Ok folks hopefully someone can help here as its baffling me. I just swapped my OEM fuel pump for a Walbro one, but Im encountering problems starting the car (FD) The car cranks and seems to start fine and rises to its normal cold start idle rpm. However it then almost immediately slows and stalls. I can keep things going for a little bit longer if I blip the throttle but it still dies in the end. I did think at first maybe I wasnt getting fuel through, but if this was the case surely it wouldnt fire at all?
Well Im confused so any help is appreciated thanks.
Well seen as no one is offering any advice I\'ll explain my current thinking.
Im guessing when I pulled the relay to stop the engine when running in order to depressurise the system that Ive flooded it.
Last few starts I could get it to run happily if I held it at 3k or more on the throttle but as soon as I lifted off it would stall. Im gueesing if the plugs were a bit contaminated this could be the case? Now it doesnt want to fire at all which seems to me its flooded. Cant check the plugs as Ive lent my mate my stubby ratchet, but thats tomorrows job.
Does my diagnosis seem feasible or am I way off?
What voltage are you seeing across the pump. Does it flow the same amount as the previous pump.
Could be chucking more fuel in and run way too rich. Sounds like it under 3k.
Easy way to de-flood is to floor the throttle and crank for no more than 20 secs at a time. Will lock off the pump. Then try and start normally.
Shaun
Quote from: shaunwil;494247What voltage are you seeing across the pump. Does it flow the same amount as the previous pump.
Could be chucking more fuel in and run way too rich. Sounds like it under 3k.
Easy way to de-flood is to floor the throttle and crank for no more than 20 secs at a time. Will lock off the pump. Then try and start normally.
Shaun
Erm to be honest I dont know what the OEM pump flows but the replacement is 255lph. Havent checked the voltage across the pump, but I will thanks.
I cant do the deflood trick unfortunately as Ive got a PFC fitted. I did it last time by pulling the main circuit relay and then cranking it. That got me so I could get it to run if revved, but things have just got worse the more Ive tried.
Would swapping the pump really make that much difference to the fueling at idle?
Shaun has a point...
I run a Walboro on my FC, and they use about half the current the stock pumps use. The result of this is that the resistor that is supposed to drop the voltage on the pump does not drop it by as much and hence raises the fuel rail pressure a little. You will therefore be seeing more fuel you did with the previous pump once at idle/low rpm\'s and possibly this may be causing your flooding
Quote from: Prof;494254Shaun has a point...
I run a Walboro on my FC, and they use about half the current the stock pumps use. The result of this is that the resistor that is supposed to drop the voltage on the pump does not drop it by as much and hence raises the fuel rail pressure a little. You will therefore be seeing more fuel you did with the previous pump once at idle/low rpm\'s and possibly this may be causing your flooding
Ah ok thanks for the explanation. How did you get round the problem? Replace the resistor?
Are you running a PFC ? If so get it re-tuned to the new pump flow !
Shaun
Quote from: shaunwil;494302Are you running a PFC ? If so get it re-tuned to the new pump flow !
Shaun
Yep I am and I can relearn the unit, I\'ll just have to wait a few days until I can borrow a datalogit kit and was hopeing there might be a way to move the car in the meantime. Just being impatient. :)
Hang on, the problem i see with the above is that, surely the whole point of the FPR is to regulate the flow of fuel?! therefore, no matter how well the pump flows, it should always be bought down to the required pressure by the FPR?
So if Meddy has not touched the FPR, and just put in a higher flow pump, why would the fuel pressure have changed?
Or am i totally missing something? (Not being confrontational, just a bit confused!:))
It\'s my understanding - and I\'ve been trying to find the post on another site where this is explained, that the stock FPR can become overwhelmed if too much fuel is coming in and not exiting via the injectors. That\'s why Mazda used the resistor relay, to throttle the pump back on idle/low load.
On idle, the injectors are running only a few percent, so most of the fuel has to pass back down the return line. Like any valve, it\'s flow rate is probably geared towards returning a certain quantity of fuel, and once that\'s reached, any excess will manifest as a pressure rise (and consequently more flow from the injectors for a given duty.
For the FC3S, the idle state does not use the narrowband, so the ECU maps injector duty on a fixed table and some temp sensors. If your fuel pressure is higher, you get more fuel and consequently a very rich idle - which is what I have. Once the ECU gets into closed loop, the injector duty can be controlled and the richness is ironed out.
At higher fuel delivery rates, the FPR pressure is raised anyway by the VAC line, and the injector duty\'s are higher resulting in less return flow required - so the FPR can cope again.