Thread: V8 Cylinder Misfire

Hi All,


Quick question.


D2 V8


I changed the spark plugs over yesterday and Hawkeye is telling me there is a misfire in cylinder 3.


Is cylinder 3. as you look at the engine, second one in on the right? When sitting in the car I can feel the engine is slightly unsettled!


Cheers, Jerry

Originally Posted by Road Stone

Hi All,


Quick question.


D2 V8


I changed the spark plugs over yesterday and Hawkeye is telling me there is a misfire in cylinder 3.


Is cylinder 3. as you look at the engine, second one in on the right? When sitting in the car I can feel the engine is slightly unsettled!


Cheers, Jerry

Whilst you could actually have a misfire in one cylinder due to an ignition or injector issue, these codes are also often caused by a failing Mass Air Flow (MAF) meter.

When the Bosch MAF fails it usually reports ever decreasing loads on the engine, rather than just dropping over stone dead. This causes the engine to run leaner and leaner, until it starts misfiring.

The quickest way to check this is to look at the air consumption of the engine using your Hawkeye. When the engine is at a warm idle with no electrical loads (especially A/C and heater blower switched off) in neutral, you should see it using around 23-24 Kg/Hour of air for a 4.0 Litre standard motor (around 20 Degrees Celsius and standard barometric pressure of 1020 hPA or milliBars). If it is substantially less than this, then you MAF is on the way out.

The nearer to the graveyard the MAF gets, the less it will report. By the time they get down to 14 Kg/ Hour, the engine will not pull any real load without misfiring. Often this shows up as several random cylinders misfiring. If you check the AFR under these conditions on the rolling road, it will often show around 16.0:1

Do make sure it's a genuine Bosch MAF, as the world is awash with junk Chinese pattern parts.