Really bad misfire, inconsistant

[trackdemon]

My NSX has developed an inconsistant problem. Basically what happens is when starting up from cold it runs just fine but once warmed through it develops a nasty misfire, mainly felt at low revs / medium throttle opening. Its normally OK when cruising 80mph but if you try to accelerate from - say - 20mph in third it misfires quite badly on one cylinder until the revs climb and then it clears.

Does anyone know what the likely cause may be, and if there's anything I can do to help? Its due for a service shortly but I'm supposed to be driving to an event tommorrow http://www.goodwood.co.uk/breakfastclub/ as I really wanted to show the NSX off so if anyone has any suggestions before I head of it'd be much appreciated!

 

[Hugh]

Did the Check Engine Light come on? Is there any possibility of condensation having formed in the gas tank? If so try adding a bottle of dry gas and see if that helps.

 

[Daedalus]

If it's a single cylinder my money's on either injector or coil. The miss is probably still there at higher RPMs, but just can't be felt. If there's no CEL I would guess coil. Don't drive it more than you have to. First step is to figure out which cylinder it is, then you can swap coils to confirm. For quick diagnosis or elimination of a bad coil this is a pretty nifty tool:
http://www.thetoolwarehouse.net/shop/WAE-76560.html

 

[Doc308]

Pull all of the coils and plugs and carefully inspect each one. The condition of the plugs should help you to diagnose which cyliders are not firing properly--specifically, the bad one(s) will look different. If you pull the plugs after idling ( misfiring ) for awhile, the misfiring plug may be wet and smell of fuel more so than the others. After fixing the problem, be sure to replace the bad plug. If it has become glazed over from unburnt fuel, it'll likely never fire right.

 

[Hondatech]

I had this issue with mine. Fine on cold start, after about 12-15 minutes of driving it would get a random misfire. Pull off your rear coil pack cover, and take out the back three coil packs. See if there's any water on the coil pack stems, and check the metal hex head of the back spark plugs for rust/signs of water. Found some? Replace the affected coil packs, plugs, and get a new gasket for the coil pack cover (make sure it's on correctly in the first place).

On mine, it turned out #1 had water in it and was going wonkey when it got up to operating temp. Since coil packs are just $80 each, I replaced all three rear bank ones, new plugs all around, and new coil pack cover gasket. Paranoia being what it is, I now also just throw a cover over the rear cylinder head in the engine bay when I wash the car :biggrin:

 

[Larry Bastanza]

If so try adding a bottle of dry gas and see if that helps.

Dry Gas is NOT recommended for ANY fuel injection system. Bad for the seals.

HTH,
LarryB

 

[kkim]

What's "dry gas"?

 

[Daedalus]

Methanol. Isopropyl alcohol works too and doesn't have the stigma that methanol carries. You can probably find Heet and Iso-Heet at Napa, or save some money and buy the stuff from Long's.

 

[dalybo]

I have the same exact symptons...code is P1204. I pulled the plugs and cylinder 4 plug was lightly green on top with corrosion. I purchased the car used and I think that these were the original 1996 plugs...60K miles so by miles I was within the specs, but still too much time in the engine. Put in new plugs and erased the code. Car ran great for weeks and then bingo I get the P1204 code with a slight backfire. I erase the code and all is fine for weeks again and then unexpectedly another P1204 code with a slight backfire.

So now, I think it is the coil. I switched cylinder 4 coil with number 5, erased the P1204 code. All is well, but I hope to get another code this time showing cylinder 5 as the source.

Stay tuned

 

[jrehner]

Well, Dalybo--u r lucky--at least u have a code. My problems have gone on for much longer--months ago Mark Basch replaced my #1 plug and that seemed to fix my issue for awhile but then it came back. Basically, an intermittent rough idle with hesitant acceleration.... The injectors were cleaned this time. Now my idle seems to be smooth but sometimes in first or shifting into 2nd have that hesitant accelaration (feels like the clutch is not engaging type of thing): I back off on the gas and then give more gas and issue resolves and sometime in 5th on freeway will get the drag. Other times it runs fine? Also my SRS light seems to stay on when the interior of car is hot but it goes off when it cools down... I just never know how it's going to run....

 

[dalybo]

update...recall that for diagnostic purposes, I switched cylinder 4 coil with number 5 and erased the P1204 code.

So yesterday I was out for a short drive and, as expected, after about 30 mins the car began to misfire and the CEL light came on. I checked the code and it was P1205. The diagnosis is a bad coil...so I'm off to buy a new coil. I expect that this will resolve my engine misfire issue.

Stand by....

 

[dalybo]

I purchased a new coil from Baranco Acura (Barancoacura.com
7060 Jonesboro Road Morrow, GA 30260) with the help of their customer focused parts guy, Chris Wilson. Chris was knowledgeable about NSX Prime and, as promised, provided a 25% part discount to a NSX Prime member.

I installed the new coil in the cylinder 5 spot and no more mis fires.

 

[UnhuZ]

i had the same problem....but no CEL.... the 4 valves from 1 cylinder were burned....and for that, no good sealm and a loss of 50%+ of compression....

$2500 and problem solved..... all that money was because i replaced other parts....