300M misfire code P0302 -> no coil codes, no injector codes?

Start with replacing the plugs if you gonna take a pot shot at it. If it didn't take care of it the next thing you can do is swap coils from one cylinder to another to see if the misfire switches, if it does...replace the effected coil. you don't specify what engine, number 2 cyl on the 3.2/3.5 is on the drivers side front. the 2.7 is on the passenger side front.

Glenn Beasley Chrysler Tech

Coil screw heads will either be torx #25 or #27 depending on engine. They can be frozen and difficult to remove without stripping the heads. Get torx bit straight and fully seated. Penetrating oil soak ahead of time wouldn't hurt. Also try good tap directly on head of the screw with a hammer to help break them loose before trying to remove.

Glenn - Every piece of documentation I have says #1 cyl. is front passenger side for all three engines (3.2, 3.5, 2.7) and therefore #2 is front drive's side. Can you check your documentation and post back?

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Replace the battery since it is on borrowed time. A bad battery with low operating voltage can mess up the sensor readings and computer controls. I'd see how it runs after that before trying anything else.

Bob

Your correct, I was thinking of the transverse set up as in a Sebring Convertible 2.7 which would put the #2 plug at the passenger side front. Must be an old age thing setting in

The coils came off easy, and so did the plugs.

I started by putting a new plug into #2 (front driver side). Original plug was dirty (8 years, 72k miles). Replacement was exact same kind (champion). I didn't gap the new plug (do you still gap plugs these days?).

That didn't work - it still idled rough.

I then replaced plug #1 (front passenger side) and swapped the coils between 1 and 2. (original plug 1 looked to be in the same shape as #2).

That didn't work - it still idled rough.

Codes still say 1684 and 0302 (still indicating the problem is with cylinder 2).

So at this point, how does the computer know that the problem is cylinder 2? What other sensor could tell the computer that #2 is the problem? If it was the injector, then why no injector codes?

Regarding the battery -

I did have to get a replacement ignition key and fob to replace a stolen one (about 2 weeks ago). The dealer reprogrammed the car to accept the new key and fob and reject the stolen ones. Would that have required disconnecting the battery?

Did you reset the codes?

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

No - how do you do that?

PS: Cylinder 2 is front driver side, with front meaning closest to the front of the car - yes?

Hypothetically, let's say my problem is a bad #2 coil. Say that's what's causing the 0302 code.

So I swap coil #2 with coil #1.

But I don't reset the codes.

So I start the car, car idles rough, and the check engine light goes on.

I then do another read of the codes.

Because I didn't reset the codes, I guess I'll still see 0302. But if cylinder #1 now has the bad coil, shouldn't I now see code 0301 ???

BTW, is there any way to reset the codes other than disconnecting the battery?

Yes. Plugs still get gapped unless they are platinum tipped.

It may help if you replace all the plugs at that mileage.

When the coil fires for cyl #2 the PCM expects to see a jump in cranshaft speed when cyl #2 fires. It reads crankshaft speed via the crank sensor. If cyl #2 doesn't fire the PCM sees no increase in crank speed and sets a code. It takes more than a single misfire to set a code.

If it was an electrical problem with the injector the PCM would be able to pick that up and set a code. If it was a mechanical problem, such as a plugged injector, the PCM would not be able to sense that.

Yes, but it may not set a code for cyl#1 right away. You may have to run it for a while for the code to set.

Yes, it can be done with a scan tool or some code readers. The easiest way to reset the codes is to diconnect the battery for a minute or two.

I would suggest you leave the coils were they are now, replace all the spark plugs, clear the codes and take it for a ride and see if the check engine light comes on again.

That's what I'm thinking. But also, if you reset the codes and you get no code later, but it still runs rough that would mean something different than resetting and getting the code for only cylinder 1. Not sure what exactly, but it would mean something. If code for cyl. 2 comes back, that would be instructive too. Right now you don't know if it would come back or if you're just seeing the old code. I think we both suspect that cyl. 2 code will come back.

Pull Fuse N in the Power Distribution Center for 15 minutes to reset the PCM.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Resetting and getting no codes, and still running like a cylinder isin't functioning doesn't make sense, given the earlier code 0302.

Do plugged injectors result in an injector code?

Or does only an electrically-inoperative injector result in an injector code?

Some references to the "Power Distribution Center" say it's located under the hood near the battery.

I have no such item (that I can see) near the battery.

I do have a "Fuse and relay center" on the driver's side, in front of the rad overflow tank. The fuses and relays are identified by name only - no numbers or letters. The relay center behind the dashboard panel on the driver's side are labelled with numbers - but I don't see anything referring to the PCM.

So basically - where is the Fuse N you're talking about?

The fault code should have gone to the other cylinder if the coil was bad, you wouldn't have to reset the codes, it would have automatically set a hard fault code for the other cylinder if it were the coil. Your gonna have to go back to basics, compression? fuel (injector). The injector pintel could be bad or the injector is stopped up, this would not set a fault code unless the injector circuit was at fault. If you have the time, swap injectors.

Glenn

I was suggesting resetting the codes first to maker sure cyl. 2 was not still having a problem that would set a code.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Please tell me what references say that so I'll know to avoid them. :)

Yep that's it.

Here's a figure from the FSM that I have labeled the fuses on:

To re-cap a little, my '00 300M abruptly started to run rough 2 days ago, obviously one cylinder wasn't working.

I was seeing code P0302 on the odometer, indicating cylinder #2.

I replaced the (original) plugs in both cyliners 1 and 2, but that didn't solve the problem.

I swapped coils 1 and 2, started the engine a few times, but the problem was still there.

I was expecting (hoping) to see code 0301 but it didn't show.

Today, I drove the car about a mile, parked it, and then read the codes. Only then did it show both 0302 and 0301.

I disconnected the negative cable from the firewall - I tried a few times but ultimately it had to be disconnected for between 30 to 45 minutes for the codes to clear. I drove the car for a few miles, but it wasn't enough for the engine light to come on, or for any codes to appear.

I did a resistance check on the suspect coil and another (presumably good) coil and found that on the suspect coil there was a measurable resistance (less than 200 ohms) between the high-tension terminal and each of the primary (low-voltage) terminals. The "good" coil had no such resistance.

I then bought a new coil at a dealership ($81 plus tax) and tested it. It also did not show any resistance between the high-tension terminal and the 2 low-voltage terminals.

I installed the new coil and the other "good" coil and started the engine. It ran and idled smoothly.

So the secondary (high-voltage) winding of the transformer had developed a short to the primary (low voltage) winding. The low-voltage winding measured about 1 ohm, but I wasn't able to measure the secondary winding because I couldn't figure out where to measure the opposite end of the coil (is it connected to the metal body of the transformer?).

I can see why it didn't generate a coil fault because the primary winding didn't fail (ie it didn't open up).

Well, that was a relatively easy fix, not requiring any expensive tools, or any servicing at the dealership.

Just a little correction of your terminology: What you observed was "*low* resistance" (or high conductivity) between the secondary and primary.

Again, you would say it didn't show any conduction... (or you could say it showed high, or "infinite", resistance...). Saying it "did not show any resistance..." technically means it was shorted, which I know you weren't meaning to say.

Way to go! Sometimes an educated guess pays off.

Reminds me of when I was in Navy electronics school over 35 years ago. They taught us troubleshooting methods. The book said to start where you have good signal, and move forward in the circuit with your troubleshooting equipment until you loose the signal. The point at which you lose it is where the problem is.

So for one of our tests, they had these radios in the lab specially built for training purposes that they would put a bad part in, and we would have to find the bad part using the troubelshooting techniques we were taught. On a hunch, instead of starting at the front end and working my way to where the signal was lost, I sarted at the bad output end and worked my way backwards until the signal was good. Just so happens the bad part was very near the output end of things. So I finished the test in record time. Should have gotten a real high score, right? No! They gave me a failing grade because I worked my way backwards instead of the way we were taught. They didn't want people thinking outside the box. LOL!

Anyway - glad you got it fixed.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

That would work if you were just clearing the codes using a scan tool. Clearing the codes by interrupting the power supply to the PCM will result in misfire monitoring being disabled. No misfire can be detected until the vehicle is driven under specific conditions to allow the PCM re-learn the baseline variance between cylinders.

Jesus christ.

Ok, that would explain a few things.

Will this OBD II tool work for my '00 300M ?