Pulse Width/acceleration enrichment

[foxspy]

Hey guys,

Can someone explain pulse width to me? What's an average pulse width number for wot? Also, what is an average "added pulse width" for acceleration enrichment? What about enrichment vs. TPS, what's an average for that? I'm having troubles getting my acceleration enrichment correct, at first I thought I didn't have enough, then I went to the track and slowed down by a full second in the 18th, so I think I added too much "added pulse width".

Any help would be greatly appreciated.

 

[bobc455]

Pulse width is the amount of time that the injector stays open, in milliseconds.

The longer the injector is open, the more fuel gets injected.

This is similar to duty cycle, however duty cycle is measured in percent.

Lets look at an example. At 6000 RPM, your engine is turning over 100 times per second. Each cylinder fires 50 times per second. The ECU fires each injector once per crankshaft revolution, so each injector will fire once every 10 milliseconds (0.010 seconds).

Assuming you are running at WOT, a typical car might have an injector pulsewidth of 7.5 milliseconds - in other words it is open for 7.5 milliseconds, then closed for 2.5 milliseconds. Therefore our injector pulsewidth is 7.5.

Also, because the injector is open for 75% of the time (7.5 out of 10 ms), we say that the injector duty cycle is 75%.

Make sense?

To your other question, AE vs. TPS is only a quick thing. When you snap the throttle open, this essentially creates a quick lean condition that requires just a bit of extra fuel (like an accelerator pump on a carb). So when the TPS is moving, it will add extra fuel. Once the TPS is stationary (at WOT), no more fuel is added by this parameter.

So if you slowed down, it's not because of the acceleration enrichment, something else happened. AE vs. TPS is used to eliminate a "bog" when you snap the throttle.

-Bob Cunningham
bobc@gnttype.org

 

[Craig Smith]

One other aspect to keep in mind is that when you ask about "typical" pulsewidths, please understand there are so many things that can affect what injector pulsewidth is right for a particular combo that there really isn't such a thing as "typical". As a simple example, if a motor running 40 lb/hr injectors has 80 lb/hr injectors installed with no other changes , the pulsewidth with the larger injectors installed would only be half of what it was with the 40 lb/hr injectors, since the fuel requirement is still the same but the injectors are twice as big.