annoying ping/detonation issue

[Vadim]

Hi all – first post for me, need some expert help!

my woman drives a mitsubishi mirage (it may be called colt over in the US) and i’ve been trying to fix a weird ping problem for many months without much luck.

first, ill describe the symptoms… it only happens when the engine is fully warm, only between 2.2k and 2.8k rpm, in a any gear, at high-ish load. seems somewhat random too as if not all cylinders are pinging. its also down on power and struggles with air conditioning switched on. sometimes, at cold start, it will run on three cylinders for about 30 seconds then clear up and idle fine.

i dont have a check engine light and haven’t had it hooked up to a OBDII scanner yet. Its got about 100,000 miles right now

and here is what i have done to fix it…
– always run 95+ fuel
– replaced the plugs (twice)
– replaced the ignition leads
– replaced the distributor rotor
– replaced the distributor cap
– bought a timing light and set ignition to factory settings as per service manual (tried tweaking the timing a few degrees up and down but that only seems to move the ping up and down in the rev range)
– cleaned out the throttle body and intake with seafoam
– had the injectors removed and cleaned on a bench by a mechanic, who also did the timing belt at the same time and made sure the cam timing was all sweet. he also did another carbon clean with a proper machine but zero improvement
– replaced the oxygen sensor and the entire distributor more recently.
– fuel filter has also been done

i want to sell the car soon and don’t want to give it away sounding like this, and at the same time, cannot spend any more $$$ on it, too much spent on this issue already. out of ideas now!

many thanks

Topic

[Dan Howie]

mr_derp,
Give this website a try:

What Causes Engine Pinging

Maybe something here that might help, i.e., engine cooling, valves, etc. Keep us posted.

[george gonzalez]

If it starts up on 3 cylinders sometimes, you have an oil or coolant leak into that cylinder. The fluids will leave deposits on the valves and head, said deposits will act like a glow-plug and detonate the fuel-air mixture. That would explain the pinging.

To fix this you have to remove the head, scraps off the deposits, and put on a new head gasket and/or new valve seals.

I’ve had to do this several times. Not a lot of fun, takes a good 6 hours on a simple engine, but it’s doable. Highest risk is in getting the exhaust manifold nuts off.

[Author]

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