Overfuelling/poor performance efi 88 RRC

[r0880]

Hi just wanting any confirmation on my 88 RRC auto 3.5 efi.

Basically its slow. Also blows some fuel smoke (and a litte tired smoke).

It floods when the cold cycle injector is connected, and sometimes when its not as well.

Checked plugs, not too bad (newish, colour indicated running a little bit rich, but not horribly black).

Leads also look newish (assume prev owner tried to solve this).

Its very slow in the low rev range (1500-3000) but get above that and it goes alright.

When free reving its kinda misses and carries on about that rev range also.

Thinking injectors are causing dramas, dribbling down low. Also getting scary fuel consumption around town varying between 20-30L 100km. Its the 30 side I'm concerned about. I don't out foot down much and don't get out of 3rd in town (to try and save fuel)...

Do the ECU in these old buses give dramas causing similar results?

Cheers for any ideas.

[RangingRover]

It floods when the cold cycle injector is connected,

Pretty common (on any of the old L-jet systems), leave it disconnected. Really not needed for Australian climate.

As far as the rest goes:
Sounds to me like the air flow meter needs a bit of a tweak. Remove the plastic cover, and hold the revs at the range its giving issues, then move the little needle (GENTLY) up and down the tracks a bit (I'd be guessing it needs to go back in the direction of the flap shutting a bit, to decrease fueling). You should find it picks up and runs a bit better when moved in one direction or another, in which case you need to set it up to run in that range. There is a spring which has one end clipped into a gear (you'll see once the cover is off what I mean). Mark with tooth the end of the spring is sitting in (so you can put it back there if you don't like it!) then move it around one tooth in the appropriate direction, then try revving it.

If it seems okay, go for a drive and see how it goes, and LISTEN CAREFULLY for pinging at the top end. The adjustment on these air flow metres adjusts the whole rev range by the same amount, but the actual fueling curve stays the same. Which is part of the reason a flapper system doesn't work too well with a 4.6 - set it up properly for high revs, it will flood at idle, set it up for low revs, and it leans out over 3500. Set it up right at about 2500 - 3000 revs, and its a bit rich down low, and a bit lean up high, but works ok.

But a final observation, an auto 3.5 with a flapper efi system is never going to be described as 'fast'. As far as fuel economy goes, in my manual car when it was a 7 cylinder 3.5 on 32s got down to 14l/100km on the highway, and sat around 20-22l/100km in the city, with me thrashing it. An auto may well use more though, others might have more comments.

[davew]

A common cause of this kind of problem is the fuel return pipe collapsing internally (the flexible sections) this restricts the return and increases the pressure in the fuel rail because the regulator can't do it's job properly. They usually run fine at high revs because you are burning the fuel fast enough not to notice but can be a real problem at low revs.

Disconnect the return pipe at the back of the engine and take a look, maybe try blowing down it and see if it's blocked/restricted. on a standard setup the flexi hose will be used at the engine and the fuel tank ends with steel pipe in between. In the UK they get replaced with flexi all the way as the steel pipes rot through in a few years.

[r0880]

Thanks for ideas, will check them out on weekend.