Pinging sound in engine

[84TG]

Hi everyone,

I have had a pinging/high pitched knock in my engine for a while now. I've thought it might be to far advanced but it will only ping in top gear, it comes in doing 80km and is completely gone by the time I reach 100km! This is the only time I hear it!! Any ideas??

[tobytj]

Only a guess but maybe a lean mix/low octane fuel issue in that rev range.

Hard to say without knowing your set up. If you have a non standard carby it could be the main jet is a bit small but the air jet is also small so the mix gets richer as the revs increase.

[84TG]

Hmm this is interesting never thought about that tobytj!
I'm running a 32/36 weber and I only use 98 fuel. So what your saying is that it's running light on fuel at that point?

[Jonno]

It could be.

Is it just a standard motor with a weber. it's definitely pinging?

How's your timing?

[moley]

Pinging is under load conditions when is it under load...

[84TG]

It's a 1.6L 40tho over standard bottom end standard head only other mods is exughst! You could call it a high pitched knock but I reackon it is more of a ping sound jonno...

Moley, yes it only does it under load between 80 and 100km, when I say under load I mean just cruising up to that speed!

[DR_GEM]

Ping = knock

If you're hearing audible knock then its pretty bad.

As Toby said could be lean knock, secondary jets not large enough or mixture is out.

Or ignition too far advanced (with mechanical advance).

Or could be pre-ignition from a hot spot in your combustion chamber

To test it (without knock ears): Put half a tank of 7/11 (Mobil) e10 (94 octane) into it. Do NOT cane it for the purposes of this test.

Drive to a semi steel hill where you can load the engine up slightly. Try to replicate the conditions (slight load 80-100kmh). Back off as soon as you hear any pinging / knock at all. Assess whether the knock got worse or better.

If the e10 helped, then its not lean knock (as e10 would make your afr slightly leaner than 98).

Also if it helped, then you can *potentially* rule out knock from too much timing (as e10 obviously has lower octane rating).

If it got worse, then it could be due to either lean or too much timing

So many different possibilities. Could even be contaminated intake from crank case recirculation feeding back to your intake.

Unless you have knock ears and an ear / eye for carby mixtures, then it will need to be found by deduction

Mick

[84TG]

Thanks Mick I will have to look into it a bit more!

Let's just say that it was a lean knock, would this do damage long term?

[DR_GEM]

Thanks Mick I will have to look into it a bit more!

Let's just say that it was a lean knock, would this do damage long term?

Yes

Worst case scenario - Crack ringlands / melt piston.

Blown headgasket from the detonation.

Or at the very least, pitted rod bearings from the knock through the rod banging onto the crank/ bearings

[84TG]

Would just regular 91 fuel do the same job for the test? Just because I've heard E10 is no good for your car?

[84TG]

And also why would it only do it in 5th gear if you get up to 100 in 4th gear no knock what so ever!??

[DR_GEM]

Would just regular 91 fuel do the same job for the test? Just because I've heard E10 is no good for your car?

No

And don't believe the crap about e10.

The original e10 that received a bad rep was only because the big fuel companies were spreading their propaganda.

Essentially they were adding 10% ethanol to rubbish fuel (something like 87 Ron fuel) and then blaming the ethanol for the ridiculous issues motorists faced when using e10.

Ethanol is God's gift to the motoring world. If e100 was available like in South America or parts of Europe, my cars would run on nothing but.

The new e10 ethanol range of reputable fuel retailers (Mobil / 7/11, united) is great and at 94 Ron reflective of the benefit of ethanol when added to s%*tty dinosaur fuel

Regular petrol is rubbish - even our best 98 Ron.

Mick

[archangel62]

Just to add to what DR_GEM said, I think E10 is slightly higher octane rating... 94RON I think. You could try it with 98 versus 91 and see if it makes a difference. Also the gear won't matter. Figure out what kind of throttle position and rev range it happens in and try it in other gears with the same throttle at the same rev range - left foot brake if you have to - it should do the same thing.

Get a timing light on it. With vac advance disconnected and blocked off, idle should see 6deg BTDC for stock tune, though up to 10deg BTDC should run fine. Rev the engine a little with the timing light on it, you should see the timing advance smoothly with RPM. Now reconnect vac advance and depress and release throttle with timing light on it. Besides the RPM (centrifugal) advance you saw before, you should also notice the throttle adjusts the timing, it's hard to explain exactly how it works on a G series but you should see it working, this is vacuum advance. If all of that is working fine I'd suggest taking it to someone who knows carby jetting and/or has an EGR analyser to check whether it's leaning out - only conclusive way to put it to bed.