Questions about TBI ignition

[rsicard]

Gentlemen:

Just very curious. Does the small cap EFI distributor used with the 16197427 ECU have a way of identifying cylinder number 1 pulse from the reluctor pickup? Trying to imagine how ignition timing is sync'd to the engine. Does the module in the distributor amplify and square the reluctor pickup signal without introducing any timing change and spit it out to the ECU? Would perhaps like to add in test wiring and connector to test the waveforms in the vehicle especially the Tach signal which may be messy. The signal from the reluctor pickup should be an AC type wave of approx 0-.5 volts? Then there are the other four wire connections to the module. One likely is a timing pulse mentioned earlier. Two of the others should be 12 volts positive and negative. Not sure what the fourth wire is for yet it likely goes to the ECU for whatever purpose. Please advise. Thanks.

[fastacton]

No, I don't think it has any ideal which is #1. The Megamanual has some good info on the 7 and 8 pin ignition modules:

http://www.megamanual.com/ms2/GM_7pinHEI.htm

[brian617]

Gentlemen:

Just very curious. Does the small cap EFI distributor used with the 16197427 ECU have a way of identifying cylinder number 1 pulse from the reluctor pickup? Trying to imagine how ignition timing is sync'd to the engine.

Synced via rotor position, the reluctor is evenly spaced, no way to identify position. When you get into OBD2 is when you begin to find crank and or cam reluctors with wide vs narrow spacing to indentify crank and cam position and correlation. This is where missfire detection comes into play.

[1project2many]

Trying to imagine how ignition timing is sync'd to the engine.

The ignition timing is not really synced to the engine. The process of delivering spark in advance of TDC is conceptually simple. The ecm receives a reference pulse from the distributor, counts off a time delay, then initiates spark. The ecm performs this task repeatedly with no feedback to indicate whether or not delivered timing matches desired. Instead the ecm uses two constants found in the calibration and the amount of time that elapses between distributor pulses to calculate the amount of necessary time delay before initiating spark.

Does the module in the distributor amplify and square the reluctor pickup signal without introducing any timing change and spit it out to the ECU?

Effectively, yes. In the timing calculations the ecm treats the reference pulse as if it happens as the preceding piston approaches TDC.

The signal from the reluctor pickup should be an AC type wave of approx 0-.5 volts?

The signal is an AC type wave of approximately 0 to 12V+ when the engine is running. Cranking voltage should be around 3VAC.

Then there are the other four wire connections to the module. One likely is a timing pulse mentioned earlier. Two of the others should be 12 volts positive and negative. Not sure what the fourth wire is for yet it likely goes to the ECU for whatever purpose.

Please see this page for additional reference information:http://chevythunder.com/ignition_sys..._operation.htm