You reduce PW at lower battery voltages to lean start-up because the starter draws down voltage when engaged.

 

The problem with big high impedance injectors is that they open slowly compared to low impedance injectors. And worse than that, they are inconsistant. Here's what I have found on my injector flow bench:

Even if I flow match a set of big high impedance injectors, meaning that I pick a set of 8 that all flow the same at 80% duty cycle, their flows at the short pulsewidths you see at idle and in-town driving will be wildly different.

Here's an example: I tested a set of MSD 50s to see what their minimum pulsewidth was. By that I mean, what is the shortest pulsewidth that will still let them open and squirt some fuel. The set I had ranged from 1.5 ms to about 1.9 ms.

What that means is, if the PCM commands a 1.4 ms pulsewidth, none of the 8 injectors would fire any fuel! At 1.5 ms, one injector fired some fuel, but the other 7 did not. I had to crank the pulsewidth up to 1.9 ms to get them all to fire.

Whenever I bring this up, someone always says "Just set the injector offset table to 1.9 ms and you're good to go. Why should I care that the injectors are slow if I can adjust for it in the PCM?". The answer is the variation on minimum pulsewidth. Back to my example:

Suppose you install my set of MSD 50s and set the injector offset to 1.9 ms. That means the PCM will add 1.9 ms to whatever it calculates for your idle pulsewidth. IOW, if it calculates that your idle pulsewidth should be 1.1 ms, it will command a (1.1 + 1.9) = 3.0 ms pulsewidth.

The problem is that the 3.0 ms pulsewidth is used for all 8 injectors, including the one that opens in 1.5 ms. With the PCM commanding 3.0 ms, that injector is open for (3.0 - 1.5) = 1.5 ms, while the slowest injector is only open for (3.0 - 1.9) = 1.1 ms.

A 0.4 ms difference is HUGE when the commanded pulsewidth is only 1.1 ms. That's a difference of 36%! Bottom line is that you have some cylinders running way rich and some running way lean. The O2 sensor sees the average of each cylinder bank. Some rich and some lean average out to "perfect", so the PCM thinks it's doing a good job of controlling the injectors. But the engine will have a ragged idle and really sluggish throttle response.

I'm running 96 lb/hr low impedance Delphi injectors driven by a VersaFueler on street with ZERO problems. The car idles all day at 900 in gear, throttle response is excellent even at very low revs, and all the plugs always come out clean and tan.

Acceleronics now offers flow matched low impedance injectors from Bosch, Delphi, and Siemens. If you add a set of 8 to your VersaFueler low impedance injector driver order, you'll save $75 over the best online price I've seen for flow matched injectors.

 

LJ just left you a vm.

 

I'll vouch for LJ's injector driver. I've been running 72#'s for two years with excellent results.

 

THat could be compensated if i had the real data of EACH injector. that way i could balance them out on the PCM at the idle point only with the balance table..