Stalling when cold
- Thread starter 944 LIL
- Start date
peanut
Active member
sorry to hear that Colin . Sounds like a nightmare .
I would be looking at the AFM (Air Flow Meter) as a starting point. or possibly the FPR (fuel pressure regulator)
The AFM is basically a variable potentiometer ( think vloume control) which is attached to a flap in the air inlet flow.
Over time the wiper arm which moves across an electrical strip wears grooves in the strip thereby reducing electrical conductivity.
The voltage change fed from this is fed to the car's DME computer
Clarkes garage site describes how you can shorten the wiper arm to contact a fresh bit of the electrical conducting strip .
Otherwise it could be the flap sticking when cold ? Look for wear marks in the housing indicating the flap is touching the inlet housing
Or the FPR . you'l need to borrow and attach a fuel pressure meter to measure the pressure in the fuel rail when ignition off and with engine off . Again the testing proceedure and fuel pressures are in the Clarkes article.
I would be looking at the AFM (Air Flow Meter) as a starting point. or possibly the FPR (fuel pressure regulator)
The AFM is basically a variable potentiometer ( think vloume control) which is attached to a flap in the air inlet flow.
Over time the wiper arm which moves across an electrical strip wears grooves in the strip thereby reducing electrical conductivity.
The voltage change fed from this is fed to the car's DME computer
Clarkes garage site describes how you can shorten the wiper arm to contact a fresh bit of the electrical conducting strip .
Otherwise it could be the flap sticking when cold ? Look for wear marks in the housing indicating the flap is touching the inlet housing
Or the FPR . you'l need to borrow and attach a fuel pressure meter to measure the pressure in the fuel rail when ignition off and with engine off . Again the testing proceedure and fuel pressures are in the Clarkes article.
peanut
Active member
unfortunately you can't do that Tom or you'll lift the throttle position switch off the rest position on the cam and screw up the idle . DME won't know the throttle is at idle.
Just looked on the Clarkes site and the troubleshooting guide suggests trying disconecting the 02 sensor . It only operates at low revs and at higher revs doesn't effect the way the car runs. If it cures the cutout problem you've found the culpret.
You can adjust the idle on the lux, one way is to move the throttle stop screw which can if moved far enough bypass the idle throttle position switch (TPS). It doesn't matter if the idle TPS is bypassed, its only purpose is for an efficiency system where when the throttle is closed and revs are above 1500 the fuel is cut off. This is what causes some cars revs to drop below idle after throttle is shut off when the car is out of gear. Imo doing so also makes the engine much smoother as the revs don't drop so quick, a downside to that is a small decrease in engine breaking.
The other way is to use the idle bypass screw, this is the textbook way to do it and will not effect the idle TPS. Remember to do all idle adjustments with a warmed up engine and the idle stabilisation valve disconnected.
Sounds like its not an idle issue anyhow. When does the engine stall, is it when under load or when the engine drops back to idle speeds.
The other way is to use the idle bypass screw, this is the textbook way to do it and will not effect the idle TPS. Remember to do all idle adjustments with a warmed up engine and the idle stabilisation valve disconnected.
Sounds like its not an idle issue anyhow. When does the engine stall, is it when under load or when the engine drops back to idle speeds.
peanut
Active member
intermitant problems like this are a license to print money with most garages.
The most common cause of this is apparently down to an over-pressured fuel rail caused by the FPR fuel pressure regulator failing in the closed position. This causes excess pressure on the injectors which is read by the injector controller which then shuts down the injectors.
An easy test to check this is to start the car with one injector electrical socket disconected. The car will start and run on 3x cylinders allbeit a little lumpy. Because one injector is not working fuel pressure is reduced and the controller doesn't shut the rest of the injectors down.
Don't let him change the fuel pump or filter before checking the fuel rail pressure first. Also he can check the flow rate easily .
Undo the fuel rail bleed nut (don't lose the ball bearing) attach a piece of garden hose run it into a largish container like a 2xlt water bottle . Remove the DME relay and stick a bit of wire between the 30 and 87b sockets. (its marked under the relay) switch the ignition on for 30 seconds and measure how much petrol the pump has flowed. Should be approx 850ml minimum although my S2 pumps that much in 15 seconds.
Two simple tests you can do yourself to prove the pump and filter are ok.
oh and did anyone mention the 02 sensor ? only operates at low revs so if you disconnect it and the idle stabilisers you know the culpret,
The most common cause of this is apparently down to an over-pressured fuel rail caused by the FPR fuel pressure regulator failing in the closed position. This causes excess pressure on the injectors which is read by the injector controller which then shuts down the injectors.
An easy test to check this is to start the car with one injector electrical socket disconected. The car will start and run on 3x cylinders allbeit a little lumpy. Because one injector is not working fuel pressure is reduced and the controller doesn't shut the rest of the injectors down.
Don't let him change the fuel pump or filter before checking the fuel rail pressure first. Also he can check the flow rate easily .
Undo the fuel rail bleed nut (don't lose the ball bearing) attach a piece of garden hose run it into a largish container like a 2xlt water bottle . Remove the DME relay and stick a bit of wire between the 30 and 87b sockets. (its marked under the relay) switch the ignition on for 30 seconds and measure how much petrol the pump has flowed. Should be approx 850ml minimum although my S2 pumps that much in 15 seconds.
Two simple tests you can do yourself to prove the pump and filter are ok.
oh and did anyone mention the 02 sensor ? only operates at low revs so if you disconnect it and the idle stabilisers you know the culpret,
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