Misfire

[LeeUK]

Hi Guys,

My car all of a sudden has developed a misfire when accelerating with load it makes the engine jump up the revs we believe that cyl 4 is the one misfiring, as the load is lowered or not load at all it uses all 4 cylinders, idling is fine.

Any ideas ?

We have checked the plugs and replaced and still got the same problem although it did improve slightly.

We think it might be the HT leads of the Distributor.

Cheers in advance,
Lee

[Brianmoooore]

The distributor cap/rotor arm is a common cause of misfire under load on the M40 engine. Genuine E30 ignition leads rarely fail, unless physically damaged.

[LeeUK]

It just randomly started ... it drove to work fine then I went out at lunch and this problem had started.

My plan was to do all the leads and the cap/arms. Could it be a blue plug problem ? I have also check the air hoses and everything looks fine.

Lee

[LeeUK]

Where the rotor arms located ?

[jmc330i]

The rotor arm is inside the distributor cap. When you remove the distributor cap you will see the rotor arm.

[LeeUK]

ok what is the best thing to do first ? I think its all original parts.

[Brianmoooore]

Check the cap and rotor, and replace if worn or cracked.
If the leads are genuine, and aren't falling apart (pulling the plug caps off by the lead), don't change them. Especially don't replace them with aftermarket leads.

[LeeUK]

is all this the same for the m42 ??

[Brianmoooore]

You'll struggle to find a distributor cap and rotor on a M42! They use a coil pack.

[LeeUK]

I had a feeling it had a coil pack I just wasnt 100%, so what is the best way to go about this ?

[LeeUK]

Bump,

Idle is very lumpy and it has hesitation when acceleration from idle (lowers in revs like jumps, this was before the misfire) and the misfire has got worse.

[Brianmoooore]

Check the big rubber air hose for splits and cracks. You will need to remove it to check it properly.