How Does the 2.8L Ignition Sytem Know Where Cylinder 1 is? (Page 2/2)
Patrick JUN 29, 07:17 PM

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Originally posted by Romsk:

Patrick,
Ignore that response, he was telling me how to align the distributor to crankshaft cylinder 1 TDC.



What Bill was saying sounded like an alternate universe method of jumping the ALDL port while doing the dynamic ignition timing.


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Originally posted by sleek fiero:

there is one more step in setting the timing and that is there is a brown wire with white stipe near the battery that you need to disconnect before you do the final timing setting and reconnect after.


[This message has been edited by Patrick (edited 06-29-2023).]

sleek fiero JUN 29, 09:29 PM
you are absolutely right Patrick . I was thinking of my s-10 I used to have and you did have to disconnect the brown wire behind the distributor. My Fiero I don't have to think about timing as I do it on my laptop. Sorry for the misinformation. the rest of the procedure is ok. But I was offtrack on the question. I see it was more of a question about the batchfire injection than the ignition but the ecu uses the ignition to time the batchfire injection.
pmbrunelle JUN 30, 09:43 AM

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Originally posted by Romsk:
From the wiring diagrams I was surprised to learn the odd injectors are on one ECM control wire, and the even injectors are on another wire. I just assumed it would fire the odd injectors for intake 1, 3, and 5, and the even injectors for 2, 4, and 6 intake. My initial idea was each injector fired independently, but that was until I saw the diagrams. But what you are saying is that both odd and even injectors fire all at the same time. Ok, I can see how that can work, but how does that make any difference (performance wise) than using just one big injector. I guess an injector spraying on its own intake valve helps the valve to stay cool. What else is going on inside the intake manifold, is all that air/fuel mist just swirling around in there waiting for the next intake valve to open? Doesn't sound much like Multi Port Fuel Injection to me [laugh].



Having the injectors separated by bank was a good choice I think to reduce the current flowing through each contact of the Weather Pack connector, and for wiring. I don't know if current capacity of the solid-state switch in the ECM would have been an issue.

Also, having two circuits gives some redundancy in case of a malfunction. The engine will run with one injector circuit dead. Not very well, but enough to limp home.

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With a carbuteror, or single injector, distributing fuel and air equally to all cylinders is a challenge. With MPFI, the manifold design is simplified, as it only needs to distribute air equally to all cylinders, not fuel.

A certain fuel quantity is injected in the runner, and is considered to stay in the runner for a particular cylinder. It stays there until the intake valve opens and the cylinder sucks in the mixture.

It is easier for all cylinders to be working closer to their ideal AFR with MPFI.

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With a carbutetor or single injector, the intake tract has a large surface area which is wetted with fuel.

Fuel wets the intake, and then re-evaporates, some time later. In steady-state operation, the wet walls don't cause any issue. However, wall-wetting creates a lag in fuel delivery, as some fuel transits through the wall puddle (which takes time) before ultimately being sucked into the cylinder.

The lag in fuel delivery makes it difficult to maintain the desired AFR when the airflow changes rapidly. If you can't keep the AFR on target, then you can have problems with throttle response, or meeting emissions targets.

Fuel condensation is especially a problem with a cold engine, before it has warmed up. Fuel does not re-evaporate readily from cold surfaces.

With MPFI, the injector is close to the intake valve. The wetted area is small, so there is less of a lag effect from wall wetting.

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With two batch injections per 4-stroke cycle, you're basically having a semi-randomized injection timing across all cylinders.

Sequential MPFI (versus batch) can bring another step of refinement, as some parts of the cycle work better than others for injecting fuel. On my stock V6, I found that end-of-injection at TDC exhaust worked well. From 1500 RPM to 3000 RPM, I add in another 45° of injection timing advance.

Where (typically, but not always) batch fire injects twice per cycle, and sequential injects once per cycle, sequential is better at spraying an exact amount of fuel, because there is a fuel quantity uncertainty associated with injector turnon / turnoff. This error happens twice as much with (twice per cycle) batch fire.

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I put a "Fuel Injection" sticker on my car, since I wanted to cover paint damage from a dealer sticker.

Also, I thought it was a feature worthy of showing off, and it seemed like an era-correct modification.
Romsk JUN 30, 11:12 AM
pmbrunelle,

Thanks for the info, I added your comments to my notes.
I love those rubber rear bumpers on your car.

I finished my ICM bench test document:

The Arduino UNO (and some interface circuitry) simulates the Pickup Coil by sending pulses to the ICM P and N pins. The Ref_Hi pin out of an Amplifier in the ICM is that signal squared up, which then goes to the Arduino as a timing trigger.

The Arduino delays that trigger (advance for next ignition spark) and sends out an EST pulse to the ICM. This causes the ICM to open its Ground on the Ignition_C pin. This causes the EM field in an Igniotion Coil simulator (a wirewound inductor similar to the coil primary, and audio transformer and filter to step down the spike to a 5V level) to collaspe where it generates a pulse and the Arduino integrates that pulse to determine if there was enough energy for a spark.

The Ardunio measures the Ref_Lo signal for a good Ground using a 0.75V reference, and it can set the ICM to bypass where the Pickup Coil squared up pulse (Ref_Hi) internally triggers the Ignition_C pin to open directly - no delay(advance).

I can set it to run from 25 to 6000 RPM with delays to achieve an advance from 0 degrees to 30 degrees. Just like the ECM does. Some parts stores have testers for ICMs but they don't push the unit under test to its limits and thus many ICMs don't work well in the car. Mine runs the Fiero ICM to its limits under a full range of tests. I can even add a Thermal Electric Cooler (TEC - which generates heat as well) to the test setup to run the ICM over varying temperatures.

I will post it soon on my website: http://www.paul.romsky.com

Thanks,
Paul