Misfire on start-up from cold?

C

CBR_TONY

New Forum User
This is my first post so hello to everyone!

I have a swb TT auto which on start up from cold has a misfire from the right hand bank. The exhaust flutters and farts on the right side until the engine warms up and then the misfire disappears. The car then drives very smoothly and starts and runs fine from hot.

I have a new set of spark plugs to go in when I get a chance, do you think it could be a dodgy spark plug or something else, perhaps possibly a coil?

Any advice on possible causes would be much appreciated.

Tony
 
It could be lots of things but it’s worth remembering that the ECU runs a preset program during start and warm-up that ignores the O2 sensors. When hot the ECU will use O2 sensors to self compensate for slight differences between the left and right side hence smoother running when hot.
 
Thanks for the reply. It seems odd as it has only been like this for a few weeks, used to warm up evenly both banks, maybe it could be fuel related then until it warms up? Do you think it could be related to a faulty O2 sensor or do these not apply when cold?
 
O2 sensor do not work when cold so unlikely to be them. You need to get the ECU fault codes checked first
 
Yeah will have to get diagnostics carried out. In the meantime I disconnected each coil this morning just after starting it and found that one did not have any effect on the running of the engine, maybe worth starting here by changing it prior to putting in new plugs.
 
CBR_TONY said:
Yeah will have to get diagnostics carried out. In the meantime I disconnected each coil this morning just after starting it and found that one did not have any effect on the running of the engine, maybe worth starting here by changing it prior to putting in new plugs.
Click to expand...

To rule out the injector get a long screwdriver and stick the tip on the injector on the suspect Cylinder put the handle to your ear and you should hear a loud ticking. Try some of the other injectors so you know what it should sound like. If its ticking then chances are its a coil pack at fault.

If the Injector is firing swap a coil pack on the neighbouring cylinder and see if that cylinder goes down. If the problem remains on the first cylinder then it could be an ECU issue. The coilpacks/injectors are at the end of the ECU connector so if its not pushed fully home on the ECU it could give you some problems.
 
Also clean the connectors on the power transistor unit - high resistance here could also disrupt the signal to the coils. In extreme cases can lead to total spark failure...
 
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