Argh yet again... misfire over 5000rpm
09-10-2014, 09:40 AM
#76
Nordschleife Master
Thread Starter
Polarity on the stock coil IS correct (black wire to (+) and green wire to (-)) - the actual stud sizes on the coil are different. One stud is larger than the other - enough of a difference to prevent you from being able to swap the connectors.
It's *possible*, I suppose, the stock coil was still weak/going/whatever, and the MSD *would have* fixed it, had I not wired it backwards (?). But something else is now definitely broken and preventing spark.
Reading up now on possible causes/reasons/fixes for why I'd have fuel, tach bounce, 12v at the coil, a clean connection from the (-) back to the DME (no shorts, did a quick ohm check last night)... and still no spark.
09-10-2014, 11:42 AM
#77
Nordschleife Master
Thread Starter
Another brief update: Traffic SUCKED this morning... after driving 1.5 hours and seeing the road sign say "110 minutes" from where I was to downtown - I turned around. F that.
Upside: took another look at the car. Hotwired the KLR (pins 9 to 16) and...... VROOM. Car starts. Reconnect KLR, no start.
I now have an official starting point to investigate.
Upside: took another look at the car. Hotwired the KLR (pins 9 to 16) and...... VROOM. Car starts. Reconnect KLR, no start.
I now have an official starting point to investigate.
09-11-2014, 01:12 AM
#78
Rennlist Member
Polarity was NOT correct on the MSD coil.
Polarity on the stock coil IS correct (black wire to (+) and green wire to (-)) - the actual stud sizes on the coil are different. One stud is larger than the other - enough of a difference to prevent you from being able to swap the connectors.
Polarity on the stock coil IS correct (black wire to (+) and green wire to (-)) - the actual stud sizes on the coil are different. One stud is larger than the other - enough of a difference to prevent you from being able to swap the connectors.
So the black wire has the larger connector and should go the (+)?
I've got that coil and can't remember for the life of me how I installed it.
09-11-2014, 08:43 AM
#80
Nordschleife Master
Thread Starter
I don't remember which had the bigger ringlet but the coil is marked.
09-14-2014, 12:05 AM
#81
Nordschleife Master
Thread Starter
Well... new KLR arrived (thanks Lart!), swapped stock coil back in... misfire still present. Swapped MSD coil back in (wired correctly this time)... misfire still present. Ohm'd out most of the wiring harness, no shorts that I could find.
My dad stopped by, we ran it in the garage with a timing light on the plug wires (to see if we could see the spark drop out) while it misfired... couldn't see anything obvious (light stayed smoothly lit) but on the 3rd rev, as I dropped the throttle, a big plume of smoke came out the tail pipe. Didn't think anything of it but when I shut the car off - noticed the coolant bottle puked coolant.
Not sure WTF broke now but I am soooo beyond pissed off at this thing!!!!!!
My dad stopped by, we ran it in the garage with a timing light on the plug wires (to see if we could see the spark drop out) while it misfired... couldn't see anything obvious (light stayed smoothly lit) but on the 3rd rev, as I dropped the throttle, a big plume of smoke came out the tail pipe. Didn't think anything of it but when I shut the car off - noticed the coolant bottle puked coolant.
Not sure WTF broke now but I am soooo beyond pissed off at this thing!!!!!!
09-14-2014, 06:57 AM
#82
Three Wheelin'
I think you may have found the cause of your misfire, hear me out and ask me how I know later 
Under high boost (high rpm and load) your head gasket was compromised enough to allow coolant into the combustion chamber and reduce the combustability of the air fuel mixture enough to cause a misfire. Under low boost (low rpm and load) the head gasket seal was "good enough" to keep the coolant where it should be and not cause a misfire.
The timing light on the plug wires wouldn't show an issue as the problem wasn't electrical, it was an issue after the spark plugs, not before them. Unforunately the strain on the cooling system of running and revving the engine without airflow over the radiator was enough to overheat the engine (coolant overflow) and finally pop the head gasket (smoke out the exhaust).
Pull head, replace gasket, re-check for misfire under load.
Under high boost (high rpm and load) your head gasket was compromised enough to allow coolant into the combustion chamber and reduce the combustability of the air fuel mixture enough to cause a misfire. Under low boost (low rpm and load) the head gasket seal was "good enough" to keep the coolant where it should be and not cause a misfire.
The timing light on the plug wires wouldn't show an issue as the problem wasn't electrical, it was an issue after the spark plugs, not before them. Unforunately the strain on the cooling system of running and revving the engine without airflow over the radiator was enough to overheat the engine (coolant overflow) and finally pop the head gasket (smoke out the exhaust).
Pull head, replace gasket, re-check for misfire under load.
09-14-2014, 02:28 PM
#83
Rennlist Member
I think you may have found the cause of your misfire, hear me out and ask me how I know later
Under high boost (high rpm and load) your head gasket was compromised enough to allow coolant into the combustion chamber and reduce the combustability of the air fuel mixture enough to cause a misfire. Under low boost (low rpm and load) the head gasket seal was "good enough" to keep the coolant where it should be and not cause a misfire.
The timing light on the plug wires wouldn't show an issue as the problem wasn't electrical, it was an issue after the spark plugs, not before them. Unforunately the strain on the cooling system of running and revving the engine without airflow over the radiator was enough to overheat the engine (coolant overflow) and finally pop the head gasket (smoke out the exhaust).
Pull head, replace gasket, re-check for misfire under load.
Under high boost (high rpm and load) your head gasket was compromised enough to allow coolant into the combustion chamber and reduce the combustability of the air fuel mixture enough to cause a misfire. Under low boost (low rpm and load) the head gasket seal was "good enough" to keep the coolant where it should be and not cause a misfire.
The timing light on the plug wires wouldn't show an issue as the problem wasn't electrical, it was an issue after the spark plugs, not before them. Unforunately the strain on the cooling system of running and revving the engine without airflow over the radiator was enough to overheat the engine (coolant overflow) and finally pop the head gasket (smoke out the exhaust).
Pull head, replace gasket, re-check for misfire under load.
09-14-2014, 10:46 PM
#85
Three Wheelin'
Weak spark + head gasket? Weakened spark from extra load of headlights causing stumble to get worse at high rpm, with the underlying cause being a head gasket on the way out? Two terrible events conspiring to annoy you? I'm not sure what the root cause of the the weak spark is, if there is one, but based on what just happened I really think you saved yourself getting stranded by a blown head gasket by having it fail in the garage. That's all the signs of a blown head gasket, and if it was failing slowly, as mine did, strange stuff happened to me at higher rpm when that happened. Crap luck but I'd do some tests for the HG, see what comes of it.
09-15-2014, 10:57 AM
#86
Nordschleife Master
Thread Starter
Definitely could be - though I'm still not convinced the spark is weak. I mean, it sure as hell behaves like a weakened spark but the fact that I ran fresh wiring and it still sputtered... *shrug*
I still haven't really truly and fully tested the theories given to me on the previous page (alternator generating A/C current, etc.) I'll try to get to that this week. Also thinking I'm going to try running a complete fresh set of reference sensor wires back to the DME. Easy enough to do, and that'll eliminate the bizarre scenario that Sid referenced.
I'll also do a quick compression test, and pressurize the cooling system, to look for obvious HG leaks. I'll also order up a new HG today - so I can do the HG over the weekend if I decide to skip going to COTA.
I still haven't really truly and fully tested the theories given to me on the previous page (alternator generating A/C current, etc.) I'll try to get to that this week. Also thinking I'm going to try running a complete fresh set of reference sensor wires back to the DME. Easy enough to do, and that'll eliminate the bizarre scenario that Sid referenced.
I'll also do a quick compression test, and pressurize the cooling system, to look for obvious HG leaks. I'll also order up a new HG today - so I can do the HG over the weekend if I decide to skip going to COTA.
09-15-2014, 12:08 PM
#87
Rennlist Member
Could you tell if the smoke was oil or coolant? Oil smells like, well, burning oil -- and lingers in the air much longer/heavier than coolant. Coolant in exhaust is essentially steam and burns off like steam. If you had coolant in the exhaust and coolant overflow after high revs, then chances are you haven't wasted money ordering the new HG... I've seen plugs literally drip coolant when removed, when the HG is completely shot. Try pulling the plugs right after running it, and look for coolant. Either way, oil or coolant can foul new plugs and create weak spark.
09-15-2014, 01:24 PM
#88
I had a similar misfire issue last year. It was in fact my head gasket. I could get a few boost runs before it would carry on. I did a leak down test with the coolant cap off and pushed coolant out of the bottle on cyl #4.
09-15-2014, 04:19 PM
#89
Nordschleife Master
Thread Starter
Could you tell if the smoke was oil or coolant? Oil smells like, well, burning oil -- and lingers in the air much longer/heavier than coolant. Coolant in exhaust is essentially steam and burns off like steam. If you had coolant in the exhaust and coolant overflow after high revs, then chances are you haven't wasted money ordering the new HG... I've seen plugs literally drip coolant when removed, when the HG is completely shot. Try pulling the plugs right after running it, and look for coolant. Either way, oil or coolant can foul new plugs and create weak spark.
Funny thing is, I was thinking it was a HG months ago.
Guess I'll just plan on doing it. Can't really hurt, it'll just cost me a few bucks in gaskets plus a weekend...
09-15-2014, 07:05 PM
#90
Burning Brakes
Ok, late to the party, but Ignition miss coupled to a Blaster Coil reminded me of Rogue_Ant's 2/10/2013 post 'Tech: The 944/951 Ignition System'. A work of literary/electronic Art. Bottom line is, compatibility of the 'Blaster' may require some electronic's adjustment depending on the Model used. just saying.