Cylinder 4 Misfire, Test Spark, Fuel and Compression

Bardd · 2025-10-16T11:05:16-0400

Hi,
I got a pretty nasty cylinder 4 misfire that resulted in a flashing engine management light, I have since replaced and checked the following,

4 x New Spark Plugs
1 x Second hand but newer coil pack that I know works
1 x Second hand fuel injector that works

Compression Test resulted in
Cyl 1 - ~175
Cyl 2 - ~175
Cyl 3 - ~175
Cyl 4 - ~175
These seemed a little too perfect, since its my first time doing a compression test I'm a bit wary I might have done that wrong somehow.
I get the following codes -
P0313 Misfire Detected with Low fuel
P0304 Cylinder 4 Misfire

I'm suspecting fuel pump or injector connector maybe but am stuck on where to look next, any help is appreciated.
Edit - This is a 2010 1.4L Petrol

TommyLT · 2025-10-16T17:18:34-0400

Hi it's possible you could have a defective compression tester sticking at 175 or leaking, did you do the test with wot-wide open throttle? If not, you could retest and should get slightly higher figures.

You can test the sparks like in the pic with a piece of copper wire to earth them, crank the engine on the key and check for sparks....100% sure then that the whole ignition system is good, sparks, coils, wiring, ecu. Unplug injectors when doing this test just to be on the safe side.

You can use noid lights to check the electrical side of the injectors. I'll pm a link to another injector test.

davidag · 2025-10-17T12:27:50-0400

Can you post a picture of the business end of the old spark plugs? This may help us to decide if the problem is fuel related or if there is oil contamination.

Cylinder 4 Misfire, Test Spark, Fuel and Compression

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