99 Miata Pinging... What to do?

Hey all,

So my '99 Miata has started pinging recently. It only happens once its decently warmed up, under load, usually on an upward incline. Also, it seems to happen most on hot days when the sun is out.

I ran mid grade gas and it seemed to lessen the frequency of occurrence. I also changed my thermostat, and this seemed to help a bit too. I went back to regular gas but it still pings a little bit under the right conditions. I was told cleaning the intake manifold and EGR valve/port could help. I also heard maybe running seafoam through could help if I had carbon buildups that were increasing the comp ratio.

Anyways, before I do either of those, I wondered what advice would be offered here. Keep in mind the timing is not adjustable on the '99 and up models, so unless my belt jumped a tooth or something, the timing has not been advanced too far or anything like that.

What about replacing the knock sensor? Could it be that mine went bad? Thanks for the advice!

Mine did it when the weather was hot. I ran mid grade and it made it go away, and I got better fuel mileage.

you might try an injector cleaner before the Seafoam.

a GRM sponsor, CRC, has this treatment called 1 tank

you tried mid-grade and it got better.. have you tried premium fuel yet?

No Mad_machine, I'm sure it would probably further improve with premium, but in the end that is really only a bandaid masking another bad condition. I suppose its better than letting the engine ping, but certainly not a permanent fix...

It's a combination of a lot of things- but two big ones- combustion deposits that increase the compression ratio, and the EGR flowing less than the computer thinks it's flowing due to deposits. Both can lead to knock by themselves, but it's a pretty common combination on this Miata.

Besides the seafoam and other treatments- you can also do just water while the car is running. That will clean out the combustion chamber. Not the EGR, though.

Or just run premium, and wait until the lack of EGR flow is actually noticed (which lights the MIL light).

In reply to oldeskewltoy:

I am curious, how does using injector cleaners help with pinging? Is the theory the system is leaning out causing the pinging. Therefore the cleaner will restore the proper AF mixture and stop pinging? This is relevant to my own interests as well.

I thought that car recommended use of premium anyways?

GTwannaB wrote: In reply to oldeskewltoy: I am curious, how does using injector cleaners help with pinging? Is the theory the system is leaning out causing the pinging. Therefore the cleaner will restore the proper AF mixture and stop pinging? This is relevant to my own interests as well.

possible 2 cures... cleaning carbon deposits from combustion chamber therby lowering actual compression, the second is cleaning the injectors and returning their spray pattern and volume

oldeskewltoy wrote:

GTwannaB wrote: In reply to oldeskewltoy: I am curious, how does using injector cleaners help with pinging? Is the theory the system is leaning out causing the pinging. Therefore the cleaner will restore the proper AF mixture and stop pinging? This is relevant to my own interests as well.

possible 2 cures... cleaning carbon deposits from combustion chamber therby lowering actual compression, the second is cleaning the injectors and returning their spray pattern and volume

Most injector cleaners will do a good job at intake system and combustion system deposits. For this one, I'd lean more toward a combustion/intake specific cleaner.

Swank Force One wrote: I thought that car recommended use of premium anyways?

Not until 2001 when the VCT was added.

Swank Force One wrote: I thought that car recommended use of premium anyways?

Only on the 01+ models with VVT. The 99 and 00 models use 87 octane.

I noticed pinging in my '91 recently as well. Same condition described by the OP. I filled it up with a tank of premium. It immediately smoothed out and ran great. I sure a load injector cleaner wouldn't hurt. Does a '91 Miata have an EGR valve?

Type Q wrote: I noticed pinging in my '91 recently as well. Same condition described by the OP. I filled it up with a tank of premium. It immediately smoothed out and ran great. I sure a load injector cleaner wouldn't hurt. Does a '91 Miata have an EGR valve?

What are you running for timing? Is it factory spec or did you advance it?

In reply to Woody:

Factory

Down shift.

Italian tune up

Cures everything.

So I still need to pull the spark plugs and see what they look like but today I noticed that my #4 cylinder plug wire doesn't seat very well. Its NRG and supposed to be of decent quality, but it keeps popping off of the plug. So what I believe is happening is that the plug pops off, and the spark begins to jump to the engine block, and perhaps that is the noise I'm hearing.

I need to investigate this further, but I had a few questions. First, is it possible that the plug has backed out a bit, and is blowing compression out the top, thus forcing the plug wire off of the plug? Second, if this is not the case, and the plug wire is just a poor fitment (which honestly when you push it down, it doesnt feel like it seals very well anyways), how can I remedy this? Gotta buy a new plug wire?

Thanks dudes!

Do you mean NGK? I have had some where the #4 wire just doesn't fit tightly.

Oops yeah, sorry, NGK!

IIRC dont 99's have a bit of an issue with buildup in the intake manifold wherein its a good idea to do a disassemble and clean every few years?

Also, it might be worthwhile to check the PCV and look for other vacuum leaks while you are at it.