I have a 2000 Honda Accord EX V6 3.0 My engine just recently began to misfire, with no previous symptoms. Bad gas has been ruled out as a cause. Ignition coils have been ruled out as a cause. Spark plugs have been ruled out as a cause. The next thing to test is the wiring harness, and then the control computer. Does anyone have any suggestions for another direction to look, or has had the same problem? Short of a physical defect (melted wire) on the harness, I can't see it going bad.

The misfire code is "1399 Manfacturer ignition misfire detected" (There are codes for misfiring cylinders, changing each time I clear the codes and run the car more. Cylinder #1 has never come up as a code, but the other 5 have several times each)

As well as the specific cylinders that misfire. 2, 3, 4, 5, 6 all misfiring at the same time. The coils have been ruled out as a cause, because A) they all started misfiring at the exact same time. And B) Switching the #1 coil into #2 and cylinder #2 still misfiring and #1 being fine. Spark plugs have been changed to brand new, and I even put in a second set of OEM and tested that too, just to make sure.

Any suggestions would be excellent. Thank you.


Edit: I've put Methyl Alcohol in the gas, to rule out bad gas. I've been filling up at the same station since I moved here, and I last got gas a week before the problem. The car runs *very* bad, but consistently bad, no change when running for an hour or more. Obvious misfires are apparent just from the "put-put" of the exhaust and shaking of the car when the throttle is applied.

Code Update:

302 Cylinder 2 Misfired
303 Cylinder 3 Misfired
304 Cylinder 4 Misfired
305 Cylinder 5 Misfired
0300 Random multiple cylinder misfire
1399 Manufacturer Control Ignition System or Misfire

 

You need to get a lab scope. Hook up the scope to each of the ignition coils and run the car. Check the waveform. The only problem here is that you have to know what to look for which takes some knowledge of computer controls. The wire going to the coil is going to turn the ignition coil on and off. I'm not completly sure how this works since i have not looked up the ignition coil for this car. It could be possible that cylinders 3, 4, and 5 are not recieving a signal to fire the spark plugs from the PCM b/c the wires are bad or something. Off the top of my head that would be my best guess. Are you sure that the fuel system (not the gas) isn' the problem? You have a code that says ignition system so this might not be the case but something wrong with the fuel injectors will cause a misfire.

I looked up your car on the database and here is what i got. It doesn't tell me how the ignition system works but does tell how to diagnose the problem

1. Check for battery voltage at #3 terminal (black with a yellow stripe) for each coil.
2. Check for continiuty between #2 and a body ground.
3. Measure the voltage at the #1 terminal (diff color for each coil, but odd one out for this) of the coil.

After you get these results post them and ill try and help some more. I'm gonna search for some more info on how the ignition sytem works since i don't really like the diagnosis procedure since i don't actually know whats going on.

I looked some more and found a little more info. Terminal 1 on the connector (diff color) comes from the PCM, what it does exactly i do not know. I think that it tells the coil to fire. Terminal 3 is the power for coil. There is a ICM in each of the coils which i'm assuming turns the coil on and off. My best guess is that either there is no power at terminal 3 or the PCM is not send a signal (or the signal is not being recieved) at terminal 1. I dunno how you will measure the voltage at terminal 1 since it should always be changing since the coil is not on all the time.

 

Well I think that I've found the problem. At first I was sort of out of my element when I was checking the coils, because I am used to ignition wires and distributor caps. I simply pulled the wires off each coil with the engine running. When I came to the cylinder that had no effect on the engine, I switched the coil position and repeated the process. Once again, the marked coil had no effect on the engine when unplugged. (dont do this) I unplugged a good coil, put a sparkplug in the end, turned on the car, grounded the coil -- big spark. Put the marked coil on the same wire as that last working coil, same spark plug, repeated the test, absolutely no spark. The coil must/is be dead. Going to buy a coil tomorrow morning. I cant see any problem with my test, or that the results may be wrong.

Any feedback?

Thanks

Mike

 

What do you think the chances are that 3/6 coils are bad? If there is no spark coming from those 3 spark plugs then it is possible that the coil is bad. However, it is also possible that the coil is not recieving a signal to spark. If the coils are actually bad the coil from #1 should fire cylinders 3, 4, and 5. I don't know if you did this b/c the write up was unclear but if this isn't the case, then the coils are prolly not bad.

 

I meant that I ignored the Engine Trouble Codes and just went back to old school diagnosing. 5 out of 6 coils are firing. 1 is not firing at all. Why that causes the computer to think every cylinder is misfiring I don't know. But I can't see any reason why my diagnosis would be wrong, especially with the data of physically watching a coil creating a spark with a plug. Both coils used the same wire and same plug. In the test sample, one coil worked, the other did not. We switched to another sample set, same bad coil and another "good one" and a different hook up. Same result!

 

Each coil has a different wiring going to it. Each one gets a seperate wire from the PCM for the signal to fire and each has a seperate wire for power. If you move the coil to a different cylinder and the misfire moves, then you have a bad coil. I'm pretty sure that a coil isn't cheap so you prolly don't wanna replace it if you don't have to.

 

Right, which the test proved a coil is bad. $55.00 at Advance Auto in Maryland!

Crappy thing is, my wife took the car to a honda dealership while i was at work. They threw it on the diagnostic machine, told her it was the spark plugs (which i had already changed the night before) and talked her into buying 6 $20 dollar spark plugs. Total cost: $178.00. I am furious!

 

Resatimm, I took mine to the dealer and they told me they wanted to pull the heads for a nice $2000. NO THANKS! I have tinkered and found one bad coil so far. Still looking

 

I have a 2005 Honda Accord EX V6, and the check engine light (CEL) came on under floor-boarding acceleration. I had the codes checked out while on a trip and 3 cylinders were misfiring. This is new, and odd because the vibration is very subtle and transient. I had the CEL reset but it came back on after 6 more hours of hard driving. The car has been getting 30 mpg highway gas mileage and accelerates like a motorcycle.

I am responding to this post because I just replaced the battery 3 weeks ago. One of the things I noticed is that the battery terminal connections are loose, no matter how far you tighten them. Can you explain where you're testing for voltage? are there recognizable terminals on each coil?

 

This is a 7 yr old thread. Post your own new thread for better help.

Tell us what codes/s were displayed; Pnnnn?

Spark plugs, valve adjustment, coil-over-plugs are all possibilities. CEL codes may narrow the search.

good luck