VW Cabriolet Engine Noise

[StevieC]

So I did the yearly change (low mileage) on the VW Cabriolet. Started it up and heard something that sounds like it is loose in the engine.

I waited for a few minutes with the engine running to see if it was just a lack of oil flow but it didn't go away.

Called my partner outside and asked him about the noise and he said it had been making it for some time.

I did a compression test, cut the old filter open to see if there was any metal shavings etc. and nothing bad could be found. The compression was just shy of factory specs on all cylinders.

Seeing as I had just put a rocker cover seal on it not that long ago I took the rocker cover off and had a look, and all looked ok.

I took the oil pan off as well and had a look and all was well. Check and made sure everything was tight with no play.

Any ideas? or anyone familiar enough with this engine that can tell me about this problem?

The car runs and operates fine, but makes the noise at hot idle up to 2K rpm, anything over that and it goes away...

Car has the 1.8L 8 valve engine with just under 200K KM on it. Timing belt was done about 20K KM ago and the tension is OK (checked it)

 

[PT1]

Originally Posted By: StevieC

Called my partner outside and asked him about the noise and he said it had been making it for some time.

I feel your pain.....I usually get the: "that annoying light has been on for several weeks and won't go off" "what is that a picture of anyway???" UH....it's the engine...

BTW, does the car have an exhaust valve that rattles until warm or until revs are high enough to hold it open?

 

[Nick R]

My friend's mom has a Cabriolet that has a squeaky wheel, and the CEL has been on forever, and he says it sounds like chitty chitty bang bang. I haven't heard it yet, but I told him I would look at it. If you figure out what it is, let me know because maybe that's the problem with theirs too.

 

[mechtech2]

Noises can be tough to determine the origin of. Any possibility that it is a driven component? Maybe take off the drive belts and start her up for a minute?

 

[StevieC]

Originally Posted By: PT1
Originally Posted By: StevieC

Called my partner outside and asked him about the noise and he said it had been making it for some time.

I feel your pain.....I usually get the: "that annoying light has been on for several weeks and won't go off" "what is that a picture of anyway???" UH....it's the engine...

BTW, does the car have an exhaust valve that rattles until warm or until revs are high enough to hold it open?
No exhaust valve...

 

[StevieC]

I also did the automotive stethoscope listening on the water pump, block, cylinder head, etc. It sounds like it it coming from the cylinder head but it is hard to determine because it could be echoing from the block.

It almost sounds like a rod knocking but not all the time and not consistent with a rod-knock type sound. The sound also seems to move around the engine.

It seems to be after the combustion cycle and before the combustion cycle so I don't think it's knocking from fuel or spark timing.

 

[Trav]

Have you tried shorting each cylinders with a test light or remove fuel to hear if the noise changes?Rod knock,piston pin,piston slap noise will decrease when combustion pressure is removed from the suspect cylinder.Main bearing noise will be unaffected.
While this may not identify the exact source it may at least help to isolate the noise to the top or bottom end.

Does this engine have a distributor?If so check the shaft bearings.

 

[StevieC]

Checked the distributor... Bearings are good. The fuel elimination to the cylinder is possible but it would be a PITA to do because it is Mechanical fuel injection under extremely high pressure.

I have tried eliminating the spark though and it didn't make a difference.

 

[OVERKILL]

Could be a wrist-pin.....

 

[StevieC]

Never thought about that... I will have to check it out in the spring.

 

[Trav]

When you killed the spark on the cylinder that is suspected to have a bad wrist pin there should have been a change in the noise,the noise will usually almost disappear.
If no change at all i would i would be leaning more to the top end though its hard to say without actually hearing it.

 

[StevieC]

I wish I could put the noise on a video for y'all but I don't have the equipment for it and my Blackberry does a horrible job of it.

No noise change with the spark being killed from each cylinder.

 

[Trav]

Does the noise mimic engine RPM or does it appear half speed?
Half speed would definitely isolate it to the valve train.

Back in the early 90s we had a Audi 1.8 doing pretty much what you describe.I don't remember exactly what was wrong but it was inside the distributor,maybe a flyweight (i don't remember if the 1.8 used one) or a bearing,whatever it was it was a pita to find.

 

[StevieC]

It doesn't speed up in proportion to the RPM but does speed up/slow down as a few hundred RPM is added/removed.

I had the distributor out and checked it for play and function in my hands... All good.

 

[Spykem4e]

could be the intake manifold shift.The OEM bushings wear quickly as far as I remember.

If the sound is like a piston slap or rattle, most likely to be the bushing that are worn.

 

[StevieC]

I'm a bit confused as to what you are talking about...

 

[Spykem4e]

is it that sound?

http://www.youtube.com/watch?v=DQ4qDqcAWhI&feature=related

 

[StevieC]

Definitely not like that... It's more like a loose wrench flopping around inside the engine every once an a while. Really hard to describe.

I will see if I can record it using my BlackBerry with its [censored] sound recording.

 

[Trav]

Originally Posted By: StevieC
It doesn't speed up in proportion to the RPM but does speed up/slow down as a few hundred RPM is added/removed.

I had the distributor out and checked it for play and function in my hands... All good.



If whatever is causing the noise is connected to a rotating internal part it should be constant or half speed with the RPM depending on if its bottom end or valve train.

Noise from accessory pulleys,tensioners,alternator,ps pump and a/c compressor bearings and internals sometimes seem to out of sync.
Does the noise diminish or change when the engine is slightly loaded?
i.e a/c on,lights on,in drive if automatic or slight clutch release if manual.

Could it be coming from the flex plate or clutch area?

 

[StevieC]

The noise doesn't change when the engine is loaded and isn't tied to the speed or half speed of the engine.

The best way to describe it is something sounds loose/banging around in the engine and it is worst at idle and or at 1,000 RPM outside of that it is virtually non-existent.

The belts and tensioners, pulleys etc. were all checked.