2003 Toyota Matrix with 217,000 miles (most on a rural mail route). Check engine light stays on with readings for multiple misfires, all four coils (which have all been replaced) and just replaced fuel pump. Gas mileage has plummeted. Any ideas?

A dirty/defective Mass Air Flow sensor can cause multiple misfires and a drop in fuel mileage. You might first try cleaning the MAF sensor with an aerosol MAF sensor cleaner to see if that helps. Tester

A misfire code indicates something in a cylinder or a number of cylinders prevented proper combustion. When this happens it causes the crankshaft rotation to slow down slightly. The computer detects this slowing down of the crankshaft thru the crankshaft position sensor. So if cylinder 2 has a misfi…

Ok, I see, thanks @tester . I think I understand this better now. A misfire means there was a detonation in a cylinder at a time when there shouldn’t have been – and for some undefined reason, could be either electrical or mechanical – which slowed the crank unexpectedly, as measured by the cran…

At 217K mail route miles, perhaps a compression test is in order,

Hook up a fuel pressure gauge and do an injector balance test.

How often do you need to add oil?

Talk about SEVERE driving conditions! It amazes me that a vehicle can still be running with 217,000 on a rural mail route. But the Mass Air Flow (MAF) would be my first guess at finding the cause for your problem.

A misfire means there was a detonation in a cylinder at a time when there shouldn’t have been No that’s not entirely true. A misfire normally means weak or missing entirely. The way the misfire is being categorized in this context is more akin to a gun misfire- weak or missing entirely. Not that …

Did u have misfire before replacing coils? Did u change coils to try and fix misfire issue?

Multiple misfires after replacing all coils and fuel pump

Maintenance/Repairs

George_San_Jose1 January 3, 2013, 5:54am 3

@Tester … just curious, what is Toyota’s def’n of a “misfire”? Does it mean a spark plug in one particular cylinder fired when it shouldn’t have? Or does it mean a detonation inside the cylinder was detected (presumably by the knock sensor) at a time when the spark plug hadn’t fired?

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Multiple misfires after replacing all coils and fuel pump

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