ktm Posted January 14, 2008 Share Posted January 14, 2008 The misfire occurs in 2nd and 3rd gear at boost pressures exceeding 10 psi. The car stumbles badly, a bit of popping in the exhaust, and I can't get it to work through the range. I do not experience this in 4th and 5th gear and I am able to hit 15 psi without a problem. I've already gapped my plugs (NGK BPRES7) to 0.03 in. with no luck. My spark plug wires at Magnecor's and I am using LS-1 coil on plugs. The coils are set at 5 ms dwell time. The car never did this before when I was running hotter plugs (6s) before my last HG failure. Does anyone have any idea why I would misfire in 2nd and 3rd but not 4th and 5th? Quote Link to comment Share on other sites More sharing options...
hughdogz Posted January 14, 2008 Share Posted January 14, 2008 Hi Bo, Do you think the spark may somehow be blowing out? You mentioned you're using NGK BPRES7 gapped at 0.030". You probably have a good reason for running these, but why not the BPR6ES-11's? Haynes says 0.039-0.043" gap, but NGK says 0.044"... I may be totally wrong about what plug we should be running with LS1 or Denso coils, but I'm curious why you're running a colder plug at a smaller gap than stock... -hughdogz Quote Link to comment Share on other sites More sharing options...
ktm Posted January 14, 2008 Author Share Posted January 14, 2008 Update: Just re-gapped the plugs to slightly smaller than 0.025 and upped the dwell to 6 ms (from 5 ms) on the coils. It seems to have done the trick and I only misfired once. However, my idle suffered a little bit as you can hear the occassional miss. Hugh: I was running the 6s which is fine for stock, but when you run more boost you should really consider going with a colder plug to prevent pre-ignition. More boost means hotter temperatures. The gap must be adjusted from the stock 0.044 for NGKs down to around 0.03 or so to prevent spark blowout. Quite a few posts here on Hybrid talk about the issue. Quote Link to comment Share on other sites More sharing options...
ktm Posted January 14, 2008 Author Share Posted January 14, 2008 I just had another thought that I may be slightly too rich over 11 psi. I have 4 to 5 logs that show my AFR is around 10.5 between 11 and 15 psi. I will also try to lean it out slightly (11ish) which will enable me to open the plugs back up to 0.03 which should help my idle. The plugs themselves look fine. The electrode is not covered in soot and neither is the ceramic tip. I may go back to 6s though. I'll keep this post updated. Quote Link to comment Share on other sites More sharing options...
Clifton Posted January 15, 2008 Share Posted January 15, 2008 Hi Bo, I'm curious why you're running a colder plug at a smaller gap than stock... -hughdogz The higher the boost, the tighter the gap. The book is considering 7 psi. I run .022", I run a little more boost though. Quote Link to comment Share on other sites More sharing options...
jeffp Posted February 2, 2008 Share Posted February 2, 2008 The gap is going to fully dependant on the ytpe of coil you are running. I don't know what system you are running, but you mentioned you set your spark duration to 6 mSec, that is much more then is required to fire a coil. Most coil primaries become fully saturated by 2-3 milli seconds for a not so good coil. You just may want to check to see if the coil is getting hot, that is the sure sign that you are turning the primary windings to the coil into a heating element. The ECU driver transistor must be getting hotter then a pistol at that duty cycle as well. I never liked the idea of adjusting the spark gap at the plug to .022-.027 or so. I have taken a look at the pulse on my oscope and the gap is not sufficient to get a proper discharge of the coil. That is why the car runs poorly at idle. To correct the misfire properly, get a coil that has a sufficient voltage potwential output that will accomidate the higher cylinder pressures. Mallory makes a very good coil for points, and a good unit for a capacitive discharge type ignition. I tried the MSD HVC coil, and it worked well but failed very quickly, two failed quickly in fact. But I was able to run high boost with the car. The output voltage on that part was 48,000 volts, and I did have to adjust the plug gap as well. The mallory coil is a bit better, @ 50,000 and they are oil bath type coils, they can handle much more heat in that configuration. anyway. Quote Link to comment Share on other sites More sharing options...
jgkurz Posted February 2, 2008 Share Posted February 2, 2008 The misfire occurs in 2nd and 3rd gear at boost pressures exceeding 10 psi. The car stumbles badly, a bit of popping in the exhaust, and I can't get it to work through the range. I do not experience this in 4th and 5th gear and I am able to hit 15 psi without a problem. I've already gapped my plugs (NGK BPRES7) to 0.03 in. with no luck. My spark plug wires at Magnecor's and I am using LS-1 coil on plugs. The coils are set at 5 ms dwell time. The car never did this before when I was running hotter plugs (6s) before my last HG failure. Does anyone have any idea why I would misfire in 2nd and 3rd but not 4th and 5th? The engine load/boost response will be much different in the lower gears vs 4th and 5th. This might be a reason why the miss occurs in 2nd and 3rd and not 4th and 5th. Your description sounds like you may have a lean condition contributing as well. Do you have a way to measure AFR's? I seriously doubt your plug gap is the issue. Coils maybe, but not plug gap. Just make sure your NGK plugs are all in good shape (no cracked insulators or damaged electrodes) and gap to .025 and move on to another area for troubleshooting. You might want to run a smaller or larger gap later on but for this purpose .025 should be a good starting point. Just my .02C Let us know what you find out. Quote Link to comment Share on other sites More sharing options...
texis30O Posted February 2, 2008 Share Posted February 2, 2008 Would this be the same for a draw-thru carb'd setup? I am running .34 on mine. I am now running her up to 15lbs of boost. But will eventualy see up to 20lbs...... Quote Link to comment Share on other sites More sharing options...
jgkurz Posted February 2, 2008 Share Posted February 2, 2008 Would this be the same for a draw-thru carb'd setup? I am running .34 on mine. I am now running her up to 15lbs of boost. But will eventualy see up to 20lbs...... Everyone's got their own opinion on plug gap. It all depends on your application, spark plugs and the quality of your ignition system. .034 is probably a bit too wide of a gap if I had to make best guess. Quote Link to comment Share on other sites More sharing options...
jgkurz Posted February 2, 2008 Share Posted February 2, 2008 Hi Bo, Do you think the spark may somehow be blowing out? You mentioned you're using NGK BPRES7 gapped at 0.030". You probably have a good reason for running these, but why not the BPR6ES-11's? Haynes says 0.039-0.043" gap, but NGK says 0.044"... I may be totally wrong about what plug we should be running with LS1 or Denso coils, but I'm curious why you're running a colder plug at a smaller gap than stock... -hughdogz Hugh, Colder plugs will help resist detonation as you increase boost. The small plug gap will help ensure the mixture fires as combustion pressure increases. As you probably know, the more HP you make the higher the combustion pressure. This is likely a substantial increase over what the L28ET was designed for. The BPR6ES-11 plugs work great but you really should consider a bit colder plugs when turning up the boost. I'm sure there are people running crazy boost with BPR6ES-11's but I like to improve my odds of survival whenever possible. The trick is to not go so cold on the plugs or too small a gap that you decrease driveability significantly. It's really a trial and error approach for what works best and when. As an example, I run different plugs on the street vs on the track. The LS1/Denso coil packs on an L28ET wouldn't necessarily require different plugs. However, they might allow you to run a bit more gap due to probable improved ignition performance. Quote Link to comment Share on other sites More sharing options...
ktm Posted February 2, 2008 Author Share Posted February 2, 2008 jgkurz, I have an Innovate LC-1, LMA3 and G3 gauge and have been tuning the car using them. My fuel map is almost ideal with my AFRs around 11 at 15 psi at peak torque....or so I believe. I just called up my latest log file and see that I am hellaciously rich at 13 to 15 psi (low 10s, high 9s) , but I know that I made adjustments since that log. I have not logged since then. I should update everyone. My coils are LS-1 coil on plugs running NKG BPRES6-11. I was running 7s, but they fouled out quickly due to very rich conditions while early tuning. I bought 3 sets of plugs and gapped them at 0.035, 0.03 and 0.025. I ran the 0.035 and was misfiring still but not nearly as bad. I upped the dwell since the AFR was still a bit rich (per z-ya's testing, LS-1 coils saturate at 8ms - I should be fine at 6ms and I was originally at 5 ms). I then switched out the 0.035 plugs for the 0.03 plugs and that helped out quite a bit. I still misfire, but I do not get the severe bucking I used to. I need to do another logging run to verify that my AFRs are still not in the low 10s, as that will definitely cause a miss, especially if the plugs are partially fouled. Quote Link to comment Share on other sites More sharing options...
Tony D Posted February 3, 2008 Share Posted February 3, 2008 I don't know what system you are running. All that time looking at the laptop in the parking lot, and he doesn't know what system you're running. Bo, you ever get the idea Jeff may have had one beer too many that night at Fuddrukers? LOL BTW, nice cameo shot of you polishing the car at MSA last year (at least I think it was you) on the MSA Event DVD (now in stores...LOL) Get that AFR ironed out and see what your spark does then. If you aren't somewhat close to optimal on the AFR (and 9's and 10's are WAY too rich) then the tendency to light off the mixture REGARDLESS of your coil/plug/gap combination will be low. Quote Link to comment Share on other sites More sharing options...
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