Kia Forum banner

1 - 2 of 2 Posts

04 Mercedes C230, 08 Rondo LX V6
367 Posts
Discussion Starter #1
I was talking with a dealer service adviser today about spark plugs. He said that a misfire frequency of about 20% is necessary to trigger the check engine light. Does this sound right to the tech gurus on our list? He also said that this misfire rate is not typically seen until 80K miles or so. Comments?

With 61K miles, he advised against plug replacement.

2,234 Posts

re: misfire rate to trigger CEL/MIL indicator -

it depends on (what) is causing the misfire to occur, and the rate per (n) revolutions the misfire occurs, some ECMs are more sensitive to random misfire codes than others..

* And a random misfire DTC is just a (result) code, it can be caused by a number of possible causes which in-turn trigger the random misfire code: ignition components, fuel delivery, illegal air / vacuum leaks, etc..

re: plugs - what does the maintenance schedule for your vehicle state?

The ECM checks for -> is sensitive to firing voltage at the spark plug, so proper spark plug gap plays a big role in proper firing..

Spark plugs are a wear item, typically, they should be inspected / replaced per the maintenance schedule..

At that time -all- other related ignition components should also undergo a full visual inspection: plug wires / HT leads for any cracks,tears,pinholes, carbon tracing at boots , coil packs for any wear, deformity, discoloration (indicating overheating), engine harness lead -> coil packs for any abrasion, brittleness, connector ends for any cracks, brittleness ..

This should be done on -all- plugs / wires / coils ...

You can't just test the ones easily accessible and call it good, "Mechanic's law 101" states that the component you fail to inspect -will- be the component to fail.. :eek: :mad: :)

* Proper spark plug gap is crucial to efficient firing of the cylinder / the ECM detecting proper firing / preventing excess stress on components leading up to the spark plug (coils / coil packs / wires)..

* Excessive plug gap requires all other components in the ignition system to "work harder" (conduct more energy) in order to initiate spark at the plug.

At 61,000 miles, -if-

the vehicle is primarily driven at highway speed for the majority of operation,

the fuel filter and air filter are delivering clean air/fuel,

the oil has been changed per schedule,

the coolant system is working properly / the coolant is fresh,

AND there are no other issues / no CEL / no MIL lights on, then (if it was me), I might let them ride until the 75,000 service - but if above is not the case, (if it was me) I'd be looking at doing some maintenance / changing some plugs, sooner vs. later.

You should signup at the kiatechinfo website (see my sig.) using Internet Explorer web browser (see right side of page for system requirements) so you can view the (Service Info) for your vehicle / the steps necessary to do a plug change, if you are so inclined by interest, or necessity..

re: "expert" - no, just a "shade-tree auto repair enthusiast" with older vehicles, an interest in auto mechanics, and few $$$.. :D But I hope the info helps,

1 - 2 of 2 Posts