P0304 code - Fiesta ST150

[TechMinerUK]

Hey all,

This is a long shot but it's driving me nuts now so I'm wondering if anyone else has any ideas or suggestions.

Last September I bought a 2008 ST150 as a project for me and my dad to work on. We've done all sorts to it and despite a few issues everything has gone relatively smoothly all things considered.

However, since buying it the car has a bit of a "bubbly" idle. Nothing awful but noticeable compared to my dads ST150 (Admittedly his has done 20K miles, mine has done 50K).

In the past 4 months every now and then a P0304 error code comes up when using an ODB2 reader. After a few days it will clear again and it can be weeks or months in-between it's next appearance.

So far we have tried:

• New spark plugs
• New injector
• New coil back
• New HT leads
• New air-filter
• New oil-filter
• Re-gapping the spark plugs
• New fuel filter
• New PCV valve and PCV hose
• Replacement of all coolant, power-steering, gearbox oil and engine oil (Just maintenance)
• ECU reset
• New camshaft sensor
• Throttle-body clean
• Airbox and return hose check

When the car is running it is as smooth as butter, there's no smoke accelerating/decelerating and nothing to suggest anything "Major" is off. It's not even as if the light comes up after a long journey or toweling it. It can be completely at random

Any help or suggestions would be ace as I'm leaning towards a sticky valve however finding a place to work on the engine near us is apparently like trying to find a needle in a haystack!

 

[Diddums]

What does P0304 indicate?

 

[Maundie]

What you need is a Carly, phenomenal piece of equipment that!!

 

[Armageus]

What does P0304 indicate?

Cylinder 4 misfire.


Forscan is the go to for Ford diagnostics, do probably worth seeing if that picks up a more specific code rather than the generic misfire

 

[TechMinerUK]

Cylinder 4 misfire.


Forscan is the go to for Ford diagnostics, do probably worth seeing if that picks up a more specific code rather than the generic misfire

That's the one which needs the ODBLink MX+ adapter to work isn't it?

Currently we have a Artidiag Lite 9000 which is pretty decent but isn't really pointing any further than the code mentioned, it's really odd as it even went into Ford this weekend for some diagnostics and they couldn't get much further than the code either.

 

[bobuk]

Hey all,

This is a long shot but it's driving me nuts now so I'm wondering if anyone else has any ideas or suggestions.

Last September I bought a 2008 ST150 as a project for me and my dad to work on. We've done all sorts to it and despite a few issues everything has gone relatively smoothly all things considered.

However, since buying it the car has a bit of a "bubbly" idle. Nothing awful but noticeable compared to my dads ST150 (Admittedly his has done 20K miles, mine has done 50K).

In the past 4 months every now and then a P0304 error code comes up when using an ODB2 reader. After a few days it will clear again and it can be weeks or months in-between it's next appearance.

So far we have tried:

• New spark plugs
• New injector
• New coil back
• New HT leads
• New air-filter
• New oil-filter
• Re-gapping the spark plugs
• New fuel filter
• New PCV valve and PCV hose
• Replacement of all coolant, power-steering, gearbox oil and engine oil (Just maintenance)
• ECU reset
• New camshaft sensor
• Throttle-body clean
• Airbox and return hose check

When the car is running it is as smooth as butter, there's no smoke accelerating/decelerating and nothing to suggest anything "Major" is off. It's not even as if the light comes up after a long journey or toweling it. It can be completely at random

Any help or suggestions would be ace as I'm leaning towards a sticky valve however finding a place to work on the engine near us is apparently like trying to find a needle in a haystack!

You would notice a sticky valve when driving, they tend shake the whole car, the ztec engine had this problem in the 90's early 2000's, they did have a spray that was directed into the manifold which worked for a while.

 

[Frozennova]

The next most logical step would probably be a compression and leakdown test. This would help identify anything like a leaky or sticky valve. stem seal or a bad headgasket.

It's possible a headgasket has failed in such a way that it's losing combustion gases but hasn't failed across a water or oil way so doesn't follow the usual symptoms of consuming coolat etc

 

[Nomisf]

Also thoroughly check the wiring loom to that injector, check plug fitment and connector condition then test the power and grounds with a fairly high draw (brake light bulbs work for this). The coil wiring gets hot and vibrates a lot and a slowly breaking wire fits your symptoms.

 

[TechMinerUK]

The next most logical step would probably be a compression and leakdown test. This would help identify anything like a leaky or sticky valve. stem seal or a bad headgasket.

It's possible a headgasket has failed in such a way that it's losing combustion gases but hasn't failed across a water or oil way so doesn't follow the usual symptoms of consuming coolat etc

I knew I meant to come back and update something!

Did a pressure test on Sunday and you were right on the money, cylinders 1-3 absolutely fine, cylinder 4 held less pressure than a bust balloon.

So, great news that I know what it is now, bad news is that it needs a rebuild

 

[aaronyuri]

Do a leak down test to narrow it down further. You may only need to touch the top end, not do a full rebuild.