Hey all, I'll just get right to it:
A little about the car, its an 03 on AEM EMS V1. Aby helped me get it running really well, well enough I enjoyed it for a couple years like it is.
Honda COP, HTA71, S2 GSC cams, full 3" exhaust, 4" intake, fully forged internals, no balance shafts.

The problem started in December when I hadn't driven it in a few weeks and got it out to give a friend a ride. It drove awesome as always, I flogged it. Brought it home and it sounded like it was idling kinda funky, almost like a dead cylinder. did the typical pull a plug wire on each coil until you find the one that doesn't change the idle. Cyl 4 some times made a change, some times it wasn't much at all.

Compression tested it, came back a good 15 psi higher than the other 3 cylinders. Not really too big of a concern until you see the plug. It was black and wet, couldn't tell if it was unburned fuel or oil. I assumed oil, replaced the plugs, it ran great... For about 5 minutes idling, decided to take it around the block, seemed good. Went down the road and as soon as I took off it sputtered and bucked and backfired and was awful. Turned around and came back, idled like a dead cylinder again. Pulled coil 4 and no change.

So I swapped coil 3 and 4 thinking maybe the coil was going bad. Dead cylinder stayed on 4.. Swapped injector 3 and 4, miss stays on cylinder 4... OK...
Took my AEM apart, remembered my friend that I bought the car from 9 years ago saying there was a burned trace on the board that caused weird issues back in the day. I have continuity across that, probed around a bit but nothing looked off. Resistance checked my injector packs, they all came back the same ohm (I forget what it was, like 5.6 or 6.4 or something, within what the book says and they were all the same) so I'm to the point where I think its the ECU because nothing that I can find, seems to point to anything else. I am going to see about maybe probing some wires to make sure its not just getting full 12v all the time or something but if that proves unfruitful I'm down to maybe trying to find another V1... good luck.. or maybe swapping to something else.

What do you guys think?

 

You could pull the connector off of the injector and use a test light hooked to battery + ( the ECU sends ground) to test for a signal. Light flashes, ecu is sending signal. No flash, no signal.

 

I've never used anything like that before.

https://www.autozone.com/test-scan-a...ece/948078_0_0

Something like this right?

 

Ooo those are nice. I have a generic test light

 

did you inspect the plug tips? I have evo9 and ngk iridiums. I got a batch of fake iridiums from my regular supplier and the tips melted when i raced

 

When I first pulled the number 4...


2 is kinda dark but wasn't wet looking.

They're NGK copper BR7es I think

 

ok. just read you replaced the plugs. what does the new ones look like now? no codes btw? my ecu always throw codes, i had to disable them

 

Looking at the state of the spark plugs, it feels like your injector may be faulty

 

Good question, I'll pull them tomorrow and see what we got.
No codes, it's an aem ems v1 so Im not sure it stores codes like stock ecu does.

 

I moved the number 4 injector to port 3 and Cyl 4 stayed being the one that didn't change the idle.

 

OK so, it's been a minute. I had to take an emergency trip for work, got home and had Corona.. Over that and feeling good enough to work on this again.

Got the plugs out, these are in order from left to right starting with cyl1
Cyl 3 is a reused plug from last time cause they only had 3 in stock when I replaced them. Other than that it seems to me like Cyl 2 and 4 are rich.. Cyl 4 has fuel sitting in it. These plugs have maybe 2 miles on them and 15 to 20 min of idle time trying to diagnose.

Nothing about the tune has changed since the last time I drove it. In fact I think I reloaded the last known good tune I had just to be sure.

I put a noid light on a couple of the injectors and Cyl 3 looks like Cyl 4. Gets brighter as it revs up.. Don't know what that should look like. It gets pulse but to solid light.
Starting to wonder if there's not something just wrong with the aem, some sensor but if there was wouldn't it just not run at all? Why would only Cyl 4 has fuel in it and not be firing

 

the same signal supplies cyl 2 and 3 on the coil packs and vice versa. when you go COP you basically double these wires up to make 4 plugs from 2. Id say theres something funky in this wiring thats causing your issue as both cyl 2 and 4 plugs are bad. If your cyl is full of fuel and your plugs look black you havnt got an issue with your injectors theres definitely fuel getting through but your not getting any spark. The issue lies in the ignition. Youve swapped coils and the issue stays on the same cylinder which means its either wiring or the ecu.

Would start with the wiring pull the insulation etc back till you get to where its been spliced and check for any damage or issues in the splice. it might not be a completely broken wire but just a loose wire. Not sure what your wiring skills are like you could either just cut the wiring to cyl 2 - 4 out and re do it or you could run the car and wiggle the wiring around and see if it makes the idle change as your wiggling.

If this all checks out then would start looking at the ecu.

 

I think the coil on cylinder 4 fires cylinder 1 and 4, and the coil on Cyl 2 fires 2 and 3?
I originally am the one that went to the COP setup. Since then I went back to factory ignition coils, factory wiring.

 

Sorry yes your right its the other way around. I would still look into the COP wiring as this is what youve changed. If youve got a bad pin or a partially broken wire somewhere it may work part of the time but part of the time not work

 

Ok, so I hate when I find a forum post that is a similar issue Im having and theres no resolution and its been 5 years so:

I decided before I tear into wiring, I'd start troubleshooting over entirely and forget everything. I popped in brand new spark plugs, left them the gap that they are out of the box even.
Started the car expecting that it'd run well and then get bad as it went, like it always does... It didn't. It never got bad. The thing idles perfectly lopey like it always has.... SOOO

I suppose what had happened is perhaps I did have a coil getting weak, I had my plug gaps very very small due to some spark blow out issues back when I was working on tuning it (2 or 3 years ago now) and I've never had an issue until now, I suspect I just needed new plugs but because that coil was weak, the spark kept getting extinguished for too many cycles, the cylinder basically flooded, when I put new plugs in the first time I gapped them small like before, there was just too much fuel to overcome and it fouled out the new plug, on top of that coil being weak. Replaced coils with stock coils and big plug gaps and it runs mint now.

I appreciate the thoughts and time to read through this with me.

TL;DR needed new plugs, might have had a bad Denso coil initially, replaced with factory coils and plugs, runs great.