Timing And Vacuum Advance

[roccorich 16]

Exactly why I want to get the timing right.

 

Whats a detcan?

[Jolly Green Monster 51 1 Cars]

Microphone that I bolt to the engine and listen with headphones for dettonation ( pinking in old money )

[roccorich 16]

Can you use it while driving?

 

Where can you get them from?

 

Cheers

 

Ricg

[Jolly Green Monster 51 1 Cars]

Phormula or you can make basic ones yourself. I have them for my day job.

[roccorich 16]

Cool.

 

I get ear defenders from work so Ill have a go at making some.

 

Where would you sayis the best place to bolt them to hear the pinking

 

Cheers

 

Rich

[Jolly Green Monster 51 1 Cars]

Inlet or exhaust manifold.

 

Get a small length (6inches or so) of copper pipe. Flatten one end and cut a v in it.

Buy some fuel hose that tightly fits in the pipe and a Y piece.

Drill holes in ear defenders and feed pipe through etc.

then bolt to engine. But you can usually hear it driving without

[roccorich 16]

Cheers thats what I was thinking.

 

There was a noise that I think may be pinking when I accellerated in 3rd, not as loud as I thought it would be.

 

I got the noise to go but had to retard it right back, so Im gonna borrow one of those home Gunson CO meters to set the mixture roughly right then try the timing again before getting the CO done accurately.

[Anthony 1,000]

Usually on a 1.9 GTi you'll first get pinking around 2000-2500rpm - 5th gear, WOT, and listen for the tale-tale metallic rattling/tinkling sort of sound.

 

All I usually do is on a warm day keep slowly advancing the timing until you hear the onset of pinking, and then knock it back a touch. That normally gets it very close for the fuel currently in the car, although clearly optimising it on the rolling road would be ideal as each engine/distributor is slightly different owing to wear and tolerances.

 

A cracked/blowing exhaust manifold (quite common) sounds similar though, so check that before trying to set the ignition timing this way!

[welshpug 1,622]

you want a wideband lambda not a CO meter.

[roccorich 16]

Ive had my hand all round the manifold and cant feel any blowing but will check again.

 

My back box has a big hole in it at the moment so thats not helping hear things to be honest but I did try that up a hill and couldnt hear much..

 

Is the mixture setting not a case of getting a reading 1.5% CO?

 

cheers

 

Rich

[Anthony 1,000]

That's mixture at idle, which has little effect on mixture throughout the rev range - to monitor that, you need a wideband lambda.

[roccorich 16]

I see.

 

And how/where do I adjust it?

[Jolly Green Monster 51 1 Cars]

You cant. Its ecu controlled.

 

If its lean - mine is leaner than I want hence replacing the pump tomorrow

[roccorich 16]

How can I tell if the pump is causing it

 

Ive blanked off the dizzy vacuum now as the diaghram is leaking so maybe that was causing the lean running.

 

I cant see any other leaks...

[Jolly Green Monster 51 1 Cars]

You cant without swapping it out but it could well be sucking air in from that leak yes.

[roccorich 16]

Whats the theory behind the fuel pump causing it?

 

Low fuel pressure?

[Jolly Green Monster 51 1 Cars]

Pressure and flow and easy for me to change as have two here

[roccorich 16]

Fair enough.

[roccorich 16]

So does tbe idle mixture not give the mixture at other revs a starting point.

 

As in if its adjusted leaner at idle it will be leaner when revving.

 

Provided the AFM is working correctly that is?

[welshpug 1,622]

yes it does to a certain extent, until you hit the WOT switch.

[roccorich 16]

Which adds further enrichment. Is that right?

[Anthony 1,000]

Idle mixture adjustment has very little effect under load - on the Jetronic system, the adjustment screw just allows a varying amount of air to bypass the metering flap in the AFM, thereby changing the mixture. The amount of air bypassing the flap is very small compared to the amount being drawn through the flap under load.

 

WOT throttle enrichment does what it says on the tin, namely enriches the mixture under WOT conditions.

 

For the most part, ignition timing is separate to the fuel mixture.

[roccorich 16]

Ok cool.

 

The reason I was mentioning mixture is your supposed to make sure timing is right before you adjust mixture as timing will effect the exhaust readings.

 

However as I was asking earlier if Im trying to set the timing by ear and the mixture is very lean it seems I need to consider that a very lean mixture will cause pinking to occur with less advance.

 

So maybe I need to try a do what I can about the mixture first.

Edited October 8, 2013 by roccorich