Strange Fuel pressure issue
02-18-17, 03:09 PM
#1
Rotary Enthusiast
Thread Starter
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.
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.
02-18-17, 05:26 PM
#2
Does this occur when the car is cold or only when warm / having been driven a good while / heatsoaked?
Curious as to whether you're having fuel pump cavitation issues. Can you hear the way the pump sounds? Are you looking at fuel pressure via mechanical gauge or digital gauge? If its mechanical, is the needle solid steady with car off, pump on, during these phases of rough running?
Curious as to whether you're having fuel pump cavitation issues. Can you hear the way the pump sounds? Are you looking at fuel pressure via mechanical gauge or digital gauge? If its mechanical, is the needle solid steady with car off, pump on, during these phases of rough running?
02-19-17, 03:24 PM
#4
Rotary Enthusiast
Thread Starter
Thanks for replies.. So you gone straight to my initial thought of heat effecting something. Not the case though as I went out next morning and fired it up cold and issue was right there. I have not. Noticed anything odd sound wise from pump? Sounds fine when you key on. I have a mechanical gauge on FPR. Solid and steady when you key on. Holds pressure for a reasonable time after key off. Idle it holds steady. Just drops like a stone when you try and pull any rpm?
when you say check the chassis plug.. Do you.. Mean the one that goes through the fuel hatch cover in the boot floor?Also check voltage? As in see if I am getting a massive voltage drop when I hit the throttle? I don't think that is the case as I would think the car would just die from lack of spark and injection if it were. It keeps running Just goes very lean! Plus would I not see a battery light if it had dropped that bad. Pump would have to almost stop I think.
Engine is on it's way out now so I can only check things that don't require engine running! Also remember the pump seemed to wind up to over 70psi static happy and held that solid at idle. Also seemed a bit better when revving but not right. It sure is a strange one.
when you say check the chassis plug.. Do you.. Mean the one that goes through the fuel hatch cover in the boot floor?Also check voltage? As in see if I am getting a massive voltage drop when I hit the throttle? I don't think that is the case as I would think the car would just die from lack of spark and injection if it were. It keeps running Just goes very lean! Plus would I not see a battery light if it had dropped that bad. Pump would have to almost stop I think.
Engine is on it's way out now so I can only check things that don't require engine running! Also remember the pump seemed to wind up to over 70psi static happy and held that solid at idle. Also seemed a bit better when revving but not right. It sure is a strange one.
02-20-17, 09:45 AM
#5
Seeing as how you "clean out" the fuel filter and it starts to run better for a while then get worse again would lead me to think you have something stuck in a fuel line or the filter sock in the tank or something like that. Replace the fuel filter with a new one and try to clean out the lines leading up to the filter if possible. Did you recently put some fuel system cleaner through the car or anything?
Also, you recently changed the primary fuel injectors. Are you sure the electrical connectors are completely seated on the new injectors? Although that obviously should not effect your fuel pressure problem. Basically I would suggest going back through anything you recently changed
Also, you recently changed the primary fuel injectors. Are you sure the electrical connectors are completely seated on the new injectors? Although that obviously should not effect your fuel pressure problem. Basically I would suggest going back through anything you recently changed
Last edited by Lavitzlegend; 02-20-17 at 09:48 AM.
02-20-17, 03:31 PM
#6
Rotary Enthusiast
Thread Starter
Fuel injector connections are all good I just pulled them off today. Like you say that should not effect fuel pressure. I am thinking something in the line maybe... hopefully! All lines filter and tank were replaced during the rebuild though. but doesn't mean something didn't get in there. I will pump fuel through the lines into a bottle and see if anything comes out. Other than that my next guess might be FPR as I have had an old FSE one do some strange things in the past and thought it was pump. then turned out to be regulator. Anyone been reporting issues running the new Walbro 450lph pumps like this one.
TIA485-2 450LPH Walbro E85 Racing Fuel Pump F90000267
I can't see it but never say never.
Cheers
Lee
TIA485-2 450LPH Walbro E85 Racing Fuel Pump F90000267
I can't see it but never say never.
Cheers
Lee
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