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Matt
Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 22261
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a seicento sporting 1.1 starts and runs fine until

Resolved Question:

I have a seicento sporting 1.1 starts and runs fine until warm and then will cut out starts again straight away but does it again after a mile or so have changed crank sensor ,coil packs ,temp sensor switch ,plugs and had ecu checked problem still here
Submitted: 2 months ago.
Category: Car
Expert:  Matt replied 2 months ago.

Hello

This sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.
1st thing to try is to remove the fuel filler cap and then flick the ignition on whilst listening for the brief ‘buzz’ of the pump

If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,
Ideally measure the pressure at the injector rail (should usually be around 3Bar / 45psi +) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

You can also get this issue with contaminated fuel , if there’s water or dirt in the tank then either the petrol floats on top of the water or the filter sock on the pump is choked up – so if the other things check out then I’d consider pulling out the fuel pump and cleaning the filter sock

And one other thing to try is to loosen off the fuel filler cap, as there’s a 1 way valve built into the cap to let air into the tank and so prevent a vacuum from being created as the fuel leaves the tank to the engine
If this helps then replace the cap with a new item

Customer: replied 2 months ago.
Car runs fine until warm every time so do not think its fuel related but will try filler cap thanks
Expert:  Matt replied 2 months ago.

Hello

if you're confident you still have fuel pressure when the issue occurs

then this could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;

Airflow meter
Crank position sensor
Cam position sensor
O2 sensor
Throttle position sensor

unplug each in turn and use some switch / contact cleaner spray on the pins to ensure its all grease / dirt free

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

as you've already replaced sensors I feel its very likely an issue with the wiring loom and checking it over as I've mentioned is the 1st check and if this shows nothing I'd then disconnect the ECU and the sensors and use a meter to continuity check between the two

Customer: replied 2 months ago.
Car has now fault code p170 fuel trim bank one.thanks
Expert:  Matt replied 2 months ago.

Hello

if you have a P170 code then its too lean and the next thing to check would be to check for exhaust leaks before the O2 sensor as if this has been experiencing an exhaust leak then it will have been running very rich as the sensor will see the extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.

this can lead to catalyst failure as the extra fuel can re-light inside and melt the catalyst

The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers

if you haven't already then measure the fuel pressure to confirm that is at least 3 bar

Customer: replied 2 months ago.
Thanks for infomation will check asap you have been a great help thanks again
Expert:  Matt replied 2 months ago.

glad to help

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