Slight Pinking?

[Chris_J]

I think my engine is pinking slightly under load. I can hear it at about half throttle and it seems to be related to engine revs. Strange thing is that it the sound seems to go away once I open the throttle more and the charger starts boosting, but I have only been doing this in short bursts for obvious reasons.

Here's what I done so far:

- Double checked timing is spot on and actually retarded it very slightly
- Replaced spark plugs with original Bosch W5DPOs
- Fresh tank of 97 RON fuel
- Replaced ECU chip with original, running standard charger pulley.

With this, I'm thinking the noise may be something else. The charger has just been rebuilt, so I guess it could be related to that.

Any ideas on how to diagnose properly?

[Yoof]

I'd be very surprised if it was actually pinking on part throttle, are you sure it's not something vibrating at part load?

[Chris_J]

Could be something rattling around, but it's so consistent and very very similar to a pinking noise.

Difficult one to find really, as it doesn't do it if you just increase the engine revs when stationary. Seems like it needs to be under load.

Engine pulls very strong though, especially for a stock setup. I guess if the timing was that far out, it would run like dog shit wouldn't it?

[Yoof]

I'd check the cam timing, and then reset the ignition timing.

Worth also driving in a condition where it's happening, and then pull the plugs asap. Generally you'll be able to see det on a plug too.

Which way did you twist the dizzy when you altered the timing?

[Chris_J]

Regarding checking cam timing, you mean just check the TDC marks line up properly on crank and cam?

Does det just show up as a mild pitting effect? Pulled the plugs shortly after I noticed the noise and they looked perfect, but they were new NGKs.

Twisted dizzy towards front of car IIRC. Did it until the '0' mark moved closer to the pointer. Probably set to around 4-5 degrees now.

[djtez]

Twisting the dizzy forwards to front of the car is advancing it ... im sure!

have you unplugged the Blue temp sensor whilst doing this ?

What spec of NGK's have you got? did you compare them to the equivalent bosch ?

Think its B7 for the ngk...but i'd check that

[Chris_J]

Can't remember which wai I turned it, but it was definitely retarding as the TDC mark was moving closer to the pointer. Yep, this was all done in service mode.

I have the B7 NGKs which are apparently the same spec as the Bosch, according to NGK's information. Just to rule these out though, I have replaced the Bosch plugs but the noise still occurs.

[djtez]

without really hearing it a could only just keep guessing ...

do you have a local mechanic friend? or maybe just extra ears!


Might be a long shot but check the HT leads make sure you dont have a bare wire grounding somewhere.. also check the Distributor for any damage on the cap on rotor arm..

easy and cheap to replace the last two items might be a shout?

[Chris_J]

Yeah, I'm local to quite a few of the Polo crew here!! 

I suspected HT grounding somewhere too, but I've replaced the dizzy cap, rotor and HT leads are in perfect condition.

I shall keep investigating!

Cheers

[ereeiz]

I've only skimmed over most this topic but could be alternator rattle. I remember having this on an astra and a few mk2 Golfs in the past. I was convinced it was pinking until I used the old screwdriver to the ear method! Can't really do it as easily on a Polo though as it's down low.

The cure is rebuild the alternator or get another that works If that's the issue of course!

[Chris_J]

Well, turns out this was not pinking.

The boost return plate was vibrating, particularly under load, making a sound that was really similar to pinking! Mental! This also explains why the noise went away under boost.

Anyhow, all sorted now.

Cheers 

[djtez]

thats excellent news..

glad it was so minor...

so damage could of really came of it! ..