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I am experiencing a drastic drop in mileage so far everything seems fine with the car so I cannot find the reason for now, but recently I replaced the spark plug wires I think it's unlikely that they affect the consumption this much but better ask. It dropped from 12km/liter to 7km/liter

I have a chevrolet sedan 1.6 4cc

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Indirectly.

Cheap wires have higher resistance in the wire, which leads to weaker spark at the plug. Weaker spark means the combustion is not optimized, thus leading to less engine power and you have to give more throttle to compensate for less power.

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    It's hard for me to see how plug wires alone would worsen fuel economy by almost 70% – Zaid Jun 12 at 8:09
  • @zaid I also have my doubts regarding 70% increased fuel consumption, but my answer was in general: can sparkplug wires affect fuel consumption. – phingoc Jun 12 at 15:53
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Unlikely,

Although technically very cheap spark plug wires could cause a weak spark, it would typically not effect combustion efficiency by enough to notice a drop in fuel economy.

Typically if you were having significant fuel economy issues, and it was caused by the spark plug wires, I would expect you to have significant miss-firing.

If the engine still sounds like it runs correctly (doesn't sound like a tractor) then it's probably not misfiring.

There's plenty of things that could cause fuel economy drop but check the basics.

  • No fuel leaking
  • Ignition Timing is still correct
  • Camshaft Timing is correct
  • Agreed. I can't see how plug wires alone would cause such a drastic reduction in fuel economy. – Zaid Jun 12 at 8:10
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In general no. Poor spark would likely make the engine run horribly, misfiring noticeably.

But badly routed cables / poorly suppressed cables can interfere with the electrical signals from various sensors triggering odd problems.

That said, for a dramatic increase in fuel consumption my first concern would be the lambda probe, followed by the MAF sensor. Note that if the battery has been disconnected then on some cars this can trigger a massive change, as the ECU tries to relearn from faulty sensors, but on a modern car I would expect this to trigger an engine warning light.

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Yes, cheap plug wires can affect performance and MPG. Did you buy high quality wires or cheapo wires?

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    They were no cheap but the brand is unkown, I will check out the box and specs and add them to the question – user37388 Jun 11 at 16:39

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