Fuel injectors and stock pcm

Is 50lbs injectors the max for the stock pcm, or is there in injectors out there that will work..

-What is the diff with the high and low injectors
-your cars need the high inj
-is 50 the max for the high
-what do people think of Mototron injrctors

thx

Is 50lbs injectors the max for the stock pcm, or is there in injectors out there that will work..

-What is the diff with the high and low injectors
-your cars need the high inj
-is 50 the max for the high
-what do people think of Mototron injrctors

thx

Im not sure what the diffenrece is between the two but I do know the stock computer cannot run them. It requires a different set of drivers to run them. Last time I check 75lb injectors were the highest you can go. Andy over at A&A performance is using them without any idle problems of any sort. Problem is there 79.00/injector so it adds up quick.

The PCM's hardware logic for the injectors was designed for the injectors to have a average pulse width of 3 mSecs for part throttle and about 1.5 mSecs for idle.
The larger the injector is the harder it is for the PCM to run with smaller pulse widths for it has more control with longer ON times.

The PCM also requires Multech-II high impedance injectors.

Those selling you large injectors like 75 lbs are not looking at the long term issues to the PCM.
I'd say to make it really work right is of going over 50 lbs/hr injectors is to get a injector controller like a FAST and have it manage injectors.

There is another path and that is your wanting larger injectors to fight off the heat conditions boost causes which induces knock and forced lower timing.

I have a water/meth injection kit that is less then $400 that has a controller that can be used with TPS, MAP or the output of the MAF as when WI is on or off.

This can drive intake temps down by 60 degrees which removes the load on the injector on times and their sizes and could allow up to 10 degrees of timing to be added back in.

If you want big injectors and keep the stock pcm you would be better off getting one of the acceleronics impedance converter boxes so you can run some low-z 72lb injectors. From what I've heard idle quality is much better with the big low-z injectors than big high-z ones.

-Tony

I agree with Mystic95Z. I have 84 lb/hr with the Impedence Converter, stock PCM. Runs and idles fine.

Are the 75+ lb/hr injectors and converter box really necessary though?

What about the Motron 60/65 pounders? What would people say is the max forced induction rwhp they are capable of sustaining without overworking them?

Mike , with your 84lbs inj how do/did you tune the injector so that your idle is fine, and part throttle driving...

your set up what kind of power are you making with pump gas and some ET and MPR

thx

I had to set the Injector Constant to 84. I also reduced the injector adjustment for battery voltage. Finally, the PE curve had to be tweeked, but that really needs to be done with any change in injector size.

550 rwhp through a TH-350 with a Vigilante 0 pump on 93 octane. Ran 10.40 at 133 mph at full stock weight plus the cage, charger, aftercooler, etc. . .

Mike

Why did you have to change the bat voltage table

Very good question. It seemed like it had a hard time starting after the injectors and smelled rich right after start-up. Reducing the PW modifier at lower batt voltages made it start up leaner.

Very good question. It seemed like it had a hard time starting after the injectors and smelled rich right after start-up. Reducing the PW modifier at lower batt voltages made it start up leaner.

What software are you using eningeermike? I also suffer from that rich start up syndrome, but don't see that table in my LT1 editor.


Is 50lbs injectors the max for the stock pcm, or is there in injectors out there that will work..

-What is the diff with the high and low injectors
-your cars need the high inj
-is 50 the max for the high.

FWIW, I'm running the SVO 42# injectors at 51psi fuel pressure (no vacuum)
Have the injector constant set at 48#, outside of rich start up, no issues. No FMU anymore and +/- 535 hp at the wheels, injectors are maxed out though.

Hope this helps

LWM

I use LT1edit and its called the Injector Offset table.

-Tony

I use TunerCat, but I think the Injector Offset is the one I was referring to.

I won't recommend running super large (>50#/hr) high impedance injectors. Then you are leave with low impedance injectors using either a stand alone computer like TeamZR1 suggest or LJ's impedance converter http://www.acceleronics.com/

Have answer to many of your questions at http://www.acceleronics.com/faq.htm

I have been running LJ's box and 72#/hr injectors for two years without any problem. Start up with no problem at all. Even without the supercharger hooked up, it droved great for a couple of weeks without any hesitation or lag.

Also very easy to tune and using stock the injector offset table.

I use LT1edit and its called the Injector Offset table.

-Tony
Begs the question. How does one modify the injector offset table so as to reduce the amount of fuel on a cold start up??

thank you in advance

LWM

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

Is 50lbs injectors the max for the stock pcm, or is there in injectors out there that will work..

-What is the diff with the high and low injectors
-your cars need the high inj
-is 50 the max for the high
-what do people think of Mototron injrctors

thxThe 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.

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.
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..