Running REALLY rich at idle.......sometimes!

[DD Phil]

Any ideas?

Sure the poor old girl has a big front mount and a GT30 on her with standard ECU, but sometimes she idles fine (if a little high, 1200 or so).

The rest the time she runs rich as, belching black smoke and chugging around at 700rpm or so. It doesn't seem to matter if the air-con is on or off either.

I can't do the intake and computer for about two months until my other car arrives, so I need some ideas to tide her over.

Thanks,

Phil

[MrBishi]

Does it otherwise drive OK?

All I can suggest is checking all vacuum lines etc, TPS can be touchy, similiarly coolant sensor.

[TD05]

I'd go for the water temp sensor, too that connector always looked sus too me.

[boostbitch]

MAke sure the fuel return line is not blocked

[TD05]

MAke sure the fuel return line is not blocked

the fuel return line diverts fuel back to the tank when the manifold vacc is high, and the regulator is open, ie idle and part throttle, during WOT the fuel return line is in fact shut off by the fuel press regulator..

[CussCuss]

MAke sure the fuel return line is not blocked

the fuel return line diverts fuel back to the tank when the manifold vacc is high, and the regulator is open, ie idle and part throttle, during WOT the fuel return line is in fact shut off by the fuel press regulator..

i would hope not, this leaves no room for extra boost using the factory fuel pump.

[boostbitch]

exactly, how can the fuel return possibly be shut off during WOT that sounds ridiculous. Fuel return shutoff = possible leakage which = probable fire !! NOT GOOD

[SpidersWeb]

The fuel pressure is raised as manifold pressure is raised. This means the amount of fuel allowed to return back to the tank is reduced. I think this is what he means, its not 100% blocked but the FPR slowly blocks it to raise fuel pressure. If you had a higher pressure fuel pump, it'd do so at a lesser rate (as it'd be able to return more fuel while maintaining the correct fuel pressure).

[Chris 83JA]

Do you have the factory boost guage working? My car had a dodgy map sensor, something wrong with the electronics I think, which meant all of a sudden it read about .5-1bar too high, so at idle it would think it was running almost .5 bar. When this happpened, the car idled lower, rougher and with a fair bit of black smoke, like you're describing

I messed around with the map sensor and other vacuum lines a bit, but eventually decided mpi was the way to go

[TD05]

exactly, how can the fuel return possibly be shut off during WOT that sounds ridiculous. Fuel return shutoff = possible leakage which = probable fire !! NOT GOOD

at WOT the injectors are IMO working pretty close to their rated flow (i,e %80 duty cycle) so I guess fuel pressure would remain pretty constant, there wouldn't be much fuel at the regulator to go back to the fuel tank anyway, you'll find that if the TBI leaks fuell it'll be doing so at idle or after a hard run followed by sudden closing of the throttle.