NB8A engine pinging noise

[Project7]

Hi guys,

my 2000 NB8A with ~160,000 kms has had this pinging noise that comes from the engine when accelerating under load.
I noticed it just after I bought it at ~155,000 kms however after an oil change it seemed to be gone.

The sound would return so upon checking the dip stick, and subsequently topping up the oil, it would disappear for a little while.
At this time I was running 91 octane fuel.
Then I upped to 95 octane and there wasn't a noticeable difference so recently I've been using 98 but it can still be heard.

I also find that it's worse when the engine is cold.
My timing is not advanced (I'm pretty sure).
I've been using 5w-40 full synthetic.
I would say the noise is most obvious between 2500 and 3000 rpm.

If anyone has any suggestions I would be super appreciative.

Project7.

[22Silver]

I had something like this recently, turned out to be a big end bearing.
I was feeling negative surges of power though.

[hks_kansei]

First up, try not to rev or load the engine up heaps when it's cold. Just be smooth and easy until everything is warmed up.


As for the pinging, take out the spark plugs and have a look at them, on an MX5 they normally have dry black sooty deposits on them.
If they are wet, then it may be either stuffed piston rings allowing oil into the cylinder, or a misfire causing the fuel to stay unburned.
If they have a white ashy tip, the engine is either running lean, hot, or possibly the plugs are the wrong temperature (NA and NB use different temp plugs)

I'd recommend changing the plugs anyway, they should be changed every 50,000km or so anyway (personally I'd do it more often since they're cheap)
Don't bother with the fancy Iridium/Platinum plugs, just get normal ones. They're a lot cheaper, and they provide a bette spark (with the tradeoff of a shorter life)

$20 should get you a set of new Bosch/NGK plugs.

[93_Clubman]

my 2000 NB8A with ~160,000 kms has had this pinging noise that comes from the engine when accelerating under load.

My timing is not advanced (I'm pretty sure).

You really need to confirm with a timing light what the actual ignition timing is.

Some years ago I bought an MX5 that was pinging under load & when I checked the timing I found it was 18 degrees BTDC.

Also worth keeping in mind that there's a few NB8As getting around with NA8 motors, from which hydraulic lifter assembly (HLA) noise can be emitted, as opposed to the sold lifter assembly of the NB8A motor.

[Project7]

Thanks for the responses so far. I'll be giving your suggestions a shot this weekend and will update as to how it works out.

hks_kansei:
Is the NGK ZFR5F-11 appropriate for my car? I believe so, because It's a non-turbo NB.
Really hope the current spark plugs aren't wet.

93_clubman:
You're right about the timing and I'll definitely be borrowing a light to check that soon.
Fortunately I'm not hearing any HLA noise.

Additional notes/questions:
My rocker cover gasket is leaking so I'll be replacing that.
Due for an oil change and I'll be switching to 10w50 with a Ryco Z79A filter.
^^ Would either of the above have any effect on my pinging issue?

Let me know if I'm about to do something wrong, or if there's anything else I should consider.

Thanks.

[hks_kansei]

Can't remember the exact product code for the plugs.

Doesn't sound right though, pretty sure mine are BK5RE or something.

Check the NGK website, they have a search thing to find the correct part number.

[sailaholic]

Nb and Na engines look different so should be an easy check. Different inlet manifold. Nb have a cam sensor on the intake? Side cam at the front. Na8 has the mushroom cam sensor at the back of the head plugged directly into the cam.


Sent from my iPhone using Tapatalk

[davekmoore]

Timing is the first thing to check. Imagine a piston hurtling up a cylinder expecting to stop at the top of its stroke and be fired downward at that split second (when stopped) by the spark plug igniting the fuel/air mixture. Then imagine the extra stress on the same piston if the plug sparks when it's still traveling upwards instead of when it's stopped. This will cause pinging noises. It will cause all sorts of other issues if not put right. Don't ask how I know. And no hating for my simplistic explanation please!

[hks_kansei]

Just checked the site.

NB8A plugs are:

BKR5E-11
or
BKR5EIX-11

IX is for the Iridium plugs, which I wouldn't bother with. Standard plugs provide a better spark (apparently they are easier to spark than the fancy metals) and cost a lot less. The downside is you need to change them more often.

[22Silver]

Timing is the first thing to check. Imagine a piston hurtling up a cylinder expecting to stop at the top of its stroke and be fired downward at that split second (when stopped) by the spark plug igniting the fuel/air mixture. Then imagine the extra stress on the same piston if the plug sparks when it's still traveling upwards instead of when it's stopped. This will cause pinging noises. It will cause all sorts of other issues if not put right. Don't ask how I know. And no hating for my simplistic explanation please!

The spark plug is meant to fire while the piston is still travelling upwards. In an NB8A it fires 10 degrees before the piston reaches the top.

This is because the fuel burns over time, and you get maximum pressure after a small delay, while the burning (chain reaction, REDOX) makes it's way through the mixture, starting at the point of the spark.
If the pressure reaches this high point when the piston is right at the top, you get a good push back down. If the pressure reaches this high point early, the additional compression that occurs when the volume of the chamber decreases as the piston hits the top causes the remaining unburned mix, which would normally have ignited through chain reaction, in due time, to detonate instantly, and further accelerate the already 'too soon' peak of pressure.

The same reason applies to low octane fuel- it burns quicker, and the peak pressure is earlier. Advancing the timing has the same effect, but is achieved by moving the start point of the reaction (sparkplug spark) earlier.

In essence, the fuel should take a moment to go from "on fire" to "fully burnt". If for any reason the peak pressure of the reaction is "too early" relative to the top position of the piston, the pressure of the reaction and the compression of the piston still traveling upwards can bring the pressure and temperature high enough to spontaneously ignite the remaining fuel/air mix which normally would have been ignited due to the chain reaction from the spark.

[Mr Morlock]

I would suggest getting the car checked by someone who knows what they hear- i.e. problem diagnosis- It might simply be ignition set incorrectly or something else.Your description of more noticeable when cold and some of the other things may suggest it is not pinging. If the problem has any connection with oil its unlikely to have anything to do with pinging and it might also be flagging another problem.

[hks_kansei]

I'm still going to say change the plugs.

The ones listed by the OP aren't the correct ones per the NGK site, I'd be first of all replacing them with the correct plugs.
If the problem persists, it's only cost you $20 and you got new plugs out of it.

Timing on the NB is set by the ECU, so unless somebody has put in one of the adjustable timing wheels (which just trick the ECU by moving the timing mark) it should be standard.

[Project7]

hks-kansei:
Yep, I'll be getting some BKR5E-11's. Thanks a lot for your help.

davekmoore and 22silver:
I will be checking the timing for sure, but in my reading last night I came to find that the variable timing and knock sensor of 1999 cars onwards means I can't adjust the timing, even if I did find it to be too far advanced (can that be the case if is not adjustable?).

MrMorlock:
Professional diagnosis will definitely be my next step if I can't figure it out. I don't believe the oil is related, I was just notifying of any changes I make in case someone picks up on correlations that I don't.
As for the cold engine's effect on the noise, you're right - my ears aren't trained and I may have only made that association because I was not being gentle during the warm-up and the usual mechanical sounds plus pinging made me jump to conclusions.

Anyway, I'm being long-winded so I'll just say... I will take some basic steps towards a solution and will share the outcome.

Thank you guys.

[davekmoore]

Timing is the first thing to check. Imagine a piston hurtling up a cylinder expecting to stop at the top of its stroke and be fired downward at that split second (when stopped) by the spark plug igniting the fuel/air mixture. Then imagine the extra stress on the same piston if the plug sparks when it's still traveling upwards instead of when it's stopped. This will cause pinging noises. It will cause all sorts of other issues if not put right. Don't ask how I know. And no hating for my simplistic explanation please!

The spark plug is meant to fire while the piston is still travelling upwards. In an NB8A it fires 10 degrees before the piston reaches the top.

This is because the fuel burns over time, and you get maximum pressure after a small delay, while the burning (chain reaction, REDOX) makes it's way through the mixture, starting at the point of the spark.
If the pressure reaches this high point when the piston is right at the top, you get a good push back down. If the pressure reaches this high point early, the additional compression that occurs when the volume of the chamber decreases as the piston hits the top causes the remaining unburned mix, which would normally have ignited through chain reaction, in due time, to detonate instantly, and further accelerate the already 'too soon' peak of pressure.

The same reason applies to low octane fuel- it burns quicker, and the peak pressure is earlier. Advancing the timing has the same effect, but is achieved by moving the start point of the reaction (sparkplug spark) earlier.

In essence, the fuel should take a moment to go from "on fire" to "fully burnt". If for any reason the peak pressure of the reaction is "too early" relative to the top position of the piston, the pressure of the reaction and the compression of the piston still traveling upwards can bring the pressure and temperature high enough to spontaneously ignite the remaining fuel/air mix which normally would have been ignited due to the chain reaction from the spark.

I did say my explanation was simplistic