Hello,

 

My 6Y Fabia has taken a turn for the worst in recent days and I'm about to give up on it :( Can anyone help? I would hate to scrap it over this silly problem.

 

About 3 weeks ago, the ECU detected a misfire detected in cylinder 1. I instinctively replaced the coil pack (I have spares in the boot!) as this happened before. This cleared the code for the rest of my journey home. Unfortunately the next day, I noticed if I put the engine under load (up a hill, pulling away quick etc), the engine light would come on again with a misfire code in cylinder 1 again. Usually restarting the engine resolves the problem temporarily. 

 

Since then the misfires became more frequent but the engine also became harder to start in the mornings. It would turn over OK but wouldn't fire unless I left it for 10 minutes or so. In the last few weeks I've had to do this routine 3 times over 30 minutes before getting the engine going. Almost immediately after setting off, the misfire code in cylinder 1 would appear again, so I'd need to restart the engine again!

 

Not sure it's related but I'm finding that the engine seems to behave better when warmer and there's no loss of power either... but the codes keep appearing.

 

I recently took it into my local trusted garage, who had it for 3 days testing different parts. They initially replaced the injector in cylinder 1, alongside a camshaft sensor. Compression came back OK too. Unfortunately the replacement parts have not resolved the issue. I now have the car back (minus £300) from the garage, who seem to think it's probably ECU now. 

 

What are your thoughts? I've got the ECU in front of me and it's showing no signs of water ingress on the connectors or inside on the board. Let me know if I can provide any more info. I have a VCDS cable to hand too.

 

Thanks,

Oli

You never mentioned the spark plugs,

were they out and checked and replaced at sometime while this was happening?

Yup the garage checked those too (sorry, forgot to mention). As I have it back, I may double check myself tomorrow.

Its not uncommon to have a dodgy coil pack even if it was new. Swap the coil pack and spark plug with another cylinder to rule them out completely.

ECUs are pretty reliable, I'd be very surprised if that's at fault. The wiring in these cars, on the other hand, seems to break quite often.

I'd be unwrapping the loom wires going to coil no.1 if I were you, and applying mk1 eyeball to them thoroughly.

This is all REALLY useful, thanks everyone.

 

Plan for tomorrow then:

- Replace coil pack in cyl 1 with last spare I have

- Swap cyl 1 + 2 spark plugs around

- Inspect wiring loom headed to cyl 1. From what I remember, it was very stiff so it could be brittle, or a broke a core pulling it out

 

I'll update this tomorrow when I'm back from work.

 

Thanks again.

Oli

More than likely the valve guides are worn giving poor valve sealing and a miss fire at lower rpm

A leak down test would show it easiest but a compression test will give an idea too.

I'd second a compression test.

Quote: "Compression came back OK too"...

Leak down, rather than compression is the test to do.

Hi everyone,

 

Thanks again for all your suggestions. I have completed the following:

 

- Reinstalled ECU

- Replaced coil pack in cylinder 1

- Swapped spark plugs between cylinders 1 and 2

- Inspected and played with wiring loom to coil packs whilst engine was idle.

 

I also called the garage, who confirmed they did NOT do a leak test because the compression came back absolutely fine.

 

Weirdly enough, the engine started first time today. The car had been stationary for 3 days so this might have something to do with it. Unfortunately, the cylinder 1 misfire error appeared as soon as I pulled out into the main road, so nothing has changed.

 

Additionally, the car was spluttering a lot and dropping revs when idle. At one point the engine stalled whilst idle. I'm not sure if this is a clue to anyone?

 

Thanks,

Oli

Just to follow on from this, I can consistently get cylinder 1 to misfire by putting it under load (full throttle through first and second gears). VCDS is occasionally reporting cylinder 3 misfiring too but I suspect it could be triggered by cylinder 1 misfiring too. Spent the evening swapping around coil packs, spark plugs and fiddling with wiring looms but it doesn't seem to change the outcome. 

 

Does anyone have any idea on what I could try next? I'm being quoted £99 for scrapping, which isn't great because it leaves me £200 out of pocket :(

 

Thanks,

Oli

Edited 17 May, 201610 yr by Mrnorm

You have all the symptoms of burnt valves, it's very common on the 12V, the only cure is to have the head reconditioned, diagnosis is by a leak-down test, NOT a compression test. The reason the garage didn't do this is because they don't know enough about it.

I thought the 6-valve engines were more prone to that, but I know both can be affected.

 

Presumably if there are valves leaking badly enough to affect starting/running this much, it could be observed DIY with a compression tester (£15?) by a noticeable difference in how fast the peak reading is reached? Cylinder 1 might be expected to take longer cranking before the reading got to be the same as the other two, if it ever got there? I would expect a professional garage to have spotted this though, so maybe my reasoning is flawed? Sepulchrave; could you elaborate on why leak-down might be the only test to reveal it, if that's the case?

 

Could ask a garage to quote for a leak-down test, if you don't want to get your hands dirty.

 

Endoscope/borescope (with mirror attachment) down cylinder 1's sparkplug hole might give another quick answer?

Edited 18 May, 201610 yr by Wino

Most mechanics simply crank the engine until a peak reading is obtained, with all the spark plugs removed the engine spins very fast so this happens too quickly to notice any anomalies.

 

A leak-down test uses a different gauge and an air line so there's no reason it can't be done, a drop of oil in the cylinders beforehand will eliminate the ring seal from the test. It needs doing.

Should be reasonably inexpensive, I guess? Half an hour's labour, tops?

Trouble is the compression is quite high on these motors and they will still make 150-170 with bad guides. Good ones are around 220 is so someone with little experience might test it and think it's OK.

Thanks for the replies everyone! 

 

Having driven the car for a bit since the garage got it, the character of the problem is slightly more simplified

 

Starting is now absolutely fine. I read on here previously that leaky injectors can cause issues when motor is left overnight and the garage replaced an injector as part of their works. So that part of the problem is solved

 

The misfires are still happening in cylinder 1. Occasionally cylinder 3 is also reported but I suspect one failure triggered another. Since running some Wynns hydraulic valve lifter through the oil, the engine has been idling smoothly. I can 100% get the car to misfire by slowly increasing the RPMs whilst stationary. Anything above 1,500 RPM seems to get the engine light flashing with a pending fault, before eventually becoming a permanent stored fault. It's worth noting that the engine doesn't sound rough during this test. I was hoping the Wynns might unclog a potentially stuck valve but this doesn't appear to be the case.

 

I worry this is valve or valve guide related now, as suggested by users here. Both jobs sound like they will cost more than I can afford on this car. It's a shame because there's a lot of memories tied up in that motor.

 

Is it time to part ways, or is there anything else I can try before a mechanic is required?

 

Thanks,

Oli

Edited 19 May, 201610 yr by Mrnorm