Hey all, my tl has a bit of a rough idle, and once in a while when I hook up my code reader I have a pending/historic misfire code for a couple of cylinders, both I've checked it's been for cylinder 5, once for cylinder 1 and once for cylinder 3, but my check engine light is never on.What terminals do I hook up my ohmmeter to for checking resistance, and what's an acceptable range? This way I can determine if it's a coil or 2, or something else. I just changed spark plugs and didn't change anything so ruling that out.

 

Did you use OEM spark plugs? Rather than use a multimeter just start your car and start unplugging coils one by one until you figure out the culprit. Then replace that one with an OEM replacement (Hitachi I believe depending on your year)

https://www.rockauto.com/en/catalog/...tion+coil,7060

 

I used Denso pk20tt platinums. They aren't oem but still correct. They shouldn't be causing the car to run rough. The old plugs were acdelco coppers that looked like the same plugs I've pulled out of a small block Chevy, so if anything Performance should be better, not worse. I only have a misfire code once in a while and my check engine light is never on, hence why I would like to check them over with an ohm meter

 

I just tried disconnecting coils 1 by 1, they all caused a misfire, I guess my idle is caused by something else, it smoothens out as soon as I bring the motor up to like 1000-1200

 

An argument can be made they are not correct; if the plugs are not the exact plug the engine was designed to run with, then then chances of them being incorrect is pretty high, regardless of what their manufacturer or an interchange guide might say.

 

The plugs I put in are fine electrode platinum, and the plugs I pulled out were traditional copper and they definitely had a bigger gap worn in them. If I had 50,000km on these spark plugs I'm sure there'd be a chance that those are the issue, but there was no difference in idle after going from old plugs to the brand new plugs. After cleaning egr valve and ports, the high idle on a cold start is definitely smoother, it's only when the car idles down to 700rpm when warm that the engine doesn't idle perfectly smoothly.

 

You're missing the point, the Denso plugs are NOT identical to the NGK plugs; yes, they may have similar design criteria, but unless the heat range and spark characteristics are the same, you're going to run the risk of having misfires.

 

The heat range of the 2 plugs are the same, and my denso plugs are gapped at .040, within spec of Acura, so I am officially ruling out spark plugs as a culprit for the idle.

 

OEM is NGK Iridiums...

but i guess you know better than we do

If you pulled all coils and they all misfire, then the culprit is the spark plug or the fuel injectors, you can either start looking at Air and Fuel if you believe you're correct and keep digging, or you can just put in the proper plugs like we suggest. Up to you on how badly you want to chase this

 

My point is that I changed the 2$ copper ACdelco plugs, (which were definitely well used and who knows if they were a proper replacement plug) and it made a very minimal effect on the way the car idled. If it was a spark plug issue to begin with, it either would have ran far better or far worse after plug change. If anything, the only thing that's made a bit of a difference is after I seafoamed the intake, cleaned the throttle body, and egr. I haven't seen a thread yet about how someone used plugs that were an oem replacement and the car started not running great, then they put in a new set of oems and they run much better. It's not like I blindly grabbed a set of plugs that were way off from factory specs and threw them in. The car has 365,000 km so I wouldn't be surprised if theres a dirty fuel injector or 2 as well.

 

Once again, you have either deliberately missed the point or you don't understand the physics involved. Just because two different manufacturers claim the same heat range for plugs does not in any way mean the plugs function the same. You can officially rule the plugs out, but if/when you finally figure out the plugs are the culprit, don't say we didn't try to tell you.

Meh, 225,000 miles is not very much; I honestly don't think I've ever seen a clogged fuel injector on any J-Series Honda engine, regardless of mileage. If you want to officially rule anything out, it would be the injectors and not the plugs.

 

Spark plugs from reputable manufacturers are most likely tested, then rated at said heat range, not just labeled at said range yet they could work totally different. I've never dealt with any car that has ran poorly due to anything other than oem plugs put in it. Hell, I've thrown E3 spark plugs in a car one time and it actually ran pretty good. This whole thing about only using 6994s would be much more believable if someone else had a similar situation, and was fixed by putting in 6994s. Does that mean that even an NGK Iridium IX line plug won't work great?

 

cyl 5 tends to blow out the spark plug... Wouldn't be surprised if it previously ejected. Check your air intake boot for rips, maybe clean the MAF?

 

Didn't have any issues installing so hard to say. These cars have MAP sensors which are slightly different, supposedly they dont get dirty and affect performance like MAF sensors do, but would probably be worth a try, and it's in the throttle body so a ripped intake shouldn't affect it too much, which I know is good

 

I'm sorry, but this is incorrect. You don't have to believe me, but that's the truth of the matter.

 

So in that case my car should run different after doing the plug swap since the platinums are totally different compared to the old copper plugs, due to that the heat they burn at and way they function are totally different, which it doesn't. it runs just about the same with the new plugs as it did with the old worn out plugs. Acceleration, power, and mileage, and the slightly rough idle are just about identical.

Unless if you personally had an experience or someone else on here has experienced changing between a new set of aftermarket plugs and OEM plugs made a drastic difference performance then I'm still not convinced. If your logic is correct, this should apply across the board to most late model cars.

 

Different engines have different sensitivities to different plugs; some could care less, the J-Series Honda engines prefer the OEM NGK plugs. Don't believe me? No problem; search this and any other Honda related forum and look at the hundreds of posts where random engine problems were cured by putting in the OEM plugs. Still don't believe? No problem, keep trying random and money wasting things. Regardless, I'm done here.

 

blah blah blah

There's no point in arguing about the plugs since you're dead set on it not being the cause.

Fine.

Most of the time resistance measurements are a waste of time.

I recommend you check the current ramps on the injector and coils. You'll be able to see something that sticks out from the rest. You'll need a wiring diagram, current clamp, and scope.

You can also check injector pressure drops if you want by using a fuel pressure gauge and a bi-directional scanner.

Hondas some times throw misleading random misfire codes for multiple cylinders, which could actually be caused by only one cylinder.

 

So cleaning my PCV valve made a huge difference in throttle response, and acceleration especially at low throttle.
I checked o2 sensor readings and found my fuel trim on bank 2 is much higher where the couple of misfires happened. I had a good check for vaccuum leaks and could hear a small hiss from the valley between the cylinders. I've heard these cars can develop intake manifold leaks so I will try replacing those gaskets.

 

Another update, I decided to replace intake manifold gaskets, and I'm sure glad I did. They have definitletely been removed and when re installed, they were covered in dirt, oil, etc. I also replaced valve cover & spark tube seals. The car runs much better, and theres a big improvement in fuel mileage. I have a bad downstream o2 sensor, so I imagine once that is replaced, itll be the cherry on top

 

So what caused your misfire?

 

Leaking lower intake manifold gaskets