Grumpy

Does injector timing matter?.

Yes (on SEFI).

At idle and low speeds there is a pronounced difference from *bad* vs *good* timing. Depending on the amount of change it takes to get the performance right, you might even have to add ALOT of fuel at WOT, ie a full 1.0 to the commanded AFRs.


Here's a little timing light I rewired to be able to see the changes as I was making them.

I **think** this might be way batch fired mode felt so good compared to SEFI, in some earlier work I'd done. A *good* batch fire system is better then a poor SEFI. Now the SEFI is *much* better then the batch fire was.

JP86SS

iTrader: (1)

Care to elaborate?
(before you and Doc go back and edit all those old posts )

TheGreatJ

He apparently scragged the inductive pickup and instead put in a jumper to hook up to the #1 injector, between the injector and the harness, so he can use the timing marks on the balancer to see when the injector opens in relation to TDC (and with some math, in relation to valve timing.)

I've heard that spraying fuel on the back of a closed intake valve will help vaporize the fuel before it makes it to the cylinder, which means a more "homogenized" charge and therefore more efficient combustion.

Am I on the right track here Grumpy?

funstick

well if you open the injector late you could definately get some reversion wash of fuel out of the cylinder. so yeah injector timing can help

TheGreatJ

It also makes sense to me that injector timing would be more critical at idle than at high loads/high RPMs. After all, you have a shorter pulsewidth, and more time between valve events, which means significantly more room for error. At say 75% DC, 2/3 of the pulse will be during the "optimum" pulse time no matter WHEN the pulse starts. At 10% DC you have TONS of room for it to be "bad."


How have you been changing the injector timing? Delay cycles in the code or an adjustable trigger or what? Or is that Top Secret?

Grumpy

Yep, rewired a timing light to work off the injector signal.

A friend made a code change that enables me to find the sweet spot, as far as what the engine likes, injector timing wise.

There's all sorts of theories, and opinions about what works best. I'm going to find out what the real answer is for what works best in my application.

Just giving the engine what it wants.......

RednGold86Z

iTrader: (1)

I hate IBM keypads. There's a forward and backward button right next to the arrow keys and I just $#@)*( deleted my post. Arghh.

Yes, sequential systems are designed to spray all of the fuel onto a closed intake valve. The idea being that there's time for the fuel to gather some heat to vaporize, and also when it first cracks open, the exhaust pulse up the intake runner will bust it up well. The thing to avoid is fuel injection on open valves which doesn't vaporize well and can collect easily on the cylinder walls.

Injecting all the fuel on a closed valve requires larger injectors for higher RPM's near max power. That is why they typically target about a 60% max duty cycle vs 80-90% for batch. The idea is to avoid beginning the next injection while the valve is still open from the last intake stroke.

Larger injectors also allow better cold cold fueling. And since it's always in single fire mode, you can run the bigger injectors with less idle problems than double fire batch mode.

Grumpy, do you know which edge of the injection your timing light is firing on? Is it the leading edge or trailing (falling or rising edge)? I'm going to say your best idle timing will end the injection about 30-60 degrees BTDC exhaust. I'm going to guess that the timing light will fire on the voltage spike as the injector closes, which is the signal that you'll want to focus on.

JPrevost

cool.
We couldn't find any difference when we were working on the restricted 600cc i4. We could phase it 180 degrees from tdc and nothing made a bit of difference. So it would be interesting to see how it effects engines with larger injectors and lower RPM.

RednGold86Z

iTrader: (1)

At WOT with injectors too small (i.e. 80+% duty cycle), it's not going to make a difference. Part throttle emissions will like it though, assuming the injectors are close enough to the port.

I also suspect at high RPMs, and high air flow rates, that there will be plenty of ability to mix whether or not the fuel sits on a valve or not.