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Over the weekend I was dyno tuning my 1993 FD with Chris Ludwig of LMS EFI- who made the wire harness for my Haltech 1500. When we started doing boost pulls, Chris showed me that the pressure differential between the manifold (MAP) and the fuel rail was not as stable as we'd like to see. Picture of the instability below, it is the green series.
My fueling setup: Walbro 450 in the tank, stock hardlines with 6an adapters. Injector Dynamics 1050 primaries and 2600 for the secondaries. FFE light fuel rails. AEM 30-2130-100 pressure sensor at the back of the primary rail. Fuel Lab Mini FPR at the back on the secondary rail.
My question for you all is options do I have to stabilize the fuel pressure? I'd rather not change my fuel rails just yet, I know the Radium rails are out there with the provision for the pressure damper...
Here is a photo of how I made an aluminum hardline between the primary and secondary FFE rails. At the time, I was quite proud of how tidy the setup was but it's definitely less clean with the wiring harness in there. I wasn't planning to remove the stock fuel lines between the tank and the engine bay and plan to keep the car running pump gas and not e85. Curious peoples thoughts!
if you decide you need to add a pulsation damper, Mazda had a few that were remote mounted, there was a 90's MPV that had one that was remote mounted, and then the NB Miata is as well.
not saying you need to use a Mazda part, but i think you could put the damper someplace more convenient
the NB miata one won't work, it uses clip on hoses, but it might give you ideas BP4X-20-180
those are awful big secondary injectors to be running in a series fuel flow system. there's going to be a lot of "noise" in the rails with those big injectors with rather substandard looking fuel flow.
you sure the dead time for the injectors is set properly as well?
Last edited by notanymore; May 5, 2025 at 11:51 AM.
Base pressure was set to 40 psi with the car idling. However, I did this at home- before DGRR. My tuner did not mention base fuel pressure during the dyno last weekend.
Base pressure was set to 40 psi with the car idling. However, I did this at home- before DGRR. My tuner did not mention base fuel pressure during the dyno last weekend.
Pull the vac line off the FPR at idle, put your finger over the vac port on the UIM, and see if the pressure changes. If there is a pressure change that could be a contributing factor and you can reset base pressure without vacuum applied. Ultimately, you may need more pump, or to upsize the fuel feed line (hopefully not the rail size too).
Have you upgraded the wiring to the fuel pump? In addition to the other suggestions, if you are using the stock wiring I would suggest to get a relay kit that a few vendors offer. They are PnP and will ensure the correct voltage gets to the pump.
it does make sense that a PD would soften the noise in the system, i just wonder how much is too much. i mean i've built a number of ~500whp cars on pump fuel with larger injectors and they ran fine for a long while, all those systems eliminated the pulsation damper. the issue is with that sensor right next to the injector those pressure waves created in the fuel system are translated into a graph form, but the fuel pressure in reality is still averaged out and still making it to the injectors.
i see the same with MAP signals on rotary engines, without a restrictor or signal filtering you can see every intake sequence on a MAP reading, it would be concerning when you'd see a 2psi variance on your MAP reading except in that event it can be catastrophic since the MAP signal corrects fueling requirements where this one does not. this is also why mazda put a restrictor inline with their factory intake pressure sensors(it's a manual way of filtering pressure differential, or waves of pressure to buffer a signal to read more accurately). i guess the point of it is, if you want to see erratic signals on an engine you can, by placing sensors very close to turbulent sources, does it really mean there is a problem though? if you placed an oil pressure sensor with an extremely high resolution next to an oil pump outlet you could probably read every pressure vane rotating.
to me i'm not sure if it really means this is an issue. are you seeing AFR's lean out as PD rises? the screenshot doesn't imply that it is. the pressure differential reading could imply a volume issue but you should also see pressure dropping if it was but it doesn't appear that occurred either. fuel injectors should easily be able to manage these pulsations, i think folks just often times don't get to see how they look inside the system, batch firing injectors exaggerates these "issues".
Last edited by notanymore; May 7, 2025 at 10:28 AM.
Update, I have the Radium inline FPD-XR with 6AN fittings. I plan to redo the fuel line from the fuel feed side, o have the damper plumbed before the primary rail.
While my aluminum hardline and FFE light rails are pretty trick, if I were to do this again I would've purchased the standard FFE secondary rail to drill/tap the FPD to that. Or the Radium rails that have the provisions on the rail.
