Misfire
Turbo Mini Forums

This is really puzzling me. The car has developed a high speed misfire, 6300rpm and above. It sounds like a soft cut rev limiter, and happens regardless of load. So far I have replaced the megajolt,edis, coilpack, crank sensor, plugs and leads to no avail. Also wound the mixture up and down and had the head off to check valves springs etc. Compression test as normal on all cylinders. Engine pulls very strongly below this critical speed. Any ideas from the collective?

'Where does the engine go?'

What RPM is the Rev limit set to?

Could you do a log to see what’s happening? Maybe it’s loosing crank position at high RPM.

In the 13's at last!.. Just

rev limiter is set to 7300, sadly I can,t do a plot. The timing is at about 38 deg at 6000, as the misfire starts the afr falls from about 15:1 but I guess that's just unburnt fuel

'Where does the engine go?'

maybe re load the mjolt software in case it has a glitch ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

In the early stages of this Robert,I discovered my old V3 was dying (13 years old) so upgraded to a spanky new v4,reloaded the map and off she went,but still the misfire.

'Where does the engine go?'

Is it loosing the crank signal?

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

apart from loosing the crank signal, you could be loosing synch between the Edis box and the jolt, which would mean it falls back to the 10 degree inbuilt timing, that should show up as loosing rpm in the jost software,

The rpm and advance are stable into the misfire so I don't think I'm losing the crank signal. Is it possible to get advance as per map on the jolt readings but have the engine seeing edis fixed timing?

'Where does the engine go?'

The rpm and advance are stable into the misfire so I don't think I'm losing the crank signal. Is it possible to get advance as per map on the jolt readings but have the engine seeing edis fixed timing?

'Where does the engine go?'

Make sure you're using resistor spark plugs.

http://www.jbperf.com/

Yes, same plugs I've always used, swopping between sets made no difference.

'Where does the engine go?'

38 degrees timing at 6,000? Is that a misprint? Is this a boosted motor?

Phil.

WWW.TURBO-MINI.COM

That's at no load Phil, it's about 17 at full load.

'Where does the engine go?'

Ah ! Makes more sense.

Phil.

WWW.TURBO-MINI.COM

perhaps try new earth leads , also a direct from battery to 12v coil supply to eradicate any ign switch or wiring problems ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

I did try putting a second battery on in case I was losing voltage. my next move is to replace the lead from edis to mj including the earth connections.

'Where does the engine go?'

crank sensor bracket not cracked and vibrating the sensor away from the wheel ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Will check Robert, I have replaced the sensor, would expect a loss of crank position to mess up the tacho reading?

'Where does the engine go?'

I had an issue when I first installed MJ, the sensor wire wasn't sufficiently shielded and it caused a number of strange running issues, that and the gap were critical.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Steve, I think your last post is in the right direction. You and I have had similar issues in the past with these connections, remember ?

Yes David, and I've had others since!

'Where does the engine go?'

So after a few diversions, i can report as follows: changing every element of the ignition system has no effect. The jolt is talking to the edis, as timing on the crank is correct, and moving the rev limiter speed also works. Tried a thick damper oil in the carb to no effect. The problem is worse before the engine is fully warmed up, starting around 5000rpm, and also worse if the engine is sharply revved as against a slow increase. Is it fuelling related after all?

'Where does the engine go?'

Do you have a wideband lambda sensor fitted, what does the fuelling do?

Yes Tom it goes from 12/13 to 10/11 as the misfire begins.

'Where does the engine go?'

Well I've now renewed every element of the ignition system to no avail. Last time out the onset of misfire was at about 5.5K but did not start until the 3rd run. Cycling the engine on no load between 5 and 7K the misfire would clear if i took it slowly. Runs very rich anyway, is this some fuelling problem after all? Could the carb be leaking?

'Where does the engine go?'