2000 Accord EX V6 misfiring

"Butcher" wrote in news:1176484711.064237.275090 @p77g2000hsh.googlegroups.com:

Assuming your errors are P03xx (the "P" means powertrain), P0300 means a random misfire (any cylinder). The other codes are misfires for specific cylinders.

A misfire DTC is not necessarily a spark issue (and often isn't).

Replacing coils is NOT a good idea, and is certainly NOT a substitute for proper diagnosis.

Misfires can also be caused by lean mixtures. such as may be caused by intake leaks or clogged EGR ports.

Some vehicles even suffer misfire codes if the battery has been disconnected and the idle-learn procedure hasn't subsequently been done.

A bad throttle position sensor or crank position sensor can also cause misfire DTCs.

Have your dealer look up the Feb '02 issue of Honda Service News. There is an article in there involving your exact problem. Dealers are supposed to keep a binder with all the HSN publications in it.

Somebody needs to do a proper diagnosis on this car with a proper OBD-II code reader that is capable of advanced reporting.

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Somebody pissed in your gas tank. I've had similar codes when I stopped suddenly at a traffic light. The Honda had been in storage all winter and there was lots of water in the gas tank. A can of injector cleaner and some gas line antifreeze fixed it up right away.

'Curly'

Thanks Tegger. I've seen your FAQ in the past, so appreciate the fact that you know your stuff. The bottom line is that there appears to be more potential causes than I can deal with as a layman. I was just going off what seemed to be black and white on the diagnostics info I got from the Honda dealer - and I quote:

"pulled codes P0302 and P0306 for misfires in cylinders 2 and 6. Pulled spark plugs and found all plugs to be very worn. Also performed balance test and found the number 6 and number 2 coils to fail. Needs spark plugs and coils number 2 and 6, EST = $340".

So to me sounded pretty cut and dried - new plugs and replace coils 2 and 6 - and all things I could do myself for way less $. I was pretty proud of myself until I started my car and it still ran like shit.

I'm reluctant to bring it to that Honda dealer, as they've raided my wallet every time I've had an issue. I have a local mechanic I trust more that I will present with some of the information you noted and see what happens. I'll post back when the mystery is solved.

"Butcher" wrote in news:1176492336.780507.222610 @b75g2000hsg.googlegroups.com:

There sure are. Engine systems tend to be interconnected, whether on purpose or not. I don't pretend to be an expert on this.

Worn-open gaps will cause the coils to fire at a higher-than-normal voltage, which has a tendency to chew up the insulation. This eventually leads to shorts to ground through the coil body (before the plug gap).

This is plausible, but, I think, unlikely.

Hmm. I wonder what the tech actually did. Did he do "freeze-frames" using the Honda HIM tester? Did he check any other values, such as fuel trim?

Except that now you're getting a P0300, meaning the ECM can't tie the "misfire" down to any particular cylinder. This means a global problem with engine management, and not likely anything to do with the ignition at all.

See below...

The problem is one of unfortunate terminology. Unfortunate for those not versed in the EPA's mandated automotive systems, that is.

"Misfire", as a term, has nothing whatever to do with the spark. All it has to do with is the ECM not seeing the crankshaft speed up like it should after a spark event.

Your engine has a firing impulse every 1/3 of a revolution. The ECM expects that the crankshaft will speed up and then slow down with each firing impulse, following a particular pattern. All the firing impulses should make the crank speed up and slow down the same way (within a range). If some of the impulses result in LESS of a speedup than expected, the ECM interprets this to mean the mixture has failed to combust correctly and sets the P030x DTC.

The failed combustion can be anything from incorrect mixture to a stuck- open valve to failed coils and a number of other problems (as I outlined in an earlier message).

See here for a good professional explanation of misfires:

Please do.

So I figured out the reason that replacing the 2 failed coils didn't fix the problem. User error - I put one of the new coils in the wrong cylinder! Took it back to Honda and after talking to the mechanic, he corrected me on how the ignition firing order is laid on on the V6's. Once I got home, I swapped out the coil I now knew was bad with one of the ones I had originally taken out. I got lucky in that I picked the good one, and the car started running right. Reset the check engine light (pull negative lead off of battery) and the things running like a top again.

As a treat, I filled her up with some Shell VPower and will throw in a new PCV and air filter this weekend (with an oil change about a month away).

Thanks again for the info. I have your FAQ bookmarked - some very useful information up there.

Butcher wrote in news:1176815948.370558.308960 @d57g2000hsg.googlegroups.com:

Huh. So in your case it appears to have actually been a spark misfire. Will wonders never cease.

Glad it's fixed, anyway.