Tyler Twerdun

So I managed to get my rx7 onto a hub dyno, surprisingly things went smoothly considering the decapitated state I got the car in. I couldn't rev it over 3000 rpms when I got the car, plugs were carbon ed over the gaps, every fluid in the car was sludge, but shockingly enough the motor had compression, all be it low 86-94 and 92-104 for ranges. Either way I wanted to put some love into it and see what it could give me this year. The car was build 11 years ago by a good shop in Vancouver, and had good parts on it (for the time) but it was so neglected.

Plugs, wires, all new fluids, a lot of degreasing, took everything apart and checked "stuff" and overhauled the fuel system for e85. I cleaned the tank, sealed it, ran -8 to the radium rails, id1050x and id1700 with -6 return. Radium rail came with fuel dampener and regulator. Also ran a new hellcat 525 pump and irp pump hanger and pump relay.

so to sum it up, this car has shocked me, its somehow came back from the dead and did okay on the dino. I ran into a fuel pressure drop around 6000rpms to about 6500 rpms where the pressure would dip 5-7 psi, and then recover on every pull.

We checked the voltage at the pump and its consistent through the entire band. The dyno was concerned with the fuel dampeners from radium, they have seen some fail and allow fuel push through the diaphragm. I just disconnected it and plugged the vac line and I will take it for a test drive (when the rain dries) and see if that solves it but I thought I would make a post to see if there are any other suggestions. They also dont like the radium FPR, so that might be the next part to swap.

It made 330 wheel on 11lbs on e85. I doubt the pump is maxed but its possible as the rotary fuel needs are new to me, I know its about 30% more, plus 30% more for e85, obviously the numbers add up quickly.

Anyways, any help or suggestions would be great. Thank you.

BLUE TII

iTrader: (9)

Just incase of brain farts-

Your boost is steady 11psi throughout the pull or does boost dip at the same rpms as fuel pressure and recover?

Manifold pressure referenced fuel pressure regulator 1:1 rate.

DaleClark

iTrader: (55)

Don't see it mentioned, did you change the fuel filter?

May be worth pulling the existing fuel filter and seeing if there is crap in it. If you had to clean out the tank it may have picked up some garbage that's now in the filter.

Dale

Tyler Twerdun

yes brand new after market fuel filter and fuel lines. 7 micron filter and -8 lines so think I'm all good there.

Tyler Twerdun

I'm fairly sure boost was holding steady, I can ask the tuner but that would be a pretty big miss on all of our behalf. Hood point though, doesnt hurt to check.

newtgomez

I just went through this exact same thing with my car. Fuel pressure would spike up, and then slowly go down during the pull. I upgraded my hard line, replaced my Walbro 450, threw a Holley Hydramat and raised the pump a little to account for sock depth, changed regulators, bypassed my fuel filter and nothing changed the issue. I did discover that my signal wire on my fuel pressure sensor was loose enough to pull out by hand, but I'm starting to think that my Radium FPD might actually be the issue as that's literally the only thing I haven't changed in my entire fuel system...You really got me thinking here...

Tyler Twerdun

I just got back from a pull, I made it on the hyway, 3rd gear, got into it and instantly the roads were wet and rainy. The fuel pressure held through 3rd to 7500 rpms with the FPD plugged off, but its too wet with drag radials on to go make another pull so I will verify tomorrow if this was in fact the problem.

Tyler Twerdun

Confirmed today, the fuel pressure does not drop when the radium fuel dampener is disconnected

newtgomez

Thanks for the follow up! That is such an easy thing to look pass and I never would have guessed it could do something like that! Glad you figured your pressure issue out!

Tyler Twerdun

So I did some more digging today.

I pulled the FPD off and inspected the diaphragm and it appears to be in good condition. I cant see any holes or damage. I am tempted to hook it back up and check again.

Either that or I may find a way to bench press the diaphragm, maybe put 60psi of air to it and see if I get a leak through the vacuum port.

Tyler Twerdun

Or... how important is it to have a fuel dampener hooked up?

cr-rex

iTrader: (114)

It's not.... its advised to DELETE the stock one if in a position to do so

DC5Daniel

iTrader: (10)

Sorry, that's old information when people just ripped everything off their cars because they could...and I'm guilty of deleting the stock one 8 years because at the time that's just what you did. It's more commonly recommended now to replace with new if stock. In the case of a decently modified car making more power with an upgraded fuel system, to integrate an upgraded FPD. If you have a stock car will you see an issue? History would tell us no. If you have big injectors and making over 400whp like many of these cars are, becomes a different scenario.

https://www.rx7club.com/single-turbo...tions-1090373/

As you'll see in the thread above, several respected names on this forum such as Chris Ludwig from LMS (thread starter) and Elliot from Turblown support and practice this concept, as well have seen results from doing so.

alexdimen

iTrader: (13)

How exactly would a FPD cause a pressure drop? Leak thru the diaphragm?

I know you checked the voltage at the pump bulkhead, but there is no easy way to tell what kind of voltage drop you have thru the bulkhead connector. If you are still using the connector on the stock bulkhead that can fry on the tank side causing a voltage drop just before the pump.

DaleClark

iTrader: (55)

The fuel pump is not supplying a steady stream of fuel, it's a pump, so it is coming in waves. Then you have injectors opening and closing, reducing pressure, also causing waves. At certain RPM's they can cause drops in pressure due to the waves hitting each other, causing drops in pressure. Read the linked thread in the single turbo forum for more info.

The pulsation dampener can absorb the spikes and valleys to smooth out fuel pressure.

Dale

Tyler Twerdun

This is true but ive had the pump hat off and its good. it also doesnt explain why the fuel pressure didnt drop once I blocked off the FPD.

So I was up late last night reading about the throttle body ports and I wonder if I had it plugged into a port that didn't supply the correct pressure. From my understanding the are all vacuum or metered ports so at wide open throttle they should all be measuring the same boost pressure unless the ports act differently. I am going to keep searching, and see if I can figure it out. I was waiting for a fuel line to connect the two rails but I am getting it tomorrow now so hopefully I can get the can back together to do some testing with the new (ish) coil packs and fixed idle air control valve.

Tyler Twerdun

Would a fuel pressure regulator not also do this? Just a curious questions I would expect the regulator to "regulate" the pressure spikes and drop offs the same as a FPD?

I am curious what the difference is with the two.

alexdimen

iTrader: (13)

Thanks - I read that thread years ago and it makes sense to me. I am not asking how a missing FPD would cause pressure drop. I am asking exactly how would the radium FPD cause a pressure drop? And removing the FPD gets rid of the pressure drop.

The way Tyler suggested was a leak thru the diaphragm to the reference hose. Possible, but easy to rule out as well by checking for gas in the unit..

Another option is that a FPD is not necessarily universal for all pressures/frequencies/injector sizes. Pressure fluctuations in a fluid system are just like vibrations in a mechanical system in that you have to choose the correct spring and damping factor to keep them from getting out of control. You choose the spring/damping factor based on frequency and magnitude of the vibrations. You can't ever design for all frequencies and magnitudes, so you try to damp out the worst resonance points of the operating range. The resonance points are going to change from system to system. It's possible that the diaphragm in this particular FPD is great at damping out fluctuations in a V8 or straight 6, but does nothing or even amplifies the fluctuations on a 13B.

In this thread two people have the radium FPD on their car and have a high RPM pressure drop.

I wonder if there are any people using this FPD that are not experiencing pressure drop and what their setup is.

I believe you, but I've looked directly at a pump hat before and not seen the burned up connector terminals hidden by the plastic connector. Just throwing it out there in case it saves you an engine.

It sounds like the Radium unit is designed to use the reference port to change the damper's characteristics as boost pressure and fuel pressure rise. I would hook that up where you would normally put a boost gauge line on the UIM per their instructions.