half tank fuel surging issues.

[wfcruzr]

Hi ladies and gents, great site. I've got a 1998 1.3 manual festiva trio (B3) and when it gets to about a half tank of fuel it seems to surge and splutter like it's missing. I've done the following, new plugs, leads, coil, fuel pump and filter and fuel filter. I've removed the throttle body and cleaned it and I've also cleaned out the egr. When I did the fuel pump I also cleaned out the swirl pot intake pipe intank and also check the return fuel line and all was good. I also replaced the fuel line between the pump and the top of the fuel pump assembly. The fuel pump was a bosch pump, brand new. it idles perfect with no noises but when it gets to half a tank at about 350klms its a grumpy girl. any ideas anyone. Thanks in advance.

[WmWatt]

Idles perfectly when tank less than half full? Can you rev engine perfectly at idle with tank less than half full?

[Stanza]

Mine starts to do that at about 1/3 of a tank. Accelerate slowly, and it's happy. Punch it, and it surges and lurches all over the place. I always assumed it was from the fuel sloshing around with a flat bottomed tank.

[wfcruzr]

Yes it seems to idle fine.

[WmWatt]

It might help to inspect the fuel line to make sure it is not constricted, say by a rock hitting it. That could cause reduced flow at higher demand. Any chance the line is good but partially blocked?

[bravekozak]

Replace the rubber elbow where the hard fuel line meets the fuel filter.

[WmWatt]

I thought the rubber elbow was only on the carburetted 88's and 89's. They have mechanical pumps on the block which suck fuel out of the tank and the low pressure in the line can collapse the rubber when it gets old and weak. The EFI engines have the fuel pump in the tank so there is postive pressure in the line and the hose is not likey to collapse? When you wrote in the original post "1998" did you mean "1988"?

I have an '89 carburetted and replaced the rubber elbow with a longer loop of rubber line, eliminating the elbow.

[bravekozak]

Maybe the fuel control valve (pressure regulator)?

[FestYboy]

Bad seal at the output tip of the pump. When the seal gets unshrouded by the fuel, it starts to push air...

[wfcruzr]

Thanks guys, a new development now. Today on a full tank of fuel it started to splutter a bit then almost died then ran ok. mmmmm... The only similar thing now is not so much the fuel level but the distance travelled, about 100klm of sustained driving (100kph) then when we back off about 80kph zone it starts to play up. The other common factor is that it's been a hot day. Thinking now it may be a heat affected sensor?

[wfcruzr]

Thanks fest boy but I've changed the pump to a new one and put a new joiner hose on as well.

[FestYboy]

Thanks guys, a new development now. Today on a full tank of fuel it started to splutter a bit then almost died then ran ok. mmmmm... The only similar thing now is not so much the fuel level but the distance travelled, about 100klm of sustained driving (100kph) then when we back off about 80kph zone it starts to play up. The other common factor is that it's been a hot day. Thinking now it may be a heat affected sensor?

Ok new symptoms then rule out my previous surmise. I would move my attention to the FPR and rail pressure, and also the intake manifold ECT sensor output. Also potentially a sticking VAF door. The biggest issue is pinpointing it's behavior when it acts up. Being half a world away certainly doesn't help

[WmWatt]

Have you tried fuel injector cleaner?

[wfcruzr]

Ok so the festy is booked in to see my mechanic who works on my HSV so anything could happen here. APS service centre Frankston. They have ask me to right a summary of the things I've done and the issues so I've also written a daily journal as well in the hope that at the end of all this i can help others. Should I start a new thread or just continue with this one guys and gals?

[FestYboy]

A new thread to consolidate the info is never a bad thing.