Odd Fire TBI

[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?

[1project2many]

The ignition module does not care what engine it is used on. It's not the problem. In bypass mode it only knows pulse out, pulse in. The problem is how the ecm interprets signals from the ICM. The code is built around the idea that the distributor pulses are equally spaced in time, and that the amount of time between pulses represents RPM. When the time is changing rapidly the ecm will calculate rapid increases and decreases in RPM. Since the odd-fire pickup coil pulses are unequally spaced to match the odd-fire firing intervals, the time between pulses will be unequal. This is not the best solution to deliver accurate ignition timing. It is possible to use a single stock ecm with odd fire. But it would require custom code and a cam position sensor. Most folks are not ready to write custom code. IMO the dual ecm solution is not a bad one.

I know of a couple of successful dual ecm project vehicles. Way back in the DIY-EFI days an individual known as "TedSCJ" used dual 7730's on a Jag V12. Following that, a member of DIY-EFI and the SyTy community piggybacked a 7749 and a 7427 in a Syclone in order to use a 4L60E. Although both solutions seemed less than ideal, they still worked. Both applications used similar combinations of shared sensors. MAP, TPS, and REF can be shared but two wire passive resistance sensors such as CTS and IAT cannot as the resistor network it creates changes the voltage the ecm will see.

The odd fire engine did use a V8 cap but it only had six terminals. Two of the six terminals had "long" contacts on the rotor side. They extended through the area where the missing V8 terminals would normally be. That was the only way to ensure spark reached the correct cylinder without making a completely new cap.

[lionelhutz]

What were the results when someone tried to use a 7 or 8 pin module and a TBI setup?

I've never read about anyone trying it, but it wouldn't work because the ECM would have a hard time figuring out the rpm and the timing advance would be completely out of whack.