944 non turbo 2.5

[p944]

Can anyone help with ideas?
My Car starts idles for a few seconds and then cuts out.
the only way i can get the car to start and idle is by introducing a 12v at the coolant temperature sensor, this will start and let the car idle but will not rev above 2500rpm, if you don't introduce a 12v at the sensor the car will not start at all.
Fuel pressure regulator, fuel pump, distributor cap, leads, crank sensors coolant sensor have all been replaced,
i had loads of running problems but when i changed the above it run beautifully, then i parked it up one day and now wont go.
any ideas would be welcomed

 

[Mike_Pollock]

Hi
There are 2 separate temp sensors, some cars have 1 two terminal and 1 single terminal, some have 2 two terminal ones. Which do you have?

 

[edh]

leaky intake pipes somewhere? - ISV perhaps?

 

[Elliot]

isv

 

[p944]

Hi,
water temp sensor has a two pin block connector (blue) and the sensor a couple of inches to the left (both in cylinder head) has a single wire on top.
Regards Lino

 

[p944]

Hi,
i took the manifold off, replaced the gaskets, made sure all the pipes were good, replaced all the jubilee clips, replaced the idle valve while the manifold was off, cleaned the earths but its exactly the same, fires up on the button runs for about 5 seconds and cuts out.
Regards Lino

 

[zcacogp]

Logic says it is starting up on some kind of start-up arrangement(/map/injector/something else) and fails when it moves to the regular arrangement.

However I don't know what is different when the car first starts up. Is there some kind of auto-enrichment system which comes into play? A cold-start injector? A different map in the ECU? A genie who pours an extra thimbleful of fuel into the inlet manifold when you first turn it on?

Swapping parts to see whether it improves the situation is a poor method of diagnosis, but I can understand why you have done what you have done. Someone will be along soon to give some better suggestions than mine.


Oli.

 

[p944]

Thanks for reply,
i didn't mind changing these parts apart from they are cheap enough my car is 30 years old and about time it had some new parts especially to the fuel side of things, taking the manifold off allowed me to get it powder coated, i know sad considering she doesn't go, but its giving me a chance to finally go through wiring modernize some fuses and re-tape the loom properly, the strange thing is that it drove perfect, i turned it off and next morning wouldn't start.
Best thing is that by the time i finish i will know her inside out, and she will be ultra reliable, cant wait to drive her through the country lanes again.

 

[944Turbo]

Has it got an immobiliser? I wonder if you are bypassing some of it with 12v on the coolant sensor, which then gets lost after cold start mode - purely a guess as I have no idea if this is possible!

 

[tref]

The usual first port of call for any starting problems is the DME relay. It kills power to the fuel pump unless it has a signal in... Now as I recall when started this is bypassed, and after turning the ignition key there is power to the fuel pump for a couple of seconds - you can hear it running if the pump is half-knackered. I would hazard to suggest that the live supply you are connecting to the temperature sensor (how on earth did you discover that worked??) is somehow back-feeding to allow the pump to run... Not a clue how, but there is no logic to an engine running with power connected to a temperature sensor... Is there?

 

[p944]

Hi,
it turned out to be the ecu, i replaced it and it drives superb again, basically the ecu sends an earth to the water temp sensor, but the moment it starts it switches to around 5 volts (pin13) and changes as the car warms up, that's why when i manually switched it to 12 volts it run.
My 944 does not have a diagnostic socket so i had to check everything with volt/ohms meter, and decided to change lot of the sensors along the way, definitely happy with this as now they are done, the fuel side was probably not necessary to change pump etc but the filter was so filthy im glad i replaced this side of things, as i said it really goes goes well so next is the bodywork, thanks to everyone that replied.