Author Topic: Mk3 1.8 GL possible engine knock?  (Read 246 times)

Offline LeonK

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Mk3 1.8 GL possible engine knock?
« on: 17 October 2020, 21:09 »
Hey everyone.

First of all let me introduce myself; I'm Leon, 23 years old and the proud owner of two mk3 Golfs (one used to be my first car, now used for parts mainly).

However, my 'newer' 1996 mk3 has developed a bit of a nasty engine noise. Now, this is all pretty new to me and I'm still trying to learn things, so bear with me.

The engine I'm talking about is the standard 1.8L mono-injected petrol.

Now this only occurs when I accelerate in third or fourth (01M automatic trans) from like 1500-2300rpm. In other words; when the engine is under load. Also happens a lot more in hot weather, or when the engine's in operating temperature (also keep in mind the engine is not overheating, coolant keeps steady at a nice 90 degrees Celsius). This is the noise I'm talking about: http://youtube.com/watch?v=iQ1A5jS0Rgs

So, after some googling I came to the conclusion that this might be engine knock or pre-detonation, right? Can anybody confirm this?

I investigated a little further, and bought a cheap OBD/VAGcom cable. I went and scanned my car with VCDS-lite, and was happy to see that no fault codes were found. However this didn't really help me much since I still didn't know what's wrong.

Together with a friend of mine, I did a couple of test runs to collect some data through VCDS. One suspicious thing that I noticed is that the Lambda value stayed at a steady -2.3%. Now I don't really know what that means, but does that mean the oxygen sensor near the exhaust manifold has gone bad? Can anybody tell me what the nominal value should be? Should it not be constant? Again, this is the part where I'm still trying to learn things.

Here is a screenshot of the VCDS log: https://pasteboard.co/JvtdYJb.jpg

(full VCDS log file available here: https://drive.google.com/file/d/1tuakMnkgzmtgDtysCY_yXhjs1u4b5cN8/view?usp=sharing)

Also, if you notice anything else unusual in there, please let me know. Thanks!
« Last Edit: 17 October 2020, 21:10 by LeonK »

Offline itavaltalainen

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Re: Mk3 1.8 GL possible engine knock?
« Reply #1 on: 18 October 2020, 08:37 »
Don't worry about the lambda percentage. The value to look at is the lambda factor, that varies somewhere between 0.9 and 1.1.

I don't think that noise is engine knocking, the 1.8 wasn't really prone to that (it's got quite low compression and can run even on 91 RON fuel and it doesn't have a knock sensor for this reason). It's a little tricky to hear the noise clearly in the video but think it's more likely a loose part, e.g. heat shield on the cat.

Does it pull normally otherwise?
2019 Seat Leon ST FR DSG 135kW - eclipse orange - 23k miles

Offline LeonK

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Re: Mk3 1.8 GL possible engine knock?
« Reply #2 on: 18 October 2020, 23:22 »
Don't worry about the lambda percentage. The value to look at is the lambda factor, that varies somewhere between 0.9 and 1.1.

I don't think that noise is engine knocking, the 1.8 wasn't really prone to that (it's got quite low compression and can run even on 91 RON fuel and it doesn't have a knock sensor for this reason). It's a little tricky to hear the noise clearly in the video but think it's more likely a loose part, e.g. heat shield on the cat.

Does it pull normally otherwise?

Hey, thanks for your response.

Yeah, the thing is that it only really happens when it's warm, and only in third and fourth (under load). Performance-wise, I'm kind of afraid to really push it. When it produces the rattlling noise however, I don't really notice a performance decrease. I'll have it on a ramp by Tuesday to have a mechanic look over it.

Offline LeonK

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Re: Mk3 1.8 GL possible engine knock?
« Reply #3 on: 21 October 2020, 19:26 »
Mechanic fixed it yesterday; timing wasn't done right the previous time they changed the belt apparently...