Question about 2008 BMW 328xi

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Engine misfireunder load

Engine runs smooth at idle and when reved up w/o load. When driving under hard acceleration there is a misfire. Plugs, cap, are new.wires are not new .

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I would check the coils...In have seen some fail at under 80k miles but mostly you can get well over 100k miles... I do not know if you have a great scanner or not, but what I do is use a scanner and run a power balance test and this graphs the cylinders performance and coil output.Also you can try cranking the car and let it get to operating temp,then go to each coil and disconnect it,you should have a rpm drop,if you do not get the rpm drop then that coil is bad.Last if you can test the resistance of the coil with a multimeter...Make sure you have the car scanned with a good scanner 1st to point you in the right direction.

Posted on Apr 15, 2014

  • Reggie Coleman
    Reggie Coleman Apr 15, 2014

    also I have also seen the crankcase vent valves begin to fail and casue similar issues

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1 Answer

I have a 1997 lumina with 3.1L. the problem started with loss of power under load and p0300 code. check coils and vacuum leaks both OK.change spark plugs and wires.[same problem] check compression OK.


Since you changed the sensor we will assume it is working. When you disconnect it you put the computer in limp mode which stops it from using sensor values. If code 300 is the only code we will assume the coolant temp sensor and others are ok.
I would check fuel pressure with a gauge next.

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2003 ford f 150 4.6 v8 and the idle went from smooth to rough also sputters and sluggish while driving check engine light is flashing.


have the vehicle scanned for error codes at autozone, its free. Post codes for more help....These engines have issues with the COPs (ignition coils-over-plugs) failing prior to 80k miles. When they fail typical problems are: Sputtering under load/acceleration, rough idle, random misfires, random stalling, light or heavy jerking under load (usually at 15-35mph and 45-65mph)..hopefully this helps!!

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I am having ongoing problems with the truck miss firing and rough running. Timing is ok, replaced cap and rotor,coil. It still starts rough,idles rough and misses when at cruising speed,although it seems...


Misfire is a common driveability problem that may or may not be easy to diagnose, depending on the cause. A misfiring cylinder in a four-cylinder engine is, pardon the pun, hard to miss. The loss of 25% of the engine's power output is the equivalent of a horse trying to run on three legs. The engine may shake so badly at idle that it causes vibrations that can be felt in the steering wheel and throughout the vehicle. The engine also may be hard to start and may even stall at idle, depending on the accessory load (air conditioning, headlights and electric rear defroster, for example).

When misfire occurs, performance suffers along with fuel economy, emissions and idle quality. And, when a misfiring vehicle is subjected to an emissions test, it will usually fail because of the unusually high levels of hydrocarbons (HC) in the exhaust.

What causes a cylinder to misfire? Basically, it's one of three things: loss of spark; the air/fuel mixture is too far out of balance to ignite; or loss of compression. Loss of spark includes anything that prevents coil voltage from jumping the electrode gap at the end of the spark plug. Causes include worn, fouled or damaged spark plugs, bad spark plug wires or even a cracked distributor cap. A weak coil or excessive rotor gas inside a distributor would affect all cylinders, not just a single cylinder.

"Lean misfire" can occur when the air/fuel mixture is too lean (not enough gasoline in the mixture) to burn. This can be caused by a dirty, clogged or inoperative fuel injector; air leaks; or low fuel pressure because of a weak pump, restricted filter or leaky pressure regulator. Low fuel pressure would affect all cylinders rather than an individual cylinder, as would most air leaks. A leaky EGR valve can also have the same effect as an air leak.

Loss of compression means the cylinder loses most of its air/fuel mixture before it can be ignited. The most likely causes here are a leaky (burned) exhaust valve or a blown head gasket. If two adjacent cylinders are misfiring, it's likely the head gasket between them has failed. Also, if an engine is overheating or losing coolant, it's likely the head gasket is the culprit.

Intermittent misfires are the worst kind to diagnose because the misfire comes and goes depending on engine load or operating conditions. They seem to occur for no apparent reason. The engine may only misfire and run rough when cold but then smooth out as it warms up. Or, it may start and idle fine but then misfire or hesitate when it comes under load. Also, it may run fine most of the time but suddenly misfire or cut out for no apparent reason. Intermittent misfires can be a real challenge to diagnose, so let's start with a steady misfire in one cylinder before moving on to intermittent misfires.

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running rough means it is misfiring.does it run smoothly without load or at idle?If it does then better check you fuel pressure as the engine needs more fuel under load.

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