LS coil misfire / DTC 21 / boosts fine

[ST240]

I have swapped LS2/truck coils that worked flawlessly last summer. New plugs this summer, with no change in ignition setup otherwise. I have a slight misfire at idle, and cruise, but it does not misfire at WOT in boost or acceleration. I'm getting a DTC 21 - ignition coil primary.

It seems I cannot isolate which cylinder it is either. I've tried swapping out all coilpacks with a working one. It seems whenever I unplug one pack, you can tell its running on 5, but the misfire is gone. WTF gives? Is the DTC normal with the LS coil swap and it's leading me astray and it's some other issue? Scratching my head over this one.

[Darius]

It isn't normal. Did you remove the ignitor when you did the swap? Dumb question, I know

[ST240]

Lol of course I did.

[Carl H]

you'll need to change the dwell to suit the ls2 coils, ecu doesnt like running them for some reason without the dwell changes.
whats odd is ls1 fires just fine...

[Darius]

I ran mine with stock PFC dwell values at 23 psi and it didn't run much different than running longer dwells.

[ST240]

you'll need to change the dwell to suit the ls2 coils, ecu doesnt like running them for some reason without the dwell changes.
whats odd is ls1 fires just fine...

I changed the dwell duty in Nistune for higher RPMs cuz I was getting some breakup. I tried messing with the dwell for idle last night but it didn't do anything. The weird thing is my motor idled fine last season before changing my head, etc.

The questionable part is why im getting DTC 21 - ignition coil primary, and can't seem to isolate it to a single cylinder.

I can't bloody well figure it out .

[ST240]

Could it be an intake manifold gasket leak? That wouldn't explain the DTC tho.

[Darius]

It doesn't hurt to check for one. It could cause a cylinder or two to run rich because it would be losing metered air right before the combustion chamber. If it is too rich, it may not fire at all.

[ST240]

Wait a tick though, at idle it's pulling vacuum, so should it not be pulling in unmetered air and running slightly lean (which would show on my WBO2)?

[julio]

If it misses only while under vacuum, you should do a good vac/boost leak check. I would check to make sure your grounds are in tip top shape also.

[Darius]

Wait a tick though, at idle it's pulling vacuum, so should it not be pulling in unmetered air and running slightly lean (which would show on my WBO2)?

Yes you are correct at idle it pulls vacuum and would be drawing in unmetered air to run lean (assuming no misfiring which would otherwise show up rich). I was referring to boost conditions because you said it was choking at around 5k rpm, which I interpretted as being rich.

[ST240]

It's a boost leak... Well there is a boost leak. Sprayed brake cleaner near the itbs of cylinder #6 and the rpm increases. I'll fix that and see if thats what the issue is. Still wondering about the DTC. I can't help but think it's been there ever since I swapped the LS2 coils.

Edit: Fawk. I think it's the ITB shaft seal :S. What a b**** this will be.