PERSISTENT LAG - POSSIBLE FUEL PROBLEM

[GAJ1]

Hi All
After running the Compact for just over a year now we still have this intermitent but persisted problem of power loss out of some corners. It's like fuel pressure loss. Now i know about adding an additional tank with another pump in it but it means fitting in the floor and firewalling it. Any other suggestions or any ideas about fitting, tank size etc. All new to me so it's a bit of a blur. I don't really want to be ripping out the standard tank if i can help it.
Phil is leaning toward a 6 pot motor so i guess this would become more prevelant feeding two more cylinders.

[roadrally_nova]

let me guess right handers your getting fuel surge mate run half a tank you wont get the problem.
or look at diashags thread and put a swirl pot in

[GAJ1]

Thanks. Thought i read something like that on here before but had a scoot through the threads and found nothing.

[bruvs1]

i've heard of people fitting pumps in both sides as a fix and generally running more fuel. fit a swirl pot under the engine bay??

[GAJ1]

Thanks for the replies. Will look at this after sourcing a new exhaust manifold

[avtovaz]

bolocks, i forgot to sort the manifold otu with mark!


why are you getting all these weird problems with your car???


My car is mint and isnt far off yours in spec...


You need to come for the manifold and talk i think...





OR, ill come up to yours and look?

[GAJ1]

I have managed to source a manifold now Avto so no worries. I've heard something about the transfer pipe or something getting knackered / blocked which can cause issues. Perhaps the twin pump set up might work.

[avtovaz]

the tank is in two halfs as you know, and im not usre exactly how but it sucks the fuel out of the sidfe with out the pump and fires it into the other side. The nozzle can get blocked from what i hear, so try taking the top off the tank and see what you can clean. Its dead easy to get to...


my catr will drive fine on auto solo or charity days with next to nothing in the tank.


Dont overcomplicate things mate!

[Daishag]

RIGHT i can help here !!!!! The tank transfer system works like this as i did a bit of diy homework into this with a spare tank to find out how the system works before i fitted a Swirl pot and high pressure pump outisde the tank to find out if i actually had to do it !!!!!

The pump within the BMW tank picks up from the O/S which happens to be the side the tank is filled from !!!!!! when the engine is started the pump draws from the O/S sends fuel to the engine and then un-wanted / un-used fuel returns into the N/S !!!!!

This is where it gets interesting when you remove the N/S cap the return pipe is like a stack pipe returning to the bottom of the tank where it takes a 90 degree turn and connects to a internal link pipe that flows over to the O/S of the tank internally etc.

On this 90 degree bend there is a small take off with a one way valve within it so when the engine is started and starts to return fuel to the O/S VIA the n/s stack pipe it then syphons fuel through the one way valve within the take off in the 90 degree bend so it transfers fuel from the N/S of the tank to the O/S of the tank !!!!!!

Problem is the way i think of it is usually yer on the fuelling pretty hard ie flat out just before the bend then you let off and enter the bend and nail it again and depending on the direction yer travelling there isn't enough syphoning effect due to the "flat out accelration ie using the fuel in the engine and not returning it to the tank to create the syphon effect" prior to the entry into the corner to supply sufficent fuel over to the O/S tank thus creating a loss of fuel pressure due to a lack of fuel in the O/S of the tank half way through the corner

Im not sure if that makes sense to everyone but once you strip a tank and then connect a pump in line with the tank and see how it works it will do !!!!!

Cheers Dave aka Daishag Rallying 07805835655

[GAJ1]

So you reckon two pumps, one in each side will compensate for the return fuel loss (syphoning effect)or would you think a small pump drawing fuel from the return side to the feed side might help bypassing this pick up pipe?