Fuelling Issue...

[450Nick]

My car is doing something strange at the moment; if I jab the throttle open and shut very quickly it seems to stutter. The same happens when travelling in any gear at low revs, if I suddenly hit full throttle. I get a very short burst of lean running and maybe the odd snap from the exhaust - Implying lean running again, and then it runs fine and picks up as normal.

The ECU seems to be fine and I can't spot any obvious problems so I'm just wondering if I may have a problem with my fuel pressure regulator?

Its the original from the factory and I've never had any issues with it previously, but I can't think what else would cause such symptoms. Is there any way of testing its operation? Or could it be something else? The pump is a brand new Bosch '044' high flow type so I wouldn't think that this is having any problems and the filter was changed a few months back so there shouldn't be any issues there.

[spend]

Aggressive overrun in your ECU (emerald IIRC?)?

[Pupp]

Is it doing somethng new/different or is it just that you've not noticed it before? If the latter, there is a an accel enrichment map that can be tweaked (FI equivalent of a carb accelerator pump)

[450Nick]

Hi Dave, yes its an Emerald... What do you mean when you say that? It does it on all 3 maps (I have one full fuel cut, one noisy across the whole rev range and one only at the top on the overrun). The agressive nature is gained by retarding the ignition and giving very little fuel on zero throttle. The rest of the map is unaffected so shouldn't make a difference?

Yes I thought about the accel fuel map, but this hasn't been modified since it ran smoothly so playing with this may just mask the problem?

Edit: Sorry yes it is a new thing, first noticed it just before xmas but just narrowed it down to rapid throttle movement.

Edited by 450Nick on Thursday 1st January 14:52

[spend]

I was under the impression that leaning out (and ign) for cackling was floating all your boats I was just suggesting re-visiting that area to ensure you haven't gone too far for these low rpm situations. Not knowing (or inclined) the Emerald s/w I cant really help any further

[450Nick]

No worries, thanks anyway!

I just don't think it could be the overrun fueling as that area is only the very top line of the fuel map on zero throttle, the problem occurs on a different area of the map where nothing has changed since it was running fine. This makes me think that its not the ECU, but the actual delivery of fuel when the taps are rapidly opened. Like the fuel pressure is dropping briefly after going from very low to high fuel demand.

[spend]

450Nick said:

No worries, thanks anyway!

I just don't think it could be the overrun fueling as that area is only the very top line of the fuel map on zero throttle, the problem occurs on a different area of the map where nothing has changed since it was running fine. This makes me think that its not the ECU, but the actual delivery of fuel when the taps are rapidly opened. Like the fuel pressure is dropping briefly after going from very low to high fuel demand.

Do you still have the vac to the fuel pressure reg with the SC? Stick a pressure gauge on if you can simulate the problem whilst you look at the gauge?

[GreenV8S]

Sounds as if you may have too much or too little transient enrichment. I had a similar problem with my MS setup due to my unusual dual fuelling system which lead to massive overfueling when I opened the throttle. Symptoms were that the engine would hesitate if I open the throttle at the wrong speed. By playing with the acceleration settings I found that it got worse when I increased the transient enrichment settings and reducing them improved things, so the solution was pretty obvious.