QuestionTed
I own a 91 4runner V6 with about 180,000km. Notice within the last year and a half that under load the engine would intermittently ping. This does not happen when the engine is cold but after it warms up. I assume there is pre-detonation, carbon build up. Tried higher grade gas but that only minimizes the problem and it's costly. Took it to the garage a few times..........tune up, timing checked, thermostat changed etc. but still an issue. I mentioned the EGR valve to the mechanic but he states that's just for emission and does not think that would cause pinging. Is there some other answer besides an engine overhaul. Thanks in advance for your help.
Gil
AnswerPossible exessive carbon builtup in the combustion chamber which raises the compression.
Have you tried retarding the timing, make sure it is set to 5 degrees with the diagnostic connector jumped between terminals TE1 and E1. The EGR valve can cause the problem,the sole function of the egr valve is to recirculate exhaust gas back into the combustion chamber to cool it down, this reduces NOX emissions, if combustion chamber temperatures get too high there will be preignition causing the pinging noise.
Usually a EGR malfunction will trigger a check engine light.
Try having the engine compression tested to see if it is exessively high(normal is about 180-195 PSI) if it is a lot higher than that there could be a lot of carbon in the combustion chambers which will raise compression pressures and can cause the pinging, in that case the cylinder heads will have to be removed and the pistons and the combustion chambers cleaned of all the carbon.
As a last resort without having to spend a lot of money check with a local autoparts store to see if they have anything that you can run through the engine to loosen the carbon and blow it out the tailpipe, although I don't advocate or really believe that these chemical solutions do much good it may be worth a try just to see if it helps.
