Tuning Fuel Injector Size & Pressure

Performance mods and Advanced Stroker discussion.
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cstephens85
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Tuning Fuel Injector Size & Pressure

Post by cstephens85 »

ATK 4.6L stroker, mostly stock engine otherwise due to needing to pass CA smog. Originally had 19# 4-hole injectors, which would bog down at around 3k RPM's (these were fine with my original 4.0L before the stroker install). I have a REM monitor and was able to see the ECU trying to increase the STFT at ~3K RPM's until it hit the max and failed back to open loop/128 STFT. Bumped up to 22# injectors and had the same issue to a lesser degree. Thought 24# would be the sweet spot, but now it runs too rich and will never enter closed loop.

I purchased the Hesco adjustable FPR and plan to install it soon. Should I try to decrease fuel pressure with the 24# injectors, or increase with the 22#? Any other tips for discovering the correct fuel pressure to reach ideal AFR?

These are the part numbers of the injectors I've tried:
22# 0280155703 Bosch EV6
24# 0280155715 Bosch EV6
Randy Bobandi
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Re: Tuning Fuel Injector Size & Pressure

Post by Randy Bobandi »

What ecu do you have? What fuel pump do you have? Also, which wide band O2 kit are you running?
Cummins90
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Re: Tuning Fuel Injector Size & Pressure

Post by Cummins90 »

What is your fuel pressure when you experience the issue?
cstephens85
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Re: Tuning Fuel Injector Size & Pressure

Post by cstephens85 »

Randy Bobandi wrote: August 2nd, 2022, 9:47 am What ecu do you have? What fuel pump do you have? Also, which wide band O2 kit are you running?
Stock '90 Renix ECU. I need to pass CA smog which requires EGR (which necessitates the Renix ECU). Stock fuel pump with ballast resistor bypassed. Not running a wide band O2, but using Nick Risley's REM to monitor O2 voltage, ST/LT fuel trim, and open/closed loop status.
Cummins90 wrote: August 3rd, 2022, 7:00 pm What is your fuel pressure when you experience the issue?
I have a fuel pressure gauge but haven't run it while driving--will test this.
Torqsplit
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Re: Tuning Fuel Injector Size & Pressure

Post by Torqsplit »

Before you get too carried-away with fuel tuning, Please ensure that your Ignition system is fresh & working good. Weak spark will throw All your adjustments and you'll end up overly lean to compensate. Same goes for your o2-sensor. They can foul-out if you run super rich for any extended stretch, and they don't really recover. I don't have much Renix tuning experience, but based on what you've mentioned here, I'd suggest trying the 24# injectors again and *Reconnect your ballast resistor*. This will help save the enrichment for hi-load/ hi-rev's and get you back in range for part throttle driving. I don't mean to sound demeaning, but make sure it's fully warmed up before measuring anything 👍 As far as fuel pressure goes, less is generally Never the better solution, unless your nearing the psi limits of your lines or system. So potentiallythe 22# injectors could still be a mid-point option but with added pressure. *You can get yourself into a frustrating scenario of good closed-loop, but no good open-loop when you start adjusting fuel psi tho. Hard to get Both dialed* Not sure about the Renix fuel pump tho. Possibly some limitations there? I've had experience with old Dodge 2.2 turbos back in the day, pulling fuel readings from the O2 sensor ECU signal. Sounds kinda similar to what your doing here? It'll get you in the neighborhood, but a True Wide-band setup would be way better and Safer. Good luck & hope you get it sorted so you can enjoy it! 🍻
cstephens85
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Re: Tuning Fuel Injector Size & Pressure

Post by cstephens85 »

Thanks for the help. I swapped back in the 23# @43.5 PSI injectors. P/N 0280155703. Appears to be running better but still staying in open loop after warming up. However, I’m not encountering the fuel starvation issue anymore at 3k RPM with STFT staying at 128 and only the injector pulse width changing with RPM/load.

Going to get some more miles on this and see how it does.
Brianj5600
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Re: Tuning Fuel Injector Size & Pressure

Post by Brianj5600 »

cstephens85 wrote: August 6th, 2022, 11:58 am Thanks for the help. I swapped back in the 23# @43.5 PSI injectors. P/N 0280155703. Appears to be running better but still staying in open loop after warming up. However, I’m not encountering the fuel starvation issue anymore at 3k RPM with STFT staying at 128 and only the injector pulse width changing with RPM/load.

Going to get some more miles on this and see how it does.
Just spitballin',,,but have you tried just focusing on light throttle and adjusting fuel pressure lower to get it in closed loop with reasonable trims? I wonder if you get a vacuum referenced regulator it should lower fuel pressure at low load and increase fuel pressure at high load. If you could vacuum reference your Hesco regulator you might find a sweet spot that it is happy.
cstephens85
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Re: Tuning Fuel Injector Size & Pressure

Post by cstephens85 »

Brianj5600 wrote: August 9th, 2022, 2:34 pm
cstephens85 wrote: August 6th, 2022, 11:58 am Thanks for the help. I swapped back in the 23# @43.5 PSI injectors. P/N 0280155703. Appears to be running better but still staying in open loop after warming up. However, I’m not encountering the fuel starvation issue anymore at 3k RPM with STFT staying at 128 and only the injector pulse width changing with RPM/load.

Going to get some more miles on this and see how it does.
Just spitballin',,,but have you tried just focusing on light throttle and adjusting fuel pressure lower to get it in closed loop with reasonable trims? I wonder if you get a vacuum referenced regulator it should lower fuel pressure at low load and increase fuel pressure at high load. If you could vacuum reference your Hesco regulator you might find a sweet spot that it is happy.
Thanks—I don’t have the Hesco APFR installed yet (still waiting for it to ship). Once I get it I plan to swap back in my 19# 4-hole injectors and slowly tune the fuel pressure up from 30 psi and see what the threshold is. I should have gone that route to begin with. Hopefully will get the AFPR soon.
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