Cylinder 1 misfire please help

[keitha]

I have an 02 Octavia 4x4 turbo with an ARX engine and it has a misfire on cylinder no1 ( according to vagcom ). At idle it dose seem like its running on 3 and it dose not like low revs but above 2500rpm it seems to run normal. My fuel economy is very poor now

So far I have

changed the plugs no change. also swapped the new plugs around the plug from cylinder 1 has some very light soot around the outside but is pretty clean the others look like new

swapped around the coil packs the misfire stays on cylinder 1

the maf was very dirty so i changed it the car dose run better but the misfire is still there

I read on some forums about problems with ICM causing misfire but i dont think mine has one

Any help would be appreciated as I like this car but I dont have the funds right now for a garage repair

[DGW]

Maybe not relevant in this case as you have swopped coilpacks around, but has your car had its coilpacks replaced in the last year? Read the thread below for details.

http://www.briskoda.net/forums/topic/193376-audi-coilpack-recall-turned-into-official-skoda-recall/page__hl__coilpack%20replacement

[Lofty79]

+1 coilpacks

[za_killer]

if you've interchanged the coilpacks but the miss fire is still present on cyl 1 it has probably the least to do with shot coilpacks.

i'd have a look at the wiring in search for cracks; it may be that the loom itself is shot

beware, running on 3 cyl's or miss fires for a longer period of time will cause your cat to fail

[keitha]

Many thanks for your replies.

I have owned the car for five years and in that time the coil packs have not been changed. I did look over the wiring that I can see and it looks OK, If it was a wiring issue would the misfire not be there all the time? right now its only there below 2000rpm and is more apparent on small throttle openings above this it runs well right up to the top speed.

I try to keep the revs up when I have to drive the car so that the misfire is minimal

If I could find the other end of the coil pack wiring I could test the integrity of the wires but I don't have enough information

Many thanks again any further thoughts on this are welcome and gratefully received

[Longyear]

The wiring looms on Octavias perish prematurely, due to poor heat protection as standard.

The symptoms you've described sound so much like a coil pack issue but if you've exchanged and the misfier stays on Cyl 1 it definitely isn't your coil packs, so I would strongly suspect the wiring to cyl 1 coil pack. I had a similar issue and mine was intermittant too ....... a new loom is only £24 but up to 6 times that to have fitted (quite a big job if having the full loom replaced as goes to the ECU and a number of sensors)..... some people buy the new loom, but then just 'splice' in the damaged sections (usually the wiring along the top of the head, that goes to the coil packs.

[za_killer]

If it was a wiring issue would the misfire not be there all the time? right now its only there below 2000rpm and is more apparent on small throttle openings above this it runs well right up to the top speed.

it happens even at high rpm, but you don't notice it exactly because of the high revs

intermittent wiring fault is my bet - have a closer look

[keitha]

Thanks I certainly will look more closely at the wiring to see if I can find anything just wish I had the ecu connection info so I could bell the wires. I was out driving today and before I left i reset the engine fault codes the car ran almost fine for 10 miles before the misfire started to come back and when it did the engine would miss and be under powered up to 2500rpm then it would take off like a scolded cat just seems like the engine gains a lot of power at that point strange i cant explain it.... maybe a sensor is throwing off the fueling or the ignition and its just cylinder 1 that's being affected strange I know... I am just throwing ideas around

[za_killer]

some wiring diagrams (google):

or: link

is the miss fire the only fault code recorded ?

in order of increasing costs, the causes for miss fire in a single cyl would be:

- ignition (spark plug, coil pack, wiring)

- fuel injection (blocked / leaking injector)

[Leeboy]

Is your coil pack for cylinder no. 1 staying firmly put and not working loose? I have previously had a similar misfire due to intermittent connection between coil pack and spark plug.

Otherwise if wiring us sound as you believe, could the injector for that cylinder be partially bunged up? You can unplug individual injectors to isolate them, and likewise you could swap the injectors from the inlet manifold and see if the misfire moves accordingly. The injectors are a simple push fit held firmly in place by a snug fitting rubber O ring.

[keitha]

Many thanks for the diagram I will see if I can test out the circuit. Its mostly just the misfire I see on vagcom I can see the misfire counter for cylinder 1 counting the other 3 are on zero. Sometimes I get pressure drop between turbo and throttle valve. As for the injector I forgot to mention my car is dual fuel and the misfire is the same on petrol and lpg so I would imagine the injectors are probably not the cause but I may be wrong it could be the electrical control of the injectors which must be common to both systems at some point I will see if I can test for the injector signal. The coil pack dose not seem to move at all.

I will go do some testing of ignition and fuel.

Thanks Guys for the help I will keep you all posted

[STSKODA]

i have some spare coils if you are stuck and need one

[keitha]

Thanks for the coil offer if it turns out I need some I will get in touch and we can do a deal of some kind

The more I look at this problem the more confused I become. The latest is I checked all the wiring for ignition and fuel all looks good I even installed led indicators for cylinders 1 and 2 on fuel and spark they both look fine.

Now when I look closer at the vagcom readout I see some interesting stuff. The pre cat voltage is on 1.6v on idle when I rev the engine it varies between 0.2 and 4v and the ignition timing is going to 20 btdc even at low ish reves I am not sure if any of this means anything but it seems wrong to me it could even be miss information from the vagcom software.

I am starting to wonder about mechanical issues like a sticky valve

Any ideas guys

[keitha]

I have had some time to look at the problem now it turns out to be low compression on cylinder 1 that is causing the misfire any thoughts on this guys valves or rings? I have heard that lpg runs hot and can damage valves guess the head needs to come off

Thanks to all that helped me getting to the bottom of this