Massive misfire over ~5000rpm

Post Mon Feb 24, 2014 8:58 am

(car - m20 with motronic 1.3 and old e30zone chip.)

Morning guys, On the way to work earlier I gave the car a boot full and the result was a hard loss of power at ~5000rpm.

Felt more like hitting the limiter than a misfire but tried to reproduce it and found that I got a similar result if I give it about 70%-100% throttle and hit 5k.
Feels like a total loss of power and sounds like a real hard misfire.

If I stay under 5k then it runs and drives fine. So I don't think it is a mechanical/internal issue, even though it felt like the bottom end was trying to leave the block.

Really odd thing is it just started doing it this morning. No symptoms up to now but I guess that's just how it goes.

I am stuck in work at the moment so can't take a look until later on today, going to check the usual suspects, my mind at the moment is on the ignition side of things but I am sure someone here has hit this issue before.

Post Mon Feb 24, 2014 1:49 pm

Just thinking about it, the car has been a little grumpy starting the last few days.

Crank sensor on the way out?
Loosing signal over 5k?

Post Mon Feb 24, 2014 2:19 pm

Could be those items. What's the state of the cambelt?

Post Mon Feb 24, 2014 4:14 pm

I'd be checking the distributor cap and rotor arm, when worn their accuracy begins to fail at high revs, bridging multiple or no points at once.

Post Mon Feb 24, 2014 5:01 pm

Cam belt has 27k on it.

Religiously do them at 30-35k.

Rotor was pretty new as was the cap, however it was my first thought.

Wondering about the coil as well, as far as i know its the oldest part on the car, could be not energising enough.

Will see how it is on the way home in a second and let you know.

OK to follow up on this, drive home was kind of uneventful, if i say out of high revs and high throttle then it drives fine.

It seemed a little less eager to start but not really by much.

Seems to have a stutter if you hold the revs around 2k out of gear/stationary. you can feel it through the car.
Also sounds a little flat.

With that said my fuel pump sounds like a clockwork toy sat on he back seat, easily audible with the engine less than 3k.

Poor fuel pressure?