Fixing a Dead Cylinder

[nsxbuilder]

I had an odd issue that left my car with a cylinder not firing, and the path to getting it fixed was a long and arduous one, so I thought I'd share.

The last few times I took the car out it felt like it was "stumbling" a bit while cold, but would eventually come back to smooth firing. Then I had it out "stretching the legs" and at around 110 at full throttle is bogged down...a lot. Letting off the gas I heard and felt a mechanical issue, and depressing the clutch let me know that the clutch was it. It didn't fully disengage, was hard to shift, etc. and I could smell clutch. It felt like it was running rough and I attributed that to the clutch, but I was incorrect.

I took out the single disc SPEC clutch (in poor shape I might add), dropped in a spare factory dual disc clutch I had laying around, and upon starting it for the first time noticed the 'missing' cylinder sound. Following the advice of others on Prime I disconnected all the injectors until I found the dead one - Driver's side rear.

I've been running the ProSpeed RSX Injector setup for over 5 years, and its been excellent, but I thought I'd start by reaching out to Brian and see what he thought. He said it could be the injector, so instead of swapping that injector over to the the middle rear and testing it there, I ordered another RDX Injector (around $60) and waited the two days for it to show up. That didn't solve the problem.

I chatted with the dealer NSX mechanic and a couple Primers and decided it had to be the ignition coil. So instead of swapping the coil over to the middle rear and testing it there, I put a multi-meter on it and found it was at 2.1-2.3 ohms, which is far from the factory spec of .8-1.0, so that had to be it. So I tried to order a new one [30521-PR7-A03] and was told Acura no longer makes that part. Of course they still make the front ones [30520-PR7-A03], the one's that see the least amount of moisture - makes perfect sense. I scoured the web and went to SOS and found nothing.

Prime to the rescue! Piran1 in Toronto had a used set for sale, so a deal was made and I waited for them to arrive. He had experienced something similar a while back, and bought a new set and replaced his, only to find they weren't the problem...more on that later.

So the used coils arrived, and just for kicks I put the meter on them and guess what - all six read 2.1-2.3 ohms. Hmmm, this isn't looking good. The factory spec states the reading is at 72 degrees, and it was quite a bit warmer in the garage, which was the difference in reading I was seeing. I put in the replacement and no change. Dammit!

Alright, back to the team for advice and the dealer said to check the plug - and it was pretty grungy - so I did the right thing and ordered a set of those at $9ea. No change.

So back to Piran1 who said he eventually found his issue was the Igniter Unit [30120-PR7-A01] that sits right on top of the motor, under the bank of small vacuum hoses. So I ordered one of those up ($350 but at least they still sell them!) and waited for its arrival.

Success! After installing, the car ran smooth as a baby, and taking it out for quick spin (now with the replacement clutch) its like a brand new car. I wonder how long that Igniter was giving less than optimal output.

So what did I learn?

- Two problems can happen at the same time - and I assumed (there's that word) incorrectly there was one.
- Testing is faster and cheaper than buying new parts, and spent a lot of time and money I didn't need to.
- Our cars are starting to lose factory new part availability, so spares are a good idea.

Also, knowing that the Igniter Unit is bolted to the engine which gets hot and vibrates, I thought why not put rubber spacers between the unit and the intake, and locktite the bolts in so they don't back out. I had a perfectly sized rubber grommet I cut in half, and it worked like a champ.

Let my lessons help you in your problem solving journey!

 

[Larry Bastanza]

BTW, you could use the front coil for the rear if required. There is a very subtle difference, in that there is a small weep hole outside the cylinder head seal on the coil for drainage. The hole is on the opposite side based on front/rear. So although this is not 100% ideal, it will work.

Regards,
LarryB

 

[nsxbuilder]

That sort of information is precisely why we keep you around Larry!

 

[Old Guy]

Just for future reference, that igniter unit is shared with some other Acura vehicles (Legend, some RL and TL). It might also be on some Honda branded vehicles. You might be able to find one really cheap at a salvage yard. The part is also available from aftermarket suppliers. Even from the aftermarket, it is a bit overpriced for what it is, which is essentially 6 power transistors in a heat sink. In a pinch, you could probably fabricate one using some Bosch BIP373 drivers for an all up cost of around $60 - $70. Wouldn't look as nice.

One of the things that screws up operation of the igniter is poor grounding. As I recall the igniter has a separate ground wire so make sure that is clean and well grounded.

 

[jwmelvin]

A poor ground, though, should cause random misfires that are not limited to one cylinder.

 

[Old Guy]

A poor ground, though, should cause random misfires that are not limited to one cylinder.

I agree. Poor grounding will affect all 6 cylinders. A poor ground may have no effect at low engine load; but, will typically materialize under higher cylinder pressures (which require a higher spark voltage to achieve ignition) when the reduced coil current because of voltage loss across the ground connection results in the coils being unable to generate enough voltage to ignite the air - fuel mixture. Those mis-fires can be random, or not. Coils, spark plug condition, cranking pressures, injector flow rates and cylinder filling all have uncertainties which may lead to the misfires occurring first on one or two cylinders rather than all six.

My comments about the grounding were about 'one of the things' that commonly screws up igniter operation and as such were out of context relative to the OP's problem which appears to have been a failure of one of the channels in the igniter.