SV21 (3S-FE 2.0 L) Engine misfires and stutters under load

[KangaRon]

I was driving normally when the engine suddenly started stuttering and misfiring under load, but the idle was almost normal.

The symptoms were consistent with faulty ignition, specifically misfiring spark-plugs or high-tension leads with faulty insulation.

A quick change of plugs did NOT cure the problem, so logically one checks the high-tension leads next, but the ohms measurement was well within spec for all of them.

Now, if the high-tension leads had had faulty insulation, i.e. arcing to earth, then usually one can hear the arc crackling, and in a darkened garage the arcing is quite visible, but there was none of this.

HOWEVER, the 3SFE engine has each spark-plug buried deep in a well in the tappet cover, and there is a rigid section of high tension lead that reaches down into the  "spark-plug well"  in order to connect with the spark plug.

This rigid section is NOT visible when the engine is running, and also, any sound of arcing will be rendered INAUDIBLE by the snug fitting boot that covers each  "spark-plug well".

A thorough inspection (of this rigid section of high-tension lead) with a magnifying glass eventually revealed the culprit. Sure enough, it had been arcing across to earth in the  "spark-plug well". There was hardly anything to see, just check out the photo below.

A new set of high-tension leads then solved the problem, and the engine ran normally again.

So, before you go and change the coil, or start to suspect the injectors or ailing fuel pump pressure, check the high-tension leads.

Finally, to give credit where credit is due, I must acknowledge that this idea had already been posted by someone else on the "whirlpool Forum".

Edited May 3 by KangaRon
minor typo's

[Tony Prodigy]

Try and avoid cheap parts as they are poorly made rubbish from China. If you can get your hands on Genuine parts or OEM quality, then you will have trouble free motoring for many, many years.

[KangaRon]

On 5/5/2025 at 5:33 PM, Tony Prodigy said:

Try and avoid cheap parts as they are poorly made rubbish from China. If you can get your hands on Genuine parts or OEM quality, then you will have trouble free motoring for many, many years.

Absolutely true.