Fuel pump.

[DarkMatter]

My car has a rather high Air/Fuel ratio above 3.5k rpm. It may be due to low fuel pressure (I haven't had it measured yet). As I had recently bought a 'new, only used once' fuel pump from the PH classifieds I decided to fit that.

Having depressurised the system I removed the hose from the outlet of the old (Lucas) pump - a little fuel drained out of the hose, but none from the pump.

I removed the inlet hose and fuel gushed out until I pushed the new (un-branded) pump onto the hose. Now when I removed the stopper/cap from the output end of the pump, ready to connect the hose, I found that fuel ran freely from the pump.

Just to make matters worse having connect the hose to the output end it actually broke off, so my £50 'new, only used once' un-branded pump was a waste of money and I have had to refit the old Lucas one.

My question is: Should fuel flow freely through the pump when it is powered off, or should fuel flow through it only when it is powered on (as was the case with my old Lucas one)??

[rev-erend]

More to the point - was it the pump at fault ?

The fuel filter is usually the culprit and is easily changed (New about £12 ~ 18).

[DarkMatter]

rev-erend said:

More to the point - was it the pump at fault ?

The fuel filter is usually the culprit and is easily changed (New about £12 ~ 18).

As yet I do not know whether the original Lucas pump is/was at fault - I really need to get a fuel pressure test done.

I renewed the fuel filter under 3k miles ago so wouldn't expect it to be at fault - other than getting blocked by crud from the fuel tank is there any other way a filter can fail?

[DarkMatter]

Quinny said:

I'm not absolutly sure on this, but I wouldn't expect gravity to be enough to allow fuel to gush through the pump... My expectation would be for fuel to flow from the outlet, the pump would need to be running

Thanks Quinny, I'd be inclined to agree that gravity should not be able to make fuel flow through a disconnected pump, but hard evidence from other owners will be welcomed.

[steve-V8s]

As the “new” pump now has a broken pipe. How about you test it away from the car with some water and a 12v supply and see if it actually pumps ? Not that it help the initial problem but it may reveal if the "new" pump works.

[clive f]

Quinny is right, as usual fuel won`t flow through the pump unless it is powered up, if you remove the bracket holding the pump to the chassis, and remove the outlet pipe from the front of the pump, you can then hold it over a bucket and get someone to quickly turn the ignition on and off to check that it works.

[ruaricoles]

If I remember right (when I broke the plastic end off my pump off too!) fuel can flow through it, so perhaps it depends on the pump position or something (?). A while back I found a small crack on the rubber hose by the pump and thought it a good idea to undo the pipe, chop an inch off the hose and put it back... but then in doing so the end of the pump pipe sheared off, leaving me with fuel running into my armpit as I stood under the car with my thumb over the hole waiting for someone else to wander past to rescue me....

Ruari

[blitzracing]

Bit that gets me is the fuel line pressure holds up on the TVR for a while even when the pump stops, so either it cant feed back through the pump when it stops or there is a valve somewhere. I think I have an identical setup on my Ginetta (but the pump is branded Bosch) and it drops its pressure as soon as you turn off the ignition. Ive had three pumps in the life of the car and two fuel pressure regulators and they all do the same, and its not a problem, just slightly confused.

[DarkMatter]

I performed a static gravity feed test with water on the broken 'new' pump (which I found IS a Bosch) and water flowed through fairly freely, but with the old/existing pump fuel does not flow through by gravity feed. The system does however maintain some pressure when the ignition is switched off.

I hope to get a proper fuel pressure test done later this week.