9KCanuck

Brief rundown of car and mods + recent history:
- 2002 s2k -- 90K km
- GReddy emanage ultimate piggyback (new)
- Karcepts tune (new)
- CAI + stock header + 70mm HFC (new) + 63mm Tanabe Medallion (70mm exhaust planned for next spring)

- car has recently developed a random, very subtle hesitation ~3-4k rpm when accelerating.
- I thought it was maybe my imagination until one day pulling the car out of the garage, it started up very rough and threw misfire codes. I turned the car off and started it again -- it started fine and ran fine, so I cleared the codes. That particular behaviour has not occurred again.
- I still notice the hesitation/hiccup every once in a while, though.
- Prior to the ECU piggyback and the new HFC, I never once noticed any kind of hiccups/hesitation, never any CELs.

What I've done since then:
- valve adjustment -- quite a few were too loose/tight
- compression test -- 240-240-230-235 (while cold, to boot!)
- cleaned IACV, since the car was also idling a bit oddly recently as well. This helped.
- cleaned TB butterfly, but it looked fine anyway
- checked spark plugs -- they looked fine. A tiny bit of oil on the 2 rear-most plugs, but nothing in the wells.

** What I am wondering **:
- is there ANY chance the 70mm HFC + 63mm exhaust could cause hesitation or even misfires?
- possibly the TPS? Is it worth trying to get it off and cleaning it somehow (if that's even a thing that's possible)
- maybe get the injectors cleaned? Can a guy just take them to any place that does this service? or should I only look for a shop that has a particular kind of machine?
- get new coils?
- replace spark plugs? They're about 4 yrs old, 10K km or so on them. Reasonable bit of track time, fwiw.
- I don't really want to, but I could always disconnect the piggyback ECU and see what happens. Maybe my car doesn't like this tune? It's the same tune by Brian at Karcepts that he has done for countless S2Ks, so I highly doubt that this is the case.

engifineer

ah the fun random misfire code. First I will say I just went through this. 1 coil pack was completely dead, 2 others were pretty bad and even the good one was not great. So do not rule out all the coil packs going bad on you. It is not intuitive for that to occur and will drive you nuts troubleshooting it And as a note, if it IS coil packs, order coil packs for an 04/05. They are about half price of the AP1 coils and work in the AP1. I think the DBW year model coils will not work though, just the 2005. Coil packs are unfortunately known to fail on the AP1s. Yours is pretty low mileage but I have heard of people having them fail that early too.

Oddly, I also had 1 - 3 giving issues at first and 4 seemed fine. But spark gap testing, even on a gap smaller than the max gap the coil should fire, killed number 4. It was firing at first but not strong and consistent and then just died. I have a overly long winded writeup on here about why I think that occurred. But, just do not rule out coil packs up front just because it does not make sense that 3 or 4 failed at the same time. You could try to move one of the others to cylinder 4 and see if the misfires move with it (aka cyl 4 now misfires but the one you swapped does not)

Do you know anyone well with an AP1 that would let you swap coils to test ? That is the easiest and cheapest test with multiple misfires like this.

I also have the Karcepts Emanage setup and I did take it out of the system to verify it is not the issue. A good idea to do that. It does not take a lot of time but it sucks getting all those connectors stuffed back in the kick panel again. But, do that just to rule it out.

You can also check coil and injector wiring back to the ECU. If you do not have a shop manual I can post up which terminals each wire goes to in order to help there. I did that as test before ordering new coil packs. One pin goes right to ground, one to 12V and one to the ECU and it will pulse when the car is running or cranking over

windhund116

Is there a set of coils that you run when on the track? A type that is better in continuous high-heat conditions.

Thanks!

engifineer

I had the originals in until they just failed at 160,000 miles. I bought NGK's to replace them so will see how they do. Given that the full set of 04/05 NGK's were $160 it was worth trying them! I think others are running them on track with no issues I know of so far.

9KCanuck

Thanks for the replies. I'll look into some NGK coils.

The problem is that the misfire CELs only happened that one time, and hasn't occurred since. The car definitely did start up in a strange state... maybe this was just a red herring/coincidence.

So all I'm experiencing now is what I can only describe as a little hiccup/hesitation on acceleration every once in a while. I'd say I notice it two or three times in a 20 min drive... it's subtle and difficult to describe. Imagine accelerating at a moderate pace and then driving over a very small speed bump.

If any real smart person could tell me whether or not the 70mm HFC + 63mm exhaust could somehow be responsible, that would be amazing. I don't really want to put the OEM cat back on for troubleshooting this, but maybe I'll have to. Ugh.

engifineer

I do not think it is the HFC and exhaust. at least the 63mm HFC is pretty much required with the Karcepts tune but the 70mm is supposed to perform just the same. If you run the stock cat you will have a BIG power dip around 3k-4k rpm. When I first got my Emanage and tune from Karcepts I did not have the HFC yet and it was pretty bad in that power range. Overall 0-60 was slower due to it. Putting in the 63mm Berk made it perfect but they said the 70mm would work just the same. The header makes very little difference with his tune but the HFC is a must.

So I do not think the 70 mm HFC + 63mm exhaust is causing the hesitation for you here and given the impact of running the stock cat with his tune, testing with it would only make it appear worse.

And if the codes are not still showing up, may just need to drive it until it happens again, but your slight hesitation could be weak coils and if so I suspect you will see the codes pop up again so you can test further. On mine, the last check I did was using a spark gap tester. The one coil would not fire it even on the smallest gap (small engine test gap). 2 others would only fire intermittently at some of the middle gaps and then stopped completely. I think the already weak coils with failing internal insulation were destroyed by testing with a higher gap (which results in a higher firing voltage).

windhund116

Bad gas? I mean, the fuel in the car, not you.

bad_driver

I do not think misfire CELs could ever ben caused by an HFC and exhaust. I don't even think bad O2 sensors could cause misfires unless something was horribly wrong...

Slowcrash_101

Me, they work just fine.

B serious

Oil in your spark plug holes probably caused the misfire the first time.

After you cleaned them out, you may still have had oil residue on the coils/plugs.

Is the oil leaking into the galleys again? Or did you fix the leak?