serega

Potentially, does it have the ability to destroy the engine ?
I had it happen to me a couple of times and it was thought as a spark plug problem so i didnt think it was particularly damaging.

What would happen is under the acceleration with half a tank or less the car would jolt/hesitate quite badly at high revs in first 3 gears and it has now been 100% confirmed as a fuel surge as under acceleration the fuel moves to the back of the tank and the pump has nothing to suck . Now the question is - does the jolt/hesitation happen because the ecu reads lack of fuel in the mixture and cuts the boost or does the actual lack of petrol cause the jolt?

And what are the consequences of that for my engine ?

ex-webby

Can be fatal for the engine.

serega

Any technical explanation please?

mellinator

I have the exact same issue!!!!!!!

serega

Im actually speaking to a few guys on another subaru forum that have that issue and didnt know what to make of it first too. So i guess its pretty common..

serega

It has been concluded that fitting a new fuel screen actually solves the problem..However we cant seem to agree how damaging it is to the engine and why.

GC8

The damage comes from running lean: thats obvious surely? If the pumps sucks air whilst youre on boost then the lean mixture can detonate destroying your pistons or big ends. Fuel surge is remedied using a swirl pot.

Simon

Shark Man

The odd time on a fast bend or roundabout isn't going to kill it.

Doing it consistantly, such as on fast bends round a race track, time and time again isn't going to be very clever though.

So if its a particular bend it happens on regulary, the remedy is simple: back off the throttle!

...pslewis...

If no fuel reaches the cylinder then it's not running lean and it won't damage your engine ...... there is nothing to burn. As far as I know the ECU cuts the spark if no fuel in any case.

serega

So herein lies the argument. Is pslewis right, or is gc8 right. I had my bet on GC8's argument, but others seem to follow pslewes's logic :/

GC8

But you dont know much Pierre...

GC8

Lif isnt black and white and the petrol supply isnt 100% constant or 100% off. You only need a grey pressure drop to lean out the mixture... The effect is cumulative and as Ali says; itll be most pronounced when youre lapping a repetitive track.

...pslewis...

I know plenty.

I suspect that this fuel surge is an urban myth .... never hear about it except on here.

A spark sparking in a cylinder with no fuel will not detontate at all, obvious - so it will not be a lean/weak mixture - there is NO fuel!!

I think, but do not know, that the ECU will not spark in when there is no fuel present (I could be wrong on this) but I am NOT wrong on the above!

GC8

pslewis is 20,000-post troll, who was banned for posting just this sort of nonsense.

Back to you Pierre.

...pslewis...

As an additional thought ..... the fuel pump delivers more fuel than is needed - hence the pressure is regulated by a regulator ...... the surplus fuel being returned to the tank.

GC8

Thats correct, but when it sucks dry due to surge then the pressure drops and hence: the volume (because the injector is only a tap). If its a problem then you use a swirl pot, but its only a real issue for a tiny minority of drivers.

...pslewis...

Remind us all please which branch your degree in Engineering is in?

I am an Engineer of many years and know about Engineering principles .... you still disconnect the crank sensor after an Oil Change don't you? Despite the overwhelming evidence that it does more harm than good!

GC8

Explain doppler shift to me again Pierre.....

serega

So how dangerous is it for a forged engine GC8? And im taking the problems expected are the same as from any detonation ? Ie burned pistons ?

...pslewis...

You say "due to surge" ...... please explain how this 'surge' happens? I am genuinely interested in how this can happen.

Fuel pick up pipe not able to suck fuel?

...pslewis...

Very good ..... hats off on that one

...pslewis...

Having a forged engine (I presume you mean pistons?) in no way affects fuel delivery ........ the two are totally seperate.

GC8

Forged pistons a re little hardier arent they? You big end bearing will take a hell of a punishment if its constant. Fuel surge is only likely to be a problem when your fuel level is dropping and youre repeatedly going around a very sharp corner or series of corners.ie. not on the road. Foam in you tank will stop surge to some degree but if it doesnt have a sufficient benefit (and a specially fabricated baffled tank is beyond your budget) then Id look at fitting a swirl pot. In fact, Id expect every car that has a fabricated tank to have swirl pots.

serega

As i mention above, its happend a few times, i'd say around 20-30 over a period of 6 months before it got to me that its not spark plugs or coil packs that is causing the hesitation.

The surge that im experiencing when the car is at half a tank petrol or below is quite real. You go full throttle in first 3 gears and at 6500 or so rpm its a violent jolt/hesitation, like you hit a wall or somethig, followed by a bang from the exhaust..

serega

If the car is full on petrol it revs fine to 8,000 rpm.

serega

How much would a swirl pot install set me back ?

...pslewis...

I would suspect a boost cut-off rather than fuel surge. Try changing gear at 5000 RPM .......... peak power is NOT at 6500 RPM so you gain nothing in near redlining it.

serega

Pslewis, im driving a 2.3 with a garret gt30/40 turbo running 30 psi, and its been mapped by a person who knows his stuff and we set the rpm limit at 8000 for a reason.

...pslewis...

WHAT!

Contact API and get them ready for an engine rebuild ...... please treat the thing with a bit more respect - it's not clever and it's not big revving to 8000 RPM

...pslewis...

OK, I thought for a moment it was a standard car

You had me in shock ......

Carry on