5S-FE pinging - trying to diagnose why

[farge]

I've been trying to find out why my Celica's engine is still pinging. It's currently set at 9 degrees BTDC (less than spec) and I run it on 98 octane fuel, so the obvious solutions are ruled out.

It pings under moderate to high acceleration, usually under 4k RPM, up hills or flat.

EDIT: It also hesitates at around 3k RPM. Maintain a constant 3k RPM and it's a bit jerky. Not sure if that's related.

My mechanic and I have been chasing this for around a year now. It's making me wonder whether what I think is pinging is actually something else...? Pretty sure not though.

So, anyone got ideas on what to check out?

Currently on my list of things to check are:

1. ignition leads

2. EGR system

3. coil

4. oxygen sensor

5. knock sensor

6. replace distributor

Anything I've missed?

Edited March 4, 2014 by farge

[LivingTheDream]

This model celica had a problem with carbon build up on top of the piston which obviously caused increased compression and therefore pinging if timing was too far advanced.

[farge]

How would I remedy that? Is there a way to remove the deposits easily, our would it be necessary to retard the timing to compensate?

[LivingTheDream]

We used to remove the heads and clean the combustion chambers and top of pistons.

[farge]

So I've discovered oil in one of the spark plug tubes... probably can't be helping. I'll try to get my hands on a torque wrench and replace the gaskets, then put in a new set of plugs and leads. Will update.

I don't want to sound like one of those noobs who just say "My mechanic says..." all the time, but... my mechanic put some kind of stuff through the engine that was supposed to remove carbon deposits at last service. For argument's sake, and because removing the head is well outside my skill level, what would you check next?

[LivingTheDream]

Well if you've got oil in the spark plug tubes, then that will certainly affect the running of the engine and ultimately misfiring/pinging. The oil will affect the rubber on the plug leads. I recommend you remove the leads & plugs (better to suck out oil in the tube before removing the plug), replace the rocker cover gasket and tube seals and possibly removing the tubes and resealing the threads. Put in new plugs and leads & re-adjust your timing to correct specs and see what happens. The oil in the tubes will cause the spark to track and ultimately misfire. See how you go.