fire engine is by not doing timing with the ECM. I this this has been well established.

[Six_Shooter]

Well established by whom? There are (single) ECMs that will run an oddfire engine without issue, definitely in the aftermarket, and I'm sure the same could be done with an OEM ECM as well with the right ICM set-up... If I cared enough about injecting an oddfire engine I think I'd use an 8 cylinder reluctor (or how ever many it would take to get even pulses between firing events), so that the pulses were even and just used the dizzy cap towers that are needed for the engine to run. Boom, one ECM, even pulses for the ECM to read, and odd fire at the ignition with timing control. Yes the RPM will read a bit high, but with a simple edit of the ADX it could be made to show accurate. No sync issues between ECMs, no ECM trying to control something it can't or isn't connected to and throwing a fit.

I'm sure I could come up with a more elegant way if I really wanted to as well. Actually that more elegant way would be an ECM that will run an oddfire engine natively without any trickery, save the headaches.

[fastacton]

I'd have to agree with Six_Shooter on this. I don't see why an odd-fire HEI distributor (which I understand is based on a V8 HEI with two dummy posts and a 6 point reluctor) couldn't be used along with a 7 or 8 pin ignition module to run TBI fairly easily. I'm relatively sure I've read about this being done on another forum. If I had an odd-fire motor here, I'd certainly give it a try. Has anyone here actually tried this?

[lionelhutz]

Odd fire V6 firing angles as you go through 720 degrees of crank revolution firing the 6 cylinders
0 90 240 330 480 570 720

Even fire V8 crank angles as you go through 720 degrees of crank revolution firing the 8 cylinders
0 90 180 270 360 450 540 630 720

As you can see, only the first 2 ignition events of the V6 engine fall at the same crank angles as the V8 engine. Hence, the V8 even firing 90* angle reluctor will not work on this engine. Period. End of story. Well established by the almost 40 years history of the engine.

[fastacton]

So, for the odd-fire HEI, they must have used a V8 sized distributor, but with a more specialized reluctor and distributor cap. What were the results when someone tried to use a 7 or 8 pin module and a TBI setup?