Engine misfire at idle

[mart155]

Hi All,
My 3.0L has a definite misfire at idle until the revs pick up to around 1500 to 2000 rpm and then it is fine. There does not appear to be any problems throughout the rest of the rev range and acceleration seems normal
I realise that there are a number of possible reasons for this and would welcome any suggestions. It is doing this whether hot or cold.

My favourite suspect at the moment is an ignition coil but I have no idea how I can identify which one of the cylinders is misfiring. Has anyone got any ideas please.

Thanks
Martin.

 

[Briank]

Can you hear the miss fire or do you feel it?

 

[nigel]

Don't put a crankshaft in it if it only needs a spark plug.

Cheers
nigel

 

[nsxotic911]

If you get enough or serious misfire you will get a CEL and the code for the exact cylinder will show up.

Check your spark plugs and replace them if they haven't been so in a while. If you don't replace them, yse brake cleaner to clean each one. I have found that if one is particularly dirty compared to the others, that cylinder will misfire. I had your exact same behavior when this was the case, one was dirtier (cuz I was lazy when I replaced them, didn't replace one).

To check the ignition coil, you just need to check the resistance with a multimeter. I don't remember what the resistance is supposed to be, but it's in the service manual. I doubt it's the coil though, they run well for a while.

You didn't get any water in there did you?

 

[mart155]

Yes, I would say that you can feel it more than you can hear it. There is a lot of vibration when the engine is idling. Even the steering wheel is visibly vibrating. Does this give you any other ideas?

It has been like this for a few weeks now so I don't think it is caused by getting wet.

The Spark Plugs were changed about 10k miles ago but I will check them.

There have not been any error lights.

 

[Daedalus]

Are you certain the coils went back the same way they came off when the plugs were done? Others have found that mixing up coils can eventually lead to misfires, since the seals aren't quite the same. If you can access the injector or coil harnesses, you can disconnect one cylinder at a time. The one that doesn't make it worse is the problem cylinder. Use a mechanic's stethoscope to listen to each injector click. Make sure they all sound roughly the same. Measuring the coil's resistances can confirm if a coil is bad, but it does not confirm that the coil is good. Often there is a breakdown in the insulation between wires, but there is no actual metal-metal contact. So resistance will read fine, but under the high voltage normally seen, arcing will occur between the wires.

 

[davidf]

I think you may be feeling the vibration and mistaking it for misfire. I did when I bought mine. It feels like a dead miss but actually it's quite normal. Search "rough Idle". You'll get your answer.:smile:

 

[Briank]

See http://www.nsxprime.com/forums/showthread.php?t=22943&highlight=motor+mounts

 

[Larry Bastanza]

If you get enough or serious misfire you will get a CEL and the code for the exact cylinder will show up.

This is true for 1995+ cars in the US with ODBII only. Not sure what year this car is, or if it has ODBII since this is not a US car. Pleae let us know year and if you can connect a scanner to it.

Regards,
LarryB

 

[Daedalus]

Profile says '96. I've also wondered whether cars made for other markets have the same OBDII system we have.

 

[goldNSX]

If you put your eyes down to the exhaust you should clearly hear that a cylinder is misfiring at idle. Has been so in my case. I went with 3 new ignition coils on the rear bank and cleaned the connectors of the spark plugs and the ignition coils on the front bank. This worked for my car perfectly.

Note: the coils resistor was still fine. By measuring them you only find really bad ones. No CEL code appeared while misfiring at idle.

 

[mart155]

I compared it to a number of other NSX's at a recent meet and none of the others were running as rough as mine. Local Honda mechanic thought it was misfiring too.

I will have a look at the plugs tomorrow and check the resistance of the coils. You never know, I might find something. Will also try disconnecting each coil in turn as suggested by Daedalus.

If all else fails, I will book it in at the Honda dealer's for some investigation.
Not sure what ODBII is Larry but it is a JDM car.
Thanks for all the comments. Will let you know how I get on.

 

[NSXGB]

Not sure what ODBII is Larry but it is a JDM car.

On Board Diagnostics (version) II

 

[davidf]

Start the car and place your hands lightly over each exhaust tip while idling. If it's a misfire you'll feel it there. I still believe it's ok {hopefully}. Good luck.:smile:

 

[RON98]

Will also try disconnecting each coil in turn as suggested by Daedalus.QUOTE]


This may damage your coil packs. I would just test each coil pack for resistance. If they are with in specs, they are fine, end of story. :wink:

 

[Larry Bastanza]

Will also try disconnecting each coil in turn as suggested by Daedalus.QUOTE]


This may damage your coil packs. I would just test each coil pack for resistance. If they are with in specs, they are fine, end of story. :wink:

Rob,

Please explain this a little further. I am thinking that Daedalus was refering to disconnecting the primary side(from the ignitor), which would be the same as having the car turned off. I cannot understand how this could damage a coil pack. What am I missing?

Thanks,
LarryB