Pinging, but no codes?

[bootstrapper]

1992 2.3L, was sitting for a few years until I revived it. Full tune up, some new parts. Now about 300 miles into driving it around town, it's developing a ping. It's most noticeable at light throttle under light load (like straightaway cruising). If I WOT or let off the gas it goes away.

So I pulled the OBD1 codes, and all it gave me was something about the AC compressor being on (#539). Nothing about the mixture, or emissions sensors, etc.

All the simple stuff is new: plugs, wires, fuel/air filters.

Is there a way the mixture could be wrong without setting a code?

Thanks in advance---

 

[RonD]

Pinging pretty much comes from the cylinder being too hot for the fuel octane.
Lean mix burns hotter than rich, the best fuel/air mix for economy would melt the piston and valves, lol.

Could be there is some carbon build up on the intake valve and in the cylinder, on the valve this absorbs some of the fuel so leans up the mix, but would expect O2 sensor to pick that up.
In the cylinder the carbon holds the heat and can cause pre-ignition(pinging), what did the old plugs look like?

To cool the cylinders the computer should open the EGR valve when engine RPM is up and there is a load on the engine.
If you don't have an EGR system then it could be that the timing is to far advanced.
People often advance the timing for a little more power but you can also get pinging.

The upstream O2 sensor could be at fault but these usually tend to cause rich mix as they get older.

MAF sensor could need cleaning, not sure if '92 2.3l had both MAF and MAP sensors.
These tell the computer the amount of air flowing in the system so play a major role in the fuel/air ratio.

My bet since there is no "lean" code, is that the timing is the issue, or EGR flow if you have one, partially blocked.

Many engines came with a Knock sensor, not sure about yours, this sensor would detect pinging and retard the timing enough to prevent it.

 

[Road Angels]

Old.... gas, did you just add to what was in the tank or did you drain and put new gas in it, my 86 with 300k pings cause of carbon build up, putting in high grade gas stops it from pinging, mid grade it still pings but not as bad as reg, Iam cheap so I use mid grade, add some top grade to it for a while