bjankuski

I have a question about the time period in milliseconds that puts an injector in a static condition? If you have an engine that is running at 6000 rpm you end up with 3000 cylinder fires per minute. This 3000 firings means you end up with 20 milliseconds between firings, If the injectors are operating at less then 20 milliseconds they should not be in a static condition, is that correct?

I have seen quite a few posts where people claim that the injectors are in a static condition at 6000 RPM if the injector pulse width exceeds 10 milliseconds, if that is true where have I made my mistake?

Thanks

Brent

iTrader: (1)

@ 6000rpm

20 msec for sequential: 1 injection event per 2 rev
10 msec for batch: 1 injection event per rev
5 msec for TBI: 2 injection events per rev /each channel

DANIELEK

Which one is the Tpi???

-sequential or batch

Twilightoptics

TPI is batch fire. 4 inj fire at each PW event.

Grumpy

On a GM v8 as used in the 3rd Gens, all 8 fire at the same time.
An ohm meter will confirm this. The *double* wiring is for redundancy.

And they all fire once per crank rev or every 4th DRP. DRP being distributor refernce pulse.

Grumpy

Yes, 10 msec at 6K RPM is static.

The problem with running injectors static, is that small time from from when they go from pusling to being static, in that area they get erratic. ie not off long enough to have the injector be accurate, so it may go lean during those periods, and cause engine damage. Not a good thing, IMO.

DANIELEK

How about this example. Am i maxing out my injectors???

3400 RPM
11.08 PW

Fuel pressure set at 42 psi at idle and injectors constatnt set to 19.46 in the chip.

As the RPM increases to 4500 the PW is coming down to like 10-9 ms.

Do i nedd 22lb injectors??

11sORbust

When talking about static injectors I think of the CPI fuel system. It seems like once past 100% dc the injectiors, the mpfi injectors turn into nozzles(like a garden hose). The constantly open nossles are then controlled by fuel pressure and there is no ecm control. I was not aware of this gray area just before going static. I guess the needles would be kind of bouncing/vibrating just like valve float? This is the point of possible engine damage,right?

Grumpy

At 6,000 RPM you have 10 msec between injector firing.
You don't want to exceed a 90% under those condition. So at 6,000 RPM you can't exceed 9 msec injector on times.

At 3,000 RPM you have 20 msec, since the engine is operating at half speed compared to at 6,000 RPM so you have 18 msec available at 3,000 RPM.

Looks like you have a little room left before having to go up in size.

Grumpy

The transistion is the problem area, if designed to operate in a given fashion, the erratic zone can be avoided.

Add that it's during transistional areas where this occurs, that means timing is ramping out, and there may or maynot be enough AE to keep the motor out of preigntion, which the knock sensor can be deaf to. So you might have detonation, preigntion going on, and not even know it. Again, plug reading is the answer.

BMmonteSS

hey grumpy would you care to comment on how low of pulse width you can get away with at idle with each of these systems. I'm running a 747 TBI setup. I have also read that you start losing resolution at a certain point also, exactly how does all this relate?

Grumpy

The suggested operating times for saturated injectors are 2-10 msec., and Peak and holds 1-5 msec..

I've never seen a saturated injector get flakey below 1 msec., and I've run Port P+Hs down to .7msec, just fine. But, those times will vary slightly by engine combo...

ALL, the injector flow sheets that I've seen show a *knee-over* point at some point in the lower operating PWs. And that can be from .9 to about 1.5msec PWs. So sometimes the changes you make don't give the expected results at low PWs.

The resolution of the code is a given. At idle, the code from what I've experienced has enough resolution to control the injectors to the limits of the injectors themselves. I've been able to run the 90PPH BBC injectors on a SBC just fine.