: Maxed injectors with only intake/pulley/tune



Xaqtly
07-14-13, 02:00 AM
A while back I got an upper pulley and airraid intake installed, with a tune from RPM motors using HP Tuner. It dynoed at 540 at the wheels, which they said was a little high on average for a V with those mods on their dyno. The tune looked good and everything was copasetic. Then I noticed at high RPMs it seemed like it was pulling timing, it was losing power and it wasn't pulling hard to redline like it used to. I brought it back to RPM today for some troubleshooting, where we learned two things:

1. The tune was still dead on. A/F ratio still right on the money, and zero retard via knock sensor, so it wasn't detonating or pulling timing.
2. Higher up in the rev band we saw the injectors hit 104% duty cycle, which explains the power loss.

My next mod now is obviously higher flow injectors, but I wanted to post this here as an example of how little it takes to max out the stock injectors. With just the pulley and intake along with the tune, my engine wants to make more power than the injectors can keep up with. So it's a little bit of good/bad, bad that I'm running out of injector, but good that it's only the injectors, and not a MAF problem or a leak somewhere, or a bad tune or any number of a dozen other things.

Just keep it in mind when you start modifying, it seems like there's a real thin margin with the stock injectors.

Tedboss1
07-15-13, 02:50 PM
What injectors are you going to go with?

4DoorV
07-15-13, 03:22 PM
Had the exact same situation (dynoed 548, AT) with same mods. Only thing different was having snout ported. Put in larger injectors, pulls hard under WOT. Only issue I have sometimes is under partial throttle the boost gauge goes up to 9-10psi and rpm's stay low and car seem to hesitate/bog down unless I hit the gas a little harder to drop back into lower gear. Tuning issue?

wait4me
07-15-13, 03:52 PM
Think about what your are saying.

1. IF AIR FUEL RATIOS ARE CORRECT< THEN YOU SHOULDNT FEEL ANY ISSUES, AS AIR FUEL RATIO IS CORRECT> DUTY CYCLE OF INJECTOR is NOT A FACTOR IN "FEELING SOMETHING" IF AIR FUEL RATIOS ARE CORRECT.

2. Have them command higher fuel pressure at full throttle and you no longer need injectors.. Even though again, IF AIR FUEL RATIO IS CORRECT, then duty cycle was not an issue.

Xaqtly
07-15-13, 05:13 PM
Duty cycle said 104%, so I'm pretty sure it was an issue. Obviously the A/F ratio is going to be off when the injectors are locked open past 100%, because then they're just dumping fuel into the cylinders. Maybe I should have been more specific and said that the A/F ratio was good everywhere else, meaning that the problem was not something like a MAF issue or an air leak somewhere or something that causes the knock sensors to tell the ECU to pull timing. As in, the problem wasn't the tune or the mods or the install.

Yes, you are correct in that when the injectors are locked open and dumping fuel, the a/f ratio will be off because there's no way to compensate for it. The loss of power comes from running rich. My point was that it wasn't the tune causing it to run rich, and when the injectors weren't locked open, the A/F ratio was perfect. When the injectors were locked open (>100% duty cycle), there was power loss because at that point the A/F ratio was off due to the fuel dump.

As far as which injectors, I was discussing that with RPM and I'm probably going to go with ID850s.

wait4me
07-15-13, 07:55 PM
If they just turn up the fuel pressure correctly then your problem goes away. It is a simple free fix.

The ZR1 has your exact same injectors in it.. Making MORE POWER TO THE WHEELS STOCK than yours with mods. Fuel pressure is the only difference. Your car has a FPDM in it that is a variable speed fuel pump controller. It can be commanded to be higher than stock settings to allow your duty cycle to come back down to desired levels.

Tedboss1
07-16-13, 10:06 AM
I also found this thread on the topic:
http://www.cadillacforums.com/forums/2009-2013-cadillac-cts-v-performance/247238-cts-v-fuel-pump-flow.html

warmwater
07-18-13, 11:40 AM
Interesting that after watching a video on YouTube I learned that in the stock injector is a screen at the bottom, people port them or remove the screen to increase the flow and can be done for $25 per injector I am guessing.
Reading the comments on the video are interesting. If this is all true or not no idea but was interesting and could save people some money.
http://www.youtube.com/watch?v=6ydwie2Ae3A