Slight misfire after timing belt replacement?

[tonyt102]

Yeh, I agree that the breather pipes couple casue idle problems but it's strange that this should occur right after the timing belt change. I can imagine that the vac pipes can become damaged from removal/refitting but I'm not sure about the breather pipes. I really don't know as I've never seen the front end of these engines and I don't know what's disconnected when the belt is replaced. I'm just really worried that the indy I have it at can't sort it and I have to get it to a specialist, doubling the money I've spent.

Thanks for the replies Conan.

[tonyt102]

Well, had all of the vacuum hoses replaced to no avail.

I have plugged VAG COM in tonight and it brought up no fault codes. I'm quite new to VAG COM so correct me if I'm wrong. I went to the measuring block section with the engine running to get some values for misfiring cylnders and ignition timing. There was no misfires logged although the timing showed between 12-14 degrees BTDC @ 800rpm - is this right as I can find out what it should be? Shouldn't it be 0 degrees or near?

[Conan_the_Librarian]

When you say vacuum hoses do you mean crank case breather hoses?

Vacuum hoses effect the variable length intake adjustment.

[Conan_the_Librarian]

If your running Vagcom and measuring Blocks 1 , 19 and 20. If you have ant misfires blocks 19 and 20 will record each misfire as it happens. If they stay at zero then no misfires are happening....... I think........

Use the Vag scope facility and record blocks 1 , 19, 20 and post the file as an attachment here. Rev up to about 4k.

[tonyt102]

Thanks Conan.

I've had the small vacuum hoses replaced as they were all perished - not the breather pipes.

Cheers for the VAG COM tip, I'll try it either tomorrow or Sunday and let you know. Wouldn't it have logged a fault if there was a misfire though?

I have phoned a local VW/Audi specialist (where I should have gone to in the first place). They say that it sound like the cam timing is out which, speaking to a few other people, sounds plausable.

[Just_Ben]

Hi there.
Sounds very much like they havent got the timing belt on correct. On most Audi engines the cam pulleys are mounted on a taper and so have to be loosened from the cams when tensioning the belt. A quick check to see if it's on wrong is pop one of the belt covers off a bit so you can see the cam pulley. If there's a Tip-Ex mark on the cam pulley and the engine then they have definately done it wrong!
As the tension settles it pulls the timing out if they havent set it correctly.

If they have done it right then check a few bits, such as spark plugs, air leaks on inlet and check the inlet manifold hasn't worked it's bolts lose - they like doing that! Also the inlet manifold has change over flaps inside and they can sieze, if during the belt change the guys have moved these then they could have upset it. You should be able to move the 2 change over valves by hand, although the springs are strong, you will get free movement.

Feel free to call me if you need advice: 01283 548 483 (although I'm not at work now!! )

[tonyt102]

Thanks very much for that, I think I now understand the reason for a tapered cam sprocked as opposed to a keyed one. I'm guessing that the cams can be completely locked in place along with the crank (?) then, the belt could be removed, refitted and tensioned without any of the engine moving. This means that no Tip-Ex marks are necessary. Does this sound right?

Like you say, I need to get the cover off to check if they've marked the sprocket and engine. I'll do it tomorrow and report back.

Thanks again.