What are some tell-tale signs that I'm running out of injector?

I'm just curious...

 

Observe duty cycle.

U can do this depending on the ecm with datalogging software or failing that, using a meter with a friend shotgun wired into the inj wires.

If u have a wideband u could try adding in a larger PE fuel change and see if u get an actual increase or not(not the safest way Iw ould recommend however)

Basic math vs number of injectrs and pound hr rating of the injectors and a conservative hp figure for you car would also possibly clue you in.

later
Jeremy

 

If you up the HP to more then stock, by 10% or more, IMO, you should be looking at running larger ones.

There's not math that will really account for figuring out how much fuel you'll need for Accleration Enrichment. You can use .65 (since your's is a turbo), and do the BSFC math, as a estimate.

IMO, GM paid some serious money for hiring the R+D people they have, and they probably considered alot of items *we've* not even thought of in their injector sizing. So, again, IMO, if you want to say double the HP from stock, then run double the injector size. I don't know where this *run the smallest injector possible* idealology started, but long term, biggers have always run faster, longer, with fewer problems from what I've seen.

 

I do plan on running biggers... I'm running 22s right now, idling/etc good. Running about 10psi, last time I checked, was just wondering if there were any tell-tale signs I'm going static

 

Ok, this is something I've been asking about with no real answers. How do you figure out the % of duty cycle your running? I think this may be how to do it, but not sure????

DC=PW*(RPM/60000)*100%

Pw I have a base pulse width in ms.

So @ 3000 rpms with an injector pulse width of 14.43 look like this;

14.43 (300\60000) = .727 = ~ 73%?

12.1 ( 5000\60000) = %100...

Thank you for your help

 

Raiden, yeah that's right except you have a typo: 3000 instead of 300 in the equation.



Grumpy: When you're doing your worst case AE, have you hooked up an oscilloscope to watch the injectors firing? Have you seen that you're getting up near 100%? If not approaching 100%, then it's a calibration or software issue (not a defect per say, just sw not capable of getting the DC up quickly enough or far enough). If you are hitting high DC, and needing it, and the SW is capable, then it's another point of reference for me.

TBI AE is the hardest to calibrate IMO. A snap from idle quite
often results in an intake backfire pop.

Just from some rough approximations, I'd say the factory injectors should be at about 70% duty cycle on a warm engine at peak HP. I could look up some old logs, I guess - ok, just did, a little less than 70%.

Keeping the injectors small enough to idle smoothly in the injection mode offered by the ECU is one critical point (that PW varies from type of injector). Keeping them big enough to supply fuel at Max HP worst case BSFC (cold engine - WOT - PE) is another. It's called Dynamic Range. FMU's and additional injectors extend the dynamic range but weren't considered in the original code = band aid. Sequential injection is one way to double the PW (good idle) while avoiding spraying the whole load into an open intake valve (lots of liquid fuel hits the cylinder walls and spark plug = not good for idle and emissions).

Enough rambling. Gotta go eat.

 

1) Nope, I've never try to drive car, and watch a scope, at the same time, never.
I data log and look at everything later. I will from the corner of my eye watch my WB LEDs to see if they're green or red, but that's it.

There's more to it then time on.
AE is delivered thur pulse width, unlike with a carb where you can use a large pump cam, and get a shorter higher volume pump shot. This having a higher initial pump shot with the larger injectors, goes a long way to keeping a motor out of tip-in preignition.

2) I don't know if I'd totally agree with that. IMO, it's also about manifold type, and injector sizing.

3) I think that's been WAYYYYYYYY over stated. I can run 60 PPH injectors in batch fire or SEFI mode on my lil 231 with just as smooth of an idle as it had with 30 PPH injectors (stock).
SEFI is just doubling the PW, and firing 1/2 as often (though in reference to cyl seq), as executed in the C3/P4 SEFIs. There's lots of room to improve on that.
Are you sure?, or repeating theory?

 

I'll test the engine out emissions, and idle quality, injector pw differences, etc.. today, at several injector closing angles, and report back. Might as well (have a car on the dyno now - EURO3 calibration). Tested WOT power (only at a single RPM - 5700, and on an engine dyno) at while shooting on an open valve, last week, and saw less than a .1 N*m change which means nothing.

 

TBI AE is tricky, at least with stock code it is. Having a wet plenum and 2 large injectors above the throttle blades doesn't exactly win any throttle responce contests... but it's acceptable and crisp if time is spent working on it. Small plenum and high fuel pressure makes short time of the tuning, or at least it's done so for me.