Hesitant at about 3k to 4k revs. Thinking caps time

[Rosc0PColtrane]

As per title, I get to about 3k revs, under load and the car hesitates all the way to 4k, loses power and just doesn't quite fire right. Also when driving in normal conditions, with no throttle, there's an underlying judder too.

So far I have replaced: The airbox and filter, afm. Inspected the rubber L thing. Changed the black and silver bit that attaches on the left as well as the other L bit into the inlet manifold.

It does feel a little better, I have another L boot thingy but it's in worse condition than the one that's on there, with respect to pitting: This one is pristine, the donor one has cracks.

I wonder if the feeling better is due to the warm weather, it seems to prefer it. Though on start up, after changing all the bits above, it was instantly more responsive, less spluttery.

My next thought is the dizzy cap, rotor arm, leads and spark plugs, unless there's anything obvious I've missed?


Questions and suggestions equally welcome. I'm losing power where the car really should be peaking!

Oh, there is a blow on the exhaust, probably on the outlet manifold, hopefully in the first section of three, I cannot hear it with my head under the bonnet.

[Rosc0PColtrane]

Bump!!

Not a sniff of an idea?

[Brianmoooore]

Usually an ignition fault of some kind - rotor, cap or plugs.

[Rosc0PColtrane]

OK, thanks Brian. I get at it tomorrow night and post the results.

[GDBN]

My 320 does the same. I thought it would be the dizzy cap and rotor arm.
Be interesting to see the outcome.

G

[georgen]

Had the exact same problem with my 325 Nathan, and it turned out that the dizzy cap had a 4in long hairline crack. Fitting a new cap and rotor cured it..

To check that the leads are ok, try pulling them off individually whilst at idle. You'll be looking for a noticable change in engine tone with each removal to prove that the leads are ok. Oh, and use plastic pliers to remove them less you'll have a shocking time !!

[Brianmoooore]

Beware of pulling ignition leads off of the plugs on an E30 while the engine is running. The HT will rise to several 10's of kilo volts, and can flash over from the coil king pin to the - terminal, feeding a large voltage spike back to the ECU!

[georgen]

Beware of pulling ignition leads off of the plugs on an E30 while the engine is running. The HT will rise to several 10's of kilo volts, and can flash over from the coil king pin to the - terminal, feeding a large voltage spike back to the ECU!

Whoops, didn't realise this !! Is there a preferred way to test the leads Brian ?

[Brianmoooore]

Pull it off with the engine stopped, connect it to a spare plug on lying on the rocker cover, and start the engine.

[Brianmoooore]

The way I normally test HT leads is to measure their DC resistance. All six plug leads should be around 5k ohms, IIRC. If they are all the same, the chances are they are all good.

[dj_raoul]

I had the exact same problems with my 325 convertible. It turned out to be the lead to cylinder 5, which was totally busted at the sparkplug-connector.

I went to a BMW specialist, who found the problem by using the original diagnosis equipment (a huge enclosure with CRT screens ). It measured a very high voltage on this lead (over 25kV!), while the others were much lower (between 5 and 10kV if I remember correctly). The diagnosis was confirmed by pulling the lead with the engine running (as mentioned above). They did not turn off the engine for this, just pulled it with a plastic plier.

So your problem is most probably caused by bad leads, distributor, and/or rotor... Good luck!

[Brianmoooore]

I've actually got a machine of this kind in my workshop, but generally it's easier just to check the resistance!