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Dodgy fuel pump?

Summer-Sickness

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hey guys ive read heaps of posts about people losing power then they take corners with a little bit of speed n at around 1/4 tank.

my car does this too but it also can struggle just to drive at around 1/4 full... sometimes even as high as 1/2 full... like ill be sittin at the lights n go to take off n it will cough n splutter a bit... what are the chances that the fuel pump isnt positioned properly?... is it hard to get to it? i dont know much bout that side of things at all. when ive got a full tank everything runs fine.

also its meant to have a 67L tank... then the cars at just under 1/4 tank n its coughing n spluttering i only get 40L in there... i havent got any noticable dents in the bottom of the fuel tank eithier.
 

feistl

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OK. Big Edit here.. Ive decided to post a few drawings created with paint :)
Yes, they are terrible but they should give you a rough idea.

Ok, Heres my masterpiece :embarrass

fuelpumpdk0.jpg


The biggest problem ive seen when changing the fuel pump (happened to me), is as you pull the sender unit out the return line hose comes off without you noticing. So when you put it back together you dont reconnect the hose.

If you look at the above drawing, ive tried to simplify the design of the fuel tank setup.

If the car is sitting stationary (lights, parked whatever) the fuel in the main tank and mini tank will equalize as there is holes in the bottom of the mini tank.

When your going around a corner, the fuel inside this minitank is trapped... and can only slosh to the side of the minitank.... So the fuel pickup line is always sucking in fuel.

If you didnt have this minitank, when you went around a corner (with >1/3 tank of fuel) the pickup would suck in air, kill the pump and stall the car.

Now, a fuel pump is either on, or off. So its either pumping 100% capacity or its switched off. Now most of the fuel that is pumped to the engine isnt used, and comes back down the return line into the fuel tank. When your using 100% throttle you'll be using all the fuel sent, but when your idling you might only use 5% or so.

Where people run into trouble is by forgetting to reconnect the return line... So rather than the unused fuel returning to the minitank, its pumped into the normal tank.

The problem with this is, the fuel pump can pump/move fuel faster than the small drain holes let it equalize back into the minitank.

So if you forget to reconnect this line (its a rubber fuel line, similar to the external (outside the tank itself) lines), the minitank is emptied, the pump cant suck in any fuel and the engine can die/run badly.

So if you have power issues/stalling/running badly when you drop below 1/2 a tank (obviously with a full tank the fuel spills over the top of the minitank) chances are its caused by the small return line.

Hopefully this all makes sense. It is a pain in the ass to reconnect it, as its very short and sort of needs to be connected inside the tank... (you cant pull the line out of the tank and connect it to the sender unit).

Good luck, Errol
 
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ephect

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that post sums it all up! top post
 

Summer-Sickness

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Hey mate,

Ill do my best to explain this but its kinda hard :p.

Ok, in the bottom of the tank there is a "mini-tank". Imagine a small ice cream container welded into the bottom. The fuel pump pickup is from inside this tank. Now there are a number of small holes in this minitank at the bottom which allows fuel in from the normal part of the tank.

So imagine the car parked... becuase of the holes in the minitank the fuel level will equalize between the minitank and the rest of the tank.

The reason for this is, when you go around a corner the fuel inside the minitank is caught... therefore the fuel pump always has fuel around it. If you didnt have this minitank the fuel would all move to one side and the fuel pump would suck in air.

I hope this makes sense.

Ok, there are 2 fuel lines in the system. The main line from the pump to the engine, and a return line. The pump always goes at 100%... the unused fuel simply comes back down the return line.

Now, the holes in the minitank are pretty small. They dont allow fuel to move very fast... (slower than the fuel pump itself). The return line from the engine bay attaches to a hose in the tank which goes into the mini-tank. So the fuel coming back from the engine lands ontop of the fuel pump.

Recently mine had come lose, meaning the return line was pumping back into the normal tank, not the minitank. The minitank is about 15-25cm high... So when you have a full tank of fuel the fuel flows over the top into the minitank. When it drops before 1/2, the fuel can only get into the minitank via the small holes...

So what this all means is... If your return line has come off/has a hole in it, the fuel has to go through the holes in the bottom of the minitank to get to the fuel pump. As the fuel pump is faster than these holes, it can pump the fuel out of the minitank, through the engine bay, down the return line and into the normal tank. So basically the pump can empty the minitank quicker than it can come back through the small holes.

So to fix this, you need to check that the return line is connected to the rubber line INSIDE the big tank. If this is split/come off, the pump will be emptying the minitank causing fuel issues below 1/2 a tank. (When the tank is full the fuel simply spills over the top edges, eg no problem).

So yeah, you'll ideally need to pull the tank out of the car, unscrew the sender unit and check the return line is connected to the rubber line that goes into the minitank.

I hope this makes sense...

Cheers


that makes perfect sense... thanks dude...
pretty big job to get the fuel tank out?
 

ephect

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nar fairly easy,

syphon the tank, place a jack under the tank, loosen 1 bolt and a nut holding the straps, then lower the jack, until u can get to the top of the tank and remove the 2 hoses from the top of the tank. undo i think 4 or 5 screws behind the drivers side rear wheel, holding a plate. undo one of the the clamps holding the filler hose onto the tank. remove the 2 hoses on the pump and unclip the wires. then drop the tank

install is the reverse
 

Summer-Sickness

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nar fairly easy,

syphon the tank, place a jack under the tank, loosen 1 bolt and a nut holding the straps, then lower the jack, until u can get to the top of the tank and remove the 2 hoses from the top of the tank. undo i think 4 or 5 screws behind the drivers side rear wheel, holding a plate. undo one of the the clamps holding the filler hose onto the tank. remove the 2 hoses on the pump and unclip the wires. then drop the tank

install is the reverse

right, ill give it a show over the next few weeks n let everyone know how i go... and in regards to this hose that came loose, will it be pretty obvious when i get the tank out?
 

ephect

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Sorry dude, forgot the important part, actually fixing your problem!

once the tank is out, remove the 5 bolts holding the sender and then slowly pull the sender out, u'll notice on the left hand side a black plastic noozle it should ahve a hose on it and clamped on. This is the hose that may not be connected. if u dont see a rubber hose on the end, grab a LED torch and shine it in the tank, u should be able to see the hose in there, long nose pliers to reach in and then connect it up.
if you cant find the hose, u need to remove the sender unit. notice the notch cut out on the very bottom of the sender hole in the tank, that is for the float rod. rotate the sender until the float rod rests in that notch, then remove. then u can see inside the tank to locate the hose.

good luck, i think thats all you'll need to know to get the job done, i've given you more info coz u may not need to remove the sender, but just in case.

cheers
 
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