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Matt
Matt, Mechanical Engineer
Category: UK Car
Satisfied Customers: 20599
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a Citroen C3 2003 reporting a P0300 fault code,

Customer Question

Hi
I have a Citroen C3 2003 reporting a P0300 fault code, flashing engine warning light, clearly misfiring but why... I'm thinking faulty Coil Pack???
Submitted: 9 months ago.
Category: UK Car
Customer: replied 9 months ago.
I've attached more detail about the P0300 error.
Customer: replied 9 months ago.
Is there anyway to check or confirm it is the coil pack before spending money? Or should I be looking at something/somewhere else.
Expert:  Matt replied 9 months ago.

hello

a faulty coil pack is quite possible and you can confirm this

You can also try spraying some water on the coil pack with the engine running. It is possible the coil is faulty and causing the misfire. If you see sparks arcing with the water, then replace the coil.

I'd check the condition of the injector plugs / connections as this could be a lean misfire if an injector isn't firing properly - the best way to check this is with a 'noid' light

http://www.noidlight.com/

Then check all the connections to the engine sensors one at a time, remove each one and examine for signs of corrosion or damage and a squirt of contact cleaner ( not WD40) will also help.

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and leans the engine out causing rough running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas around each joint in turn. If the engine rev's up you've found your leak.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Customer: replied 9 months ago.
Thanks for the info. Much appreciated. Could you explain a little more about spraying water on the coil pack. It is single sealed plastic unit for all 4 cylinders so wouldn't expect it to spark. In that case I would only be spraying water on the electrics running on top of the coil pack.?The noidlight test, there is only a single plug on the coil pack. I don't understand how this test would help identify a fault on a particular injector.I've checked all connectors, removed the coil pack and re-connected everything but still the same issue. All connectors seem ok, no sign of corrosion, no loose wires/connections. Everything looks in good condition. A new code has also popped up P0203 - misfire on cylinder 3. Should I just replace the spark plugs and coil pack?
Expert:  Matt replied 9 months ago.

hello

the spraying of water can expose where the insulation is broken down and the sealing is no longer perfect and you might otherwise not see it - so thats the reasoning there

the noid light is used on the back of each injector not the coil pack?

so its meant to check that the injector is firing as it should

and as you now have a misfire code then yes I'd replace the plugs 1st to see if that helps and check the resistance of the spark plug leads ( 13-15Kohm / metre) and replace if any doubt or high resistance .

Expert:  Matt replied 9 months ago.

Hi

do you still need help?

Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you

Customer: replied 9 months ago.
please. I was wondering about the cylinder order. With the bonnet up, looking down, is cylinder number 1 the closest to the air filter or furthest away from air filter? Changed the spark plugs - no joy. Coil Pack didn't spark/arc while spraying water on it. However the I have decided to replace the coil pack anyway.
Expert:  Matt replied 9 months ago.

Hello

cylinder 1 is the opposite end of the engine , so furthest away from the air filter

also I'd say to check over the engine earth connections , the large one leading from the battery negative post and down to the engine and then the smaller connections that run out of the engine bay wiring loom and are terminated onto the engine with small bolts and ring terminals

Expert:  Matt replied 9 months ago.

Hi

do you still need help?

Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you