P0305 - Cyl 5 misfire

[CrashTestDummy]

Well, after giving us a little stumble a couple of times before, the car is now officially running on 7, and it's 'Christmas in Capriceland' again, with the dash all lit up. It's obvious it's running on 7, and I can now feel the downshifts when rolling to a stop. ODB reader says P0305. Haven't dived under the hood yet, but wondering if anyone has enjoyed that code, and what did they find? Thanks.

[Mooseman]

Classic misfire diagnosing. Do the following:

- Check for spark at #5. If no spark, swap that coil and wire with another (ie: #3), clear the codes and see if the misfire follows the coil. If it does, replace the coil. If it stays at #5 and still no spark, check for power and trigger at the coil plug. An LED Noid light would work for that.

- If spark is good, check compression on all cylinders. If #5 is low, it's a mechanical issue that will need to be diagnosed further.

- If compression is good, check for fuel at #5. Check that the injector is getting power and being triggered with a Noid light. If power is good, swap the fuel injector from #5 to #3, clear codes and see if the misfire follows. If it does, replace the injector.

An LED test light should work the same as a Noid light or you can make your own with an LED with the appropriate resistor for 12V.

[CrashTestDummy]

That was the plan. I'm hearing no odd noises, and while it seems a quick total failure, it did happen gradually, starting with a notable stumble while occasionally waiting at a light, then the occasional stumble while at constant speed.

While annoyed if it is, I'm kind of hoping it's a failed coil. This would be the first such failure if it is, in several decades of having cars with LS-based engines.

damn, I HATE autocorrect!! The title is supposed to be 'P0305 - cyl 5 misfire'!! That got 'corrected' on posting!!

[Pursuit]

Gene,
I corrected the otto-cowrecked...

[CrashTestDummy]

Bless you, sir!! And, thank you!

Got out and swapped the 3 & 5 coil and plug wire, and checked the no. 5 plug. It looked good, other than being a used plug. It looked like it had been running, as expected, dry and nice color. Swapping the coil made no difference in the way the car ran, and even though I cleared the codes, the P0305 came right back, along with a P0300 (multiple misfires). Not sure if the P0300 is because I cleared the codes, or if, indeed, I have multiple misfiring cylinders. Pointing a IR thermometer at the exhaust primaries wasn't very conclusive.

Sooooo, I'm loading up the parts shotgun, and will tackle some replacements this weekend. Since the car has nearly 100K miles on it, and I don't know the history of the ignition components, other than it having the wrong plugs, according to O'Reilly's web site. We'll start with the plugs and wires. I also ordered up the belts and idlers, since it sounds like one of the idler bearings is complaining about being under the hood.

Updates as they occur.

P0305 codes.JPG (215.07 KiB) Viewed 2954 times

[Mooseman]

Drop that shotgun partner

Is there actual spark? If not, then it could be a wiring problem to that coil.

If there is spark, when cranking, is the sound "even and regular"? If not, then it could be low compression on the one cylinder.



I would hate for you to throw a bunch of part$ at something that is either something else (wiring) or unfixable (low compression).

[s/c'd cav]

dont forget to do the same thing with the fuel injectors , swap #5 with one of the others

[CrashTestDummy]

The car is in surprising shape, considering its life. Look under the hood, and you'd swear it's a much later model car with maybe 50K miles on the clock. All wiring and hoses look great for their age, are still flexible and soft. I ALWAYS run premium fuel in the car, although it does sit a while between uses. It's had the fuel pump TSB done. I just can't understand why it's all of a sudden started acting up. I guess I'll do plugs and wires, then see if the stealership can have a go at it.

[s/c'd cav]

The car is in surprising shape, considering its life. Look under the hood, and you'd swear it's a much later model car with maybe 50K miles on the clock. All wiring and hoses look great for their age, are still flexible and soft. I ALWAYS run premium fuel in the car, although it does sit a while between uses. It's had the fuel pump TSB done. I just can't understand why it's all of a sudden started acting up. I guess I'll do plugs and wires, then see if the stealership can have a go at it.

if its sitting outside , waskly waskles could have gotten to the wires

also that injector could have gotten stuck or be partially clogged

[CrashTestDummy]

It stays in the garage. Quite the garage queen. BUT, we do have visitors on occasion. I've inspected the wiring, and have found no clues of intruders under the hood. That was something I looked for when chasing the TPMS/Stabilitrack/ABS fault issue a month ago. Zero signs of any chewing. I also pulled the filter box off to look in there to make sure we didn't have any nests. Clean as a whistle.

We'll do plugs and wires today. I'll check that each is at least firing. I'll stick a screwdriver to the injectors to have a listen to them to see if they're at least clicking.