Technical surging turbo

[peterfirecat]

Tried posting this a week or so ago but message never appeared :-(

I have a Mk1 Uno Turbo engine in my kit car. Car runs very well at idle and under medium accceleration.

Problem is when I floor it (and who wouldn't) - when the boost goes about about 0.4 bar, the engine seems to surge - accelerate, hesitate, accelerate etc.

Have had the air system to bits - can't find any leaks. Have replaced the plugs and tried another air flow meter (though it came from E-bay so could have also been faulty).

Anyone got any ideas where to look next??

 

[alexGS]

Presumably you've disconnected the pressure switch that is screwed into the left (gearbox) end of the cylindrical plenum chamber? The wires must be taped up - if they short, that cuts ignition. I think the switch is calibrated to close around 0.7 bar.

It sounds like a situation where the fuel pressure is insufficient to fuel correctly during that on-boost transition. Have you replaced the fuel filters? I think there are two - the canister with threaded fittings usually found in the engine bay (on the Uno Turbo) and the assembly mounted just ahead of the fuel tank which I've never taken apart. It has the pump and a pressure damper, and (I think) a pre-filter. People who have taken it apart report it being full of crud, which explains the odd groaning noises the pump sometimes makes.

Another suspect for a go-lean condition could be the fuel pressure regulator, which is that capsule-thing on the fuel rail in case you were wondering Again, I've never had to touch mine, so I'm not the best person to advise here. Just throwing out some ideas.

Might be worth scrutinising the plug leads/coil lead again? - compare resistances.

-Alex

 

[peterfirecat]

thanks for the ideas - does sounds like a fuel / mixture problem.

Vacuume connection to pressure regulator looks OK. Connectios to the pressure switch look fine.

Will strip filter / pump assembly at by the tank and see if I can find anything that shouldn't be in there. Would suspect this more if the car didn't idle or drive so well under gentle acceleration.

Wonder if it could be a problem with the air sensor in the ECU??