Renix Adjustable Fuel Pressure Regulator

Performance mods and Advanced Stroker discussion.
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cstephens85
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Renix Adjustable Fuel Pressure Regulator

Post by cstephens85 »

Anyone know where to find one of these? I placed an order with Hesco, but they are out of stock for the foreseeable future.  Unfortunately, can't find anywhere else that sells these for the Renix fuel rail.

I've been playing "fuel injector roulette" trying to find the optimal AFR in my 4.6L stroker and would like to simply have the ability to finely adjust fuel pressure.  19 lb injectors are too small.  23 lb injectors are too large.

I know that I could converter to a later-model fuel rail and a standalone regulator, but I believe that may impact my ability to pass CA emissions test, so trying to keep it looking "stock-ish".
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Re: Renix Adjustable Fuel Pressure Regulator

Post by Randy Bobandi »

cstephens85 wrote: August 15th, 2022, 10:48 am 23 lb injectors are too large.

I know that I could converter to a later-model fuel rail and a standalone regulator, but I believe that may impact my ability to pass CA emissions test, so trying to keep it looking "stock-ish".
What issues are you having? 23# injectors are very mild and can't support much more than stock form 4.0 output. The most that 23# injectors can support in an NA inline 6 is 220 flywheel HP.

What model year is the Jeep?
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Re: Renix Adjustable Fuel Pressure Regulator

Post by Cheromaniac »

I believe he has an '88 Comanche.
There IS an alternative solution to the problem in the form of a MAP adjuster. You could either make your own by replicating the one I had on my '92 XJ, or buy one ready made:

https://www.angelfire.com/my/fan/MAP_adjuster.html

http://www.strokedjeep.com/regulator.html
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cstephens85
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Re: Renix Adjustable Fuel Pressure Regulator

Post by cstephens85 »

Randy Bobandi wrote: August 15th, 2022, 8:04 pm
cstephens85 wrote: August 15th, 2022, 10:48 am 23 lb injectors are too large.

I know that I could converter to a later-model fuel rail and a standalone regulator, but I believe that may impact my ability to pass CA emissions test, so trying to keep it looking "stock-ish".
What issues are you having? 23# injectors are very mild and can't support much more than stock form 4.0 output. The most that 23# injectors can support in an NA inline 6 is 220 flywheel HP.

What model year is the Jeep?
From my understanding, ~24# injectors are perfect for a 91+ HO stroker, but for a RENIX (87-90) they are way too rich. With 23/24# injectors, the truck won't enter closed loop once warmed up and the AFR is constantly "RICH" based on my REM scanner (replicates Snap-On MT-2500 output).

The truck is an 88 Comanche with RENIX EFI and stock intake/head/exhaust (as I need to retain EGR in order to pass CA emissions).

I've heard that a MAP adjuster can only be used for fine-tuned adjustments, hence wanting to test out fuel pressure adjustment first.
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Re: Renix Adjustable Fuel Pressure Regulator

Post by Cheromaniac »

Does your stroker have a performance cam?
Do you have any external performance bolt ons such as a cold air intake, larger throttle body, or aftermarket exhaust?
You mentioned that you're running the stock intake/exhaust manifolds and stock Renix head, so your stroker may not be making much more than the stock 177 crank hp if it's merely a bigger lung trying to breathe in and out through the same straw as the original 4.0.
My rule of thumb for selecting an injector size for a stroker Jeep I6 is simply:

Actual injector flow (lb/hr) = Expected crank HP/10

So for example, if you have something like 210hp you'll need injectors that flow roughly 21lb/hr. I need more information about your set up to make a reasonable estimate.
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Re: Renix Adjustable Fuel Pressure Regulator

Post by cstephens85 »

Cheromaniac wrote: August 17th, 2022, 2:36 am Does your stroker have a performance cam?
Do you have any external performance bolt ons such as a cold air intake, larger throttle body, or aftermarket exhaust?
You mentioned that you're running the stock intake/exhaust manifolds and stock Renix head, so your stroker may not be making much more than the stock 177 crank hp if it's merely a bigger lung trying to breathe in and out through the same straw as the original 4.0.
My rule of thumb for selecting an injector size for a stroker Jeep I6 is simply:

Actual injector flow (lb/hr) = Expected crank HP/10

So for example, if you have something like 210hp you'll need injectors that flow roughly 21lb/hr. I need more information about your set up to make a reasonable estimate.
I have a Comp Cams 68-232-4 cam, bored Renix throttle body, stock airbox, Renix head/intake, and newer CA cat with flow master muffler (w/ stock 2.25” exhaust tubing). I would guess about 205-210 HP.

I’ve ordered Bosch 20# injectors (0280155909). Fingers crossed those are sufficient, with perhaps using a MAP adjuster.
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Re: Renix Adjustable Fuel Pressure Regulator

Post by Cheromaniac »

cstephens85 wrote: August 17th, 2022, 5:08 amI have a Comp Cams 68-232-4 cam, bored Renix throttle body, stock airbox, Renix head/intake, and newer CA cat with flow master muffler (w/ stock 2.25” exhaust tubing). I would guess about 205-210 HP.

I’ve ordered Bosch 20# injectors (0280155909). Fingers crossed those are sufficient, with perhaps using a MAP adjuster.
I think you've nailed it right there.
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Re: Renix Adjustable Fuel Pressure Regulator

Post by cstephens85 »

Cheromaniac wrote: August 17th, 2022, 10:28 pm
cstephens85 wrote: August 17th, 2022, 5:08 am I’ve ordered Bosch 20# injectors (0280155909). Fingers crossed those are sufficient, with perhaps using a MAP adjuster.
I think you've nailed it right there.
Thanks--will let you guys know how it runs once I get them swapped in.
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Re: Renix Adjustable Fuel Pressure Regulator

Post by cstephens85 »

Swapped in the 20lb injectors (Bosch 0280155909) and it's still slightly lean. I also ordered a new FPR to ensure that's not causing a problem, as disconnecting the vacuum line going to the current one results in some weird air/fuel ratios. While trying to find someone to sell me an adjustable MAP sensor, I decided to just build my own following the schematic found here: https://www.angelfire.com/my/fan/MAP_adjuster.html

Will let you know how it goes. I think I'm very close to getting to the ideal AFR with these injectors once I get the MAP adjuster installed and fine-tuned.
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Re: Renix Adjustable Fuel Pressure Regulator

Post by Cheromaniac »

The MAP adjuster certainly did the trick for me when my 4.6 stroker initially ran slightly lean on Ford 24lb injectors. I only needed to raise the MAP input to 5.3v to get the A:F ratio properly dialed in.
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cstephens85
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Re: Renix Adjustable Fuel Pressure Regulator

Post by cstephens85 »

I built the adjustable MAP sensor yesterday and tuned the voltage up to ~6v with the Bosch 20 lb/hr injectors @ 3 bar (P/N 0-280-155-909), but still am experiencing a lean condition. After warming up, I can see the STFT staying around 200 at idle in CLOSED loop, but once I start to accelerate it quickly builds to 255 and then resets to OPEN loop/default fuel trim (128). I'm going to try to do some additional trips with these injectors to see if the ECU will "learn" a bit better. If that doesn't work, I may swap the 23 lb/hr injectors back in (P/N 0-280-155-703) and try to decrease the MAP voltage a bit.

Unfortunately, it doesn't seem like Hesco is still making the RENIX AFPR and any other aftermarket solutions are way too obvious for me to be able to pass CA smog. If I can't find a sweet spot with the 20 or 23 lb/hr Bosch injectors, I may pony up for Accel 21 lb/hr injectors (https://www.summitracing.com/parts/acc-150121).

I'm also going to do some additional verification of my fuel pump voltage and fuel pressure at the rail. I installed a new non-adjustable FPR and had no improvement, so I don't believe that's an issue.
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Re: Renix Adjustable Fuel Pressure Regulator

Post by Randy Bobandi »

An 88 Comanche is quite the classic. Are you sure there aren't any smog exemptions that the Comanche might qualify for? If you could register it as an antique/historic/special interest, your best bet would be a Holley Sniper. Those units run so sweet.
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Re: Renix Adjustable Fuel Pressure Regulator

Post by cstephens85 »

Randy Bobandi wrote: August 28th, 2022, 5:39 pm An 88 Comanche is quite the classic. Are you sure there aren't any smog exemptions that the Comanche might qualify for? If you could register it as an antique/historic/special interest, your best bet would be a Holley Sniper. Those units run so sweet.
As much as I would love that to be the case, unfortunately anything 1976 and newer (unless it’s diesel) must be smogged in CA. I could hypothetically circumvent by registering in another state, but it’s originally a southern CA truck and I’d like to keep it that way.
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Re: Renix Adjustable Fuel Pressure Regulator

Post by cstephens85 »

Quick update on this--I built an adjustable MAP sensor and cranked it up to ~6v to see if that would solve the issue. It helped, but the truck would still stay stuck in open loop mode. After checking the fuel pressure at the rail, it appeared to decrease below 30# under load, even with a new FPR. My fuel pump was about 4 years old and had been run dry a few times (long story that involves a cross-country shipping company). I also had a fuel leak from the tank when filling up, so I decided to swap in a new pump and address the leak. After dropping the old tank, I also found it to be rusted and leaking (so I ordered a new tank). After pulling the pump, I also found a loose positive terminal and very tight bend on one of the internal hoses.

After fixing that and swapping in the new tank, new pump, and new seals for the vapor valves, the truck is running a bit better, but not perfect. O2 sensor voltage will hover between high 2.x and 3.5 volts (better than the ~4.x volt range before), but will bog down when it attempts to enter closed loop mode.

The symptom I'm seeing is that it will idle well in open loop, then switch to closed loop and attempt to increase fuel trim, which results in the RPM's dropping for ~10 seconds until it flips back into open loop mode. This seems counterintuitive--if it is running lean and enters close loop and begins cranking up the fuel trim, you would expect RPM's to stay the same. Based on this behavior I believe the O2 sensor may be bad and providing an incorrect sensor reading.

I've ordered a new NTK 23553 sensor and will let you guys know how it looks when installed tomorrow.
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