fuel pressure, fuel temp, fuel coolers, noisy fuel pump

[adamaw11]

I hear that standard base fuel pressure is 300kpa or 43.5psi.
I'd been running at more like 330kpa for a while, and have been wondering how this effects fuel temp and strain on the fuel pump.

The pump I have is a walbro 255, which are known for being quite noisy, mine gets pretty noisy after a good 30 minutes running, especially on a hot day.
When this happens, base fuel pressure seems to drop lower, down to 270kpa or less, and is enough to effect AFR. I suspect the fuel temp is climbing when this happens.

In theory, would running higher fuel pressure cause the fuel to heat up more?
does higher fuel pressure put more load on the pump?
Lower fuel pressure might actually cause the pump to flow more fuel and spin faster? which which wouldn't necessarily be easier on the pump anyway?

Is it worth looking into using a fuel cooler for this issue? or can I expect to moderate the problem by compensating with fuel pressure adjustment.

The setup is:
aw11
blacktop 4agte
850cc side feed injectors - low impedance peak and hold
Fuel: E85
Haltech Elite 550
Walbro 255 fuel pump in tank ~ 2 years old.

cheers,

Adam.

[jondee86]

Wow... big question Maybe consider the FPR first as there are several things going on at the same time. Technically, the FPR is a pressure sustaining valve as its job is to try and maintain the upstream pressure at a constant level. And unless you have something pretty special, it will be a variation of this...



The vacuum reference is to compensate for changes in manifold pressure, so not relevant to constant speed operation. Basically the pump is opening the valve against spring pressure, and if the flow increases the valve will need to open a little more, and the spring pressure will increase slightly. The spring rate will be chosen so that the pressure increase over the valves design operating range is minimal.

Assuming that your FPR returns excess fuel to the tank, the pump should be pumping a constant mass of fuel and drawing constant current. NB: DC motors are voltage sensitive so the current will go up if the supply voltage goes down. The pump uses fuel for cooling and the fuel also picks up heat from the rail as excess fuel circulates between the tank and the engine.

Raising the fuel pressure will put more load on the pump, and may shift its operating point to a less efficient point on its curve drawing more current. Fuel density will reduce as it heats up, and so mass flow will reduce. The net effect will likely be a small increase in current draw which will raise the pump operating temperature slightly.

Off the cuff I don't see why any of this should cause the rail pressure to drop unless there is some cavitation issue with the pump on e85 ?? Maybe someone else can explain.

EDIT: Doing a little digging on this subject (a bit of self-education) I see a couple of potential issues mentioned. Apparently e85 can cause problems with pumps not specifically designed for e85. The pumps relies on gasoline for lubrication, and the lesser amount of gasoline in e85 can cause premature failure of the pump.

As e85 requires the pump to flow at least 35% more volume than pump gas, it may not be able to keep up with demand causing pressure to drop off under high engine load. On the other hand, e85 appears to have a higher boiling point than gasoline, so pump cavitation is less likely to be a problem.

Cheers... jondee86

[knightrous]

What fuel temperature is the flex fuel sensor reading?
Have you looked at doing PWM fuel pump control using an SSR? (ie: ramp the pump down to 40% power under 2000rpm).

[adamaw11]

I don't have anything to measure fuel temp currently, and am not actually using a flex fuel sensor. Getting fuel temp reading would be usefull though
Controlling pump speed with PWM is an interesting idea, wonder what options I'll have with doing that. I think this issue has actually became more pronounced since I rewired the 12v supply for the pump, for its relay, maybe it was seeing a lower voltage before.

Jondee, fair suggestions about the FPR, I guess it only varies the pressure based on manifold reference, and wouldn't compensate for fuel density / temp.
I wonder if the lube-ing effect mentioned could be coming into play here. I don't see the extra flow volume required for E85 being a problem though, but I suppose it could contribute to the pressure drop at idle if the temp/density changes.
If I run higher fuel pressure, less flow, the pump may spin more slowly I guess - whether thats a good thing or not is unknown to me, I wonder if there'd be downsides to running more like 350kpa fuel pressure, as long as there's no leaks....

[jondee86]

Both the pump and injectors look like they have you well covered for the amount of fuel your engine requires at 300 kPa, so I don't know why you would want to use the FPR to tune your AFR when you have the Haltech ? Raising the fuel pressure will add more fuel right across the rpm range. Here is a chart with data for a Walbro 255 on gasoline...



It might be worthwhile to look into getting a pump designed for use with e85. I don't know exactly how "lack of lubrication" affects the pump operation, but typically lack of lubrication increases friction between moving parts and this could be loading the pump motor. Measuring pump current might give you some insight.

Cheers... jondee86

[knightrous]

I don't have anything to measure fuel temp currently, and am not actually using a flex fuel sensor. Getting fuel temp reading would be usefull though
Controlling pump speed with PWM is an interesting idea, wonder what options I'll have with doing that. I think this issue has actually became more pronounced since I rewired the 12v supply for the pump, for its relay, maybe it was seeing a lower voltage before.

Flex sensor to get Eth% and temp.
https://www.summitracing.com/int/par...7429/overview/
SSR for PWM fuel pump control
https://www.jaycar.com.au/solid-stat...ching/p/SY4086

Do it right

[feral4mr2]

The walbro 255 in feral has always been noisy, but as of late last year and this year it'll start screaming like it's starving for fuel and the car will die. 1st time it happened i did think i had ran out of fuel. Now i know this is not the case. Seems to be on longer runs, worse when there's less fuel in the tank, so i have been thinking more of a overheating issue.
Today i changed the fuel filter, which did have a lot of brown gunk come out over me when i undid the bottom bolt. Pump still sounds the same, havn't taken it on big enough drive to see if i still have the same issue.

Got a DW200 coming anyways, so going to swap that noisy pos out. haha


What filtration setup are you using pre and post pump with the e85?

I know a lot of people do, but Winebro themselves don't recommend the 255 with e85.

[adamaw11]

Pre pump, I think I used the sock thing that came with it. post pump, just used a new standard type EFI filter, standard location. Maybe I should try checking / replacing the filter since its been a few years since I installed the pump I think.

How long have you been running your 255? I wonder what their life span usually is.

I dropped my fuel pressure down to around 280kpa at idle when cold, and I think it helped a little bit. I nudged the tune a bit richer to compensate also.

[feral4mr2]

From my understanding some pre pump socks have glue etc that aren't e85 friendly, and post pump should be a 10 micron stainless washable filter that can be periodically cleaned.

Wouldn't surprise me if the stock filter is gummed up a bit causing back pressure back on the pump making it noisier and lose flow....

Sent from my SM-G930F using Tapatalk

[adamaw11]

Flex sensor to get Eth% and temp.
https://www.summitracing.com/int/par...7429/overview/
SSR for PWM fuel pump control
https://www.jaycar.com.au/solid-stat...ching/p/SY4086

Do it right

The SSR for pwm control was a good suggestion, even the haltech manual talks about controlling the fuel pump speed. Seems like its a done thing these days for setups with high flow pumps to reduce heating of the fuel..

I'm not sure what frequency is reasonable for it though. I've tried it at 200hz, might be better off to go higher for the pump's sake, but don't know what the safe limits of the SSR would be.

[trdee]

I know this isnt a very "scientific" answer, but I and a bunch of other friends have found that the walbro 255 gets hot and loses pressure on long runs. This has happened across multiple cars with multiple pumps, so it isnt an isolated incident

My recommendation would be to piss off the whinebro and upgrade to a walbro 460. It is much quieter, flows a lot more, and seems to be far more stable in terms of maintaining pressure