Losing spark on 2 cylinders above 2k rpm

[mafhoward]

I've got a confusing situation occuring with my MJLJR installation.

Spec: MJLJR V3, EDIS 4 coilpack and module, MAP setup, used on a BL Mini 1380, running 11.25:1 compression ratio. Everything installation wise works fine initially. On idle it sparks nicely on all four cylinders. I've got a problem when I rev the car above abour 2-2.5krpm though.

With my timing strobe connected to cylinder 1, I rev the engine and a misfire develops at around 2500rpm. This also shows up with the timing light as no spark when revved. The same happens on cylinder three. When I tried to diagnose this last night, I tried switching the two leads around on coil A (I switched lead 1 to where 4 was on the coil output) and coil B (2 to where 3 was) to remove the HT leads from the equation. I found that this caused the same fault to appear on cylinders 1 and 2. So this meant I went out today and spent £20 on a new EDIS 4 coil and swapped the old coil out. However, the problem still remains.

When revved, the coil seems to lose spark above 2krpm at one outlet on each coil. On coil A it's the top outlet (traditionally cylinder 1 on an OE install) on coil B, it's the bottom outlet (cylinder 3 on an OE install).

I wondered if this could be caused by resonance, or by MAP sensor problems, but surely that would manifest itself on all four cylinders (well, on all four coil outputs).

Please help, I'm thinking of going back to a stock distributor if I can't get this sorted soon, I can't drive my fresh built mini as it is

My last guess is that it could be an issue with wiring from the EDIS module to the coil, but again I would expect this to manifest itself on all four coil outputs, not just these two.

Matt

[MartinM]

So the MJLJ(R?) is on the bench, completely disconnnected? It should be as this sounds like a basic EDIS installation problem. So it can't be a MAP sensor problem.

If the MJLJ is connected up, then disconnect it completely for now.

With my timing strobe connected to cylinder 1, I rev the engine and a misfire develops at around 2500rpm. This also shows up with the timing light as no spark when revved. The same happens on cylinder three. When I tried to diagnose this last night, I tried switching the two leads around on coil A (I switched lead 1 to where 4 was on the coil output) and coil B (2 to where 3 was) to remove the HT leads from the equation. I found that this caused the same fault to appear on cylinders 1 and 2.

Do you really mean this - the problem was initially on cylinders 1 and 3 and by swapping the leads the problem appeared on cylinders 1 and 2? That sounds weird

What timing is the strobe showing at idle to 2000rpm? Should be rock solid 10BTDC. Is it?

[mafhoward]

Sorry, MJLJr (Junior)

The megajolt is connected to the EDIS module. I will disconnect MJ tomorrow and try again though.

Basically, the problem is on the coil outputs. On coil A (cylinder 1 output) I am getting a fault. On Coil B (cylinder 3 output) I am getting a fault. I know the problem is not HT leads as I have tried switching them around to see if the problem moves with the leads or not.

So, if I look at the coil from above, with the coil outlets facing towards me, the top right coil outlet is showing up the fault mentioned above. The bottom left coil outlet is also showing the same fault.

The timing light picks up no signal from whichever lead is connected to either of these two coil outputs. This is what confuses me. Coil A, outputs cylinder 1 and 4, has a fault on cylinder one. How can it not have the same fault on cylinder 4??? They're both driven by the same input, they both have the same power supply. Is it possibly down to the wiring between the coil and EDIS module? Again, surely this would show a problem on both cylinders on each coil, not just one cylinder on each coil?

Oooh, perhaps the problem is down to the EDIS coil not being externally earthed? I did try an earth loop connected to the chassis of the coil, but that didn't remedy the problem. Also, this is showing on 3 different coils, it's not the coil that's for sure.

[mafhoward]

Do you really mean this - the problem was initially on cylinders 1 and 3 and by swapping the leads the problem appeared on cylinders 1 and 2? That sounds weird

What timing is the strobe showing at idle to 2000rpm? Should be rock solid 10BTDC. Is it?

No, the problem was initially on cylinders 1 and 3, by swapping the leads around the problem was then on cylinders 2 and 4. This was to prove if the problem was on the coil outputs or the HT leads.

Sorry for my confusing typing, it's just that I am VERY confused by this! lol

If I can't get it sorted tomorrow night, I'm in the poop as I'm moving house on Friday and HAVE to have the car running.

[david jenkins]

I saw similar problems on my car - I even posted a similar question on this forum. The answer (for me anyway) was quite simple.

The EDIS coil is wired to fire 2 spark plugs at the same time. One spark gets a negative polarity impulse, the other gets a positive one. My timing light has a clip that goes over the plug's ignition wire and has an arrow that points towards the plug, suggesting that it expects an induced voltage in a specific direction.

If you have a similar sensor clip on your timing light, try turning the clip over on the cylinders you think are faulty, and see if the timing flashes improve. This may not be the answer to your problem - but it's a really cheap test before you spend any more money!

In my case, I decided to ignore the timing light result as the engine was running properly!

Let me know the outcome if you decide to try this...

cheers,
David

[mafhoward]

Thanks for the reply, unfortunately the timing light recieving no signal coincides with a nice misfire on the engine, so I am pretty sure it's actually losing sparks.

But, your post has got me thinking if it's something to do with the coil not earthing correctly????

[luke6040]

id say doublr and tripple check your earths, iv had so many electracle probs on my mini and shortly after pullin a large amount of hair out its just an earth issue, maybe check the earth strap from the bulkhead to your engine as these always play up lol.

[MartinM]

'fraid not - the coil doesn't need explicit earthing...the centre pin is +12v and the outer pins are open circuited/connected to earth at the appropriate times by the EDIS module.

[mafhoward]

'fraid not - the coil doesn't need explicit earthing...the centre pin is +12v and the outer pins are open circuited/connected to earth at the appropriate times by the EDIS module.

Well, this is what I'd read (on here I think) and that's why I didn't initially fit a specific earth for the coil.

It's confusing the heck out of me, I just can't understand how each coil can have one faulty output above ~2krpm when they work OK below ~2krpm.

[brentp]

Matt,

Do the problems center around a certain RPM range? Does the engine smooth out after you push past the problem RPM region?

Often, the problem with mis-fires around a certain RPM is related to a crank sensor bracket vibrating at it's harmonic frequency, which distorts the VR signal to the EDIS module. The EDIS module looses sync with the trigger wheel and you have your misfire. Usually it's seen at about 4K RPMs, however.

What else... Earthing the coil is not necessary. Yes, good to test without the MJLJ plugged in, as it eliminates that variable. Your advance should be rock steady at 10 degrees BTDC.

Have you tried attaching the inductive clamp along various points on the HV leads?

Have you routed the VR sensor cable well away from the HV leads? Is this cable shielded, and with the shield grounded at the EDIS module end?

[mafhoward]

Matt,

Do the problems center around a certain RPM range? Does the engine smooth out after you push past the problem RPM region?

I've not 'pushed past' the problem yet, it's a fresh built engine so I don't want to over-rev it just yet as it's not even run in. It doesn't seem to clear though, there's basically little or no spark on the two coil outlets above around 2-2.5krpm.

Often, the problem with mis-fires around a certain RPM is related to a crank sensor bracket vibrating at it's harmonic frequency, which distorts the VR signal to the EDIS module. The EDIS module looses sync with the trigger wheel and you have your misfire. Usually it's seen at about 4K RPMs, however.

I'm using a pre-built bracket, bought from 'Specialist Components' that is tried and tested on many engine builds, a lot more extreme than mine. I'm not saying it's definitely not that, but it's low down my list of suspected problems. But again, why would this only be on two outlets on each coil?

What else... Earthing the coil is not necessary. Yes, good to test without the MJLJ plugged in, as it eliminates that variable. Your advance should be rock steady at 10 degrees BTDC.

I shall test it tomorrow night, I will report back on that, but I am failry sure it's an EDIS issue.

Have you tried attaching the inductive clamp along various points on the HV leads?

Yep, I've tried at various points along the lead, plus I've tried turning it around. When turned around there was no 'light' below 2krpm at all.

Have you routed the VR sensor cable well away from the HV leads? Is this cable shielded, and with the shield grounded at the EDIS module end?

The sheilded cable is about 1ft away from the leads, the nearest it gets is actually near the coil and it's still around 8" away from the coil there.

Thanks for all of the help though guys, I've got a few ideas to try tomorrow.

EDIT: Yes, sorry, it's a shielded cable, which is grounded at the module end too.

[mafhoward]

Also, I think I may try a fresh +12v supply to the coil tomorrow. Rather than using the existing one that also powers the MJLJ and the EDIS module. I suspect that my problems may be there somehow!

[brentp]

Hmm-- if the system is power starved that would certainly cause problems at some point when RPMs (and power demand) increases.

keep us posted!

[brentp]

One more quick thought on this. If you are suspecting power supply issues, be aware of the following when considering your 12V supply:

High current demand: coil pack
Lower current demand: MJLJ, EDIS module

The one additional note is that the EDIS module should have a robust ground connection as the module controls the coil charging/firing by switching the coil ground connections on and off. The thick ground connection on the EDIS module harness is a give-away as well.

[mafhoward]

Brent, many thanks for the reply...

Tonight I shall attempt the following,

1. Replace ground/earth wire for EDIS module and 'Jolt unit. One thought I had late last night (whilst awake at a stupid hour) was that I currently have the EDIS module and 'Jolt ECU grounded to the engine on a loop terminal, rather than on the body/chassis of the car. I beieve that this may be one of the problems?

2. Supply coil with fresh ignition switched (and fused) +12v, fed through a relay and some nice fat 17A wire.

3. Pull more hair out!