Chasing a misfire

spandit · Post by **spandit** » Mon Jun 27, 2011 7:49 pm

Had the first real world test of my MegaJolt powered Pinzgauer at the weekend with some serious off-roading. However, on the way home, the engine was badly misfiring to the point when it would stall instead of idling. This evening, I have done the following:

1) Removed and cleaned the plugs (they all looked the same)
2) Sprayed all electrical connections with WD40
3) Tried disabling the MJLJ to run off EDIS alone
4) Run the engine with those spark plug lights in - as far as I could tell, it looked OK

To no avail. It still runs as rough as an alligator with acne.

I did notice, whilst running the laptop that on a few occasions at idle, the RPM would drop to zero. Didn't happen for every misfire but might be a clue as to what is happening.

Engine seems to run OK with higher revs. Is there a product out there than can tell me which cylinder isn't firing and when?

FULMNTE · Post by **FULMNTE** » Tue Jun 28, 2011 3:18 pm

This sounds like exactly the same symptoms I hed recently with a bad EDIS module.
No misfires when you ran the EDIS without the MJ?

spandit · Post by **spandit** » Tue Jun 28, 2011 10:02 pm

Missing with or without MJ. I'll see about sourcing another EDIS module. Have ordered a compression kit in the meantime. I'll try testing HT lead resistance tomorrow

spandit · Post by **spandit** » Thu Jun 30, 2011 3:38 pm

Well, HT leads seem fine and compression is roughly the same on all cylinders (after getting the crappy kit to sort of work). I've won another EDIS module off eBay for £14 delivered, which isn't too bad. However, I've realised the exhaust has moved quite a bit with my extreme off-roading and thinking that could be the culprit. Have removed the manifolds anyway as I was missing a stud (it was snapped off and I've managed to get it out - what a relief!)

If it isn't the EDIS at least I'll have a spare and it's the easiest thing to replace

cng1 · Post by **cng1** » Sat Jul 02, 2011 7:37 am

If the RPM was dropping to 0 then it implies that the EDIS module has lost synchronization with the trigger pattern. So check that you haven't knocked the crank sensor/wheel out of alignment.

spandit · Post by **spandit** » Sat Jul 02, 2011 5:37 pm

cng1 wrote:If the RPM was dropping to 0 then it implies that the EDIS module has lost synchronization with the trigger pattern. So check that you haven't knocked the crank sensor/wheel out of alignment.

It seemed pretty solid when I had a look/feel - wondering whether dirt in the end of the sensor might have affected things? I've got a spare EDIS now so once I get the exhaust bolted back on, I'll see what's what.

I'll also have a good look to see whether any moisture has got into the wiring - pretty sure the stuff from the sensor to the EDIS was well sealed

cng1 · Post by **cng1** » Sat Jul 02, 2011 6:11 pm

Just because it looks solid doesn't mean that it hasn't got knocked. Measure the gap at 4 different points and check that they are all the same to be sure.

spandit · Post by **spandit** » Mon Jul 04, 2011 11:01 am

I'll do that this afternoon if I have time. Just tried swapping the EDIS module and didn't seem to make a difference (so at least I know I've got 2 that work... or 2 that don't!). Going to see if a new coil pack makes a difference too. I'll have spares of everything by the time I've finished...

If it makes a difference, the misfire seems to be at low revs only - at high revs the engine seems to run quite smoothly

Ferraripilot · Post by **Ferraripilot** » Wed May 09, 2012 3:00 pm

spandit wrote:I'll do that this afternoon if I have time. Just tried swapping the EDIS module and didn't seem to make a difference (so at least I know I've got 2 that work... or 2 that don't!). Going to see if a new coil pack makes a difference too. I'll have spares of everything by the time I've finished...

If it makes a difference, the misfire seems to be at low revs only - at high revs the engine seems to run quite smoothly

I'm having this exact same issue. Anyone know a fix?

Post by **brentp** » Wed May 09, 2012 3:21 pm

Misfiring is often attributed to a vibrating sensor mount causing the EDIS module to lose sync with the trigger wheel. The losing sync / re-acquiring signal causes gaps in the ignition firing, resulting in the 'mis-firing' effect.

As usual, checking the gap, reinforcing the sensor mount, etc. will often help pinpoint the problem.

Of course, failing components and bad connections on wiring always present a potential problem. For example, a coil pack with a broken connection in the secondary windings will manifest itself as a misfire during high RPM / high load conditions, gradually getting worse.