wendy-lad Posted March 8, 2023 Report Share Posted March 8, 2023 Hey guys, My car sat for 8 months, only being started and idled and free revved every now and then. It's back on the road now and I'm hitting a rather violent jerking misfire under load, with full throttle it's when the boost hits about 4psi. I can feather the throttle and lower the load and get it to rev out cleanly under that 4psi or so. I whacked new plugs in, and even gapped them down to 0.4mm so far. I had the old plugs gapped down to about 0.5mm and it ran smoothly under all conditions. I'm getting no trigger errors and not hitting any limiters as far as I'm aware of. Does anyone have any ideas I can try out, short of just replacing the leads and dizzy cap? I've attached the tune, and a couple of trigger scope captures as it's hitting the misfire I'm not sure how to attached a log as the maximum file size is 843.95kB...? Thanks legends! holden 304 dog.pclx on boost cut out 2.llgx on boost cut out.llgx Quote Link to comment Share on other sites More sharing options...
koracing Posted March 8, 2023 Report Share Posted March 8, 2023 Can you tell us what the engine and vehicle are? What coil/coils you're running? Do you have a PC datalog of when it hits the cut? You can upload to a free dropbox account or google drive or something similar and post the link in here. I see your file name is Holden, but the firing order doesn't match any v8 I've seen before. I see it's a distributor and you're also on an old version of the firmware. You have a GP limit set up for going lean on boost and perhaps that is what you're hitting, but without a datalog-it's hard to see what's going on. The trigger scopes look fine but they only typically capture one full engine cycle (2 rotations of the crank) plus a little more so it's unlikely you would capture the issue right when it occurs on a trigger scope. Quote Link to comment Share on other sites More sharing options...
wendy-lad Posted March 8, 2023 Author Report Share Posted March 8, 2023 Hey Kris, The engine is a Holden 304 V8 running a VT distributor so it has a home and 8 pulses. It's running a single GM LS coil. Link to log here if this works: https://www.dropbox.com/s/x8fvc831ptyg175/cutut 3.llgx?dl=0 I'm scratching my head as nothing changed in the tune while it sat for that time. Link to log from last year before it got parked: https://www.dropbox.com/s/c7mz9yj8394jz1u/last year lap.llgx?dl=0 Thanks Quote Link to comment Share on other sites More sharing options...
Vaughan Posted March 8, 2023 Report Share Posted March 8, 2023 It's not misfiring or cutting as the Lambda/AFR is still fine (there is a little bump to 0.877), a misfire introduces oxygen to the exhaust which results in a lean reading which you don't have but I can see the engine speed bouncing up and down and boost spiking which suggests it's an airflow through the engine problem, are you sure you're not valve floating or similar. You might be able to rev past it gently as the reduction of VE of whichever cylinder/cylinders are having issues is less of a difference between other cylinders issue at light load. I did just watch the skid factory video yesterday where they ran into a valve float issue on a very similar motor. Quote Link to comment Share on other sites More sharing options...
wendy-lad Posted March 8, 2023 Author Report Share Posted March 8, 2023 Hey Vaughan, I had the dump pipe off the turbo removed for those 8 months while it sat, but nothing would've fit through the turbine blades to be able to crawl into the exhaust to be choking it, and the intake has been sealed the whole time so I'm assuming it's not blocked. Unless the throttle body is being pushed shut or something now if the return spring has weakened randomly, but the TPS is still showing 100%... The cam is barely a bump above stock and has relatively new springs when the cam went in a couple of years, probs done 10 000kms since. It's not a gentle float limiter, it's a power noses off, then instantly jerks violently if the throttle is still held flat, identical sensation to the GP air/fuel ratio limiter I've got set, from 400hp to zero in an instant. A throw you forward out of the seat sort of feeling. Would a bad set of plug leads show as trigger errors? As if all the engine timing is still okay, just the leads are arcing on each other somehow. Or some corrosion or crud on the 8 terminals under the dizzy cap causing a weak spark? I'll pull the plugs again today, as yesterday when I gapped the plugs down further I sorta noticed the left banks plugs were maybe more sooted than the right... but I was too focused on closing the gap and didn't look into into that further... Thanks Quote Link to comment Share on other sites More sharing options...
Vaughan Posted March 8, 2023 Report Share Posted March 8, 2023 Trigger errors only happen when it is expecting a tooth that doesn't happen or it gets a tooth when it doesn't expect to. Note your dwell (measured not requested) does drop off under load so it could be blowing the spark out. @Adamw can probably provide a better evaluation than me. Quote Link to comment Share on other sites More sharing options...
Adamw Posted March 9, 2023 Report Share Posted March 9, 2023 I dont see any obvious causes in the log. A couple of thoughts: Check distributor rotor phasing. You dont have a massive range of advance in your map so you should have some room for less than perfect phasing but I would do a quick check anyhow. Just the trigger offset is quite unusual and makes me a little suspicious, usually with "1 tooth per TDC" type distributors the offset is very close to zero. Turn the engine by hand to 10-20BTDC, and pull the dizzy cap off to confirm the centre of the rotor is directly under a post. Check compression on all cyl (warm engine WOT). possibly a sticky hyd lifter? Possibly water in the fuel? Quote Link to comment Share on other sites More sharing options...
wendy-lad Posted March 19, 2023 Author Report Share Posted March 19, 2023 I had the tune trying to ramp to 11.2 AFR at only 4psi of boost and that was causing a rich misfire, so I leaned that right back to 13.0-ish and it began revving through under boost, only to hit a misfire at about 11psi then. This is all on pump 98. Gapped some new plugs down to 0.4mm ,still misfired. Whacked a new LS coil in it and still misfired. Gapped plugs down to 0.3mm and it would rev out and start making 14psi (what it should be), but felt quite noticeably down on power and sorta feels like it's misfiring, just doesn't noticeably sound like it's misfiring. Plus still has that terribly spikey rpm scatter that can't be helping it. So wiring in 8x LS coils and a crank trigger setup, that should sort it out once and for all... Quote Link to comment Share on other sites More sharing options...
Adamw Posted March 19, 2023 Report Share Posted March 19, 2023 Yep, trying to charge and spark a single LS coil 8 times per cycle isn't doing you any favours. Even if you did have enough cycle time for 8 x dwell and 8 x spark it is going to have very little time in between to reject heat so it is going to get overheated pretty quick and ign energy takes a dive as temperature increases. Quote Link to comment Share on other sites More sharing options...
Stevieturbo Posted March 19, 2023 Report Share Posted March 19, 2023 On 3/8/2023 at 7:49 PM, wendy-lad said: Hey Kris, It's running a single GM LS coil. A single GM coil was never designed to run at the sort of duties it would see firing an 8cyl engine, for all cylinders. It is a very bad choice of coil for a coil/dizzy application. Either use 8 of them, or none at all. Quote Link to comment Share on other sites More sharing options...
koracing Posted March 20, 2023 Report Share Posted March 20, 2023 A discreet igniter and V8/single application coil shouldn't set you back too much - MSD blaster SS coil is the old standby for me (has worked well with just one of these coils on 4cyl applications with distributor up to 30psi boost and 600whp on e85). There are any number of used easy to obtain igniters that could fire the coil with the ecu output - I personally have several Toyota non-turbo mr2 igniters I use for this type of thing (last one I did was a 69 Dodge Dart with a turbo on a slant 6 225cid engine with Link Storm - I think it had an accel performance coil - but we have run 24psi on e85 with it - custom hall effect 36-2 crank trigger wheel kit and a single sync coming from a modified 85 dodge pickup slant 6 efi distributor). Quote Link to comment Share on other sites More sharing options...
gmac355 Posted November 28, 2023 Report Share Posted November 28, 2023 Hi guys. I have similar issues 355 stroker 9psi intercooler cam tech cam. Single dizzy msd ignition box goes super rich over4500 rpm. Is this due to batch fire. Keen to see if anyone has a fuel map to suit cheers Greg Quote Link to comment Share on other sites More sharing options...
koracing Posted November 29, 2023 Report Share Posted November 29, 2023 If it's rich - tune the fuel table so it's hitting target. Quote Link to comment Share on other sites More sharing options...
gmac355 Posted November 29, 2023 Report Share Posted November 29, 2023 Cheers. The fuel map is looking weird numbers reduced for more boost and it’s finally into 11. Instead of 10 afr. I was told it’s because of Batchfire injection fuel will need to be reduced higher in the rpm it’s only getting to about 9psi hence 90/100 Kpa rich numbers Quote Link to comment Share on other sites More sharing options...
koracing Posted November 30, 2023 Report Share Posted November 30, 2023 That's not a lot of change to the values to get a full 1 point of AFR change (assuming you were 10.5 going to 11.5 for example). Is this being tuned on traditional mode? Is this a Vipec ecu as your profile shows? Moderators may want to move these posts to the Vipec forum. Quote Link to comment Share on other sites More sharing options...
gmac355 Posted November 30, 2023 Report Share Posted November 30, 2023 Ok cheers Quote Link to comment Share on other sites More sharing options...
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