Written by wolfems on September 7, 2009 – 2:50 pm
Most of us know that you cannot begin to even try to start an engine without a timing light (although many have tried in the past – including myself in my early days). But, without knowing that your ECU is delivering the ignition timing that you think it is delivering, at best you can guess what the real ignition timing is, and at worst you can potentially cause damage to your engine.
We don’t want that.
So the first thing we have to do before we tune an engine – either dyno or track tuning, is to make sure the ignition timing the ECU is displaying corresponds to where the engine is when the spark event occurs. That is: If the ECU says 10 degrees BTDC, the spark event must be 10 degrees BTDC. If it is not, change the ECU configuration so it is correct.
Just quickly though, there is one thing to test. Even though you have the correct ignition timing at idle, what is to say that it is correct at say, 3,000 RPM? With modern ECU’s being so configurable, you must check the ignition timing at 2 RPM points. If the timing is correct at both RPM’s you are good-to-go.
If the timing is not correct at both RPM’s you may have a configuration problem, or a triggering issue.
There are two main types of timing lights. Dial Back, and Fixed.
Fixed Timing Lights just flash when the spark event occurs. They may have a button or a trigger, but they have no smarts to make working out the actual ignition timing easier.
As you will see, this may be an advantage.
Dial Back Timing Light – either with a rotating knob, or buttons. These are the top of the line timing lights. But they do have one problem:- If you have a wasted spark ignition system, either with dual output coils, or individual coils fired twice per engine cycle, a dial back timing light may show you the INCORRECT ignition timing. and worse still, this is not an offset from the real timing, it varies depending on the engine RPM.
This is due to the fact that the timing light is using the speed of the ignition pulses to determine the engine RPM. And it uses that engine speed to work out how long to delay the flash event so it shows on its display or dial, what the ignition timing is. Since it thinks the engine is running twice as fast as it actually is, it cannot determine what the CORRECT ignition timing actually is.
I have seen seasoned mechanics have trouble with this many times over the years. It is more common than you may think.
The basic symptom is that they have set the timing, and it is correct at idle, but when they rev up the engine, the timing changes away from what the ECU is saying it is delivering.
So. Make sure you either use a fixed timing light, or, set the dial back to zero if you are checking the ignition timing of any engine running any type of waste-spark ignition system.
If you’d like some more info on Tools for EFI Diagnostics, you can have a look at http://www.wolfems.com/support/EFIFuelInjectionTools.html . There is info on Timing Lights, Pressure Gauges and Multimeters.
