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Surge Tank Low Level Detection/monitoring

kitto

By kitto,
in Engines & Forced Induction

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rob82 Mentor

rob82

Posted
Posted

Pressure between lift pump and surge tank would be low - less than 3psi I would think. Depends on hose length and diameter.

I think you would be better off using a single fluid sensor/switch. We use a capacitance style switch that changes state if the fluid doesn't surround the sensor. Can't remember who makes it - some German company.

Also I wouldn't ever map effective fuel pump duty vs tps on a turocharged car especially on a non positive displacement pump. Really need to map pump duty vs manifold pressure.

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Duncan Grand Master

Duncan

Posted
Posted

I am not sure where the experience of empty surge tanks killing engines comes from...to me it sounds a like a bit of an internet myth.

I have run the race car out of fuel a twice during races- surge tank empties, car coughs in corner, driver backs off. I have also had a fuel pump fail (came loose in tank tearing wiring off after a rally crash). In 3 cases, even though it has happened to me at full throttle and very hot motor each time, it has not resulted in any damage.

The fact is, it is vey unlikely that a car will fire with insufficient fuel pressure. You need approx 7:1 to 20:1 for a cylinder to fire. If you drop to 50% or less of the expected pressure, you can almost guarantee a missfire, not a lean out. And even in a cylinder or 2 fires lean once or twice, there is no way it will keep firing at that level, it will almost instantly start missifirng.

I run Paul's Engine Monitor too, and that is defiantely your answer. Just set a warning on low fuel pressure. That way not matter whether it is the main pump, lift pump, main tank, surge tank or even regulator that fails, you will be warned.

Duncan Grand Master

Duncan

Posted
Posted

actually, on second thoughts I have run out of fuel 3 times. Happened at an enduro at Oran Park years ago too.

Same thing....it coughed coming off the bridge, I backed off and drove into the pits swearing.

No engine damage

kitto Mentor

kitto

Posted
  • Author
Posted

Pressure between lift pump and surge tank would be low - less than 3psi I would think. Depends on hose length and diameter.

I think you would be better off using a single fluid sensor/switch. We use a capacitance style switch that changes state if the fluid doesn't surround the sensor. Can't remember who makes it - some German company.

Also I wouldn't ever map effective fuel pump duty vs tps on a turocharged car especially on a non positive displacement pump. Really need to map pump duty vs manifold pressure.

Firstly, the fuel pump duty wont be based on TPS posistion. I should have furthered what i was trying to say. I'm using a fuel lab pump. It has a voltage input for speed control or you can use a PWM to control it. I'm using the voltage input to control it. Under 2.5V to the input, the pump runs low duty, above 2.5V the pump runs at full duty. I'm simply pulling the 0-5V off the TPS and feeding it into the signal input on the pump. So at around 40-50% TPS the pump will then change over to full duty.

Yes a capacitance sensor would be very good, however, seeing that my surge tank is already made, this would be hard to fit as i have no way of accessing the inside of the tank.

The length from the lift pump to the surge tank is about 1 metre of 5/16" fuel line with a Ryco fuel filter in this line.

I am not sure where the experience of empty surge tanks killing engines comes from...to me it sounds a like a bit of an internet myth.

I have run the race car out of fuel a twice during races- surge tank empties, car coughs in corner, driver backs off. I have also had a fuel pump fail (came loose in tank tearing wiring off after a rally crash). In 3 cases, even though it has happened to me at full throttle and very hot motor each time, it has not resulted in any damage.

The fact is, it is vey unlikely that a car will fire with insufficient fuel pressure. You need approx 7:1 to 20:1 for a cylinder to fire. If you drop to 50% or less of the expected pressure, you can almost guarantee a missfire, not a lean out. And even in a cylinder or 2 fires lean once or twice, there is no way it will keep firing at that level, it will almost instantly start missifirng.

I run Paul's Engine Monitor too, and that is defiantely your answer. Just set a warning on low fuel pressure. That way not matter whether it is the main pump, lift pump, main tank, surge tank or even regulator that fails, you will be warned.

Yes, theory would say the engine would just cut out when it runs out of fuel. Simon a friend of mine who had this issue said that his lift pump failed, BUT the two 044's he had created enough suction to actually draw fuel from the main tank into the surge tank and allow the engine to run. But surging and lean out occurred.

KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted

Put an fpr in the line just before the surge tank so only that part of the line will be pressurised (not the surge tank). Adapt an oil pressure warning light switch and T it in before the fpr. You can have a buzzer or light on your dash. When your tank is running low the buzzer will come on and off (as petrol surges away fom the pickup) and when its buzzing continuously you will know you are down to the 3L in your surge tank.

JonnoHR31 Grand Master

JonnoHR31

Posted
Posted

I am not sure where the experience of empty surge tanks killing engines comes from...to me it sounds a like a bit of an internet myth.

I have run the race car out of fuel a twice during races- surge tank empties, car coughs in corner, driver backs off. I have also had a fuel pump fail (came loose in tank tearing wiring off after a rally crash). In 3 cases, even though it has happened to me at full throttle and very hot motor each time, it has not resulted in any damage.

The fact is, it is vey unlikely that a car will fire with insufficient fuel pressure. You need approx 7:1 to 20:1 for a cylinder to fire. If you drop to 50% or less of the expected pressure, you can almost guarantee a missfire, not a lean out. And even in a cylinder or 2 fires lean once or twice, there is no way it will keep firing at that level, it will almost instantly start missifirng.

I run Paul's Engine Monitor too, and that is defiantely your answer. Just set a warning on low fuel pressure. That way not matter whether it is the main pump, lift pump, main tank, surge tank or even regulator that fails, you will be warned.

This, if your lift pump dies, as soon as you use up whats in the surge tank your engine will simply cough then die. Sure, it might run lean for a split second but no where near long enough to kill it. As for the main pump drawing fuel from the tank, thats simply not possible with a conventional surge tank setup (as in a recirculating setup, with an overflow back to the main tank) as even if they managed to create enough suction they'd simply suck air from the return, not fuel through the dead pump. The only time its possible for a lift pump to kill your motor is if it flows the exact amount needed to create a lean out without going lean enough to miss and even then you'd have to be on WOT for a long time to drain the surge tank whilst its still being partially refilled.

Simon-S14 Grand Master

Simon-S14

Posted
Posted

as kitto said... i melted 2 pistons as a result of leaning out with a dead pump... certainly didnt cough and die.. didnt even know it had happened. the two 044's continued to suck fuel thro the lift pump and full tank. all the signs of leaning out were there tho. engine ran hotter, overheating issues etc.

JonnoHR31 Grand Master

JonnoHR31

Posted
Posted

as kitto said... i melted 2 pistons as a result of leaning out with a dead pump... certainly didnt cough and die.. didnt even know it had happened. the two 044's continued to suck fuel thro the lift pump and full tank. all the signs of leaning out were there tho. engine ran hotter, overheating issues etc.

weird. how was the surge tank plumbed?

Dobz Experienced

Dobz

Posted
Posted

as kitto said... i melted 2 pistons as a result of leaning out with a dead pump... certainly didnt cough and die.. didnt even know it had happened. the two 044's continued to suck fuel thro the lift pump and full tank. all the signs of leaning out were there tho. engine ran hotter, overheating issues etc.

How full was your fuel tank when this happened?

Dobz Experienced

Dobz

Posted
Posted

about 3/4 full

The short fuel return tube that is in the tank may have been sucking a good amount of air bubbles in along with the fuel whan it surges around the tank, causing your 044's to cavitate and lose a lot of pressure.

That would have lead to a lean out condition for sure.

If the tank was a bit lower on fuel the suction would never have happened and the surge tank would have just run out of fuel.

kitto Mentor

kitto

Posted
  • Author
Posted

either way. the lift pump died and i had no way of knowing about it.

will be wiring a fuel pressure sensor into the reg and wiring into the haltech to monitor it in future.

Simon, do you believe that monitoring just the rail pressure is ok? Or should we also be trying to monitor how much fuel is in the surge tank and/or if the lift pump has failed?

kitto Mentor

kitto

Posted
  • Author
Posted

monitoring rail pressure is the best way, as it covers everything except injectors failing. a surge tank level monitor wont cover the main pump dying.

No it wont, but if you monitor both then you've got both avenues covered. I plan on having the Engine Monitior monitor fuel rail pressure vs boost pressure and i just thought it would be a good idea to keep an eye on the surge tank.

JonnoHR31 Grand Master

JonnoHR31

Posted
Posted (edited)

Pointless if you have a pressure monitor. If the intank does die your motors not going to instantly blow into oblivion the second fuel pressure drops 5psi. Even if you somehow managed to empty the surge tank at the same time as being on WOT at 7000rpm your pressure monitor will stop you well before you kill the motor.

Edit: Also, I'm not sure what happened in Simons case but i've had my intank stop pumping several times (due to blocked filters, bad wiring etc) and every time the tank simply empties and the car misses then dies, the first sign is actually the 044 cavitating, you can hear it even with the windows up and music playing. It'd be cool to have a level monitor for it but it's just not needed.

Edited by JonnoHR31

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