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Fuel pressure problem

EFI Wiring Fundamentals

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So when i reconnected the battery the fuel pump module went pop, I had the ignition on at same time. WRX 2010 , Anyway I decided to go a relay and fused from battery on a switch and it has been ok. But I never had any real time driving it yet till today and now when the cars has been driven for 20mins the pressure is getting down to low 30's and starting to stall.. I made it home in the low 30's and do see a raise when pulsing the throttle to keep above 33psi otherwise it stalls. Now that Im home and given it 15mins been off the static off fuel pressure is back up to 43.5 and running pressure 39psi. I've done the basic checks on FPR , looked for leaks but it seems to be a heat issue.

I know Im driving the pump at 100% duty cycle but would this be silly thing to do on a wrx?

Not running PWM control for the fuel pump should be fine as far as fuel heating. EFI cars have had fuel pumps in them for alot longer than they have had fuel controllers in them. Most people swap out the Subaru fuel pumps when they modify the cars.

But making it work from the Subaru system without the fuel pump controller is troublesome. I dont like the idea of just having ignition switch feeding the fuel pump relay. As the fuel pump wont shut off if the engine stalls out. Which means it wont shut off if the car has a crash or fuel leak or whatever else. It will just pump until switched off manually. And the Subaru fuel pump relay on the controller equipped cars doesnt work like a normal fuel pump relay. It basically switchs on when the key is on, and stays that way. The prime/control of the pump is handled by the controller.

You are probably better off getting another controller from a wrecker. Or fitting a tachometric relay to control the pump, and upgrading to a common performance drop-in pump.

thanks for the feedback . I know the car has a safety issue now but as long as it's not a technical issue , I'm new to the game and only really getting into it in the last 7 months. I'm thinking the fuel pressure problem might be fuel pump cell in tank has a o-ring leaking or fatigue from the fuel pump running flat out. DW300c . Wish i had a surge tank cause i think that would be easier.... lol . Maybe the fuel is getting warmer and i might try filling the tank right up to see if the problem is cured. Only running 1/4 tank atm moment and large AN parallel lines back to standard fuel line. Trying to run this motor in and only done 10km a trip before returning home. just starting to test 20km range and copped this fault. cheers mate

Check the wiring connections for melted pins/terminals. Check the plug on the fuel pump lid. And also check the plug where the wiring comes into the cabin about 500mm upstream from the fuel pump lid. These are known to melt with bigger fuel pumps. (Espesially if run flat out.)

With regards to the DW300. Ive had alot of trouble with early DW300 pumps failing. I think they have fixed them failing now as that was many years ago.

Other things to check are clogged fuel filter and the operating voltage - if it's a fresh build may even be a bad or loose terminal ground. If it is an old fuel cell, with a foam insert, the foam may be breaking up (why you use a pre', and post, pump filter), especially if running a fuel with alcohol as some of the older 'cells were affected by it - either way, most have a 5 year service life.

Back in the day, it was common for a race car to have the fuel pumps powered by a relay operated by an oil pressure operated switch - you may recall seeing some old race cars with big "Pumps On" signs by toggle switches, these manual over-ride switches were normally turned on for priming and starting the vehicle and turned off when the vehicle had oil pressure. Power from the ignition switch wouldrun to the relay windings and be split into two ground wires, one was through the manual toggle switch and the other through an oil pressure switch.

06+ subaru are known for having trouble with Oring sealing on the fuel pump/filter carrier. Very common for people to instal an aftermarket pump and then pinch the o-ring in the fuel basket when re-assembling.

Bram you might be right, It's all new in the fuel cell. Gord thanks for ur input. there such a shit fuel cell and horrible plastic that contains the unit. I cant explain how fustrated i am, as when its cold even now it runs so good . I will pull the intank stuff tomorrow and check the unit out. I've got a Sard FPS and all new lines in engine bay plus 1050x injectors running such a low duty cycle I cant believe this is happening. I seen 30 psi on the way home but now when i test it I've got 44psi static 41 when running and plusing the throttle i get 45psi .

Is the sard reg legit. There are so many china knockoffs out there. Next time it happens try pinching the return line

Pretty sure it is. Came from gotitrex . I will try today by driving it 1st and getting the fault to reappear then clamp the return line 1st before pulling the tank apart. Cheers mate.

Just found that when i pump fuel into jerry can from engine bay the fuel pump is staving after 5 seconds of good flow, Think that pump housing bucket is not capable of good fuel pickup. Thinking a couple of drill holes in the base might open it up... Still could be a bad seal on the o-ring and will check that out also still .

5 seconds is a bit quick, but lack of a vent to the fuel cell can lead to the pump not being able to pull a vacuum in the fuel cell. Usually happens after 1 lap on the track, get back to the paddock and everything is fine.

David Ferguson so would it be a good idea to put a 10mm hole in the base at the side to allow more fuel to enter or does it effect the pump? I would have thought the pump would only need to be submerged in the fuel and it would work fine.

A fuel cell vent in a race car fuel cell can be accomplished several ways. One, put a one-way check valve (typically a -6 or 3/8" ID) into the fill plate (usually located at the top of the cell -- the valve should allow air in, but not let fuel come out if the car is overturned. Other way done with formula cars, is to have a hose exit the top of the cell, go to the very top of the chassis, then come down one side, across the bottom, and up again. this 360 degree loop will prevent fuel from spilling, but will allow air into the cell.

This is how we do it on purpose built race cars -- I'm sure the factory WRX had some provision to allow venting -- but sometimes people remove that or block the plumbing thinking it was just for emissions compliance. The need for a vent is real.

BTW - I did have a problem that nearly stopped the fuel flow after only a few seconds. It was a Bosch 044 pump, and the inlet fitting thread was too long and it was nearly closing off the inlet to the pump. We swapped pumps between two cars and the problem stayed with the plumbing...

David thanks for the reply. Yes the wrx has 3 line from tank and normally the vent is piped to the intake with a solenoid that opens and closes by the ecu i believe. I'v just go that going to atmosphere since late March this year and was working good. I reposition the o-ring on the fuel pump and seems to be better but still got this fault where the pressure seems to drop 10psi when the engine bay is hot so I will change out the FPR tomorrow if i can source one quickly. Spent so much money on this car the accounts are starting to run low. I've just dropped a new cosworth based motor and heaps of other stuff in and this motor has been such a pain to get right... thanks again mate.

The subaru tanks have 2 massive vents on them. Those vents do a bit of an S bend, then T into each other, then go to the charcoal tank, then into the purge solenoid and sometimes a second vacuum operated valve, then into the intake. (I literally pulled a fuel tank out of a WRX wreck yesterday in order to measure up a race fuel cell install into my car)

I doubt the tank is suffering from pressure/vent problems. The vents on the tank are like 50mm diameter with some kind of roll-over shut off built into them. And even though the vent hose is only 8mm or so, i seriously doubt enough fuel is leaving the tank, fast enough to over whelm that. Thats alot of fuel use for a sustained amount of time. (Provided its not blocked off like David suggested.) If its now vent to atmo, and the car has been sitting for a long time, check the hose for bees or wasps. This will sound crazy, but the little bastards go in there and clog the holes up. Ive had this happen with diff breathers before.

With regards to the pump emptying the pump pickup. 5 seconds sounds pretty quick. But at the same time, all the return fuel should be going in there, and the return flow also drives a little venturi pump thing that siphons fuel from the other side of the saddle-bag shape tank as the return fuel returns. And pumping the fuel out of the tank, means you are pumping it out un-regulated, so a much higher volume of flow than a regulated supply. I dont think there is too many issues getting fuel into the in-tank pickup under normal-ish driving conditions. As its not really an issue until you start running lots and lots a fuel with some twisty cornering. But not in just normal driving. Typically a extra surge can is used in order to run multiple pumps, as you cant fit them in the OEM tank, and has the added bonus of being an anti-surge system. I think most people do it to facilate fitting large or multiple pumps on high fuel demand vehicle.

What does cause issues on these car is lots of right hand corners, as it literally sloshs's all the fuel to the left side of the tank faster than the venturi siphon can return it. And even with surge tank equipped cars, you can still starve the engine easily on a very fast clockwise track. As you starve the supply to the surge tank, which then runs out and starves the engine, as the in-tank pickup to the surge tank either pulls too much air, or cant supply enough fuel fast enough to replenish the surge tank.

The reason i am measuring up the race fuel cell is I have had trouble keeping fuel supplied to the surge system. So figured a race cell with integrated multipump anti surge system is a proper fix, rather than band-aiding it with bigger surge tanks and such. But i think you have to be demanding alot of fuel and driving the absolute ring out of it before that is an issue.

SARD have a guide on-line on how to identify the genuine and counterfeit regulators - think I saw it on their interweb site.

Might be worth having a careful check of the entire system for kinks as it may be upstream of the pump. Also check the rail is correctly plumbed as with some vehicles it is possible to get it the wrong way round and have weird running issues.

Have you tried running the fuel rail feed line, or better the outlet, into a container to check it is managing a good flow of fuel through the lines?

Ended up being the Sard fuel pressure regulator guys. Now have a GFB . The fault finding experience was worth the effort i got to learn so much about the intank setup and looking forward to the surge tank setup now without been to scared. I like to do stuff myself and learn. Thanks again guys .

Glad you got it sorted - here is the guide to the SARD genuine/counterfeit guide - https://www.sard.co.jp/after_eng/products/engine/regulator/regulator_pirated/regulator_pireted.html