My injectors pulse at 11.3 at 5800rpm to my understanding that means that the duty cycles are above 100%. Grumpy said that my injectors went static I think I understand what was meant by the term injector gone static but to be sure enlighten me please;also how do I correct this problem. THANKS FOR ALL AND ANY REPLYS

 

If your car is batch fire then YES, they are going static. Those values yield a 109% duty cycle. What can you do?

1) Increase Fuel Pressure and then burn a new PROM with a higher injector flow rate. The new injector flow rate can be calculated via the change in pressure.
2) Buy new injectors and program the calibration accordingly.

I would definitely recommend new injectors. You won't be able to increase the pressure enough to compensate for such a huge saturation of the injectors. Plus, you don't want to increase the pressure to a point where the Fuel Pump can't keep up.

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

[This message has been edited by TRAXION (edited July 18, 2001).]

 

I have 24pd injectors in the engine now but I guess thats not enough I am thinking I need 28to30pd injectors I think I remember you (TRAXION)using 30pd injectors and making ajustments to obtain 77% duty cycle.I have a 85 Iroc with 400 and miniram 58mm throttle body 1- 3/4 headers and a few other mods. THANKS FOR YOUR REPLYS

 

I'm also seeing 11's on my injector PW at WOT. What signal tells the injectors to go 100% or more duty cycle?

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'87 Formula WS6 - ZZ4 Crate TPI, ported heads, LT4 hot cam, 1.6RR, Accel runners, Accel lower, ported plenum, Edelbrock 58mm TB, pulleys, SLP cold air, headers and full exhaust, gutted cat, Walbro 255, Koni yellows, aftermarket panhard & LCA's.

 

Your duty cycle depends on the length of the pulse width and the rpm. 11 ms @ 3,000 means just over 50% while 11 ms @ 6,000 rpms means over 100%.

And you cannot exceed 100%. It really means that there isn't enough time in an engine revolution for the injector to deliver all of the fuel the ecm is commanding the injectors...hence they are static or constantly open.

 

Just a lil nitpick.
They are commanded to 100%.
In making the transistion to **static** they can hang 1/2 way open (or closed depending on point of view). This can be a really bad thing.

Hence, in my Final answer why I suggest relating Injector size to oem HP, rahter then BMFC.....

 

If you are maxing out with 24lb injectors then I would recommend at the very least 36lb injectors. I listed 109% DCs to illustrate just how 'maxed out' you really are ... .. . 'maxed out' in terms of what the ECM is commanding.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

Thanks for all the information but could you enlighten again what is the oem and bmfc I know they are abreviations but what for. THANKS FOR ALL REPLYS

 

Ok if I put in 36pd injectors and change notthing else it going to be to rich I know could I lower fuel pressure enough to keep it driveable and if so about how much will the duty cycles change.Right now it so lean that if I hold it at 2400rpm for 20 seconds the headers turn red hot. THANKS FOR ALL THE HELP,SUGGESTIONS,IDEAS,REPLYS.

 

oem, original equipment manufacturer
BMFC, Brake Mean Fuel Consumption. In rough terms takes .5lb per hour of fuel to make 1 HP.

 

The ecm has a variable that allows you to change to allow for different sized injectors.

Just as an example.
My GN came with 30 lb/hr injectors and made 250ish HP.
I wanted to be able to about double that, so I installed 55 lb/hr injectors.
Looking back at the previous posting about BMFC, 6x55=330 at .5 BMFC in theory I should be good for 660 HP. There is just no way to tune to that HP (using a stock ecm), and have a really nice daily driver.

There are alot of finer points you need to research to get all your answers.

 

Changing injectors without changing the calibration is begging for trouble. So, NO, you can't just put 36lb/hr injectors in your car and play with the fuel pressure. This is a DIY (Do It Yourself) PROM Programming forum.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

To further Tim's comment about the effects of fuel pressure. Altering fuel pressure has it's least effect at low load/high vacuum and it's greatest effect at high load/low vacuum. Adjusting fuel pressure does not have a liner effect so cranking up the fuel pressure of a smaller injector will not make it behave like a larger injector throughout the "load range". It will behave more like its original size at low load/high vacuum and "per the formula for calculating effective flow" at high load/low vacuum.

E.G. If you crank up the fuel pressure on a 22# injector to equate to a 26# injector, it will flow more like a 22# at low load/high vacuum (such as idle or deceleration) and then flow more like a 26# injector at high load/low vacuum (such as WOT or climbing a steep hill in high gear).

Conversely, lowering the fuel pressure of a 36# injector to equate to a 30# injector will be the opposite. It will behave like a 36# injector at low load/high vacuum and a 30# at high load/low vacuum.

Altering fuel pressure really requires a modification to the VE tables if you have SD or the MAF Scalar tables to get the mixture right, along with playing with the "Injector Constant".

I prefer to use fuel pressure to give me a psi that will produce a good spray pattern but not burn out my fuel pump. And do the "tuning" within the prom, which is the correct place.

 

You guys donot think that 36pd injectors are a bit to much or is this done to give more working room when programming prom.Please bare with me on this subject matter.THANKS FOR ALL REPLYS.MR.KIDD

 

Find out what your idle pulse widths are, and then compare the injectors you have to the ones you want, and size the injector from there.

ie you have 24s, you have a 2.2 msec idle PW, so you would probably get away with some as large as 48s, and still have a decent idle.
The thing to watch is as you get to a 1msec PW some injectors get erratic, and the idle suffers. Using Peak and Hold injectors helps the situation, but the ecm can't fire those, well, for very long.