(G) Turbo woes

Ok, dont worry, its nothing really serious but its there and its more of a pain in the arse more then anything although ive learnt to drive around it so it doesnt happen anymore heh but i still want it fixed

basicly,

the engine cuts out if you quickly let off the throttle when on boost. It doesnt completly die at first but will drop the revs as normal but instead of stopping at 1000rpm and idling normaly it will just cut out.. starts perfect again once its cutout.

Ive at first I thought it was just random but ive worked out that it will only cut out if you come off the throttle when you have been using boost. can just be a tiny bit of boost (as in a slight over rev when moving in traffic) or a bit lot of boost (as in 0.7 bar at 120mph)..

If you dont go on boost then the car drops and idles normaly and is fine.

I dont know if its anything to do with it but I know the car is overfueling as it was setup and tunned to run 1 bar but has now been returned to standard boost. Would that possibly cause the cutting out?

Apart from this, the car drives, boosts and revs perfectly so I doubt its a boost leak etc as the car would suffer elseware

Anyone any ideas of what I can check as im lost Dunc suggested the idle sensor thing but i cant see why a faulty one of those would cause it to cut out on boost but be fine off boost...

help

Interesting one Bushboy,
I'm at work so this is just a quick reply

Sounds like fuel cutoff coming into effect (as it should) and then fuel not being restored correctly for engine idle. Suggest you check throttle linkage adjustment and throttle position switch (needs to be enough slack to ensure the switch clicks reliably when throttle closed). Could be that the residual boost holds the throttle open just enough to not click the switch. Also the switch itself is not immune to failure... so check it with a multimeter for a few dozen clicks.

-Alex

cheersmate,

Ive checked that and it does definatly click.. i might loosen the cable slightly to allow it to press right on it but it definatly presses it everytime.

as you say though, the switch may have failed but then I would expect the cutout to either be random or all the time... it is only when you rev enough to get the turbo going.

also, you can stop it from cutting out by just giving it a little on the throttle to get the fuel going again, and if it does cut out (too busy braking to press the throttle) then you start it again by just bringing the clutch up (jump start) so the fuel must be there... maybe it is a faulty idle switchy thing.. but i just dont see why it only affects it on boost.

Ive just checked and theres no way it cant click in.. ive loosened the throttle cable slightly anyway but the spring forces it back everytime beyond where it clicks in.

Oh god!

i can see this being sold like the car with the speedo problem

To be honest, my turbo does something broadly similar, except that mine will cut out when returning to idle with the engine cold and not having 'boosted'. Basically, after decelerating and when putting the foot on the clutch, the tachometer needle literally bounces off the bottom stop, presumably because the engine has no fuel to run on (briefly).

This is probably why the idle speed was jacked up a bit (to 1000RPM) when I bought the car. I drive it so little, I'm not really concerned. It's worth it to have it idling nicely at 900RPM when warmed up.

I think that there is a delicate interplay between the throttle plate opening base setting and the idle bypass speed screw. I suspect that if I increase the throttle plate opening slightly and turn the speed screw down, I might solve my problem. Dunno about yours?

-Alex

doh well ive just been playin around a bit.. decided to disconnect the idle sensor thing whilst the car was running... no difference
... was expecting the car to stall at idle as there is nothing telling it to idle right?

I dont know But surely I should notice a difference when disconnecting the idle sensor? Maybe this proves that it is broken as disconnecting it would make no difference if it was broken in the first place ... i think

makes sense i think.did you rev it after disconnecting the sensor?just to see what happened when it returned to idle

yeah.. it just did exacxtly what its always done.. be fine with a little rev and then either die or nearly die when you rev it enough to get the turbo going

So i suppose its the most likely suspect anyway! .. anyone know if you can still buy them new?

What is the idle sensor? Is that what the haynes manual refers to as the engine speed sensor on the flywheel? Can you check the resistance, haynes says 612 - 748 ohms for normal operation.

noo, the idle sensor is the bit that bolts onto the oposite side of the butterfly (in the throttle body) to which the throttle cable is attatched to.

Here :

If you're keen, you can take it apart and clean its contacts... though while trying, you will realise that it wasn't *intended* to come apart...

I wonder if disconnecting the throttle position switch (thepottleflump: note correct name ) would cause any difference? These computerised engines are quite clever in the case of sensor input failure. I suggest that if the switch never closed, then the fuel would not be cut when it should be during deceleration (as the ECU will not 'see' the closed throttle), and thus the fuel would not need to be restored at idle (and you have disguised your fault!)

But try another switch anyway, perhaps?
I'd like to fire up my Uno Turbo and try unplugging its switch. I'll do it tomorrow for you...

-Alex

good call alaex,i noticed my oil didnt looked like it had been changed in a while.
assumed it was the turbo's heat causing it.i'll follow your routine for the next change if i ever get it out of the car park

Do a wriggle test on the auxillaly air valve wires and check all boost pipes for leaks as my old UT did it after giving it some throttle (boost irrelevant)

turned out to be the dump valve T-piece connections to the inlet piping before the throttle butterfly

have take a number of bits off and put back on and still does it.. im gonna replace the idle sensor thing first and make sure its not that.. its defo broken as there would be a difference when disconnecting it (such as the car not being able to hold an idea after reving).

just need to find where to get one