So, I'm having some problems with my old Fabia HTP from 2006 (115.000 km so far) and I'm hoping for some guidance:

I got an engine fault code P0341 and had the camshaft sensor replaced in hope that this would fix the issue.

Now I'm experiencing some strange behaviour from the engine: About every third(+/-) time I start the car the starter cranks two or three times more than usual. The car does start but engine revs are limited to 4000 rpm in all gears and neutral. If I turn the car off and on again - and is starts normally - the engine runs just fine. I'm not getting any warning lamps at the moment and I'm not hearing any unusual noises.

So the question is: What causes this behaviour?
From what I have read so far it could be one of the following:
- Cheap knock-off camshaft sensor

- Timing chain loose or skipped a tooth (however some say this is usual on HTP models?)

- Engine misfire / not all cylinders running (but I'm not hearing anything unusual from the engine)

- Bad coil pack (same as above)

The mechanics I've asked so far are eager to replace the timing chain but I would prefer a less expensive fix.

Can someone give me a hint what to do? Any help is appreciated - I'm not a gearhead and would consider myself a noob regarding engine mechanics.

Could it be a possibility that the ECU needs some kind of adjustment after a sensor replacement? I've seen some mention a ECU remap and/or reset?

12 minutes ago, JohanW said:

Could it be a possibility that the ECU needs some kind of adjustment after a sensor replacement? I've seen some mention a ECU remap and/or reset?

I'm not aware of any such requirement when replacing cam sensor.

 

Is your 1.2 the 6-valve or 12-valve variant?

@JohanW - I would be most surprised if a cam chain skipped a tooth. Other than being duplex chains and sprockets they look a lot like you'll find on a single speed bicycle.

2 hours ago, Wino said:

I'm not aware of any such requirement when replacing cam sensor.

 

Is your 1.2 the 6-valve or 12-valve variant?

 

Yeah, I thougt it was a long shot.

 

I believe it's the 6-valve as it only produces 54 HP.

Best thing to do is to hook up to VCDS and see which, if any, fault codes are logged.

Misfires caused by bad coilpacks or compression problems are both common on this engine. They should bring on a warning light, but that may have been obscured by a previous owner or an incompetent garage.

Check that you see the emissions warning light come on briefly at ignition on, as a first step, to rule out tampering.

 

2 hours ago, KenONeill said:

@JohanW - I would be most surprised if a cam chain skipped a tooth. Other than being duplex chains and sprockets they look a lot like you'll find on a single speed bicycle. 

How about a loose chain? Would that explain the problem I'm having with the limited RPMs?

Limited RPM is the ECU in limp home mode which is why it resets when you cycle the ignition, you need to get the fault codes read.

Hooking up a VCDS is a bit out of my area of expertise. I wouldn't know where to start.

The emissions warning light comes on at ignition every time - this was also the lamp that was showing when I had the first camshaft sensor error. I think the mechanic reset the error, but I'm sure it will popup again if I keep driving.

 

If it is 'limp home mode' wouldn't it then show me in the dashboard?  No warning lamps are showing when i drive the car.

I will try to get my hands on a OBD-reader and see if it spits out some errorcodes.

1 hour ago, JohanW said:

How about a loose chain? Would that explain the problem I'm having with the limited RPMs?

My experience says that you will HEAR A LOOSE CHAIN, and not much else.

36 minutes ago, KenONeill said:

My experience says that you will HEAR A LOOSE CHAIN, and not much else.

 

Damn.
So I should hear a loose chain - but I'm not.

It's unlikely to be a skipped tooth.

I'm not getting any warnings in the dashboard.

The camshaft sensor should not require ECU modifications.

 

Is my best option for debugging to read the errorcodes? I'll have to buy a scanner then...

How about the ignition/coil pack - can I measure/see/hear/feel if this is running as it should?

 

@JohanW - I've never heard (of) this engine having a loose timing chain, unless the tensioner has failed.  Which isn't impossible at that kilometerage, but takes us back to the "noisy" thing.

 

I think it now all points back to a good code reader, like shareware VCDS and a cable, and then check the camshaft timing with that.

You have three separate ignition coilpacks, one on each sparkplug. 

Chain jumping teeth is by no means unheard of.

Does need scanning for fault codes, to see if you still have a cam sensor related one, and any others.

Should be able to pick up a handheld scanner pretty cheaply. Pick one that claims VW-group compatibility, or ideally get a cheap lead that will work with vcds lite.

2 hours ago, Wino said:

Chain jumping teeth is by no means unheard of.

 

Thats also what the two mechanics said who I've been talking too so far - but the symptoms are weird. And people in here seem to have some different opinions. I just want to make sure I don't spend a lot of money without fixing the problem.

 

I can manage to get a OBD2-scanner for the errorcodes, but I don't understand the VCDS system. What is the difference between that and OBD?

I understand that the cam chain can give problems but it wouldn't be fixed by cycling the ignition so it can't be that, it's impossible to proceed without fault codes really.

I'll scan for fault codes this weekend and keep you posted on my findings. Please stand by
Thank you so far for all of your comments.

Okay, so I had a VCDS hooked up to the car yesterday. Luckily my brother knew someone with a HEX-V2 reader.

We had some trouble recreating the startup error but we did notice a few things:

When the car starts fine no faultcode is produced.

When the car does the extra cranking during start the crankshaft sensor faultcode reappears.

The computer didn't exactly give alot of information otherwise. The readings looked fine and within spec.

 

I'm guessing that i'm back to the chain somehow messing with the timing.

If you have a crank sensor fault then you should replace it before messing about with the cam timing.

11 minutes ago, sepulchrave said:

If you have a crank sensor fault then you should replace it before messing about with the cam timing.

 

It has already been replaced once. I get the same errorcode on the replacement sensor.

I guess your not saying that I should replace the crankshaft?

I just realized that my description isn't that accurate: It's not a fault on the sensor but instead a fault on the sensor reading - something with inconsistency in the readings.

I heard there are two sensors, top and bottom, and I guess they measure different.

Crank to cam sensor correlation fault?

2 minutes ago, Wino said:

Crank to cam sensor correlation fault?

 

That's my guess. The actual error description was more like: inconsistency in crankshaft sensor reading - check timing chain.

Since I already had the sensor replaced I guess the timing is off.

28 minutes ago, JohanW said:

 

That's my guess. The actual error description was more like: inconsistency in crankshaft sensor reading - check timing chain.

Since I already had the sensor replaced I guess the timing is off.

 

Finally, enough information to actually diagnose the problem!

1 hour ago, sepulchrave said:

 

Finally, enough information to actually diagnose the problem!

 

Well, nothing new really - it's more or less what I expected. It still doesn't explain why the car behaves like it does. It just seems a bit random.

7 hours ago, JohanW said:

 

That's my guess. The actual error description was more like: inconsistency in crankshaft sensor reading - check timing chain.

Since I already had the sensor replaced I guess the timing is off.

I thought it was the cam sensor you'd replaced?