Brettspeed Fuel Pump Solution - FI on high speed corners
09-23-2014, 03:59 PM
#76
I changed out my stock pump a couple years ago to a Walbro. I was seeing 60-61 PSI on the pressure gauge when eventually it started to drop lower and lower until I saw pressure ranges of about 52-58 PSI. I replaced the Walbro last year with a DW200 and I consistently see pressures between 52psi and 58psi. Typically runs around 56PSI then when I floor it and fully spool up I see the pressure drop pretty linearly through the RPM band down to about 52 or 53PSI. I always keep a close eye on my AFR's through both the COBB and my AEM Wideband and it doesnt seem to be affecting my AFR's so I chalked it up to being an inaccurate gauge (Autometer mechancial gauge). After reading through this I'm hearing people say that their pressure is increasing when they accelerate..... Is there a chance I am having issues with my pump kicking into high speed? or apart from seeming a bit low of pressure is this pretty typical for some of you other FI guys?
09-23-2014, 04:38 PM
#77
I also believe that the assembly at the bottom of the siphon tube is actually designed to draw fuel into the bowl from the tank . So at below 1/4 tank (when the tank level goes below the bowl level) , Mazda attempted to turn the bowl into a mini surge tank and the level in the bowl is supposed to end up higher than the level in the tank.
I'm going to try some modifications to the siphon o get it to flow more fuel .In MMs' thread he originally drilled out the siphon to 1/8" (at least that is what is quoted in the thread)which I think was way too big .
I still have been getting fuel starvation under hard acceleration once the fuel light comes on so want to see if i can fix that .
Last edited by Brettus; 09-23-2014 at 05:05 PM.
09-23-2014, 05:42 PM
#78
Driving my unreliable rx8
I was thinking that moving the siphon to your secondary bowl might help also.
It would be a good way to test if its the Venturi blowing fuel out of the stock bowl.
It would be a good way to test if its the Venturi blowing fuel out of the stock bowl.
09-23-2014, 05:53 PM
#79
When I first tried the outer bowl idea i didn't have the two holes drilled into the inner bowl ............ when that didn't work I realised that the pump was actually emptying the inner bowl somehow and that is why drilling the holes in the side fixed it .
Putting the siphon in the outer bowl can only make the problem worse as now you are drawing all the fuel flow out of the inner bowl and pumping it straight into the outer bowl .
So ........................... I am thinking if I can increase the flow through the siphon enough , I wont need the holes drilled into the side of the inner bowl as now the inner bowl can maintain a fuel level HIGHER than the outer bowl..................
Last edited by Brettus; 09-23-2014 at 06:01 PM.
09-24-2014, 04:34 AM
#81
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Ok . How about the first stage resistor ? Is it possible that is shorted out and running the pump at full speed continuously . Or the reverse , resistance has increased to the point it runs too slow and the pump motor overheats as a result of that ? What do you get when you run an ohmeter across it ?
logalinipoo mentioned about voltage. we should measure at the pump itself and how much should we be getting?
will fluctuating voltage damaged the pump? i checked at my battery and it's not really stable and varies with the rpm.
09-24-2014, 07:42 AM
#82
Driving my unreliable rx8
Ive never monitered my car but it should be 13.8-14 volts at the battery. It will vary a bit but should be pretty darn close during every day driving at any rpm.
63 psi sounds high at idle. My s1 assembly with a dw300 only puts out 58 at idle, 66 is the highest I've seen with it at wot.
63 psi sounds high at idle. My s1 assembly with a dw300 only puts out 58 at idle, 66 is the highest I've seen with it at wot.
Last edited by logalinipoo; 09-24-2014 at 07:44 AM.
09-24-2014, 03:34 PM
#83
what's the good range for the resistor? i measured mine and i got 0.5ohm. my fuel pressure is at about 63psi idle and will vary about 58-63psi depending on how i drive.
logalinipoo mentioned about voltage. we should measure at the pump itself and how much should we be getting?
will fluctuating voltage damaged the pump? i checked at my battery and it's not really stable and varies with the rpm.
logalinipoo mentioned about voltage. we should measure at the pump itself and how much should we be getting?
will fluctuating voltage damaged the pump? i checked at my battery and it's not really stable and varies with the rpm.
Last edited by Brettus; 09-24-2014 at 03:37 PM.
09-25-2014, 07:27 AM
#86
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09-25-2014, 11:43 AM
#88
Fuel pressure is determined by the regulator in the fuel pump assembly as long as there is enough flow from the pump to supply the fuel needed
If the flow of the pump is lower than the amount needed by the engine then the fuel pressure will drop to below where the regulator cracks
The fuel system on the RX-8 has a resistor that drops voltage when it is active...and therefore pump will produce less flow at lower rpm's when not needed by the engine
If the flow of the pump is lower than the amount needed by the engine then the fuel pressure will drop to below where the regulator cracks
The fuel system on the RX-8 has a resistor that drops voltage when it is active...and therefore pump will produce less flow at lower rpm's when not needed by the engine
09-25-2014, 02:17 PM
#89
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I think what you are seeing is normal . Mine does the same now . However I have the DW 300 and when that kicked into high speed mode I would see an increase in pressure (corresponding with rich afrs)for about 1000rpm after which it would start declining again . I changed the wiring so it now doesn't kick in till later in the rpm range.
What is a regular pressure to see the system at after your car has been shut down for say for like 12 - 24 hrs?
09-25-2014, 08:43 PM
#95
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i checked voltage across the resistor and i got about 2.3v. the resistor suppose to drop the voltage by 2v right?
i've seen posts in which some are trying to slow down the pump by increasing the resistor, so my resistor of 0.5ohm will slow down the pump and should be beneficial since i'm only NA?
getting confused...
btw, my fuel pressure doesn't go to zero and will drop to about 55psi after 12hr overnight.
09-25-2014, 09:17 PM
#96
you mentioned that the voltage shouldn't be less than 9v?
i checked voltage across the resistor and i got about 2.3v. the resistor suppose to drop the voltage by 2v right?
i've seen posts in which some are trying to slow down the pump by increasing the resistor, so my resistor of 0.5ohm will slow down the pump and should be beneficial since i'm only NA?
getting confused...
btw, my fuel pressure doesn't go to zero and will drop to about 55psi after 12hr overnight.
i checked voltage across the resistor and i got about 2.3v. the resistor suppose to drop the voltage by 2v right?
i've seen posts in which some are trying to slow down the pump by increasing the resistor, so my resistor of 0.5ohm will slow down the pump and should be beneficial since i'm only NA?
getting confused...
btw, my fuel pressure doesn't go to zero and will drop to about 55psi after 12hr overnight.
Just went out and remeasured mine . So with car at idle , measureing from the earth terminal of the batt. to the green wire should be around 14v and earth to the white wire should be more than 9V .
FWIW : i see 14v in and 10v out with the DW 300 pump but i think it will be a higher out voltage for a smaller pump .
But yeah , the 9V figure as a minimum out voltage i gave you , was a recommendation from a company that makes variable resitors for this purpose.
09-26-2014, 12:03 AM
#97
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I'm sorry , I didn't explain that well. Sounds like the 2.3v across it is about right though.
Just went out and remeasured mine . So with car at idle , measureing from the earth terminal of the batt. to the green wire should be around 14v and earth to the white wire should be more than 9V .
FWIW : i see 14v in and 10v out with the DW 300 pump but i think it will be a higher out voltage for a smaller pump .
But yeah , the 9V figure as a minimum out voltage i gave you , was a recommendation from a company that makes variable resitors for this purpose.
Just went out and remeasured mine . So with car at idle , measureing from the earth terminal of the batt. to the green wire should be around 14v and earth to the white wire should be more than 9V .
FWIW : i see 14v in and 10v out with the DW 300 pump but i think it will be a higher out voltage for a smaller pump .
But yeah , the 9V figure as a minimum out voltage i gave you , was a recommendation from a company that makes variable resitors for this purpose.
Anyway, i've decided to try running direct power to the pump bypassing the ecu.