Misfire - O2, Piston Problem?

[MM92]

Hi,

I've just my car back from the garage (Focus 51 1.6).

The past few weeks it's been juddering when I first drive off and in second gear.

The bloke has spent the day testing etc and seems to think one of the cilenders if misfiring and is something to do with an 02 sensor which has in turn caused a problem with the piston.

When it's ticking over you can hear and feel it mis/backfiring and I'm looking at £550 for it to be sorted.

Is there anything else it may be or a cheaper way of confirming if it is the piston or another part being the problem?

Thanks.

[MrRedman]

Hi not saying dont trust the garage but have u pulled the leads off one by one to see if they are sparking against the block its a simple check to rule out an ignition problem

[btmaldon]

There are a lot of things that can cause it. Partially blocked injector, coil pack, leads, plugs, fuel filter, air or vacuum leak on the intake system, sticky valve. The last thing it is likely to be is a piston

[MM92]

Hi not saying dont trust the garage but have u pulled the leads off one by one to see if they are sparking against the block its a simple check to rule out an ignition problem

Not yet, but I've just been told take it for a run, then lift the bonnet in the dark for blue sparks, if so there's my problem?

There are a lot of things that can cause it. Partially blocked injector, coil pack, leads, plugs, fuel filter, air or vacuum leak on the intake system, sticky valve. The last thing it is likely to be is a piston

I could change/check a couple of the things you've mentioned. What would I be looking at for a garage to test/replace them options excluding the piston

[wase16ll]

classic :(

sorry mate, but a garage can check for a piston/cylinder/compression problem with a very simple compression test

a compression test takes seconds, so really dont understand how on earth you can spend a day testing and come to the conclusion its an 02 sensor thats caused a problem with a piston...a compression test does exactly what it says on the tin, tests the compression...would instantly eliminate any mechanical problem with each cylinder, including pistons, valves, rings or even gaket problem.

if what you have typed is correct, then bin that garage now and take it to someone that knows what they're doing...

if they were confident in there diagnosis, why the hell are they asking to check for sparks in the dark..tells you nothing beyond you have a misfire, which, basicly, you already know....

[mintalkin]

get to a garage who knows what they are doing, how can an O2 sensor effect one pot?,i would say its a plug,lead or a coil pack causing the missfire.

[MM92]

They did the compression test three times apparently, in order to know for sure if it was the piston or another part (still expensive) he would have to take it all apart etc.

I'm guessing that was all cobblers, if the test can tell you what's wrong?

[jeebowhite]

Which garage you using in kent?

Moving to the Focus forums...

[wase16ll]

confusing or what

so they HAVE done a compression test

then what the hell was the point of checking for blue spark in the dark????????

you either have low compression, or you dont, spark is irrelevent until you sort out the low compression if that is the case

compression tests wont pinpoint a problem unless its compression rings, just gives you a clue..

think you need to ask the results of tests they have carried out, forget their opinion, you just want the actual results

especially of

compression test readings...ideally you want to know the total compression figure as well as number of strokes to reach that figure...plus, with your symptoms, would ask what compression was on first stroke...those figures for all cylinders, so a comparison can be made...all helps

exhaust gas readout, if they have done one plus any stored codes

if results of compression warrants it, also need to check valve clearances..they are adjustable according to autodata, though have never done this myself..was always under the impression they were hydraulic.

still doesnt make sense to me...either compression is poor, in which case concentrate on why by stripping it down, the condition of the spark is totally irrelevent at this time...if compression is good ,then you dont have a mechanical problem with the cylinder beyond tight valve clearances????...which leaves fuel/ignition fault

very odd

[MM92]

Had a look around it yesterday - was some oil in cilender 1 and 2 where the spark plugs are.

Changed the plugs as long overdue anyway, the judder doesn't seem nowhere near as much as it was before they was changed.

According to the garage, it's cilinder 1 with the issue/low compression.

The engine light is still on so gonna get the HT leads/plugs changed and go from there.

I don't think the garage wrote down the readings so would need doing again - but he said they was low.