Hoping somebody can help or suggest possible checks which I may not have done so far. I have a Stilo, 1.8, 2005. The car went in for an MOT on the view if successful the car would be sold. The car failed its MOT on high emissions. The car has been displaying poor performance for the past week (week before MOT test), over the past week it appears to be using large amount of fuel, car idle speed varies, cuts out sometimes at slow speeds. Engine light displayed on dash, light is blinking.

Checks so far.

>Connected fault reader, code PO303 - Cylinder 3 misfire displayed.
>Swapped coils (3 and 4), restarted engine same fault code appears PO303.
>Checked spark plugs (changed 2 months ago), seem ok, slightly dark on the tip however look ok. Swapped spark plugs (swapped 3 and 4), same fault code displayed.
> Visual check done on wiring from coils on main harness back to ECU.
> All connections checked.
> Measured resistance on coil inputs (3 wire connection block), on all 4 coils I get around 3.4K when checking across pin 1 and pin 2. Assumed this would be in the lower ohms however with all of them giving the same result I'm assuming all coils are good.

was thinking of starting the car up and disconnecting each coil one at a time to see if this makes a change in the engine speed.
can I measure the input wiring for volts ? if so what would I expect and at one terminals ? presume if I don't get the correct voltage on one of them its probably the ECU. might measure all four and confirm if they all display the same voltage.
was also thinking about sending the ECU away to get checked / repaired (if needed).
should I check the injectors ? is this the same for testing ? check across them for a good low resistance.

any further ideas ?

Try cleaning the plugs. I had trouble with my landrover last week. No computer so had to diagnose old school. Even though the plugs were relatively new it was misfiring. Cleaned plugs and put 98 octane fuel in it.

Cleaned all the plugs using wire brush and emery paper. When I removed the plug from cylinder 1 (far left looking at front) there was a fair amount of oil on the end of the plug. Other three where dry however I'm concerned with plug 1, also don't understand why I'm receiving the error code for cylinder 3. When the car is started all warning lights on dash go off after a few sections, after about 10 secs the engine management line flashes and I obtain a fault code of PO303 on my fault reader.

Any further suggestions ?

Was thinking of doing a compression test on cylinder 1, suppose this would tell me if I've got an issue, however still don't know why Cylinder one is not showing up as an error.

A manifold leak to that cylinder make throw up an error too.

I've read on other posts that its normal to get oil in the spark plug hole on the spark plug on the far left as the oil spills into here when the oil is filled. Assuming this is the case do I need to remove the spark plug and attempt to remove the oil from this area. Not sure how I would do this however I'm presuming I would need to do it. Guessing its unlikely to burn off.

Any further ideas on what I could check for the fault code PO303, could it be a faulty ECU, can any checks be done on the Secondary wiring connector of each coil ? voltage checks, etc ?

SteveDC said:

I've read on other posts that its normal to get oil in the spark plug hole on the spark plug on the far left as the oil spills into here when the oil is filled. Assuming this is the case do I need to remove the spark plug and attempt to remove the oil from this area. Not sure how I would do this however I'm presuming I would need to do it. Guessing its unlikely to burn off.

Any further ideas on what I could check for the fault code PO303, could it be a faulty ECU, can any checks be done on the Secondary wiring connector of each coil ? voltage checks, etc ?

Click to expand...

It will run fine with the oil in there anyway if you really want to get it out then leave the plug in place, dilute the oil with a splash of petrol/whitespirit/diesel and use a rag pushed down with a a thin screwdriver to soak it up. Then you can take out the plug and clean the plug and remaining oils from the plug well.

Did you swap the plug and coils e.g. swap coil 1 to 3 and see if the error moves, if not swap the plugs. Do this before looking any further.

The ecus are know for dry/broken solder joints:
https://www.fiatforum.com/stilo/352287-phase-sensor-camshaft-position-sensor.html?p=3500259

Sorry, probably didn't explain very well. When the spark plug is removed I have oil on the bottom of the spark plug. I appear to have oil in the engine on where to spark plugs screws into. This is the far left, presume this is not good, however I have read on here that the oil should be removed by inserting a rag to get the oil out. Presume a new spark plug is required as the electrode is soaked in oil unless I could spray wd40 on it to clean it.

I might have a look at the Ecu, looks like a bugger to remove, it has 4 star screws but screws are facing windscreen side so difficult to get access.

Hi,


Did you try to change HT wires ??
Last week, I had the same DTC (P0301) and there was oïl on the 1st spark plug thread.
After changing the whole HT wires, everything is alright now.


Regards

RQ3ZQTB said:

Did you try to change HT wires ??
Last week, I had the same DTC (P0301) and there was oïl on the 1st spark plug thread.
After changing the whole HT wires, everything is alright now.

Click to expand...

They are individual coils (1 per cylinder), there are no HT wires.
.

Not changed any HT wires as per Davren these are separate LT wires to individual coils. Coils have been swapped, still same error (PO303), swapped spark plugs, still same error (PO303). I'm planning this weekend to clean out the oil from the hole for Spark Plug 1 inside the engine using a rag.
I'm also planning to remove the ECU, split the unit and I've going to check all soldered joints.

Failing that I'm struggling ! Was thinking of leaving the existing ECU connected, remove the spark plugs, lay them down on an isolated mat, keep them connected to the LT wiring and see if they all spark when the car is started. Presume if Spark Plug 3 is not sparking then its either the wiring back to the ECU or its the ECU. (coil and spark plug already swapped). If they all spark then I'm struggling. Can a voltage on the LT wiring be measured when the car is started ? will save coming into contact with the spark plugs if I use this method.

Presume the fault code of PO303 will be the main reason that I'm getting high emissions ?

All, still struggling with this issue. Finally removed the Ecu however looks like a sealed unit. Is there any benefit in splitting this unit to check the soldered joints ?

Take the injector spark pug and coil from cylinder 3 and swap them to cylinder 2.

If the error nos not move i would check for intake manifold leak around cylinder 3 (as it's been suggested by Maigretnz)


Do not disassemble the ECU.
you can check for spark with something as simple as a check light

Many thanks for the info. If I need to check for leaks on the manifold how would I do this ? Would o need to do a compression test on cylinder 3 if moving the coils does change the fault code ?

I have only done this with old school non computer engines with a few drops of oil to see if it got sucked away and looking for a puff of smoke. Idea, use engine start, a momentary increase in revs if a leak?