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Cold Start spray fixed it . How ?
Three mornings last week my Punto 60 wouldn't start from cold and each time a blast from Holts Cold Start into the throttle body got it to fire up. The engine ran really rough for a few minutes after that and then it was fine.
Anyone got any idea as to whats going wrong and why Cold Start fixes it. ?
The AA man reckoned there was a faulty temperature sensor but how does Cold Start get around this ?
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If your "cold start" is the stuff for getting knackered old diesels going it's ether, which is highly inflammable.
You squirt this stuff down the throttle body, your sparks light this stuff (and any petrol there too), and the engine speeds up faster than cranking, then the slightly weak (for starting) mixture your ECU is providing is enough to keep it going once the initial couple of turns has happened.
If the ECU knew how cold it was (according to ATS) it would give an appropriate mixture from its look-up table.
I wouldn't keep doing it if I was you: old diesels get addicted to it, and won't start without it[xx(]
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Did the AA man fix it?
John is right about the cold start, it makes it easier to start the engine, a bit like snorting nitro.
mmm... engines getting addicted:)
If you imagine that the engine is gradually getting harder to start and that one day it won't start...
Cold start makes it easier to start, so an engine that wouldn't start normally may start with cold start...
If you start using cold start before the engine gets so bad that it won't start without it you don't notice it passing that point...AND SO...the engine won't start without it's fix of cold start, hence it is now addicted. PHEW;)
85% of Marea HLX drivers have speeding tickets.... lol they'll have to catch me first.
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I can see how cold start gets the engine to fire but what puzzles me is why it continues to run once the initial blast has been burned.
I doubt the engine has warmed up enough to affect the temperature sensors so something else must be telling the ECU to send petrol to the injection system.
A couple of other questions for anyone who might know,
Does the fuel pump work independantly of the ECU ? Is it the case that once switched on petrol constantly cycles round and it is a valve controlled by the ECU that lets petrol into the injection system ?
How does the ECU know that the engine is running ? How can it know that the engine is running under its own power and not been turned by a starter motor ?
The AA got the car started but I have the problem of fixing it.
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How much fuel is injected depends on many things -
engine speed is one of them.
The ECU knows engine speed, as it has pickups (commonly on the flywheel).
Less than 200 rpm is cranking speed.
Tick-over is maybe 900rpm or more.
But that (tick-over) speed is decided by the ECU driving the stepper motor for air, and the injectors for fuel.
Once you're in that speed range the ECU will juggle to keep it going..
How the fuel pump is driven depends on the system:
AFAIK, on my Panda the Bosch unit gives the pump power for a few seconds to ensure there's fuel at the injector, then holds off until things start to happen.
But power to the pump is firmly under control of the ECU so it doesn't pump gallons of petrol out when the engine is stopped if you have an accident and burst a fuel line.
The injector head has a return pipe and the injector maintains a pressure of about 15 PSI (SPI) - the pump can deliver in excess of this..
Some MPI injector systems have a feed of manifold vacuum to the injector rail and the valve associated with it increases fuel pressure when the vacuum drops to give the acceleration shot needed to stop the "lean misfire" which would otherwise happen.
There are other ways of doing that sort of thing, though.
If you have CTS or ATS fault the voltage to, and across the sensor(s) should give you a clue.
AFAIK it will be 5 volts measuring the lead with it disconnected from the sensor.
Around 3 volts across the sensor cold.
Less than 1 volt hot.
Those are typical figures.
You want to get some from a Punto 60 that works OK, and compare.
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