[SOLVED] Port Injection Return Line Pulsing

[JohnnyTightlips]

I finished my port injection setup and I have noticed a strange issue. I thought I was alone in this but it appears that @andale927 and @Bigelow have similar issues.

The issue I have noticed is that the FPR is pulsing, it will pulse + or - 3psi at idle. This pulse can be both heard and felt in the return line. It is noisy but the car seems to run without issue. It sounds like someone is drumming under the car and against the firewall. With any throttle it will go away but returns at idle.


Setup:
Fuel Pump: WALBRO HELLCAT 525LPH F90000285
Fuel Pressure Regulator: Aeromotive Universal Bypass Regulators 13301
PI : JMF Rail
Pressure with Vac: 40
Injectors: 1200cc fuel injector for MITSUBISHI EVO X 4B11T BOSCH style EV14 Evolution

Layout:
8an feed line from Fuel Pump to 8an-6an-6an Y adapter
From Y port - 6an to HPFP
From Y port - 6an to PI Rail
PI Rail to FPR
FPR to OEM Feed Line "used for return"

What I have tried:

Bypass PI rail but keep regulator "on Y goes to reg one Y goes to HPFP"
This did not change anything and might have made it more prevlant.

Jumper the Fuel Pump Resistor "thing on the frame rail that says hot don't touch" Was hoping this would keep the pump and full power and it would not pulse , it did not help.

What's next:
No Vac line - try 60 psi without it.

I am also going to re-route my setup so that the FPR is before the HPFP and on a single line removing the Y adapter. Like the image below but without the PI rail at first. I will adjust pressure and see how it does. I will then try it will the PI rail involved.

Here is the Gauge and how it looks at idle.

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Here is the cabin, you can hear it at idle and see what it sounds like under light throttle.

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[andale927]

Thanks for writing up the post.

For reference here is my setup, I have the same issue:

Setup:
Fuel Pump: Aeromotive 325
Fuel Pressure Regulator: Fuelab 52503-1-L-E
PI : ST Manifold Rail Adapter
Pressure with Vac: 32 PSI
Injectors: Siemens Deka 875cc

Layout:
6an feed line from Fuel Pump to 6an T adapter
From T port - 6an to HPFP
From T port - 6an to PI Rail
PI Rail to FPR
FPR to OEM Feed Line "used for return"

Have not done any troubleshooting.. Although I think mine makes less noise than @JohnnyTightlips since I find it somewhat tolerable.

 

[JohnnyTightlips]

Thanks for writing up the post.

For reference here is my setup, I have the same issue:

Setup:
Fuel Pump: Aeromotive 325
Fuel Pressure Regulator: Fuelab 52503-1-L-E
PI : ST Manifold Rail Adapter
Pressure with Vac: 32 PSI
Injectors: Siemens Deka 875cc

Layout:
6an feed line from Fuel Pump to 6an T adapter
From T port - 6an to HPFP
From T port - 6an to PI Rail
PI Rail to FPR
FPR to OEM Feed Line "used for return"

Have not done any troubleshooting.. Although I think mine makes less noise than @JohnnyTightlips since I find it somewhat tolerable.

It's possible that if I insulate the return in a few places so it does not tap the firewall and other spots it might also be tolerable so this could be a solution as well. BUT with the COVID I can play around and test a few things as I have nothing else to do and can't really drive anywhere.

 

[JohnnyTightlips]

Updated my original post with some videos. Also this guy had a similar issue but I am not ready to drop that kind of money on anything yet.

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[Mauro_Penguin]

This might be fuel pulsating from the ginormous fuel pumps you guys have.

Instead of getting a Radium unit, have you guys considered looking into a Honda or Toyota fuel pulse damper?

 

[JohnnyTightlips]

This might be fuel pulsating from the ginormous fuel pumps you guys have.

Instead of getting a Radium unit, have you guys considered looking into a Honda or Toyota fuel pulse damper?

Yes, I did think about that but was not sure how it would handle the fuel pressure in boost and how I would make it work with my current setup. Nice thing about the radium is that it is already 6an.

 

[Mauro_Penguin]

It shouldn't matter.

Fuel pressure is handled by the regulator, which you guys have aftermarket units for. Fuel flow is built up by the pump. Regardless of fuel demand (be it boost or vacuum), the damper just absorbs all those pulses.

OEM design has the FPR in the tank basket, which reduces (but doesn't eliminate) pulse pressure to the HPFP feed line. The HPFP has 2 giant diaphragms that absorb all the pulse from the feed line, and also from the relief valve return line.

You should technically only need to put a pulse damper at the return somewhere to eliminate those vibes on the fuel line.

 

[JohnnyTightlips]

I tried to put the damper on the return side and it did help a little bit but the sounds was still very noticeable.


I then decided to re-route the lines like the diagram above. I ran out of time to actually start the car tonight so I will check for leaks and start it up tomorrow if I can.

I also hooked up a digital gauge that I will ghetto connect tomorrow so that I can see my pressure with this new setup at least to get a base set. Snuck the pressure sensor under the FPR.

 

[Mauro_Penguin]

I can't make it out in the reroute picture, but in the first picture the pulse damper is in a poor position.

You want it parallel to fuel flow direction, not perpendicular. This will ensure max absorption of vibes. So essentially if you still kept it like the first pic, switch the pulse damper and the return line positions.

 

[Tomas]

Why don't yer just simply eliminate the complete return set up after the injector rail? If you are not running a dedicated type of fuel to the injectors like ethanol then the whole return line set up is useless. I've been running my PI rail without a return and it works flawless.

 

[JohnnyTightlips]

I can't make it out in the reroute picture, but in the first picture the pulse damper is in a poor position.

You want it parallel to fuel flow direction, not perpendicular. This will ensure max absorption of vibes. So essentially if you still kept it like the first pic, switch the pulse damper and the return line positions.

I did not add it back to the re-route setup yet, going to see how it does without it. Everything I have read and seen "OEM" style it does not matter what direction the damper is as it is just a cavity with a spring/diaphragm that should absorb the pulses. I have watched a few plumbing videos that use them and they are all setup the way I had it. If you look at Radiums pictures they also set it up this way.

So really the main difference is that they are close to or on the fuel rail which I could also try but with DI and PI my setup is not identical to this as the DI is probably introducing the fluctuation to begin with. Testing will continue.

 

[JohnnyTightlips]

Why don't yer just simply eliminate the complete return set up after the injector rail? If you are not running a dedicated type of fuel to the injectors like ethanol then the whole return line set up is useless. I've been running my PI rail without a return and it works flawless.

I do not have a pressure regulator in the stock basket so that is why I am using the FPR with a return. If it comes down to that I can surely update it but right now I have the time to test out a few configurations.

 

[JohnnyTightlips]

I had a few thoughts on this. I am sure it is the HPFP causing this but not completely sure how still. I realized that the damper will not work at all on the return side as there is not really any pressure in that line since it just dumps back into the gas tank.

Then I thought about that a little more and how on my old DSM I just used a rubber fuel line as return since the line does not really see pressure. This fixed it, the rubber line absorbs all the vibrations that was causing the OEM hardline to vibrate on the firewall and other places. I also made it a little shorter and it still absorbs the sound enough that it is rarely noticeable.

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So this seems to be the fix, might be able to get away with a rubber 6an push lock hose as well. Yes, I know the rubber line will not be full e85 compatible, this is the fix for now and I will keep an eye on it. I also clamped it but forgot to take a pic.

 

[JohnnyTightlips]

Welp the noise is back, still not as loud but still annoying. But after some more fiddling I believe I know what part of the issue is at least why mine is more pronounced.

My regulator is BIG and allows a lot of flow as it was designed to do CARB as well as PI. Which looking deeper at it the return on it is also larger. This leads me to believe that I am over working the spring as it is letting pressure out then quickly goes back to stable then quickly back out again. That is the pulsing I am feeling in the line. I could fix this a few ways.

I could put some sort of restriction in the return line "like a pill" so that it does now allow return fuel as easily and helps the FPR to not regulate so wildly. Which I did test just by pinching the line and the sound went away and return fuel no longer pulsed but was steady. With some research I also see that Aeromotive discusses having the right size return line. Too small and you get bad readings as the FPR can not do it's job.

My issue is that it is too large and it allows too much flow when it releases pressure so the change is too drastic causing pulsing. My fpr also adjust's all the way down to 21 psi so I definitely have return some flow to spare. I also noticed that aeromotive themselves do this for diff GPH flows using a poppet seat. I don't have this fancy of a regulator but it is food for thought.

The hellcat pump at 525 LPH only flows 138 GPH at max tilt so having a really big opening on the return at idle when the car is using the least amount of fuel and needs to return the most would cause the regulator to work over time. Aeromotive suggest a 3mm opening for anything like the pump I have am more than double that with a 3/8 port to a 6an line.

I know this is all kinda silly and it is just an annoying noise but it is bothering me, I am work from home "thanks covid" and I have time to mess with it. Plus I don't think it is great for the FPR to be working so hard to maintain pressure as it should not be pulsing so much.

Right now I ended up doing a small restriction to return flow and bumping the FPR to 50psi on vac at idle. This seems to be working well but I will update as things change.

 

[Mauro_Penguin]

It is not silly, this can be a problem. If your fuel pressure fluctuates that drastically due to the oversized return and FPR, that could potentially cause issues with AFR. Maybe even ZZB, although I am not hoping that at all.

 

[JohnnyTightlips]

Update, I bought a knock off more modern style AFR that only does PI and not Carb and I noticed a pretty big difference. My current FPR is pretty wide open in the middle without much restrictions. I believe this allows for the lower pressure carb stuff to work but is causing headaches for my particular PI stuff. Right now my current FPR is working well with a restriction on the return side so I have no installed or tested this one but it does look like it would be better as far as design goes.

You can see how tiny the channel for the return is.


And fuel flowing in and out of the FPR have to hit this wall and then go over and around it.

This is likely the reason that these do not pulse as much with the higher PSI. The spring does not fluctuate as rapidly.

This is the legit one it is based off of.

 

[anthony]

What usually fails on the offbrand ones? The assembly looks pretty simple when you tear them down

 

[JohnnyTightlips]

What usually fails on the offbrand ones? The assembly looks pretty simple when you tear them down

The diaphragm usually just needs to be replaced by a legit one. And clean out for any shavings. A lot of the knock off ones on amazon have decent reviews and people replace the diaphragm with legit versions. Probably want to use better 6an orb fittings as well.

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and buy
Part # 13001 rebuild kit from aeromotive
https://www.ebay.com/itm/Aeromotive-13001-EFI-Fuel-Pressure-Regulator-Kit-Fits-13101-13109-13151-13159/143494703235?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

For some reason the knock off I got on ebay was cut for a M14x1.5 to 6AN Fitting but advertised ass 6an orb they actually gave me 10$ back and told me to keep it lol so it was like 15$ total.

 

[andale927]

To add to this, it looks like I made a similar mistake. I found the correct fuel labs regulator and looked for the cheapest one I could find. Didn't notice that the part number I purchased was off by one.

Its built for EFI, but in the fine print it states "Large Seat, 1,000 LPH"



Might work for all you dual hellcat pump guys out there though lol.

 

[andale927]

Picked up a different FPR with smaller valve seat per @JohnnyTightlips recommendation, it fully resolved the noise. So nice to idle without the annoying rattling.

Edit: Specifically model Fuelab 52501-1