fuel pump losing the plot ??

[ed]

does anyone have a clue as to why a fuel pump (walbro 341) would *pogressively* drop pressure over a number of full noise dyno runs.

ie: warm engine, 9.5k full noise pull - perfect fuel trim, next pull, starts to lean out at 8k, next pull leans out at 7.5k, next pull 7k etc etc. the leaning out is due to a fuel pressure drop as read on the reg gauge.... then we take a break for 45mins, and return. first pull goes back to perfect, then subsequent pulls repeat the same pattern? as if the fuel pump was suffering from prolonged use and failing, but progressively, and in a way that it recovered as it 'cooled down' so to speak.

note: tank was pretty much 1/4 full only, so pump not bathed in fuel

possible causes of fuel pressure failure?

cheers
ed

[JustCallMeOrlando]

Pump pump pump pump pump That is all. I'd hazard a guess it's just getting hot and not pumping enough, and resting it allows it to cool.

[oldcorollas]

what is base fuel pressure?
it will be pumping the same amount of fuel at idle and full noise.. and since you don't have any vacuum, it will be pumping at about same pressure...
in which case, you should be able to measure a pressure loss with the pump just running with engine not on......

shouldn't be fuel heating from circulating as you are probably consuming most of it in the rails...

is there anything funny abotu the pickup? can you ry say.. leaving pump circulating for 10 mins and log fuel pressure (with 1/4 tank or less) then add more fuel and see if there is a difference?

[cambelt]

Is it a genuine walbro , maybe the chinaman is taking a rest when he gets hot .
Dave

[roadsailing]

Fuel was heating up? (shouldnt affect pressure reading)

FUel pump wiring was heating up causing increased resistance and greater voltage drop, leading to lower pressure? (maybe not, as the load on a fuel pump would probably be consistent regardless of what the engine is doing)

answer your PMs?

[thechuckster]

is connection on pump good? is inlet sock correct for that pump/flow (too small or soft and it'll compress and restrict fuel into pump, the otherwise, what JCMO said.

[ed]

genuine walbro

it could be a fuel starvation issue *i suppose* but the repeatability of the fuel pressure drop and the subsequent lean out is odd. that, plus the fact that once occuring, the lean point gets progressively earlier and earlier in the RPM band, not reflective of a standard 'emptying time' for the swirl pot in the tank or anything....

[oldcorollas]

size of cable for power to pump? iirc these things like 10-15amps at full noise.... needs big wires...
could even be relay heating up etc....put multimeter at pump...
if volts go down, your relay/wiring is shit.. if it stays at 14V, the pump is shit

edit: the bosch take less power for same output due to diameter apparently?

[ed]

im womderting if the low tank was just fuel surging

[Draven]

mine's an expert at that

I'd love to go your plan of surge tank in wheel well, but the whole legalities/practicalities thing gets in my way

[-GT-]

im womderting if the low tank was just fuel surging

How would letting it cool for 45mins get it back to perfect if you haven't filled the tank at the same time?

How's your surge set up? Is it an in tank baffle essentially? How does fuel get into the surge pickup point? If you've got a few holes around the base of a plate/baffle, is it possible these holes can't flow enough fuel to keep up with full noise? ie Is it just gravity and pressure head of tank level feeding your surge tank?

I guess that's one difficulty with that style, is making sure that by stopping fuel getting away from the pump too quickly, you also stop it getting TO the pump too quickly...

[clubagreenie]

I've found someone over at wetherill park who makes an off the shelf surge tank for the 80. Sits in the passenger side and wraps around the spare.

Buggered if I can remember their name at the moment though. Will look for them around work though. wait a moment...

http://www.dnamotorsport.com/Supra_J...erformance.htm

[Draven]

fark me dead that's useful!
+ rep.

I know what next pay is buying me

[SillyCarS]

yeh +rep indeed

that is fking neat as!

[Norbie]

Are you sure this is a fuel pump issue and not the regulator? I'm thinking the regulator is more likely to have this sort of effect on fuel pressure, as opposed to a dying fuel pump which just dies and doesn't "fix" itself.