Injector pulse width at startup

[Viprklr]

What's the injector pulse width supposed to be when trying to start the car? I'm trying to chase down a hot start issue on my dad's 87 GN.
According to the scan tool he's getting about 10ms.

BTW - new to this site but not new to cars. I have built and still tinkering with a 92 GTA NA with 544hp and 547lb ft torque and still computer controlled.

 

[Chuck Leeper]

The inj size and the temp sensor input will affect such a calculation.
The chip goorus should be able to make some predictions, using the inj size, temps, etc.

 

[Viprklr]

It does have some mods done to it. I'll see what I can find out.

 

[dennisL]

Are you asking about cranking pw or warmup pw? Since they are both controlled by the chip, which chip is in the car?

During warmup, injector pw is determined by coolant temp and a series of tables. Without seeing these tables, it's hard to say for sure but from my experience, 10 msec is a pinch high unless its really cold. During warmup the pw in my GN is 4 - 7 msec which is similar to what a stock chip uses.

There is a portion of the chip devoted to hot restart so the chip designer could have done something here.

 

[Viprklr]

Cranking pw. Chasing down a hot start issue.
There has been chip work done to it. I'm trying to find out what brand it is and who did it.

Working on a previously modded car is a pain.

 

[dennisL]

The cranking injector pw is determined by:

• throttle position - normally zero
• coolant temp
• Reference Pulse count - originates from crank sensor, is like rpm until engine is running

From a coolant temp of about 120 degF on up, the stock '87 GN chip produces cranking pulses well below 10 msec. They vary from 2ms to a max of 6 or 7ms. At 68 degF to 120 degF, you'll briefly get a 10ms pulse at the start of cranking but it drops quick.

Also, since all the injectors fire at the same time during cranking, a larger than necessary pw dumps fuel into all cylinders.

Hope this info is helpful.

Dennis