Injector opening times

[z-ya]

Hear are some measurements I made on various injectors I have kicking around. All of them are low impedance. For these tests I used a Megasquirt v3.0 to fire the injectors in non-PWM mode. There is a 6.8 Ohm resistor in series with the injector. I used a inductive current probe to measure dynamic current using an oscilloscope.

 

Hear is what a 280ZX turbo injector looks like:

 

 

As the injector opens, the current increases at a fairly linear rate until it is completely open (the small blip indicated with the label). The current spike after the injector opens is the DC resistance of the injector (2.6 Ohm), plus the 6.8 Ohm series resistor across the 13v on the injectors. So Ohms law, I = V/R, the hold current is 1.38A. A little bit high as most injects want between 0.75 and 1.0A of hold current.

 

 

To demonstrate what a "lazy" injectors does, look at the screen shot below:

 

 

Both are identical used Bosch 36lb injectors, but you can see that the opening times are not the same. In fact there is about a 50% difference between the two. This is typical of used injectors. This can cause a problem on turbo cars that don't require a lot of fuel to idle, but need large injectors for full boost. The idle will be lumpy because this one lazy injector may not open all the way, when the rest do. This is apparent at small injector opening times. Sometimes a cold injector will not open quick enough but be fine once the engine warms up.

[mario_82_ZXT]

So your stock injector takes about 1.4ms to open?

 

Hmm... now that I think about it your description of those idle conditions sounds familiar with my turbo car. I believe it has 5 recall injectors and an original injector and the idle has always been kind of lumpy.

Mario

[cygnusx1]

Is "cold" injector behavior, distinguished enough to need a temperature driven "Opening Time" into MS?

 

I will be using high impedance injectors. Would they tend to exhibit this more, less, or the same?

[eec564]

Interesting reading: http://yarchive.net/car/injectors.html

 

Without the resistor opening time was 1.25ms. How do the rest of your ZX Turbo injectors look? I'd like to think our parts are made to a decent degree of quality.

 

P.S. Note on quality: Nearly 1500 problems in 1000 cars in three months? This is "On Par"? http://www.thetorquereport.com/2007/04/ford_quality_is_on_par_with_to.html

[RTz]

Hear are some measurements I made on various injectors I have kicking around.

 

 

Great work Pete!

 

This might prove useful for establishing battery voltage compensation tables more empirically.

 

Question... what is the reasoning for measuring inductively rather than directly?

[Gavin]

Nice! I have some re-tuning to do!

 

Wanna test some SW20 3S-GTE injectors?

Have any DSM 450s lyin' 'round?

[z-ya]

Is "cold" injector behavior, distinguished enough to need a temperature driven "Opening Time" into MS?

 

I will be using high impedance injectors. Would they tend to exhibit this more, less, or the same?

 

I don't think high Z injectors are any more or less prone to a slow opening time. This problem is caused by any number of problems, including wear, and gunk.

 

New injectors I've measured are all within 5% of each other.

[z-ya]

 

Without the resistor opening time was 1.25ms. How do the rest of your ZX Turbo injectors look? I'd like to think our parts are made to a decent degree of quality.

http://www.thetorquereport.com/2007/04/ford_quality_is_on_par_with_to.html

 

I was surprised to see that changing the series resistor did not have a large effect on opening time. The resistor should be selected so the hold current is around 1A.

 

In PWM mode, which does not limit peak current (only hold current), the opening time is about the same. I will post later this week my measurements in PWM mode.

 

Opening time tolerance for new injectors should be in the 5%-10% range, so 1.25ms is most likely OK.

[z-ya]

Nice! I have some re-tuning to do!

 

Wanna test some SW20 3S-GTE injectors?

Have any DSM 450s lyin' 'round?

 

Gavin, I will test Hybridz donating members injectors for free as long as the demand doesn't go way up. I will also determine what the optimal PWM settings are for your injectors.

[z-ya]

Great work Pete!

 

This might prove useful for establishing battery voltage compensation tables more empirically.

 

Question... what is the reasoning for measuring inductively rather than directly?

 

I made all the measurements at 13V. Voltage compensation on the MS doesn't seem to make noticable difference in opening times.

 

Measuring the dynamic current is the most accurate way (and easiest) to measure opening time. How else would you do it? Maybe some sort of fluid with a strobe light? The current tells the whole story. When the current starts to drop, the injector is open. The current increase after that is the DC resistance of the coil and series resistor combined.

[RTz]

Measuring the dynamic current is the most accurate way (and easiest) to measure opening time. How else would you do it?

 

I guess I made the poor assumption that you could run the scope in series to take a current reading directly.

 

Will you ever forgive me?

[z-ya]

I guess I made the poor assumption that you could run the scope in series to take a current reading directly.

 

Will you ever forgive me?

 

I've learned a lot from reading your posts Ron, just thought I would return the favor

 

That is basically what I am doing. An inductive current probe clamps on the wire like an inductive timing light clamps on a spark plug wire. The probe I used is a 1:1 probe, so for every amp of current, it outputs one volt. So the probe is really a current to voltage converter.

 

Yes, I could have added a 1 Ohm resistor in series with the circuit, and then measured the voltage across it with a voltage probe. The problem is in adding a new component to the circuit. Any component added will have an effect on the circuit. The current probe has zero effect on the circuit, and therefore gives you the most accurate measurement.