Strange fuel pressure Issue
Not sure where best to post this. So might drop it in a couple of places. Hope mods don't mind. I need some help!
So I have a 20b converted FD3 with single turbo. I went to dyno a few months back and had no fuel pressure issues that we noticed. I have since changed my primary injectors for smaller more manageable ones and the car had been run in the workshop a few times setting up the ECU. Nothing else has changed. The rest of the fuel system is as follows. New AN6 nylon braided fuel lines all the way from tank. AN6 inline cartridge filter. Extreme Rotaries fuel rails, SARD FPR. Quite possibly copy. Walbro 450lph pump. Fuel system tested up to 80psi static with no issues.
So car drove 10miles to dyno doing some road mapping on the way. Seemed fine but kept it off boost anyway.
first 30mins on dyno it ran fine. Then suddenly started missing and going lean with even light load coming on throttle. I noticed the fuel pressure was dropping off to basically zero as the throttle was opened. Shorter run to try and suss it of course. Tried pulling off vacuum line and putting to a other point on side of the plenum. No difference. Tried with the mine off all together so vac could not effect FPR still dropped off as soon as throttle started to open. With little. Other options I decided to pull the filter off and check it. It had a bit of crap in there. Maybe debris from new lines. Blew it out and put it all back. Fired up and all appeared perfect? Ran for about another 15mins and seemed okay. Fuel pressure increasing with boost. All good, then had to call it a day.
pulling off the dyno it seemed a bit off again and i. The way home it went from bad to worse and was lucky to make it back driving on light throttle and no load as much as possible.
I wondered if it might be pump going weak after a while or best effecting FPR as it is mounted to back of engine. Bearing in mind we had it really dine any power runs just setting up the matrix table on the ECU up to 5500rpm or so and no mega heavy load yet?
I went out this morning and fired it up. Ran like a bag of crap and fuel pressure was off just how it ended yesterday. I whipped of the filter and had a look. Seemed clean. Tiny, tiny bit of stuff there. Blew it out and put it back. I initially it seemed a bit better but then clearly started to drop almost immediately and revving the engine the pressure was dropping off to 20psi or less. Then decided to turn engine off and wind up FPR pressure. Went up to 75psi no worries. Then started the car same fuel pressure and it seemed to hold fine. But when you rev it drops more than it should. Was much better with the pressure wound up but maybe that is to be expected? So backed pressure back down to 43psi idle and same story. Pressure dropping way off. So big question is what the hell is it? Pump messing about? Seems unlikely if it can push the static and idle fuel pressure okay? Dicky FPR with a mind of its own. Or a lump of crap in the fuel line blocking the filter then going back down the line when I disconnect it?
Let me know your thoughts.