Suddenly started cutting out - graphs attached

Ouster · Post by **Ouster** » Sun Mar 20, 2011 6:25 pm

Hi All,

I've been running megajolt for several months now on my mini with no problems whatsoever. Now though it's developed a bit of a backfiring habit. When I'm accelerating hard under load the advance backs all the way off to 12 degrees until I drop the revs whereupon the advance gets back to normal.
I've swapped the coilpack and checked all my grounds, still the same problem. It's weird as the unit has been working fine for several months.

Attached are the two graph files I made - one shows a large "misfire", the other shows two smaller ones. You can clearly see the advance going to 12 degrees and also curiously during this time megajolt isn't registering the revs. The rev counter in the car also dies.

I've also attached the map I am using.

Please help!

Toby

cng1 · Post by **cng1** » Mon Mar 21, 2011 10:43 am

A few possibilities to check here as it's not clear from the logs what is going on.

First can you confirm that you are running resisitive spark plugs - they're usually identified by an 'R' in the part number.

Second check your trigger wheel alignment - your crank sensor needs to be about 0.5-1mm away from the teeth of the trigger wheel on the A-series engine. Whilst you are there check that there is no runout on the wheel, in other words that the gap between teeth and sensor is the same all the way round.

Third check that your crank sensor wiring in particular isn't going past any sources of interference - that means alternator and HT leads. The shielding on the crank sensor cabling needs to be connected to earth at the EDIS module but not connected to anything at the sensor end.

The final possibility is that the issue is on the fuelling side causing the miss. Given the RPM dropoff seen by the ECU it seems unlikely but I have occasionally seen issues like that before where the miss causes the engine to shudder so dramatically that it causes the engine speed signal to drop out.

Post by **brentp** » Mon Mar 21, 2011 5:06 pm

Hi Toby,

Also- how is your tachometer wired?

Ouster · Post by **Ouster** » Mon Mar 21, 2011 8:10 pm

Brent - the tach is connected to what would have been the negative wire of the coil. Why do you ask?

I'm convinced it isn't a fuelling issue, it just doesn't feel like it.

The plugs are BPR6ES - so resisitive.

The crank sensor is right beneath the alternator. I'll check if my cable tied wiring has come loose. I'll also give the sensor the once over, although last time I checked it was rock steady.

Thanks guys, this gives me something to work on now.

Toby

Post by **brentp** » Tue Mar 22, 2011 3:02 pm

Hi Toby,

So I presume you're running the diode circuit to bridge the signal between both coil packs?

Since the tach is reading off of the coil packs, a cut-out on the tachometer would indicate the EDIS module is not firing the plugs during the time you're experiencing this problem.

I would say your problem revolves around the crank sensor and it's ability to reliably read the signal from the wheel. Check if something came loose, went out of aligment, etc.

Also, your bracket needs to be very rigid. If it seems to cut out at certain RPMs this could point to a harmonic resonance of the bracket which will affect the signal, causing the EDIS module lose sync with the signal.

NITROPIXIE · Post by **NITROPIXIE** » Tue Mar 22, 2011 6:55 pm

I had this a bit and found to have 2 faults. Firstly the mis-firing got worse and worse which happened to be the coil pack. Also my head gasket had gone (between cylinders 2 & 3 on a mini) and a valve seat had cracked, bugger (which i still haven't repaired).

If you can get hold of a compression gauge to test your cylinders for symptoms. They aren't to expensive on fleabay or ask a friendly garage to borrow theirs. Remember to floor the throttle and turn the engine over a similar amount on each cylinder.

Ouster · Post by **Ouster** » Fri Apr 01, 2011 5:28 pm

Looks like I was too quick to point the finger at the megajolt....I appear to be missing a rather important component!

toenee · Post by **toenee** » Fri Apr 01, 2011 5:42 pm

LOL that could well be the problem, has it fallen out or did you forget.....a good idea to help prevent the bolt coming loose is to use a verto flywheel bolt. Cut about quarter inch off, this will give more thread engagement over the standard bolt which is too short imho.

Ouster · Post by **Ouster** » Fri Apr 01, 2011 7:07 pm

I definitely put the bolt on when I built the engine. My guess is it's worked its way loose recently and has started to cause this problem. Would explain the strange rattling sound in the engine bay. Maybe I forgot to knock back the locktab washer? I'm surprised the wheel hasnt come off completely - thank you fanbelt!