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Sept 21, 2017 10:01:12 GMT
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Does anyone have any knowledge of how to use the Link Xtreme ECU outputs to control fuel pump speed. I have two lift pumps two FIP's which will be working to about 80% max when on full boost and high revs. Under normal, usual running they flow far too much fuel which is flowed straight back to the tanks.
As the pump are sighted in the tanks and the fuel is flowing at a rate of 11 ltr/min, the fuel can get a bit warm. Plus the pump are working at max chat when they don't need to. So to reduce the pumps work and fuel flow i need to use a method to slow them down, PWM from the ECU. I know there's the Aeromotive one's available but at a cost and they aren't that good. I know one of two car companies make them but I have no idea which can be made to work.
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“It Doesn’t Feel Pity, Or Remorse, Or Fear, And It Absolutely Will Not Stop, Ever, Until You Are Dead!”
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Phil H
Posted a lot
Posts: 1,448
Club RR Member Number: 133
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Link ECU Fuel Pump Speed ControlPhil H
@philhoward
Club Retro Rides Member 133
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Sept 28, 2017 8:00:13 GMT
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Pumps are designed to run flat out all the time but I see where you are going with this.
Wouldn't a fuel cooler be better and simpler? You could probably use an aircon condenser as they tend to come with about the right size tails on them.
Jaguar used the aircon to keep the fuel cool on the XJ-S but that might be a bit OTT!
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Sept 28, 2017 11:27:46 GMT
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AS far as i can tell its possible with the ECU. I've ordered a DC Solid State Relay (SSR) which is fine with PMW and a decent fuel pressure sender. The ECU will modulate the PW to the SSR and that in turn power both fuel pumps. To keep the Fuel pressure at 43 PSI the conditions set on the ECU will be power on until fuel reaches 42.9 psi, or when MAP is over 100 kpa or revs are above 5000 rpm. I might change one of them to fuel injection time over 6ms or something. The Pumps will run full with what seems like a lower voltage.
This will will lower the fuel temp by
a) Not sending so much fuel through the system as hopefully no fuel will be returned by the regulator
b) Not working the pump so hard.
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“It Doesn’t Feel Pity, Or Remorse, Or Fear, And It Absolutely Will Not Stop, Ever, Until You Are Dead!”
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Phil H
Posted a lot
Posts: 1,448
Club RR Member Number: 133
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Link ECU Fuel Pump Speed ControlPhil H
@philhoward
Club Retro Rides Member 133
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Sept 28, 2017 12:31:52 GMT
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Sounds like the feature is to mimic those OEM ECUs that don't have a pressure regulator fitted to the rail if it takes a pressure sensor then. I suspect you'll need a little going through the regulator but the way you describe should work fine. You'll probably need this to prevent the fuel getting too hot in the rail when you get heat soak at idle but I'm sure a bit of tweaking will get it right?
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Sept 28, 2017 20:10:12 GMT
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As with everything there will be a lot of test and adjust.
The system could work just off of one pump but at high revs and a lot of boost the pumps flow would be nearly 100% used (1050cc injectors x 8, 8000 rpm @ 2 bar boost).
I wasn't sure if there pressure of the fuel starts to slowly drop as you get to the higher % of the pumps flow limits, or the pressure remains constant until you use 100% of the fuel flow and it drops to 0.
Neither sounds too good for the engine so i went for two pump system.
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“It Doesn’t Feel Pity, Or Remorse, Or Fear, And It Absolutely Will Not Stop, Ever, Until You Are Dead!”
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Phil H
Posted a lot
Posts: 1,448
Club RR Member Number: 133
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Link ECU Fuel Pump Speed ControlPhil H
@philhoward
Club Retro Rides Member 133
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Sept 29, 2017 10:34:39 GMT
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Don't forget that rail pressure should rise with boost pressure otherwise the pressure across the injectors drops (flow and pressure being a reasonably direct correlation) - likewise the rail pressure (normally) drops when the manifold is under vaccuum so it will only be 3 bar at a manifold pressure of (effective) zero. What you should be looking for is for the rail pressure to be manifold pressure + 3 bar + a bit of a safety offset (to have some return to tank) - but something tells me that the PWM % to flow rate ratio won't be a linear one (i.e. 50% PWM won't be 50% flow) as I don't believe they are positive displacement pumps (and even they won't be 1:1 due to losses). By the sounds of it, somewhere between 30% and 50% PWM off boost would work to reduce the load/heat, then let the pumps run at 100% when on boost as you don't want to risk the pumps being a bit slow to pick up when the boost comes in (as there will be a time delay as they're a mechanical device at the end of the day).
When you hit the max duty of the pump the relative rail pressure will start to drop off as it simply can't maintain it - not good when you're running at 2 bar of boost! It doesn't immediately drop to 0, but will tail off gradually. Probably more dangerous as you'll end up in lean mixture territory rather than a fuel cut (limiter). I'd go with the same rule of thumb for the pumps as injectors - if you're over about 85% then it needs addressing which sounds like what you've done anyway.
Do you have a wideband Lambda sensor - and is the ECU clever enough to activate shutdown/cutoff if it sees too low (high) an AFR when on boost?
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froggy
Posted a lot
Posts: 1,099
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Sept 29, 2017 19:47:36 GMT
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No need for any pump control , you will need to make sure the relays and wiring is well up to the max current draw at full load though . Ran twin pumps for years with no control .
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Sept 30, 2017 12:54:52 GMT
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I was running one 40 amp relay but the terminals were getting a bit warm, so i went to two 40 amps relays. With the speed control I'm going to use one Solid State Relay its still 40 amp but more industrial so take the can current. The only reason for speed control is its going to be a road car so most of the time it will not be on boost unlike a drag/race car. The car also has an electric PAS pump that draws a fair amount of current. That to will be controlled by the ECU to limit power being drawn so it will be switched off over 30 mph or limited. The ecu has a lot of control and wide band Lambda. I think one of the problems i did have was the MAP sensor gave an incorrect readings. Looking at the data logger frame by frame it showed that the MAP went high, over 100 Kpa (without boost)just for a 10th of a second . The injectors went to 6-8ms too much fuel and stalled the engine. So i got a Link 4 Bar MAP sensor which seem do have done the trick, easy to calibrate. It gave the exactly the same reading as the ECU's internal sensor.  |
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“It Doesn’t Feel Pity, Or Remorse, Or Fear, And It Absolutely Will Not Stop, Ever, Until You Are Dead!”
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