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Multiple misfires after replacing all coils and fuel pump

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

@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?

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 misfire and the crankshaft slows down the computer will set a code that cylinder 2 had a misfire.

Tester

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 crank sensor.

To the OP’er: I’d have to agree with Tester, this seems like it may be due to a problem with the fuel/air ratio. Either too rich or too lean could cause a (mechanical-caused) misfire. The MAF is a good place to start. O2 sensors and air leaks (Including vacuum devices) would probably be next.

There’s a possibility of course it could be electrical. Mabye do a visual. Check the spark plug wires to make sure they are oriented in the same positions (with respect to each other) as when the car was new. Sometimes spark plug wires run in parallel over a long distance can cross talk with each other, causing a misfire. Plug wires which cross at a 90 degree angle seldom cross talk. I doubt this is the cause though, unless the spark plug wires have been reconfigured somewhere along the line. While doing this, good idea to make sure the insulation isn’t cracking.

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 it’s happening at a different period in time than expected.

Tester’s definition was accurate- A misfire code indicates something in a cylinder or a number of cylinders prevented proper combustion

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

'03 & '04 Matrix’s commonly get a leaky intake manifold gasket.
Gets worse in cold weather.
Causes a lean code and/or misfire code.

Thanks @TwinTurbo for the clarification, yes, I understand from your comment it could be a missing or weak firing (rather than one occuring at the wrong time) that could cause the crank to slow unexpectedly.

Yes I had misfires before repacing coils and changed all of them to try to fix problem and changed plugs.

Today after about 2 hours on route, Matrix sort of hesitates, dies and then will start right up. This happened 6 times in about thirty minutes and then the rest of my driving day it ran fine.
Codes again indicated multiple misfires.

As Tester and TT said, a misfire means the ABSENSE of combustion.

A detonation in a cylinder at a time when there shouldn’t have been will be detected by the “knock sensor”. The knock sensor is an accelerometer that senses a mechanical “shock”, a pulse where there should be none. Technically, it’s a crystal that emits an electrical output when irritated by a specific frequency that an erractic combustion pulse creates, called a “piezoelectric” device.

Technically, it’s a crystal that emits an electrical output when irritated by a specific frequency

I love it!
Consider it stolen, to be used at the first opportunity…