Advance Curve for Fuel Injected X1/9

[dcioccarelli]

Hi all,

forgive my ignorance but I just bought a fuel injected X1/9 (after many years of carburettor versions) and would like to understand how the ignition advance works. On a carburettor car, there are weights in the distributor which advance the timing as the car revs. Is this the same in the Fuel Injected version or is the advance controlled directly from the electronic control unit?

I also note that there is a vacuum connection which I assume alters the timing (somehow) according to the manifold air pressure.

Any explanations would be appreciated.

Regards,
Dominic.

[budgetzagato]

The ignition is pretty simple. Ported throttle body vacuum provides vacuum signal to the advance module on the distributor for vacuum advance of 16º - 18º at 12 in. Hg w/air pump, and 26º - 30º at 12 in. HG w/o air pump.

Above a certain rpm mechanical (centrifugal) advance (23º - 27º at 5500rpm) kicks in for a total advance (includes static 5º timing) of around 28º-30º at 5500 rpm.

The ECU has nothing to do with ignition save it uses a pulse from the coil to set the frequency of the injector pulses.

[dcioccarelli]

Hi Greg,

ok, thanks for the info. By Electronic Control Unit I was referring to the ignition unit (not the L Jetronic control unit). The reason for my question was that modern units take an input signal and vary it according to the RPM in the same way as the centrifugal advance works (and therefore define the timing curve). Typically these systems also have a MAP sensor for the load (vacuum).

Anyway, it would seem that I'm overly optimistic in thinking that this might have been implemented on a car of this vintage!

Thanks again,
Dominic.

[ng_randolph]

On them there modern cars, the ECU sets the ignition timing based on RPM, manifold vacuum, throttle position etc. (On somewhat older cars an ignition control module would do it). Not so on the L-Jetronic X1/9. Here the timing is set by mechanical (centrifugal) advance and vacuum advance only. The electronic control module does not alter the timing, it simply reads the pulses from the magnetic pickup in the distributor to turns on and off a transistor (or perhaps it is a thyristor) that grounds the coil primary.

[Black-Tooth]

... but here's a little bit of twist for you to store away for a rainy day.

The vacuum advance, but for a moment, actually causes the dizzy to RETARD, or not advance further, when the throttle is initially opened, especially if stomped on, going to WIDE OPEN THROTTLE (WOT).

For an instant in time, when the carb or FI throttle plate is opened, there is a DROP in vacuum which causes the advance plate in the dizzy to spring back to normal until the engine speed catches up and creates a vacuum again. This will aid in preventing PINGING and offers a smoother transition, especially on carbed cars, and especially for street use.

If yur racing, its probably best NOT to have any vacuum advance function at all, as the engine should be operating on and off of WOT most of the time... the fuel should be of sufficient octane to care for any pinging, and the timing compensated for in the tune up.

Hope all this is of an interest to you, don't mean to confuse.

[dcioccarelli]

Thanks guys,

this is exactly the information that I was after. I'm looking at installing a programmable ignition system which allows you to program your own ignition curve (and switch between 2 programmed curves). Does anyone have the data for the standard advance curve for an injected X1/9?

With the programmable system I will need to basically weld the standard advance within the distributor so that it is determined completely electronically (as responds faster than the centrifugal advance). For the vacuum I'm going to need to get a manifold air pressure (MAP) sensor so that I can adjust the advance curve to the engine load.

Anyway, thanks again for your input.

Cheers,
Dominic.

[ng_randolph]

From the shop manual:

Static timing is 10° BTDC at 800 - 850 RPM
Centrifugal advance is 16° - 20° at 3500 RPM (so, total of 26° - 30° for static + centrifugal).
Vacuum advance is 12° - 16° at 11 inches of mercury.

Now for the caveats: The carbureted engines used ported vacuum for the advance, meaning at idle the vacuum port for the advance is closed off by the throttle plate. So, no vacuum and thus no vacuum advance at idle, plenty of vacuum at part throttle, and again no vacuum at wide open throttle. I do not know the arrangement for the FI engine, but would assume it uses ported vacuum as well.

In most cases, a spec. like 16° - 20° at 3500" implies no further advance beyond 3500 RPM. This is certainly the case for the carbureted engines (I have the actual curve for these). Same for the vacuum advance, no further advance beyond 11 mm Hg.

Finally, the "curves" are not necessarily straight lines. For the carb version, the centrifugal advance increases quickly (and in a straight line) between 1000 and 1500 RPM, then slower (but again in a straight line) from 1500 up to max advance. Similar for the vacuum advance for non-California cars, advance increasing rapidly up to about halfway on the curve, more slowly thereafter.