How can I diagnose which cylinder a missfire is occurring in?

[Landboat G80]

This vehicle is not under warranty.

Current modification list:
- JB4
- Intakes
- Exhaust (Secondary Delete)

I currently have a missfire issue that is not throwing codes. There are rarely any misses in MAP 0 (They do still occur) however between MAP 1 and 3 the miss-fires get progressively worse at anything over around 30% throttle. These seem to only happen during the first 3-4 seconds of heavy acceleration and then they're gone. The missfires are pretty violent, sounds like a big stutter, a small but quiet pop, the car kicks a little and immediately picks back up.


This issue started when I installed an ECU Tune which had some over-boosting issues. It's been removed and returned for the time being. I had to replace all of my plugs after that which cleared up around 99% of the issues, before I couldn't even accelerate, I had to limp the car to a mechanic to have the plugs changed to HKS M45IL's. I only did 3 WOT pulls on this tune, the rest of it was just limped around to get home and to a mechanic.


It doesn't matter how often this miss happens, it will not throw a code. I've even (against my better judgement) made it miss a few times on purpose to get one, no luck.

I'm running 93 Octane Fuel, According to the JB4 "Virtual E85" Gauge my estimated E content is around 13.
I thought maybe this could have been a bad tank of fuel, but I ran it empty and filled back up and still no luck.

I don't *think* it would be a coil since it only happens under heavy throttle, but I'm not very mechanically inclined.

Any guidance of diagnosing this issue would be greatly appreciated.

I currently have WMI, Fuel-It, and EWG wires sitting in my garage and an intercooler in my shopping card, but I'm waiting to install it because of the missfires, lol.

Trying to figure out which cylinder so I can check the coils.

EDIT: I have gone over several of my JB4 logs during this happening and event sent some to Terry, fueling isn't perfect but it's not maxing out trims by any means. I don't feel like it's a fueling issue, but I may be wrong.

Also I noticed my Idle AFR is sometimes sitting at around 12.9/13.0 but most of the time it's 14.7 like you'd expect.

 

[oddball]

A good code reader will pull the ECU misfire count per cylinder.

Were you running the stock plugs with the stock gap previously??? It's entirely possible that one or more of the coils were damaged due to the misfires.
Were the old plugs in good shape when they were pulled out? I'd be worried there was physical damage at this point. Beating on an unprepared engine can cause spark plug porcelain to break apart.

 

[Landboat G80]

A good code reader will pull the ECU misfire count per cylinder.

Were you running the stock plugs with the stock gap previously??? It's entirely possible that one or more of the coils were damaged due to the misfires.
Were the old plugs in good shape when they were pulled out? I'd be worried there was physical damage at this point. Beating on an unprepared engine can cause spark plug porcelain to break apart.

I was not running stock plugs and haven't since I bought the vehicle. The gap on the plugs that were pulled out were all messed up, but nothing was broken. I'm being very light on the throttle and only chilling in MAP0 for the time being, as there's no missing under these conditions. Can you recommend a code reader that could check the missfire count for our cars? My life would be so much easier if I could just diagnose where the problem was, before I go and start replacing random coils and plugs, then testing in a relatively dangerous manner.

 

[Terry@BMS]

If its not triggering a misfire code you'd need a scan tool that has misfire counters per cylinder. Tricky to diagnose without the code though.

 

[Landboat G80]

If its not triggering a misfire code you'd need a scan tool that has misfire counters per cylinder. Tricky to diagnose without the code though.

I’m going to rip the plugs out and check them in a day or two, then start replacing coils. I have a creeping suspicion that the mechanic that I had do my plugs regapped them to stock gap.

What gap do you recommend for the HKS M45IL for the following mods, I was at 0.022 before with the denzos, changing brands due to forum FUD.

- Intake
- Exhaust
- EWG
- Fuel-It
- WMI
- FMIC

 

[oddball]

0.22 to 0.25 is fine.
Generally as long as you pay more than $200 then it'll probably do it. I have a Autel Maxisys 808 All Systems. It's slow, but works well. I don't know if they have Stinger support because my update license expired in 2018.
Getting the straight scoop on scan tools - what they will and will not do, especially per-car for the manufacturer specific stuff - is incredibly difficult. At least until you hit the pro level tools that run >$1k