Hey guys,

2000 T/A, Stock LS1 w/ 241 heads.
Mods are seen in my sig.

I noticed that my injector duty cycle goes up to 97% when going WOT and revving high (about 6K). I put the car on the dyno to check the fuel pressure, and I've got 52-58psi throughout the run, so the fuel-pump seems good.

However, is it possible to max out the injectors on a non h/c car?
I mean, the easy fix is to put bigger injectors on it, but I'm thinking there might be something else to it, as I think I shouldn't max the stockers out on ~340RWHP.

What do you guys think?

 

When was the last time the fuel filter was changed?

 

Changed the fuel filter about 2 months ago. However, since I measure the fuel pressure at the rail, I doubt that could be the problem, as I would see a much lower pressure under load then, right ?

 

Correct. If your pressure is correct at the rail then it should be fine. Considering thats the last stop it makes before it gets injected.

If you have good pressure at the rail that kinda rules out the pump... sorry if it was stated above but whats your F.P at WOT?

 

FP at WOT is 52psi, down from about 60psi at idle.

 

WOT FP is normal, injector duty cycle is probably right depending on set AFR, 99-00 vehicles also had smaller 26lb injectors compared to the 98,01-02 cars which had 28 lb injectors

 

Up them to like 36lbs/hr or maybe even a 30lbs/hr. But 30 seems a little on the small side if your maxing 26's...

 

has the car been tuned?

 

Injector Duty Cycle is based on three things: AFR, Injector Flow Rate and RPM

So if you are running very rich, you could be exceeding the injector's capability even with no mods. On a non-H/C setup I would say you are running into COT and the ECM is commanding 11.7 AFR, hence the higher then typical IDC. What AFR are you seeing when you scan it with a wideband?

 

The car is tuned, and COT is disabled.

Can't recall the specific AFRs (I'm at work), but it's running slightly rich at about 6000rpm. Not overly rich though.

I guess it's time for new injectors. Thanks guys.

 

Just get a nice set of used 28.8lbs injectors (usually had for around $75). Should be good to about 375 RWHP; problem solved.

 

That's hardly worth it IMHO. He'd probably still be in the 80% range which is still max duty cycle range for injectors. I'd go with 36lbs or bigger depending on future plans.

 

Although I do not agree on going bigger then 28-30lb injectors for his current setup, as 80% IDC is perfect, but your last comment is the decisive point on what size injectors to get.

 

8 psi drop in fuel pressure is over 10%. Fix that, and get the WOT AFR dialed in and you'll be fine with what ya got.

 

yeah, no way can I believe that your maxing out your stock inj.s now. my dads 02 (yeah bigger 28lb inj.s, but...) made like 420 rwhp on stock inj.s *mustang dyno too* and his are maxed at high rpms. I think holding him back on power too but, anyhoo...

maybe your injs. are dirty/clogged? have you had them flushed out ever? how many miles?

 

Just to follow up on an old thread.

Swapped my fuel-pump for a Walbro 255, and the duty-cycle went down to 87% at WOT.
The old pump was sputtering out the fuel, so it was definitely on its way out.

 

Um.... What does that have to do with ****? He's got good fuel pressure, and his injectors are obviously working.

To answer your question, hook up a wideband, if your AFRs are good, then you don't need to swap injectors. The only reason you should start worrying is when an injector breaks, and you'd know because your car would run like ***.
Problem solved.

 

How many miles were on your pump?

My car has about the same mods and when logging with HPTuners it said it was up to 86%. A lot of people said that was high also. I just installed a Racetronix kit.

 

Not to hijack but I logged my Sierra with a stock 6.0 LQ4 and I saw 101% injector duty cycle under WOT. What is up with that? It's stock, and under 30K miles!

 

72K on the stock pump.

87% is probably about right with the 26lb injectors for my mods.
At least now I've got a pump that can supply bigger injectors later on, and that can support a wet-shot as well.